2017-11-07 16:22:27 +08:00
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< title > Documentation - The Zig Programming Language< / title >
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< / style >
< / head >
< body >
< div id = "nav" >
< ul >
< li > < a href = "#introduction" > Introduction< / a > < / li >
< li > < a href = "#hello-world" > Hello World< / a > < / li >
< li > < a href = "#values" > Values< / a > < / li >
< ul >
< li > < a href = "#primitive-types" > Primitive Types< / a > < / li >
< li > < a href = "#primitive-values" > Primitive Values< / a > < / li >
< li > < a href = "#string-literals" > String Literals< / a >
< ul >
< li > < a href = "#string-literal-escapes" > Escape Sequences< / a > < / li >
< li > < a href = "#multiline-string-literals" > Multiline String Literals< / a > < / li >
< / ul >
< / li >
< li > < a href = "#values-assignment" > Assignment< / a > < / li >
< / ul >
< / li >
< li > < a href = "#integers" > Integers< / a >
< ul >
< li > < a href = "#integer-literals" > Integer Literals< / a > < / li >
< li > < a href = "#runtime-integer-values" > Runtime Integer Values< / a > < / li >
< / ul >
< / li >
< li > < a href = "#floats" > Floats< / a >
< ul >
< li > < a href = "#float-literals" > Float Literals< / a > < / li >
< li > < a href = "#float-operations" > Floating Point Operations< / a > < / li >
< / ul >
< / li >
< li > < a href = "#operators" > Operators< / a >
< ul >
< li > < a href = "#operators-table" > Table of Operators< / a > < / li >
< li > < a href = "#operators-precedence" > Precedence< / a > < / li >
< / ul >
< / li >
< li > < a href = "#arrays" > Arrays< / a > < / li >
< li > < a href = "#pointers" > Pointers< / a >
< ul >
< li > < a href = "#alignment" > Alignment< / a > < / li >
< li > < a href = "#type-based-alias-analysis" > Type Based Alias Analysis< / a > < / li >
< / ul >
< / li >
< li > < a href = "#slices" > Slices< / a > < / li >
< li > < a href = "#struct" > struct< / a > < / li >
< li > < a href = "#enum" > enum< / a > < / li >
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< li > < a href = "#union" > union< / a > < / li >
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< li > < a href = "#switch" > switch< / a > < / li >
< li > < a href = "#while" > while< / a > < / li >
< li > < a href = "#for" > for< / a > < / li >
< li > < a href = "#if" > if< / a > < / li >
< li > < a href = "#goto" > goto< / a > < / li >
< li > < a href = "#defer" > defer< / a > < / li >
< li > < a href = "#unreachable" > unreachable< / a >
< ul >
< li > < a href = "#unreachable-basics" > Basics< / a > < / li >
< li > < a href = "#unreachable-comptime" > At Compile-Time< / a > < / li >
< / ul >
< / li >
< li > < a href = "#noreturn" > noreturn< / a > < / li >
< li > < a href = "#functions" > Functions< / a >
< ul >
< li > < a href = "#functions-by-val-params" > Pass-by-val Parameters< / a >
< / ul >
< / li >
< li > < a href = "#errors" > Errors< / a > < / li >
< li > < a href = "#nullables" > Nullables< / a > < / li >
< li > < a href = "#casting" > Casting< / a > < / li >
< li > < a href = "#void" > void< / a > < / li >
< li > < a href = "#this" > this< / a > < / li >
< li > < a href = "#comptime" > comptime< / a >
< ul >
< li > < a href = "#introducing-compile-time-concept" > Introducing the Compile-Time Concept< / a > < / li >
< ul >
< li > < a href = "#compile-time-parameters" > Compile-time parameters< / a > < / li >
< li > < a href = "#compile-time-variables" > Compile-time variables< / a > < / li >
< li > < a href = "#compile-time-expressions" > Compile-time expressions< / a > < / li >
< / ul >
< li > < a href = "#generic-data-structures" > Generic Data Structures< / a > < / li >
< li > < a href = "#case-study-printf" > Case Study: printf in Zig< / a > < / li >
< / ul >
< / li >
< li > < a href = "#inline" > inline< / a > < / li >
< li > < a href = "#assembly" > assembly< / a > < / li >
< li > < a href = "#atomics" > Atomics< / a > < / li >
< li > < a href = "#builtin-functions" > Builtin Functions< / a >
< ul >
< li > < a href = "#builtin-addWithOverflow" > @addWithOverflow< / a > < / li >
< li > < a href = "#builtin-alignCast" > @alignCast< / a > < / li >
< li > < a href = "#builtin-alignOf" > @alignOf< / a > < / li >
< li > < a href = "#builtin-ArgType" > @ArgType< / a > < / li >
< li > < a href = "#builtin-bitCast" > @bitCast< / a > < / li >
< li > < a href = "#builtin-breakpoint" > @breakpoint< / a > < / li >
< li > < a href = "#builtin-cDefine" > @cDefine< / a > < / li >
< li > < a href = "#builtin-cImport" > @cImport< / a > < / li >
< li > < a href = "#builtin-cInclude" > @cInclude< / a > < / li >
< li > < a href = "#builtin-cUndef" > @cUndef< / a > < / li >
< li > < a href = "#builtin-canImplicitCast" > @canImplicitCast< / a > < / li >
< li > < a href = "#builtin-clz" > @clz< / a > < / li >
< li > < a href = "#builtin-cmpxchg" > @cmpxchg< / a > < / li >
< li > < a href = "#builtin-compileError" > @compileError< / a > < / li >
< li > < a href = "#builtin-compileLog" > @compileLog< / a > < / li >
< li > < a href = "#builtin-ctz" > @ctz< / a > < / li >
< li > < a href = "#builtin-divExact" > @divExact< / a > < / li >
< li > < a href = "#builtin-divFloor" > @divFloor< / a > < / li >
< li > < a href = "#builtin-divTrunc" > @divTrunc< / a > < / li >
< li > < a href = "#builtin-embedFile" > @embedFile< / a > < / li >
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< li > < a href = "#builtin-export" > @export< / a > < / li >
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< li > < a href = "#builtin-tagName" > @tagName< / a > < / li >
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< li > < a href = "#builtin-EnumTagType" > @EnumTagType< / a > < / li >
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< li > < a href = "#builtin-errorName" > @errorName< / a > < / li >
< li > < a href = "#builtin-fence" > @fence< / a > < / li >
< li > < a href = "#builtin-fieldParentPtr" > @fieldParentPtr< / a > < / li >
< li > < a href = "#builtin-frameAddress" > @frameAddress< / a > < / li >
< li > < a href = "#builtin-import" > @import< / a > < / li >
< li > < a href = "#builtin-inlineCall" > @inlineCall< / a > < / li >
< li > < a href = "#builtin-intToPtr" > @intToPtr< / a > < / li >
< li > < a href = "#builtin-IntType" > @IntType< / a > < / li >
< li > < a href = "#builtin-maxValue" > @maxValue< / a > < / li >
< li > < a href = "#builtin-memberCount" > @memberCount< / a > < / li >
< li > < a href = "#builtin-memberName" > @memberName< / a > < / li >
< li > < a href = "#builtin-memberType" > @memberType< / a > < / li >
< li > < a href = "#builtin-memcpy" > @memcpy< / a > < / li >
< li > < a href = "#builtin-memset" > @memset< / a > < / li >
< li > < a href = "#builtin-minValue" > @minValue< / a > < / li >
< li > < a href = "#builtin-mod" > @mod< / a > < / li >
< li > < a href = "#builtin-mulWithOverflow" > @mulWithOverflow< / a > < / li >
< li > < a href = "#builtin-offsetOf" > @offsetOf< / a > < / li >
< li > < a href = "#builtin-OpaqueType" > @OpaqueType< / a > < / li >
< li > < a href = "#builtin-panic" > @panic< / a > < / li >
< li > < a href = "#builtin-ptrCast" > @ptrCast< / a > < / li >
< li > < a href = "#builtin-ptrToInt" > @ptrToInt< / a > < / li >
< li > < a href = "#builtin-rem" > @rem< / a > < / li >
< li > < a href = "#builtin-returnAddress" > @returnAddress< / a > < / li >
< li > < a href = "#builtin-setDebugSafety" > @setDebugSafety< / a > < / li >
< li > < a href = "#builtin-setEvalBranchQuota" > @setEvalBranchQuota< / a > < / li >
< li > < a href = "#builtin-setFloatMode" > @setFloatMode< / a > < / li >
< li > < a href = "#builtin-setGlobalLinkage" > @setGlobalLinkage< / a > < / li >
< li > < a href = "#builtin-setGlobalSection" > @setGlobalSection< / a > < / li >
< li > < a href = "#builtin-shlExact" > @shlExact< / a > < / li >
< li > < a href = "#builtin-shlWithOverflow" > @shlWithOverflow< / a > < / li >
< li > < a href = "#builtin-shrExact" > @shrExact< / a > < / li >
< li > < a href = "#builtin-sizeOf" > @sizeOf< / a > < / li >
< li > < a href = "#builtin-subWithOverflow" > @subWithOverflow< / a > < / li >
< li > < a href = "#builtin-truncate" > @truncate< / a > < / li >
< li > < a href = "#builtin-typeId" > @typeId< / a > < / li >
< li > < a href = "#builtin-typeName" > @typeName< / a > < / li >
< li > < a href = "#builtin-typeOf" > @typeOf< / a > < / li >
< / ul >
< / li >
< li > < a href = "#build-mode" > Build Mode< / a >
< ul >
< li > < a href = "#build-mode-debug" > Debug< / a > < / li >
< li > < a href = "#build-mode-release-fast" > ReleaseFast< / a > < / li >
< li > < a href = "#build-mode-release-safe" > ReleaseSafe< / a > < / li >
< / ul >
< / li >
< li > < a href = "#undefined-behavior" > Undefined Behavior< / a >
< ul >
< li > < a href = "#undef-unreachable" > Reaching Unreachable Code< / a > < / li >
< li > < a href = "#undef-index-out-of-bounds" > Index out of Bounds< / a > < / li >
< li > < a href = "#undef-cast-negative-unsigned" > Cast Negative Number to Unsigned Integer< / a > < / li >
< li > < a href = "#undef-cast-truncates-data" > Cast Truncates Data< / a > < / li >
< li > < a href = "#undef-integer-overflow" > Integer Overflow< / a >
< ul >
< li > < a href = "#undef-int-overflow-default" > Default Operations< / a > < / li >
< li > < a href = "#undef-int-overflow-std" > Standard Library Math Functions< / a > < / li >
< li > < a href = "#undef-int-overflow-builtin" > Builtin Overflow Functions< / a > < / li >
< li > < a href = "#undef-int-overflow-wrap" > Wrapping Operations< / a > < / li >
< / ul >
< / li >
< li > < a href = "#undef-shl-overflow" > Exact Left Shift Overflow< / a > < / li >
< li > < a href = "#undef-shr-overflow" > Exact Right Shift Overflow< / a > < / li >
< li > < a href = "#undef-division-by-zero" > Division by Zero< / a > < / li >
< li > < a href = "#undef-remainder-division-by-zero" > Remainder Division by Zero< / a > < / li >
< li > < a href = "#undef-exact-division-remainder" > Exact Division Remainder< / a > < / li >
< li > < a href = "#undef-slice-widen-remainder" > Slice Widen Remainder< / a > < / li >
< li > < a href = "#undef-attempt-unwrap-null" > Attempt to Unwrap Null< / a > < / li >
< li > < a href = "#undef-attempt-unwrap-error" > Attempt to Unwrap Error< / a > < / li >
< li > < a href = "#undef-invalid-error-code" > Invalid Error Code< / a > < / li >
< li > < a href = "#undef-invalid-enum-cast" > Invalid Enum Cast< / a > < / li >
< li > < a href = "#undef-incorrect-pointer-alignment" > Incorrect Pointer Alignment< / a > < / li >
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< li > < a href = "#undef-bad-union-field" > Wrong Union Field Access< / a > < / li >
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< / ul >
< / li >
< li > < a href = "#memory" > Memory< / a > < / li >
< li > < a href = "#compile-variables" > Compile Variables< / a > < / li >
< li > < a href = "#root-source-file" > Root Source File< / a > < / li >
< li > < a href = "#zig-test" > Zig Test< / a > < / li >
< li > < a href = "#zig-build-system" > Zig Build System< / a > < / li >
< li > < a href = "#c" > C< / a >
< ul >
< li > < a href = "#c-type-primitives" > C Type Primitives< / a > < / li >
< li > < a href = "#c-string-literals" > C String Literals< / a > < / li >
< li > < a href = "#c-import" > Import from C Header File< / a > < / li >
< li > < a href = "#mixing-object-files" > Mixing Object Files< / a > < / li >
< / ul >
< / li >
< li > < a href = "#targets" > Targets< / a > < / li >
< li > < a href = "#style-guide" > Style Guide< / a >
< ul >
< li > < a href = "#style-guide-whitespace" > Whitespace< / a > < / li >
< li > < a href = "#style-guide-names" > Names< / a > < / li >
< li > < a href = "#style-guide-examples" > Examples< / a > < / li >
< / ul >
< / li >
< li > < a href = "#grammar" > Grammar< / a > < / li >
< li > < a href = "#zen" > Zen< / a > < / li >
< / ul >
< / div >
< div id = "contents" >
< h1 id = "introduction" > Zig Documentation< / h1 >
< p >
Zig is an open-source programming language designed for < strong > robustness< / strong > ,
< strong > optimality< / strong > , and < strong > clarity< / strong > .
< / p >
< ul >
< li > < strong > Robust< / strong > - behavior is correct even for edge cases such as out of memory.< / li >
< li > < strong > Optimal< / strong > - write programs the best way they can behave and perform.< / li >
< li > < strong > Clear< / strong > - precisely communicate your intent to the compiler and other programmers. The language imposes a low overhead to reading code.< / li >
< / ul >
< p >
Often the most efficient way to learn something new is to see examples, so
this documentation shows how to use each of Zig's features. It is
all on one page so you can search with your browser's search tool.
< / p >
< p >
If you search for something specific in this documentation and do not find it,
please < a href = "https://github.com/zig-lang/www.ziglang.org/issues/new?title=I%20searched%20for%20___%20in%20the%20docs%20and%20didn%27t%20find%20it" > file an issue< / a > or < a href = "https://webchat.freenode.net/?channels=%23zig" > say something on IRC< / a > .
< / p >
< h2 id = "hello-world" > Hello World< / h2 >
< pre > < code class = "zig" > const io = @import("std").io;
pub fn main() -> %void {
// If this program is run without stdout attached, exit with an error.
var stdout_file = %return io.getStdOut();
const stdout = & stdout_file.out_stream;
// If this program encounters pipe failure when printing to stdout, exit
// with an error.
%return stdout.print("Hello, world!\n");
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-exe hello.zig
$ ./hello
Hello, world!< / code > < / pre >
< p >
Usually you don't want to write to stdout. You want to write to stderr. And you
don't care if it fails. It's more like a < em > warning message< / em > that you want
to emit. For that you can use a simpler API:
< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
pub fn main() -> %void {
warn("Hello, world!\n");
}< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#values" > Values< / a > < / li >
< li > < a href = "#builtin-import" > @import< / a > < / li >
< li > < a href = "#errors" > Errors< / a > < / li >
< li > < a href = "#root-source-file" > Root Source File< / a > < / li >
< / ul >
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< h2 id = "values" > Source encoding< / h2 >
< p > Zig source code is encoded in UTF-8. An invalid UTF-8 byte sequence results in a compile error.< / p >
< p > Throughout all zig source code (including in comments), some codepoints are never allowed:< / p >
< ul >
< li > Ascii control characters, except for U+000a (LF): U+0000 - U+0009, U+000b - U+0001f, U+007f. (Note that Windows line endings (CRLF) are not allowed, and hard tabs are not allowed.)< / li >
< li > Non-Ascii Unicode line endings: U+0085 (NEL), U+2028 (LS), U+2029 (PS).< / li >
< / ul >
< p > The codepoint U+000a (LF) (which is encoded as the single-byte value 0x0a) is the line terminator character. This character always terminates a line of zig source code. A non-empty zig source must end with the line terminator character.< / p >
< p > For some discussion on the rationale behind these designe decisions, see < a href = "https://github.com/zig-lang/zig/issues/663" > issue #663< / a > < / p >
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< h2 id = "values" > Values< / h2 >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
const os = @import("std").os;
const assert = @import("std").debug.assert;
// error declaration, makes `error.ArgNotFound` available
error ArgNotFound;
pub fn main() -> %void {
// integers
const one_plus_one: i32 = 1 + 1;
warn("1 + 1 = {}\n", one_plus_one);
// floats
const seven_div_three: f32 = 7.0 / 3.0;
warn("7.0 / 3.0 = {}\n", seven_div_three);
// boolean
warn("{}\n{}\n{}\n",
true and false,
true or false,
!true);
// nullable
var nullable_value: ?[]const u8 = null;
assert(nullable_value == null);
warn("\nnullable 1\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(nullable_value)), nullable_value);
nullable_value = "hi";
assert(nullable_value != null);
warn("\nnullable 2\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(nullable_value)), nullable_value);
// error union
var number_or_error: %i32 = error.ArgNotFound;
warn("\nerror union 1\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(number_or_error)), number_or_error);
number_or_error = 1234;
warn("\nerror union 2\ntype: {}\nvalue: {}\n",
@typeName(@typeOf(number_or_error)), number_or_error);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-exe values.zig
$ ./values
1 + 1 = 2
7.0 / 3.0 = 2.333333
false
true
false
nullable 1
type: ?[]const u8
value: null
nullable 2
type: ?[]const u8
value: hi
error union 1
type: %i32
value: error.ArgNotFound
error union 2
type: %i32
value: 1234< / code > < / pre >
< h3 id = "primitive-types" > Primitive Types< / h2 >
< table >
< tr >
< th >
Name
< / th >
< th >
C Equivalent
< / th >
< th >
Description
< / th >
< / tr >
< tr >
< td > < code > i2< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > signed 2-bit integer< / td >
< / tr >
< tr >
< td > < code > u2< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > unsigned 2-bit integer< / td >
< / tr >
< tr >
< td > < code > i3< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > signed 3-bit integer< / td >
< / tr >
< tr >
< td > < code > u3< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > unsigned 3-bit integer< / td >
< / tr >
< tr >
< td > < code > i4< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > signed 4-bit integer< / td >
< / tr >
< tr >
< td > < code > u4< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > unsigned 4-bit integer< / td >
< / tr >
< tr >
< td > < code > i5< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > signed 5-bit integer< / td >
< / tr >
< tr >
< td > < code > u5< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > unsigned 5-bit integer< / td >
< / tr >
< tr >
< td > < code > i6< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > signed 6-bit integer< / td >
< / tr >
< tr >
< td > < code > u6< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > unsigned 6-bit integer< / td >
< / tr >
< tr >
< td > < code > i7< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > signed 7-bit integer< / td >
< / tr >
< tr >
< td > < code > u7< / code > < / td >
< td > < code > (none)< / code > < / td >
< td > unsigned 7-bit integer< / td >
< / tr >
< tr >
< td > < code > i8< / code > < / td >
< td > < code > int8_t< / code > < / td >
< td > signed 8-bit integer< / td >
< / tr >
< tr >
< td > < code > u8< / code > < / td >
< td > < code > uint8_t< / code > < / td >
< td > unsigned 8-bit integer< / td >
< / tr >
< tr >
< td > < code > i16< / code > < / td >
< td > < code > int16_t< / code > < / td >
< td > signed 16-bit integer< / td >
< / tr >
< tr >
< td > < code > u16< / code > < / td >
< td > < code > uint16_t< / code > < / td >
< td > unsigned 16-bit integer< / td >
< / tr >
< tr >
< td > < code > i32< / code > < / td >
< td > < code > int32_t< / code > < / td >
< td > signed 32-bit integer< / td >
< / tr >
< tr >
< td > < code > u32< / code > < / td >
< td > < code > uint32_t< / code > < / td >
< td > unsigned 32-bit integer< / td >
< / tr >
< tr >
< td > < code > i64< / code > < / td >
< td > < code > int64_t< / code > < / td >
< td > signed 64-bit integer< / td >
< / tr >
< tr >
< td > < code > u64< / code > < / td >
< td > < code > uint64_t< / code > < / td >
< td > unsigned 64-bit integer< / td >
< / tr >
< tr >
< td > < code > i128< / code > < / td >
< td > < code > __int128< / code > < / td >
< td > signed 128-bit integer< / td >
< / tr >
< tr >
< td > < code > u128< / code > < / td >
< td > < code > unsigned __int128< / code > < / td >
< td > unsigned 128-bit integer< / td >
< / tr >
< tr >
< td > < code > isize< / code > < / td >
< td > < code > intptr_t< / code > < / td >
< td > signed pointer sized integer< / td >
< / tr >
< tr >
< td > < code > usize< / code > < / td >
< td > < code > uintptr_t< / code > < / td >
< td > unsigned pointer sized integer< / td >
< / tr >
< tr >
< td > < code > c_short< / code > < / td >
< td > < code > short< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_ushort< / code > < / td >
< td > < code > unsigned short< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_int< / code > < / td >
< td > < code > int< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_uint< / code > < / td >
< td > < code > unsigned int< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_long< / code > < / td >
< td > < code > long< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_ulong< / code > < / td >
< td > < code > unsigned long< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_longlong< / code > < / td >
< td > < code > long long< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_ulonglong< / code > < / td >
< td > < code > unsigned long long< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_longdouble< / code > < / td >
< td > < code > long double< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > c_void< / code > < / td >
< td > < code > void< / code > < / td >
< td > for ABI compatibility with C< / td >
< / tr >
< tr >
< td > < code > f32< / code > < / td >
< td > < code > float< / code > < / td >
< td > 32-bit floating point (23-bit mantissa)< / td >
< / tr >
< tr >
< td > < code > f64< / code > < / td >
< td > < code > double< / code > < / td >
< td > 64-bit floating point (52-bit mantissa)< / td >
< / tr >
< tr >
< td > < code > f128< / code > < / td >
< td > (none)< / td >
< td > 128-bit floating point (112-bit mantissa)< / td >
< / tr >
< tr >
< td > < code > bool< / code > < / td >
< td > < code > bool< / code > < / td >
< td > < code > true< / code > or < code > false< / code > < / td >
< / tr >
< tr >
< td > < code > void< / code > < / td >
< td > (none)< / td >
< td > 0 bit type< / td >
< / tr >
< tr >
< td > < code > noreturn< / code > < / td >
< td > (none)< / td >
< td > the type of < code > break< / code > , < code > continue< / code > , < code > goto< / code > , < code > return< / code > , < code > unreachable< / code > , and < code > while (true) {}< / code > < / td >
< / tr >
< tr >
< td > < code > type< / code > < / td >
< td > (none)< / td >
< td > the type of types< / td >
< / tr >
< tr >
< td > < code > error< / code > < / td >
< td > (none)< / td >
< td > an error code< / td >
< / tr >
< / table >
< p > See also:< / p >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< li > < a href = "#void" > void< / a > < / li >
< li > < a href = "#errors" > Errors< / a > < / li >
< / ul >
< h3 id = "primitive-values" > Primitive Values< / h3 >
< table >
< tr >
< th >
Name
< / th >
< th >
Description
< / th >
< / tr >
< tr >
< td > < code > true< / code > and < code > false< / code > < / td >
< td > < code > bool< / code > values< / td >
< / tr >
< tr >
< td > < code > null< / code > < / td >
< td > used to set a nullable type to < code > null< / code > < / td >
< / tr >
< tr >
< td > < code > undefined< / code > < / td >
< td > used to leave a value unspecified< / td >
< / tr >
< tr >
< td > < code > this< / code > < / td >
< td > refers to the thing in immediate scope< / td >
< / tr >
< / table >
< p > See also:< / p >
< ul >
< li > < a href = "#nullables" > Nullables< / a > < / li >
< li > < a href = "#this" > this< / a > < / li >
< / ul >
< h3 id = "string-literals" > String Literals< / h3 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const mem = @import("std").mem;
test "string literals" {
// In Zig a string literal is an array of bytes.
const normal_bytes = "hello";
assert(@typeOf(normal_bytes) == [5]u8);
assert(normal_bytes.len == 5);
assert(normal_bytes[1] == 'e');
assert('e' == '\x65');
assert(mem.eql(u8, "hello", "h\x65llo"));
// A C string literal is a null terminated pointer.
const null_terminated_bytes = c"hello";
assert(@typeOf(null_terminated_bytes) == & const u8);
assert(null_terminated_bytes[5] == 0);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test string_literals.zig
Test 1/1 string literals...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#arrays" > Arrays< / a > < / li >
< li > < a href = "#zig-test" > Zig Test< / a > < / li >
< / ul >
< h4 id = "string-literal-escapes" > Escape Sequences< / h4 >
< table >
< tr >
< th >
Escape Sequence
< / th >
< th >
Name
< / th >
< / tr >
< tr >
< td > < code > \n< / code > < / td >
< td > Newline< / td >
< / tr >
< tr >
< td > < code > \r< / code > < / td >
< td > Carriage Return< / td >
< / tr >
< tr >
< td > < code > \t< / code > < / td >
< td > Tab< / td >
< / tr >
< tr >
< td > < code > \\< / code > < / td >
< td > Backslash< / td >
< / tr >
< tr >
< td > < code > \'< / code > < / td >
< td > Single Quote< / td >
< / tr >
< tr >
< td > < code > \"< / code > < / td >
< td > Double Quote< / td >
< / tr >
< tr >
< td > < code > \xNN< / code > < / td >
< td > hexadecimal 8-bit character code (2 digits)< / td >
< / tr >
< tr >
< td > < code > \uNNNN< / code > < / td >
< td > hexadecimal 16-bit Unicode character code UTF-8 encoded (4 digits)< / td >
< / tr >
< tr >
< td > < code > \UNNNNNN< / code > < / td >
< td > hexadecimal 24-bit Unicode character code UTF-8 encoded (6 digits)< / td >
< / tr >
< / table >
< p > Note that the maximum valid Unicode point is < code > 0x10ffff< / code > .< / p >
< h4 id = "multiline-string-literals" > Multiline String Literals< / h4 >
< p >
Multiline string literals have no escapes and can span across multiple lines.
To start a multiline string literal, use the < code > \\< / code > token. Just like a comment,
the string literal goes until the end of the line. The end of the line is
not included in the string literal.
However, if the next line begins with < code > \\< / code > then a newline is appended and
the string literal continues.
< / p >
< pre > < code class = "zig" > const hello_world_in_c =
\\#include < stdio.h>
\\
\\int main(int argc, char **argv) {
\\ printf("hello world\n");
\\ return 0;
\\}
;< / code > < / pre >
< p >
For a multiline C string literal, prepend < code > c< / code > to each < code > \\< / code > :
< / p >
< pre > < code class = "zig" > const c_string_literal =
c\\#include < stdio.h>
c\\
c\\int main(int argc, char **argv) {
c\\ printf("hello world\n");
c\\ return 0;
c\\}
;< / code > < / pre >
< p >
In this example the variable < code > c_string_literal< / code > has type < code > & const char< / code > and
has a terminating null byte.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-embedFile" > @embedFile< / a > < / li >
< / ul >
< h3 id = "values-assignment" > Assignment< / h3 >
< p > Use < code > const< / code > to assign a value to an identifier:< / p >
< pre > < code class = "zig" > const x = 1234;
fn foo() {
// It works at global scope as well as inside functions.
const y = 5678;
// Once assigned, an identifier cannot be changed.
y += 1;
}
test "assignment" {
foo();
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
test.zig:8:7: error: cannot assign to constant
y += 1;
^< / code > < / pre >
< p > If you need a variable that you can modify, use < code > var< / code > :< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "var" {
var y: i32 = 5678;
y += 1;
assert(y == 5679);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/1 assignment...OK< / code > < / pre >
< p > Variables must be initialized:< / p >
< pre > < code class = "zig" > test "initialization" {
var x: i32;
x = 1;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
test.zig:3:5: error: variables must be initialized
var x: i32;
^< / code > < / pre >
< p > Use < code > undefined< / code > to leave variables uninitialized:< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "init with undefined" {
var x: i32 = undefined;
x = 1;
assert(x == 1);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/1 init with undefined...OK< / code > < / pre >
< h2 id = "integers" > Integers< / h2 >
< h3 id = "integer-literals" > Integer Literals< / h3 >
< pre > < code class = "zig" > const decimal_int = 98222;
const hex_int = 0xff;
const another_hex_int = 0xFF;
const octal_int = 0o755;
const binary_int = 0b11110000;< / code > < / pre >
< h3 id = "runtime-integer-values" > Runtime Integer Values< / h3 >
< p >
Integer literals have no size limitation, and if any undefined behavior occurs,
the compiler catches it.
< / p >
< p >
However, once an integer value is no longer known at compile-time, it must have a
known size, and is vulnerable to undefined behavior.
< / p >
< pre > < code class = "zig" > fn divide(a: i32, b: i32) -> i32 {
return a / b;
}< / code > < / pre >
< p >
In this function, values < code > a< / code > and < code > b< / code > are known only at runtime,
and thus this division operation is vulnerable to both integer overflow and
division by zero.
< / p >
< p >
Operators such as < code > +< / code > and < code > -< / code > cause undefined behavior on
integer overflow. Also available are operations such as < code > +%< / code > and
< code > -%< / code > which are defined to have wrapping arithmetic on all targets.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#undef-integer-overflow" > Integer Overflow< / a > < / li >
< li > < a href = "#undef-division-by-zero" > Division By Zero< / a > < / li >
< li > < a href = "#undef-int-overflow-wrap" > Wrapping Operations< / a > < / li >
< / ul >
< h2 id = "floats" > Floats< / h2 >
< h3 id = "float-literals" > Float Literals< / h3 >
< pre > < code class = "zig" > const floating_point = 123.0E+77;
const another_float = 123.0;
const yet_another = 123.0e+77;
const hex_floating_point = 0x103.70p-5;
const another_hex_float = 0x103.70;
const yet_another_hex_float = 0x103.70P-5;< / code > < / pre >
< h3 id = "float-operations" > Floating Point Operations< / h3 >
< p > By default floating point operations use < code > Optimized< / code > mode,
but you can switch to < code > Strict< / code > mode on a per-block basis:< / p >
< p > foo.zig< / p >
< pre > < code class = "zig" > const builtin = @import("builtin");
const big = f64(1 < < 40);
export fn foo_strict(x: f64) -> f64 {
@setFloatMode(this, builtin.FloatMode.Strict);
return x + big - big;
}
export fn foo_optimized(x: f64) -> f64 {
return x + big - big;
}< / code > < / pre >
< p > test.zig< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
extern fn foo_strict(x: f64) -> f64;
extern fn foo_optimized(x: f64) -> f64;
pub fn main() -> %void {
const x = 0.001;
warn("optimized = {}\n", foo_optimized(x));
warn("strict = {}\n", foo_strict(x));
}< / code > < / pre >
< p > For this test we have to separate code into two object files -
otherwise the optimizer figures out all the values at compile-time,
which operates in strict mode.< / p >
< pre > < code class = "sh" > $ zig build-obj foo.zig --release-fast
$ zig build-exe test.zig --object foo.o
$ ./test
optimized = 1.0e-2
strict = 9.765625e-3< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-setFloatMode" > @setFloatMode< / a > < / li >
< li > < a href = "#undef-division-by-zero" > Division By Zero< / a > < / li >
< / ul >
< h2 id = "operators" > Operators< / h2 >
< h3 id = "operators-table" > Table of Operators< / h2 >
< table >
< tr >
< th >
Syntax
< / th >
< th >
Relevant Types
< / th >
< th >
Description
< / th >
< th >
Example
< / th >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a + b
a += b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td > Addition.
< ul >
< li > Can cause < a href = "#undef-integer-overflow" > overflow< / a > for integers.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > 2 + 5 == 7< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a +% b
a +%= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Wrapping Addition.
< ul >
< li > Guaranteed to have twos-complement wrapping behavior.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > u32(@maxValue(u32)) +% 1 == 0< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a - b
a -= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td > Subtraction.
< ul >
< li > Can cause < a href = "#undef-integer-overflow" > overflow< / a > for integers.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > 2 - 5 == -3< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a -% b
a -%= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Wrapping Subtraction.
< ul >
< li > Guaranteed to have twos-complement wrapping behavior.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > u32(0) -% 1 == @maxValue(u32)< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > -a< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td >
Negation.
< ul >
< li > Can cause < a href = "#undef-integer-overflow" > overflow< / a > for integers.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > -1 == 0 - 1< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > -%a< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td >
Wrapping Negation.
< ul >
< li > Guaranteed to have twos-complement wrapping behavior.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > -%i32(@minValue(i32)) == @minValue(i32)< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a * b
a *= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td > Multiplication.
< ul >
< li > Can cause < a href = "#undef-integer-overflow" > overflow< / a > for integers.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > 2 * 5 == 10< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a *% b
a *%= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Wrapping Multiplication.
< ul >
< li > Guaranteed to have twos-complement wrapping behavior.< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > u8(200) *% 2 == 144< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a / b
a /= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td > Divison.
< ul >
< li > Can cause < a href = "#undef-integer-overflow" > overflow< / a > for integers.< / li >
< li > Can cause < a href = "#undef-division-by-zero" > division by zero< / a > for integers.< / li >
< li > Can cause < a href = "#undef-division-by-zero" > division by zero< / a > for floats in < a href = "#float-operations" > FloatMode.Optimized Mode< / a > .< / li >
< li > For non-compile-time-known signed integers, must use
< a href = "#builtin-divTrunc" > @divTrunc< / a > ,
< a href = "#builtin-divFloor" > @divFloor< / a > , or
< a href = "#builtin-divExact" > @divExact< / a > instead of < code > /< / code > .
< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > 10 / 5 == 2< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a % b
a %= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td > Remainder Division.
< ul >
< li > Can cause < a href = "#undef-division-by-zero" > division by zero< / a > for integers.< / li >
< li > Can cause < a href = "#undef-division-by-zero" > division by zero< / a > for floats in < a href = "#float-operations" > FloatMode.Optimized Mode< / a > .< / li >
< li > For non-compile-time-known signed integers, must use
< a href = "#builtin-rem" > @rem< / a > or
< a href = "#builtin-mod" > @mod< / a > instead of < code > %< / code > .
< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > 10 % 3 == 1< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a < < b
a < < = b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Bit Shift Left.
< ul >
< li > See also < a href = "#builtin-shlExact" > @shlExact< / a > .< / li >
< li > See also < a href = "#builtin-shlWithOverflow" > @shlWithOverflow< / a > .< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > 1 < < 8 == 256< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a > > b
a > > = b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Bit Shift Right.
< ul >
< li > See also < a href = "#builtin-shrExact" > @shrExact< / a > .< / li >
< / ul >
< / td >
< td >
< pre > < code class = "zig" > 10 > > 1 == 5< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a & b
a & = b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Bitwise AND.
< / td >
< td >
< pre > < code class = "zig" > 0b011 & 0b101 == 0b001< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a | b
a |= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Bitwise OR.
< / td >
< td >
< pre > < code class = "zig" > 0b010 | 0b100 == 0b110< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a ^ b
a ^= b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td > Bitwise XOR.
< / td >
< td >
< pre > < code class = "zig" > 0b011 ^ 0b101 == 0b110< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > ~a< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< / ul >
< / td >
< td >
Bitwise NOT.
< / td >
< td >
< pre > < code class = "zig" > ~u8(0b0101111) == 0b1010000< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a ?? b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#nullables" > Nullables< / a > < / li >
< / ul >
< / td >
< td > If < code > a< / code > is < code > null< / code > ,
returns < code > b< / code > ("default value"),
otherwise returns the unwrapped value of < code > a< / code > .
Note that < code > b< / code > may be a value of type < a href = "#noreturn" > noreturn< / a > .
< / td >
< td >
< pre > < code class = "zig" > const value: ?u32 = null;
const unwrapped = value ?? 1234;
unwrapped == 1234< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > ??a< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#nullables" > Nullables< / a > < / li >
< / ul >
< / td >
< td >
Equivalent to:
< pre > < code class = "zig" > a ?? unreachable< / code > < / pre >
< / td >
< td >
< pre > < code class = "zig" > const value: ?u32 = 5678;
??value == 5678< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a %% b
a %% |err| b< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#errors" > Error Unions< / a > < / li >
< / ul >
< / td >
< td > If < code > a< / code > is an < code > error< / code > ,
returns < code > b< / code > ("default value"),
otherwise returns the unwrapped value of < code > a< / code > .
Note that < code > b< / code > may be a value of type < a href = "#noreturn" > noreturn< / a > .
< code > err< / code > is the < code > error< / code > and is in scope of the expression < code > b< / code > .
< / td >
< td >
< pre > < code class = "zig" > const value: %u32 = null;
const unwrapped = value %% 1234;
unwrapped == 1234< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > %%a< / code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#errors" > Error Unions< / a > < / li >
< / ul >
< / td >
< td > Equivalent to:
< pre > < code class = "zig" > a %% unreachable< / code > < / pre >
< / td >
< td >
< pre > < code class = "zig" > const value: %u32 = 5678;
%%value == 5678< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a and b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#primitive-types" > bool< / a > < / li >
< / ul >
< / td >
< td >
If < code > a< / code > is < code > false< / code > , returns < code > false< / code >
without evaluating < code > b< / code > . Otherwise, retuns < code > b< / code > .
< / td >
< td >
< pre > < code class = "zig" > false and true == false< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a or b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#primitive-types" > bool< / a > < / li >
< / ul >
< / td >
< td >
If < code > a< / code > is < code > true< / code > , returns < code > true< / code >
without evaluating < code > b< / code > . Otherwise, retuns < code > b< / code > .
< / td >
< td >
< pre > < code class = "zig" > false or true == true< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > !a< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#primitive-types" > bool< / a > < / li >
< / ul >
< / td >
< td >
Boolean NOT.
< / td >
< td >
< pre > < code class = "zig" > !false == true< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a == b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< li > < a href = "#primitive-types" > bool< / a > < / li >
< li > < a href = "#primitive-types" > type< / a > < / li >
< / ul >
< / td >
< td >
Returns < code > true< / code > if a and b are equal, otherwise returns < code > false< / code > .
< / td >
< td >
< pre > < code class = "zig" > (1 == 1) == true< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a == null< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#nullables" > Nullables< / a > < / li >
< / ul >
< / td >
< td >
Returns < code > true< / code > if a is < code > null< / code > , otherwise returns < code > false< / code > .
< / td >
< td >
< pre > < code class = "zig" > const value: ?u32 = null;
value == null< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a != b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< li > < a href = "#primitive-types" > bool< / a > < / li >
< li > < a href = "#primitive-types" > type< / a > < / li >
< / ul >
< / td >
< td >
Returns < code > false< / code > if a and b are equal, otherwise returns < code > true< / code > .
< / td >
< td >
< pre > < code class = "zig" > (1 != 1) == false< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a > b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td >
Returns < code > true< / code > if a is greater than b, otherwise returns < code > false< / code > .
< / td >
< td >
< pre > < code class = "zig" > (2 > 1) == true< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a > = b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td >
Returns < code > true< / code > if a is greater than or equal to b, otherwise returns < code > false< / code > .
< / td >
< td >
< pre > < code class = "zig" > (2 > = 1) == true< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a < b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td >
Returns < code > true< / code > if a is less than b, otherwise returns < code > false< / code > .
< / td >
< td >
< pre > < code class = "zig" > (1 < 2) == true< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a < = b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#integers" > Integers< / a > < / li >
< li > < a href = "#floats" > Floats< / a > < / li >
< / ul >
< / td >
< td >
Returns < code > true< / code > if a is less than or equal to b, otherwise returns < code > false< / code > .
< / td >
< td >
< pre > < code class = "zig" > (1 < = 2) == true< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a ++ b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#arrays" > Arrays< / a > < / li >
< / ul >
< / td >
< td >
Array concatenation.
< ul >
< li > Only available when < code > a< / code > and < code > b< / code > are < a href = "#comptime" > compile-time known< / a > .
< / ul >
< / td >
< td >
< pre > < code class = "zig" > const mem = @import("std").mem;
const array1 = []u32{1,2};
const array2 = []u32{3,4};
const together = array1 ++ array2;
mem.eql(u32, together, []u32{1,2,3,4})< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > a ** b< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#arrays" > Arrays< / a > < / li >
< / ul >
< / td >
< td >
Array multiplication.
< ul >
< li > Only available when < code > a< / code > and < code > b< / code > are < a href = "#comptime" > compile-time known< / a > .
< / ul >
< / td >
< td >
< pre > < code class = "zig" > const mem = @import("std").mem;
const pattern = "ab" ** 3;
mem.eql(u8, pattern, "ababab")< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > *a< code > < / pre > < / td >
< td >
< ul >
< li > < a href = "#pointers" > Pointers< / a > < / li >
< / ul >
< / td >
< td >
Pointer dereference.
< / td >
< td >
< pre > < code class = "zig" > const x: u32 = 1234;
const ptr = & x;
*x == 1234< / code > < / pre >
< / td >
< / tr >
< tr >
< td > < pre > < code class = "zig" > & a< code > < / pre > < / td >
< td >
All types
< / td >
< td >
Address of.
< / td >
< td >
< pre > < code class = "zig" > const x: u32 = 1234;
const ptr = & x;
*x == 1234< / code > < / pre >
< / td >
< / tr >
< / table >
< h3 id = "operators-precedence" > Precedence< / h3 >
< pre > < code > x() x[] x.y
!x -x -%x ~x *x & x ?x %x %%x ??x
x{}
* / % ** *%
+ - ++ +% -%
< < > >
&
^
|
== != < > < = > =
and
or
?? %%
= *= /= %= += -= < < = > > = & = ^= |=< / code > < / pre >
< h2 id = "arrays" > Arrays< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const mem = @import("std").mem;
// array literal
const message = []u8{'h', 'e', 'l', 'l', 'o'};
// get the size of an array
comptime {
assert(message.len == 5);
}
// a string literal is an array literal
const same_message = "hello";
comptime {
assert(mem.eql(u8, message, same_message));
assert(@typeOf(message) == @typeOf(same_message));
}
test "iterate over an array" {
var sum: usize = 0;
for (message) |byte| {
sum += byte;
}
assert(sum == usize('h') + usize('e') + usize('l') * 2 + usize('o'));
}
// modifiable array
var some_integers: [100]i32 = undefined;
test "modify an array" {
for (some_integers) |*item, i| {
*item = i32(i);
}
assert(some_integers[10] == 10);
assert(some_integers[99] == 99);
}
// array concatenation works if the values are known
// at compile time
const part_one = []i32{1, 2, 3, 4};
const part_two = []i32{5, 6, 7, 8};
const all_of_it = part_one ++ part_two;
comptime {
assert(mem.eql(i32, all_of_it, []i32{1,2,3,4,5,6,7,8}));
}
// remember that string literals are arrays
const hello = "hello";
const world = "world";
const hello_world = hello ++ " " ++ world;
comptime {
assert(mem.eql(u8, hello_world, "hello world"));
}
// ** does repeating patterns
const pattern = "ab" ** 3;
comptime {
assert(mem.eql(u8, pattern, "ababab"));
}
// initialize an array to zero
const all_zero = []u16{0} ** 10;
comptime {
assert(all_zero.len == 10);
assert(all_zero[5] == 0);
}
// use compile-time code to initialize an array
var fancy_array = {
var initial_value: [10]Point = undefined;
for (initial_value) |*pt, i| {
*pt = Point {
.x = i32(i),
.y = i32(i) * 2,
};
}
initial_value
};
const Point = struct {
x: i32,
y: i32,
};
test "compile-time array initalization" {
assert(fancy_array[4].x == 4);
assert(fancy_array[4].y == 8);
}
// call a function to initialize an array
var more_points = []Point{makePoint(3)} ** 10;
fn makePoint(x: i32) -> Point {
Point {
.x = x,
.y = x * 2,
}
}
test "array initialization with function calls" {
assert(more_points[4].x == 3);
assert(more_points[4].y == 6);
assert(more_points.len == 10);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test arrays.zig
Test 1/4 iterate over an array...OK
Test 2/4 modify an array...OK
Test 3/4 compile-time array initalization...OK
Test 4/4 array initialization with function calls...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#for" > for< / a > < / li >
< li > < a href = "#slices" > Slices< / a > < / li >
< / ul >
< h2 id = "pointers" > Pointers< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "address of syntax" {
// Get the address of a variable:
const x: i32 = 1234;
const x_ptr = &x;
// Deference a pointer:
assert(*x_ptr == 1234);
// When you get the address of a const variable, you get a const pointer.
assert(@typeOf(x_ptr) == & const i32);
// If you want to mutate the value, you'd need an address of a mutable variable:
var y: i32 = 5678;
const y_ptr = &y;
assert(@typeOf(y_ptr) == & i32);
*y_ptr += 1;
assert(*y_ptr == 5679);
}
test "pointer array access" {
// Pointers do not support pointer arithmetic. If you
// need such a thing, use array index syntax:
var array = []u8{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
const ptr = & array[1];
assert(array[2] == 3);
ptr[1] += 1;
assert(array[2] == 4);
}
test "pointer slicing" {
// In Zig, we prefer using slices over null-terminated pointers.
// You can turn a pointer into a slice using slice syntax:
var array = []u8{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
const ptr = & array[1];
const slice = ptr[1..3];
assert(slice.ptr == & ptr[1]);
assert(slice.len == 2);
// Slices have bounds checking and are therefore protected
// against this kind of undefined behavior. This is one reason
// we prefer slices to pointers.
assert(array[3] == 4);
slice[1] += 1;
assert(array[3] == 5);
}
comptime {
// Pointers work at compile-time too, as long as you don't use
// @ptrCast.
var x: i32 = 1;
const ptr = & x;
*ptr += 1;
x += 1;
assert(*ptr == 3);
}
test "@ptrToInt and @intToPtr" {
// To convert an integer address into a pointer, use @intToPtr:
const ptr = @intToPtr(& i32, 0xdeadbeef);
// To convert a pointer to an integer, use @ptrToInt:
const addr = @ptrToInt(ptr);
assert(@typeOf(addr) == usize);
assert(addr == 0xdeadbeef);
}
comptime {
// Zig is able to do this at compile-time, as long as
// ptr is never dereferenced.
const ptr = @intToPtr(& i32, 0xdeadbeef);
const addr = @ptrToInt(ptr);
assert(@typeOf(addr) == usize);
assert(addr == 0xdeadbeef);
}
test "volatile" {
// In Zig, loads and stores are assumed to not have side effects.
// If a given load or store should have side effects, such as
// Memory Mapped Input/Output (MMIO), use `volatile`:
const mmio_ptr = @intToPtr(& volatile u8, 0x12345678);
// Now loads and stores with mmio_ptr are guaranteed to all happen
// and in the same order as in source code.
assert(@typeOf(mmio_ptr) == & volatile u8);
}
test "nullable pointers" {
// Pointers cannot be null. If you want a null pointer, use the nullable
// prefix `?` to make the pointer type nullable.
var ptr: ?& i32 = null;
var x: i32 = 1;
ptr = & x;
assert(*??ptr == 1);
// Nullable pointers are the same size as normal pointers, because pointer
// value 0 is used as the null value.
assert(@sizeOf(?& i32) == @sizeOf(& i32));
}
test "pointer casting" {
// To convert one pointer type to another, use @ptrCast. This is an unsafe
// operation that Zig cannot protect you against. Use @ptrCast only when other
// conversions are not possible.
const bytes = []u8{0x12, 0x12, 0x12, 0x12};
const u32_ptr = @ptrCast(& const u32, & bytes[0]);
assert(*u32_ptr == 0x12121212);
// Even this example is contrived - there are better ways to do the above than
// pointer casting. For example, using a slice narrowing cast:
const u32_value = ([]const u32)(bytes[0..])[0];
assert(u32_value == 0x12121212);
// And even another way, the most straightforward way to do it:
assert(@bitCast(u32, bytes) == 0x12121212);
}
test "pointer child type" {
// pointer types have a `child` field which tells you the type they point to.
assert((& u32).child == u32);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/8 address of syntax...OK
Test 2/8 pointer array access...OK
Test 3/8 pointer slicing...OK
Test 4/8 @ptrToInt and @intToPtr...OK
Test 5/8 volatile...OK
Test 6/8 nullable pointers...OK
Test 7/8 pointer casting...OK
Test 8/8 pointer child type...OK< / code > < / pre >
< h3 id = "alignment" > Alignment< / h3 >
< p >
Each type has an < strong > alignment< / strong > - a number of bytes such that,
when a value of the type is loaded from or stored to memory,
the memory address must be evenly divisible by this number. You can use
< a href = "#builtin-alignOf" > @alignOf< / a > to find out this value for any type.
< / p >
< p >
Alignment depends on the CPU architecture, but is always a power of two, and
less than < code > 1 < < 29< / code > .
< / p >
< p >
In Zig, a pointer type has an alignment value. If the value is equal to the
alignment of the underlying type, it can be omitted from the type:
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const builtin = @import("builtin");
test "variable alignment" {
var x: i32 = 1234;
const align_of_i32 = @alignOf(@typeOf(x));
assert(@typeOf(& x) == & i32);
assert(& i32 == & align(align_of_i32) i32);
if (builtin.arch == builtin.Arch.x86_64) {
assert((& i32).alignment == 4);
}
}< / code > < / pre >
< p > In the same way that a < code > & i32< / code > can be implicitly cast to a
< code > & const i32< / code > , a pointer with a larger alignment can be implicitly
cast to a pointer with a smaller alignment, but not vice versa.
< / p >
< p >
You can specify alignment on variables and functions. If you do this, then
pointers to them get the specified alignment:
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
var foo: u8 align(4) = 100;
test "global variable alignment" {
assert(@typeOf(& foo).alignment == 4);
assert(@typeOf(& foo) == & align(4) u8);
const slice = (& foo)[0..1];
assert(@typeOf(slice) == []align(4) u8);
}
fn derp() align(@sizeOf(usize) * 2) -> i32 { 1234 }
fn noop1() align(1) {}
fn noop4() align(4) {}
test "function alignment" {
assert(derp() == 1234);
assert(@typeOf(noop1) == fn() align(1));
assert(@typeOf(noop4) == fn() align(4));
noop1();
noop4();
}< / code > < / pre >
< p >
If you have a pointer or a slice that has a small alignment, but you know that it actually
has a bigger alignment, use < a href = "#builtin-alignCast" > @alignCast< / a > to change the
pointer into a more aligned pointer. This is a no-op at runtime, but inserts a
< a href = "#undef-incorrect-pointer-alignment" > safety check< / a > :
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "pointer alignment safety" {
var array align(4) = []u32{0x11111111, 0x11111111};
const bytes = ([]u8)(array[0..]);
assert(foo(bytes) == 0x11111111);
}
fn foo(bytes: []u8) -> u32 {
const slice4 = bytes[1..5];
const int_slice = ([]u32)(@alignCast(4, slice4));
return int_slice[0];
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/1 pointer alignment safety...incorrect alignment
/home/andy/dev/zig/build/lib/zig/std/special/zigrt.zig:16:35: 0x0000000000203525 in ??? (test)
@import("std").debug.panic("{}", message_ptr[0..message_len]);
^
/home/andy/dev/zig/build/test.zig:10:45: 0x00000000002035ec in ??? (test)
const int_slice = ([]u32)(@alignCast(4, slice4));
^
/home/andy/dev/zig/build/test.zig:6:15: 0x0000000000203439 in ??? (test)
assert(foo(bytes) == 0x11111111);
^
/home/andy/dev/zig/build/lib/zig/std/special/test_runner.zig:9:21: 0x00000000002162d8 in ??? (test)
test_fn.func();
^
/home/andy/dev/zig/build/lib/zig/std/special/bootstrap.zig:60:21: 0x0000000000216197 in ??? (test)
return root.main();
^
/home/andy/dev/zig/build/lib/zig/std/special/bootstrap.zig:47:13: 0x0000000000216050 in ??? (test)
callMain(argc, argv, envp) %% std.os.posix.exit(1);
^
/home/andy/dev/zig/build/lib/zig/std/special/bootstrap.zig:34:25: 0x0000000000215fa0 in ??? (test)
posixCallMainAndExit()
^
Tests failed. Use the following command to reproduce the failure:
./test< / code > < / pre >
< h3 id = "type-based-alias-analysis" > Type Based Alias Analysis< / h3 >
< p > Zig uses Type Based Alias Analysis (also known as Strict Aliasing) to
perform some optimizations. This means that pointers of different types must
not alias the same memory, with the exception of < code > u8< / code > . Pointers to
< code > u8< / code > can alias any memory.
< / p >
< p > As an example, this code produces undefined behavior:< / p >
< pre > < code class = "zig" > *@ptrCast(& u32, f32(12.34))< / code > < / pre >
< p > Instead, use < a href = "#builtin-bitCast" > @bitCast< / a > :
< pre > < code class = "zig" > @bitCast(u32, f32(12.34))< / code > < / pre >
< p > As an added benefit, the < code > @bitcast< / code > version works at compile-time.< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#slices" > Slices< / a > < / li >
< li > < a href = "#memory" > Memory< / a > < / li >
< / ul >
< h2 id = "slices" > Slices< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "basic slices" {
var array = []i32{1, 2, 3, 4};
// A slice is a pointer and a length. The difference between an array and
// a slice is that the array's length is part of the type and known at
// compile-time, whereas the slice's length is known at runtime.
// Both can be accessed with the `len` field.
const slice = array[0..array.len];
assert(slice.ptr == & array[0]);
assert(slice.len == array.len);
// Slices have array bounds checking. If you try to access something out
// of bounds, you'll get a safety check failure:
slice[10] += 1;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/1 basic slices...index out of bounds
lib/zig/std/special/zigrt.zig:16:35: 0x0000000000203455 in ??? (test)
@import("std").debug.panic("{}", message_ptr[0..message_len]);
^
test.zig:15:10: 0x0000000000203334 in ??? (test)
slice[10] += 1;
^
lib/zig/std/special/test_runner.zig:9:21: 0x0000000000214b1a in ??? (test)
test_fn.func();
^
lib/zig/std/special/bootstrap.zig:60:21: 0x00000000002149e7 in ??? (test)
return root.main();
^
lib/zig/std/special/bootstrap.zig:47:13: 0x00000000002148a0 in ??? (test)
callMain(argc, argv, envp) %% std.os.posix.exit(1);
^
lib/zig/std/special/bootstrap.zig:34:25: 0x00000000002147f0 in ??? (test)
posixCallMainAndExit()
^
Tests failed. Use the following command to reproduce the failure:
./test< / code > < / pre >
< p > This is one reason we prefer slices to pointers.< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const mem = @import("std").mem;
const fmt = @import("std").fmt;
test "using slices for strings" {
// Zig has no concept of strings. String literals are arrays of u8, and
// in general the string type is []u8 (slice of u8).
// Here we implicitly cast [5]u8 to []const u8
const hello: []const u8 = "hello";
const world: []const u8 = "世界";
var all_together: [100]u8 = undefined;
// You can use slice syntax on an array to convert an array into a slice.
const all_together_slice = all_together[0..];
// String concatenation example:
const hello_world = fmt.bufPrint(all_together_slice, "{} {}", hello, world);
// Generally, you can use UTF-8 and not worry about whether something is a
// string. If you don't need to deal with individual characters, no need
// to decode.
assert(mem.eql(u8, hello_world, "hello 世界"));
}
test "slice pointer" {
var array: [10]u8 = undefined;
const ptr = & array[0];
// You can use slicing syntax to convert a pointer into a slice:
const slice = ptr[0..5];
slice[2] = 3;
assert(slice[2] == 3);
// The slice is mutable because we sliced a mutable pointer.
assert(@typeOf(slice) == []u8);
// You can also slice a slice:
const slice2 = slice[2..3];
assert(slice2.len == 1);
assert(slice2[0] == 3);
}
test "slice widening" {
// Zig supports slice widening and slice narrowing. Cast a slice of u8
// to a slice of anything else, and Zig will perform the length conversion.
const array = []u8{0x12, 0x12, 0x12, 0x12, 0x13, 0x13, 0x13, 0x13};
const slice = ([]const u32)(array[0..]);
assert(slice.len == 2);
assert(slice[0] == 0x12121212);
assert(slice[1] == 0x13131313);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/3 using slices for strings...OK
Test 2/3 slice pointer...OK
Test 3/3 slice widening...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#pointers" > Pointers< / a > < / li >
< li > < a href = "#for" > for< / a > < / li >
< li > < a href = "#arrays" > Arrays< / a > < / li >
< / ul >
< h2 id = "struct" > struct< / h2 >
< pre > < code class = "zig" > // Declare a struct.
// Zig gives no guarantees about the order of fields and whether or
// not there will be padding.
const Point = struct {
x: f32,
y: f32,
};
// Maybe we want to pass it to OpenGL so we want to be particular about
// how the bytes are arranged.
const Point2 = packed struct {
x: f32,
y: f32,
};
// Declare an instance of a struct.
const p = Point {
.x = 0.12,
.y = 0.34,
};
// Maybe we're not ready to fill out some of the fields.
var p2 = Point {
.x = 0.12,
.y = undefined,
};
// Structs can have methods
// Struct methods are not special, they are only namespaced
// functions that you can call with dot syntax.
const Vec3 = struct {
x: f32,
y: f32,
z: f32,
pub fn init(x: f32, y: f32, z: f32) -> Vec3 {
return Vec3 {
.x = x,
.y = y,
.z = z,
};
}
pub fn dot(self: & const Vec3, other: & const Vec3) -> f32 {
return self.x * other.x + self.y * other.y + self.z * other.z;
}
};
const assert = @import("std").debug.assert;
test "dot product" {
const v1 = Vec3.init(1.0, 0.0, 0.0);
const v2 = Vec3.init(0.0, 1.0, 0.0);
assert(v1.dot(v2) == 0.0);
// Other than being available to call with dot syntax, struct methods are
// not special. You can reference them as any other declaration inside
// the struct:
assert(Vec3.dot(v1, v2) == 0.0);
}
// Structs can have global declarations.
// Structs can have 0 fields.
const Empty = struct {
pub const PI = 3.14;
};
test "struct namespaced variable" {
assert(Empty.PI == 3.14);
assert(@sizeOf(Empty) == 0);
// you can still instantiate an empty struct
const does_nothing = Empty {};
}
// struct field order is determined by the compiler for optimal performance.
// however, you can still calculate a struct base pointer given a field pointer:
fn setYBasedOnX(x: & f32, y: f32) {
const point = @fieldParentPtr(Point, "x", x);
point.y = y;
}
test "field parent pointer" {
var point = Point {
.x = 0.1234,
.y = 0.5678,
};
setYBasedOnX(& point.x, 0.9);
assert(point.y == 0.9);
}
// You can return a struct from a function. This is how we do generics
// in Zig:
fn LinkedList(comptime T: type) -> type {
return struct {
pub const Node = struct {
prev: ?& Node,
next: ?& Node,
data: T,
};
first: ?& Node,
last: ?& Node,
len: usize,
};
}
test "linked list" {
// Functions called at compile-time are memoized. This means you can
// do this:
assert(LinkedList(i32) == LinkedList(i32));
var list = LinkedList(i32) {
.first = null,
.last = null,
.len = 0,
};
assert(list.len == 0);
// Since types are first class values you can instantiate the type
// by assigning it to a variable:
const ListOfInts = LinkedList(i32);
assert(ListOfInts == LinkedList(i32));
var node = ListOfInts.Node {
.prev = null,
.next = null,
.data = 1234,
};
var list2 = LinkedList(i32) {
.first = & node,
.last = & node,
.len = 1,
};
assert((??list2.first).data == 1234);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test structs.zig
Test 1/4 dot product...OK
Test 2/4 struct namespaced variable...OK
Test 3/4 field parent pointer...OK
Test 4/4 linked list...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#comptime" > comptime< / a > < / li >
< li > < a href = "#builtin-fieldParentPtr" > @fieldParentPtr< / a > < / li >
< / ul >
< h2 id = "enum" > enum< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const mem = @import("std").mem;
// Declare an enum.
const Type = enum {
Ok,
NotOk,
};
// Declare a specific instance of the enum variant.
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const c = Type.Ok;
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// If you want access to the ordinal value of an enum, you
// can specify the tag type.
const Value = enum(u2) {
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Zero,
One,
Two,
};
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// Now you can cast between u2 and Value.
// The ordinal value starts from 0, counting up for each member.
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test "enum ordinal value" {
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assert(u2(Value.Zero) == 0);
assert(u2(Value.One) == 1);
assert(u2(Value.Two) == 2);
}
// You can override the ordinal value for an enum.
const Value2 = enum(u32) {
Hundred = 100,
Thousand = 1000,
Million = 1000000,
};
test "set enum ordinal value" {
assert(u32(Value2.Hundred) == 100);
assert(u32(Value2.Thousand) == 1000);
assert(u32(Value2.Million) == 1000000);
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}
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// Enums can have methods, the same as structs and unions.
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// Enum methods are not special, they are only namespaced
// functions that you can call with dot syntax.
const Suit = enum {
Clubs,
Spades,
Diamonds,
Hearts,
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pub fn isClubs(self: Suit) -> bool {
return self == Suit.Clubs;
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}
};
test "enum method" {
const p = Suit.Spades;
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assert(!p.isClubs());
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}
// An enum variant of different types can be switched upon.
const Foo = enum {
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String,
Number,
None,
};
test "enum variant switch" {
const p = Foo.Number;
const what_is_it = switch (p) {
Foo.String => "this is a string",
Foo.Number => "this is a number",
Foo.None => "this is a none",
};
assert(mem.eql(u8, what_is_it, "this is a number"));
}
// @TagType can be used to access the integer tag type of an enum.
const Small = enum {
One,
Two,
Three,
Four,
};
test "@TagType" {
assert(@TagType(Small) == u2);
}
// @memberCount tells how many fields an enum has:
test "@memberCount" {
assert(@memberCount(Small) == 4);
}
// @memberName tells the name of a field in an enum:
test "@memberName" {
assert(mem.eql(u8, @memberName(Small, 1), "Two"));
}
// @tagName gives a []const u8 representation of an enum value:
test "@tagName" {
assert(mem.eql(u8, @tagName(Small.Three), "Three"));
}< / code > < / pre >
< p > TODO extern enum< / p >
< p > TODO packed enum< / p >
< pre > < code class = "sh" > $ zig test enum.zig
Test 1/8 enum ordinal value...OK
Test 2/8 set enum ordinal value...OK
Test 3/8 enum method...OK
Test 4/8 enum variant switch...OK
Test 5/8 @TagType...OK
Test 6/8 @memberCount...OK
Test 7/8 @memberName...OK
Test 8/8 @tagName...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-memberName" > @memberName< / a > < / li >
< li > < a href = "#builtin-memberCount" > @memberCount< / a > < / li >
< li > < a href = "#builtin-tagName" > @tagName< / a > < / li >
< / ul >
< h2 id = "union" > union< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const mem = @import("std").mem;
// A union has only 1 active field at a time.
const Payload = union {
Int: i64,
Float: f64,
Bool: bool,
};
test "simple union" {
var payload = Payload {.Int = 1234};
// payload.Float = 12.34; // ERROR! field not active
assert(payload.Int == 1234);
// You can activate another field by assigning the entire union.
payload = Payload {.Float = 12.34};
assert(payload.Float == 12.34);
}
// Unions can be given an enum tag type:
const ComplexTypeTag = enum { Ok, NotOk };
const ComplexType = union(ComplexTypeTag) {
Ok: u8,
NotOk: void,
};
// Declare a specific instance of the union variant.
test "declare union value" {
const c = ComplexType { .Ok = 0 };
assert(ComplexTypeTag(c) == ComplexTypeTag.Ok);
}
// @TagType can be used to access the enum tag type of a union.
test "@TagType" {
assert(@TagType(ComplexType) == ComplexTypeTag);
}
// Unions can be made to infer the enum tag type.
const Foo = union(enum) {
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String: []const u8,
Number: u64,
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// void can be omitted when inferring enum tag type.
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None,
};
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test "union variant switch" {
const p = Foo { .Number = 54 };
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const what_is_it = switch (p) {
// Capture by reference
Foo.String => |*x| {
"this is a string"
},
// Capture by value
Foo.Number => |x| {
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assert(x == 54);
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"this is a number"
},
Foo.None => {
"this is a none"
}
};
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assert(mem.eql(u8, what_is_it, "this is a number"));
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}
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// TODO union methods
const Small = union {
A: i32,
B: bool,
C: u8,
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};
2017-12-04 14:42:02 +08:00
// @memberCount tells how many fields a union has:
test "@memberCount" {
assert(@memberCount(Small) == 3);
}
// @memberName tells the name of a field in an enum:
test "@memberName" {
assert(mem.eql(u8, @memberName(Small, 1), "B"));
}
// @tagName gives a []const u8 representation of an enum value,
// but only if the union has an enum tag type.
const Small2 = union(enum) {
A: i32,
B: bool,
C: u8,
};
test "@tagName" {
assert(mem.eql(u8, @tagName(Small2.C), "C"));
2017-11-07 16:22:27 +08:00
}< / code > < / pre >
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< pre > < code class = "sh" > $ zig test union.zig
Test 1/7 simple union...OK
Test 2/7 declare union value...OK
Test 3/7 @TagType...OK
Test 4/7 union variant switch...OK
Test 5/7 @memberCount...OK
Test 6/7 @memberName...OK
Test 7/7 @tagName...OK< / code > < / pre >
2017-11-07 16:22:27 +08:00
< p >
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Unions with an enum tag are generated as a struct with a tag field and union field. Zig
2017-11-07 16:22:27 +08:00
sorts the order of the tag and union field by the largest alignment.
< / p >
< h2 id = "switch" > switch< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const builtin = @import("builtin");
test "switch simple" {
const a: u64 = 10;
const zz: u64 = 103;
// All branches of a switch expression must be able to be coerced to a
// common type.
//
// Branches cannot fallthrough. If fallthrough behavior is desired, combine
// the cases and use an if.
const b = switch (a) {
// Multiple cases can be combined via a ','
1, 2, 3 => 0,
// Ranges can be specified using the ... syntax. These are inclusive
// both ends.
5 ... 100 => 1,
// Branches can be arbitrarily complex.
101 => {
const c: u64 = 5;
c * 2 + 1
},
// Switching on arbitrary expressions is allowed as long as the
// expression is known at compile-time.
zz => zz,
comptime {
const d: u32 = 5;
const e: u32 = 100;
d + e
} => 107,
// The else branch catches everything not already captured.
// Else branches are mandatory unless the entire range of values
// is handled.
else => 9,
};
assert(b == 1);
}
test "switch enum" {
const Item = enum {
A: u32,
C: struct { x: u8, y: u8 },
D,
};
var a = Item.A { 3 };
// Switching on more complex enums is allowed.
const b = switch (a) {
// A capture group is allowed on a match, and will return the enum
// value matched.
Item.A => |item| item,
// A reference to the matched value can be obtained using `*` syntax.
Item.C => |*item| {
(*item).x += 1;
6
},
// No else is required if the types cases was exhaustively handled
Item.D => 8,
};
assert(b == 3);
}
// Switch expressions can be used outside a function:
const os_msg = switch (builtin.os) {
builtin.Os.linux => "we found a linux user",
else => "not a linux user",
};
// Inside a function, switch statements implicitly are compile-time
// evaluated if the target expression is compile-time known.
test "switch inside function" {
switch (builtin.os) {
builtin.Os.windows => {
// On an OS other than windows, block is not even analyzed,
// so this compile error is not triggered.
// On windows this compile error would be triggered.
@compileError("windows not supported");
},
else => {},
};
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test switch.zig
Test 1/2 switch simple...OK
Test 2/2 switch enum...OK
Test 3/3 switch inside function...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#comptime" > comptime< / a > < / li >
< li > < a href = "#enum" > enum< / a > < / li >
< li > < a href = "#builtin-compileError" > @compileError< / a > < / li >
< li > < a href = "#compile-variables" > Compile Variables< / a > < / li >
< / ul >
< h2 id = "while" > while< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "while basic" {
// A while loop is used to repeatedly execute an expression until
// some condition is no longer true.
var i: usize = 0;
while (i < 10) {
i += 1;
}
assert(i == 10);
}
test "while break" {
// You can use break to exit a while loop early.
var i: usize = 0;
while (true) {
if (i == 10)
break;
i += 1;
}
assert(i == 10);
}
test "while continue" {
// You can use continue to jump back to the beginning of the loop.
var i: usize = 0;
while (true) {
i += 1;
if (i < 10)
continue;
break;
}
assert(i == 10);
}
test "while loop continuation expression" {
// You can give an expression to the while loop to execute when
// the loop is continued. This is respected by the continue control flow.
var i: usize = 0;
while (i < 10) : (i += 1) {}
assert(i == 10);
}
test "while loop continuation expression, more complicated" {
// More complex blocks can be used as an expression in the loop continue
// expression.
var i1: usize = 1;
var j1: usize = 1;
while (i1 * j1 < 2000) : ({ i1 *= 2; j1 *= 3; }) {
const my_ij1 = i1 * j1;
assert(my_ij1 < 2000);
}
}
test "while else" {
assert(rangeHasNumber(0, 10, 5));
assert(!rangeHasNumber(0, 10, 15));
}
fn rangeHasNumber(begin: usize, end: usize, number: usize) -> bool {
var i = begin;
// While loops are expressions. The result of the expression is the
// result of the else clause of a while loop, which is executed when
// the condition of the while loop is tested as false.
return while (i < end) : (i += 1) {
if (i == number) {
// break expressions, like return expressions, accept a value
// parameter. This is the result of the while expression.
// When you break from a while loop, the else branch is not
// evaluated.
break true;
}
} else {
false
}
}
test "while null capture" {
// Just like if expressions, while loops can take a nullable as the
// condition and capture the payload. When null is encountered the loop
// exits.
var sum1: u32 = 0;
numbers_left = 3;
while (eventuallyNullSequence()) |value| {
sum1 += value;
}
assert(sum1 == 3);
// The else branch is allowed on nullable iteration. In this case, it will
// be executed on the first null value encountered.
var sum2: u32 = 0;
numbers_left = 3;
while (eventuallyNullSequence()) |value| {
sum2 += value;
} else {
assert(sum1 == 3);
}
// Just like if expressions, while loops can also take an error union as
// the condition and capture the payload or the error code. When the
// condition results in an error code the else branch is evaluated and
// the loop is finished.
var sum3: u32 = 0;
numbers_left = 3;
while (eventuallyErrorSequence()) |value| {
sum3 += value;
} else |err| {
assert(err == error.ReachedZero);
}
}
var numbers_left: u32 = undefined;
fn eventuallyNullSequence() -> ?u32 {
return if (numbers_left == 0) {
null
} else {
numbers_left -= 1;
numbers_left
}
}
error ReachedZero;
fn eventuallyErrorSequence() -> %u32 {
return if (numbers_left == 0) {
error.ReachedZero
} else {
numbers_left -= 1;
numbers_left
}
}
test "inline while loop" {
// While loops can be inlined. This causes the loop to be unrolled, which
// allows the code to do some things which only work at compile time,
// such as use types as first class values.
comptime var i = 0;
var sum: usize = 0;
inline while (i < 3) : (i += 1) {
const T = switch (i) {
0 => f32,
1 => i8,
2 => bool,
else => unreachable,
};
sum += typeNameLength(T);
}
assert(sum == 9);
}
fn typeNameLength(comptime T: type) -> usize {
return @typeName(T).len;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig while.zig
Test 1/8 while basic...OK
Test 2/8 while break...OK
Test 3/8 while continue...OK
Test 4/8 while loop continuation expression...OK
Test 5/8 while loop continuation expression, more complicated...OK
Test 6/8 while else...OK
Test 7/8 while null capture...OK
Test 8/8 inline while loop...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#if" > if< / a > < / li >
< li > < a href = "#nullables" > Nullables< / a > < / li >
< li > < a href = "#errors" > Errors< / a > < / li >
< li > < a href = "#comptime" > comptime< / a > < / li >
< li > < a href = "#unreachable" > unreachable< / a > < / li >
< / ul >
< h2 id = "for" > for< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "for basics" {
const items = []i32 { 4, 5, 3, 4, 0 };
var sum: i32 = 0;
// For loops iterate over slices and arrays.
for (items) |value| {
// Break and continue are supported.
if (value == 0) {
continue;
}
sum += value;
}
assert(sum == 16);
// To iterate over a portion of a slice, reslice.
for (items[0..1]) |value| {
sum += value;
}
assert(sum == 20);
// To access the index of iteration, specify a second capture value.
// This is zero-indexed.
var sum2: i32 = 0;
for (items) |value, i| {
assert(@typeOf(i) == usize);
sum2 += i32(i);
}
assert(sum2 == 10);
}
test "for reference" {
var items = []i32 { 3, 4, 2 };
// Iterate over the slice by reference by
// specifying that the capture value is a pointer.
for (items) |*value| {
*value += 1;
}
assert(items[0] == 4);
assert(items[1] == 5);
assert(items[2] == 3);
}
test "for else" {
// For allows an else attached to it, the same as a while loop.
var items = []?i32 { 3, 4, null, 5 };
// For loops can also be used as expressions.
var sum: i32 = 0;
const result = for (items) |value| {
if (value == null) {
break 9;
} else {
sum += ??value;
}
} else {
assert(sum == 7);
sum
};
}
test "inline for loop" {
const nums = []i32{2, 4, 6};
// For loops can be inlined. This causes the loop to be unrolled, which
// allows the code to do some things which only work at compile time,
// such as use types as first class values.
// The capture value and iterator value of inlined for loops are
// compile-time known.
var sum: usize = 0;
inline for (nums) |i| {
const T = switch (i) {
2 => f32,
4 => i8,
6 => bool,
else => unreachable,
};
sum += typeNameLength(T);
}
assert(sum == 9);
}
fn typeNameLength(comptime T: type) -> usize {
return @typeName(T).len;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test for.zig
Test 1/4 for basics...OK
Test 2/4 for reference...OK
Test 3/4 for else...OK
Test 4/4 inline for loop...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#while" > while< / a > < / li >
< li > < a href = "#comptime" > comptime< / a > < / li >
< li > < a href = "#arrays" > Arrays< / a > < / li >
< li > < a href = "#slices" > Slices< / a > < / li >
< / ul >
< h2 id = "if" > if< / h2 >
< pre > < code class = "zig" > // If expressions have three uses, corresponding to the three types:
// * bool
// * ?T
// * %T
const assert = @import("std").debug.assert;
test "if boolean" {
// If expressions test boolean conditions.
const a: u32 = 5;
const b: u32 = 4;
if (a != b) {
assert(true);
} else if (a == 9) {
unreachable
} else {
unreachable
}
// If expressions are used instead of a ternary expression.
const result = if (a != b) 47 else 3089;
assert(result == 47);
}
test "if nullable" {
// If expressions test for null.
const a: ?u32 = 0;
if (a) |value| {
assert(value == 0);
} else {
unreachable;
}
const b: ?u32 = null;
if (b) |value| {
unreachable;
} else {
assert(true);
}
// The else is not required.
if (a) |value| {
assert(value == 0);
}
// To test against null only, use the binary equality operator.
if (b == null) {
assert(true);
}
// Access the value by reference using a pointer capture.
var c: ?u32 = 3;
if (c) |*value| {
*value = 2;
}
if (c) |value| {
assert(value == 2);
} else {
unreachable;
}
}
error BadValue;
error LessBadValue;
test "if error union" {
// If expressions test for errors.
// Note the |err| capture on the else.
const a: %u32 = 0;
if (a) |value| {
assert(value == 0);
} else |err| {
unreachable
}
const b: %u32 = error.BadValue;
if (b) |value| {
unreachable
} else |err| {
assert(err == error.BadValue);
}
// The else and |err| capture is strictly required.
if (a) |value| {
assert(value == 0);
} else |_| {}
// To check only the error value, use an empty block expression.
if (b) |_| {} else |err| {
assert(err == error.BadValue);
}
// Access the value by reference using a pointer capture.
var c: %u32 = 3;
if (c) |*value| {
*value = 9;
} else |err| {
unreachable
}
if (c) |value| {
assert(value == 9);
} else |err| {
unreachable
}
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test if.zig
Test 1/3 if boolean...OK
Test 2/3 if nullable...OK
Test 3/3 if error union...OK< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#nullables" > Nullables< / a > < / li >
< li > < a href = "#errors" > Errors< / a > < / li >
< / ul >
< h2 id = "goto" > goto< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "goto" {
var value = false;
goto label;
value = true;
label:
assert(value == false);
}
< / code > < / pre >
< pre > < code class = "sh" > $ zig test goto.zig
Test 1/1 goto...OK
< / code > < / pre >
< p > Note that there are < a href = "https://github.com/zig-lang/zig/issues/346" > plans to remove goto< / a > < / p >
< h2 id = "defer" > defer< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const printf = @import("std").io.stdout.printf;
// defer will execute an expression at the end of the current scope.
fn deferExample() -> usize {
var a: usize = 1;
{
defer a = 2;
a = 1;
}
assert(a == 2);
a = 5;
a
}
test "defer basics" {
assert(deferExample() == 5);
}
// If multiple defer statements are specified, they will be executed in
// the reverse order they were run.
fn deferUnwindExample() {
%%printf("\n");
defer {
%%printf("1 ");
}
defer {
%%printf("2 ");
}
if (false) {
// defers are not run if they are never executed.
defer {
%%printf("3 ");
}
}
}
test "defer unwinding" {
deferUnwindExample()
}
// The %defer keyword is similar to defer, but will only execute if the
// scope returns with an error.
//
// This is especially useful in allowing a function to clean up properly
// on error, and replaces goto error handling tactics as seen in c.
error DeferError;
fn deferErrorExample(is_error: bool) -> %void {
%%printf("\nstart of function\n");
// This will always be executed on exit
defer {
%%printf("end of function\n");
}
%defer {
%%printf("encountered an error!\n");
}
if (is_error) {
return error.DeferError;
}
}
test "%defer unwinding" {
_ = deferErrorExample(false);
_ = deferErrorExample(true);
}
< / code > < / pre >
< pre > < code class = "sh" > $ zig test defer.zig
Test 1/3 defer basics...OK
Test 2/3 defer unwinding...
2 1 OK
Test 3/3 %defer unwinding...
start of function
end of function
start of function
encountered an error!
end of function
OK
< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#errors" > Errors< / a > < / li >
< / ul >
< h2 id = "unreachable" > unreachable< / h2 >
< p >
In < code > Debug< / code > and < code > ReleaseSafe< / code > mode, and when using < code > zig test< / code > ,
< code > unreachable< / code > emits a call to < code > panic< / code > with the message < code > reached unreachable code< / code > .
< / p >
< p >
In < code > ReleaseFast< / code > mode, the optimizer uses the assumption that < code > unreachable< / code > code
will never be hit to perform optimizations. However, < code > zig test< / code > even in < code > ReleaseFast< / code > mode
still emits < code > unreachable< / code > as calls to < code > panic< / code > .
< / p >
< h3 id = "unreachable-basics" > Basics< / h3 >
< pre > < code class = "zig" > // unreachable is used to assert that control flow will never happen upon a
// particular location:
test "basic math" {
const x = 1;
const y = 2;
if (x + y != 3) {
unreachable;
}
}
// in fact, this is how assert is implemented:
fn assert(ok: bool) {
if (!ok) unreachable; // assertion failure
}
// This test will fail because we hit unreachable.
test "this will fail" {
assert(false);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/2 basic math...OK
Test 2/2 this will fail...reached unreachable code
test.zig:13:14: 0x00000000002033ac in ??? (test)
if (!ok) unreachable; // assertion failure
^
test.zig:18:11: 0x000000000020329b in ??? (test)
assert(false);
^
lib/zig/std/special/test_runner.zig:9:21: 0x0000000000214a7a in ??? (test)
test_fn.func();
^
lib/zig/std/special/bootstrap.zig:60:21: 0x0000000000214947 in ??? (test)
return root.main();
^
lib/zig/std/special/bootstrap.zig:47:13: 0x0000000000214800 in ??? (test)
callMain(argc, argv, envp) %% std.os.posix.exit(1);
^
lib/zig/std/special/bootstrap.zig:34:25: 0x0000000000214750 in ??? (test)
posixCallMainAndExit()
^
Tests failed. Use the following command to reproduce the failure:
./test< / code > < / pre >
< h3 id = "unreachable-comptime" > At Compile-Time< / h3 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
comptime {
// The type of unreachable is noreturn.
// However this assertion will still fail because
// evaluating unreachable at compile-time is a compile error.
assert(@typeOf(unreachable) == noreturn);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
test.zig:9:12: error: unreachable code
assert(@typeOf(unreachable) == noreturn);
^< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#zig-test" > Zig Test< / a > < / li >
< li > < a href = "#build-mode" > Build Mode< / a > < / li >
< li > < a href = "#comptime" > comptime< / a > < / li >
< / ul >
< h2 id = "noreturn" > noreturn< / h2 >
< p >
< code > noreturn< / code > is the type of:
< / p >
< ul >
< li > < code > break< / code > < / li >
< li > < code > continue< / code > < / li >
< li > < code > goto< / code > < / li >
< li > < code > return< / code > < / li >
< li > < code > unreachable< / code > < / li >
< li > < code > while (true) {}< / code > < / li >
< / ul >
< p > When resolving types together, such as < code > if< / code > clauses or < code > switch< / code > prongs,
the < code > noreturn< / code > type is compatible with every other type. Consider:
< / p >
< pre > < code class = "zig" > fn foo(condition: bool, b: u32) {
const a = if (condition) b else return;
bar(a);
}
extern fn bar(value: u32);< / code > < / pre >
< p > Another use case for < code > noreturn< / code > is the < code > exit< / code > function:< / p >
< pre > < code class = "zig" > pub extern "kernel32" stdcallcc fn ExitProcess(exit_code: c_uint) -> noreturn;
fn foo() {
const value = bar() %% ExitProcess(1);
assert(value == 1234);
}
fn bar() -> %u32 {
return 1234;
}
const assert = @import("std").debug.assert;< / code > < / pre >
< h2 id = "functions" > Functions< / h2 >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
// Functions are declared like this
fn add(a: i8, b: i8) -> i8 {
if (a == 0) {
// You can still return manually if needed.
return b;
}
2017-12-22 13:50:30 +08:00
return a + b;
2017-11-07 16:22:27 +08:00
}
// The export specifier makes a function externally visible in the generated
// object file, and makes it use the C ABI.
export fn sub(a: i8, b: i8) -> i8 { a - b }
// The extern specifier is used to declare a function that will be resolved
// at link time, when linking statically, or at runtime, when linking
// dynamically.
// The stdcallcc specifier changes the calling convention of the function.
extern "kernel32" stdcallcc fn ExitProcess(exit_code: u32) -> noreturn;
extern "c" fn atan2(a: f64, b: f64) -> f64;
// coldcc makes a function use the cold calling convention.
coldcc fn abort() -> noreturn {
while (true) {}
}
// nakedcc makes a function not have any function prologue or epilogue.
// This can be useful when integrating with assembly.
nakedcc fn _start() -> noreturn {
abort();
}
// The pub specifier allows the function to be visible when importing.
// Another file can use @import and call sub2
pub fn sub2(a: i8, b: i8) -> i8 { a - b }
// Functions can be used as values and are equivalent to pointers.
const call2_op = fn (a: i8, b: i8) -> i8;
fn do_op(fn_call: call2_op, op1: i8, op2: i8) -> i8 {
fn_call(op1, op2)
}
test "function" {
assert(do_op(add, 5, 6) == 11);
assert(do_op(sub2, 5, 6) == -1);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test function.zig
Test 1/1 function...OK
< / code > < / pre >
< p > Function values are like pointers:< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
comptime {
assert(@typeOf(foo) == fn());
assert(@sizeOf(fn()) == @sizeOf(?fn()));
}
fn foo() { }< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig< / code > < / pre >
< h3 id = "functions-by-val-params" > Pass-by-value Parameters< / h3 >
< p >
In Zig, structs, unions, and enums with payloads cannot be passed by value
to a function.
< / p >
< pre > < code class = "zig" > const Foo = struct {
x: i32,
};
fn bar(foo: Foo) {}
export fn entry() {
bar(Foo {.x = 12,});
}< / code > < / pre >
< pre > < code class = "sh" > $ ./zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:5:13: error: type 'Foo' is not copyable; cannot pass by value
fn bar(foo: Foo) {}
^< / code > < / pre >
< p >
Instead, one must use < code > & const< / code > . Zig allows implicitly casting something
to a const pointer to it:
< / p >
< pre > < code class = "zig" > const Foo = struct {
x: i32,
};
fn bar(foo: & const Foo) {}
export fn entry() {
bar(Foo {.x = 12,});
}< / code > < / pre >
< p >
However,
the C ABI does allow passing structs and unions by value. So functions which
use the C calling convention may pass structs and unions by value.
< / p >
< h2 id = "errors" > Errors< / h2 >
< p >
One of the distinguishing features of Zig is its exception handling strategy.
< / p >
< p >
Among the top level declarations available is the error value declaration:
< / p >
< pre > < code class = "zig" > error FileNotFound;
error OutOfMemory;
error UnexpectedToken;< / code > < / pre >
< p >
These error values are assigned an unsigned integer value greater than 0 at
compile time. You are allowed to declare the same error value more than once,
and if you do, it gets assigned the same integer value.
< / p >
< p >
You can refer to these error values with the error namespace such as
< code > error.FileNotFound< / code > .
< / p >
< p >
Each error value across the entire compilation unit gets a unique integer,
and this determines the size of the pure error type.
< / p >
< p >
The pure error type is one of the error values, and in the same way that pointers
cannot be null, a pure error is always an error.
< / p >
< pre > < code class = "zig" > const pure_error = error.FileNotFound;< / code > < / pre >
< p >
Most of the time you will not find yourself using a pure error type. Instead,
likely you will be using the error union type. This is when you take a normal type,
and prefix it with the < code > %< / code > operator.
< / p >
< p >
Here is a function to parse a string into a 64-bit integer:
< / p >
< pre > < code class = "zig" > error InvalidChar;
error Overflow;
pub fn parseU64(buf: []const u8, radix: u8) -> %u64 {
var x: u64 = 0;
for (buf) |c| {
const digit = charToDigit(c);
if (digit > = radix) {
return error.InvalidChar;
}
// x *= radix
if (@mulWithOverflow(u64, x, radix, & x)) {
return error.Overflow;
}
// x += digit
if (@addWithOverflow(u64, x, digit, & x)) {
return error.Overflow;
}
}
return x;
}< / code > < / pre >
< p >
Notice the return type is < code > %u64< / code > . This means that the function
either returns an unsigned 64 bit integer, or an error.
< / p >
< p >
Within the function definition, you can see some return statements that return
a pure error, and at the bottom a return statement that returns a < code > u64< / code > .
Both types implicitly cast to < code > %u64< / code > .
< / p >
< p >
What it looks like to use this function varies depending on what you're
trying to do. One of the following:
< / p >
< ul >
< li > You want to provide a default value if it returned an error.< / li >
< li > If it returned an error then you want to return the same error.< / li >
< li > You know with complete certainty it will not return an error, so want to unconditionally unwrap it.< / li >
< li > You want to take a different action for each possible error.< / li >
< / ul >
< p > If you want to provide a default value, you can use the < code > %%< / code > binary operator:< / p >
< pre > < code class = "zig" > fn doAThing(str: []u8) {
const number = parseU64(str, 10) %% 13;
// ...
}< / code > < / pre >
< p >
In this code, < code > number< / code > will be equal to the successfully parsed string, or
a default value of 13. The type of the right hand side of the binary < code > %%< / code > operator must
match the unwrapped error union type, or be of type < code > noreturn< / code > .
< / p >
< p > Let's say you wanted to return the error if you got one, otherwise continue with the
function logic:< / p >
< pre > < code class = "zig" > fn doAThing(str: []u8) -> %void {
const number = parseU64(str, 10) %% |err| return err;
// ...
}< / code > < / pre >
< p >
There is a shortcut for this. The < code > %return< / code > expression:
< / p >
< pre > < code class = "zig" > fn doAThing(str: []u8) -> %void {
const number = %return parseU64(str, 10);
// ...
}< / code > < / pre >
< p >
< code > %return< / code > evaluates an error union expression. If it is an error, it returns
from the current function with the same error. Otherwise, the expression results in
the unwrapped value.
< / p >
< p >
Maybe you know with complete certainty that an expression will never be an error.
In this case you can do this:
< / p >
< pre > < code class = "zig" > const number = parseU64("1234", 10) %% unreachable;< / code > < / pre >
< p >
Here we know for sure that "1234" will parse successfully. So we put the
< code > unreachable< / code > value on the right hand side. < code > unreachable< / code > generates
a panic in Debug and ReleaseSafe modes and undefined behavior in ReleaseFast mode. So, while we're debugging the
application, if there < em > was< / em > a surprise error here, the application would crash
appropriately.
< / p >
< p > Again there is a syntactic shortcut for this:< / p >
< pre > < code class = "zig" > const number = %%parseU64("1234", 10);< / code > < / pre >
< p >
The < code > %%< / code > < em > prefix< / em > operator is equivalent to < code class = "zig" > expression %% unreachable< / code > . It unwraps an error union type,
and panics in debug mode if the value was an error.
< / p >
< p >
Finally, you may want to take a different action for every situation. For that, we combine
the < code > if< / code > and < code > switch< / code > expression:
< / p >
< pre > < code class = "zig" > fn doAThing(str: []u8) {
if (parseU64(str, 10)) |number| {
doSomethingWithNumber(number);
} else |err| switch (err) {
error.Overflow => {
// handle overflow...
},
// we promise that InvalidChar won't happen (or crash in debug mode if it does)
error.InvalidChar => unreachable,
}
}< / code > < / pre >
< p >
The other component to error handling is defer statements.
In addition to an unconditional < code > defer< / code > , Zig has < code > %defer< / code > ,
which evaluates the deferred expression on block exit path if and only if
the function returned with an error from the block.
< / p >
< p >
Example:
< / p >
< pre > < code class = "zig" > fn createFoo(param: i32) -> %Foo {
const foo = %return tryToAllocateFoo();
// now we have allocated foo. we need to free it if the function fails.
// but we want to return it if the function succeeds.
%defer deallocateFoo(foo);
const tmp_buf = allocateTmpBuffer() ?? return error.OutOfMemory;
// tmp_buf is truly a temporary resource, and we for sure want to clean it up
// before this block leaves scope
defer deallocateTmpBuffer(tmp_buf);
if (param > 1337) return error.InvalidParam;
// here the %defer will not run since we're returning success from the function.
// but the defer will run!
return foo;
}< / code > < / pre >
< p >
The neat thing about this is that you get robust error handling without
the verbosity and cognitive overhead of trying to make sure every exit path
is covered. The deallocation code is always directly following the allocation code.
< / p >
< p >
A couple of other tidbits about error handling:
< / p >
< ul >
< li > These primitives give enough expressiveness that it's completely practical
to have failing to check for an error be a compile error. If you really want
to ignore the error, you can use the < code > %%< / code > prefix operator and
get the added benefit of crashing in Debug and ReleaseSafe modes if your assumption was wrong.
< / li >
< li >
Since Zig understands error types, it can pre-weight branches in favor of
errors not occuring. Just a small optimization benefit that is not available
in other languages.
< / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#defer" > defer< / a > < / li >
< li > < a href = "#if" > if< / a > < / li >
< li > < a href = "#switch" > switch< / a > < / li >
< / ul >
< h2 id = "nullables" > Nullables< / h2 >
< p >
One area that Zig provides safety without compromising efficiency or
readability is with the nullable type.
< / p >
< p >
The question mark symbolizes the nullable type. You can convert a type to a nullable
type by putting a question mark in front of it, like this:
< / p >
< pre > < code class = "zig" > // normal integer
const normal_int: i32 = 1234;
// nullable integer
const nullable_int: ?i32 = 5678;< / code > < / pre >
< p >
Now the variable < code > nullable_int< / code > could be an < code > i32< / code > , or < code > null< / code > .
< / p >
< p >
Instead of integers, let's talk about pointers. Null references are the source of many runtime
exceptions, and even stand accused of being
< a href = "https://www.lucidchart.com/techblog/2015/08/31/the-worst-mistake-of-computer-science/" > the worst mistake of computer science< / a > .
< / p >
< p > Zig does not have them.< / p >
< p >
Instead, you can use a nullable pointer. This secretly compiles down to a normal pointer,
since we know we can use 0 as the null value for the nullable type. But the compiler
can check your work and make sure you don't assign null to something that can't be null.
< / p >
< p >
Typically the downside of not having null is that it makes the code more verbose to
write. But, let's compare some equivalent C code and Zig code.
< / p >
< p >
Task: call malloc, if the result is null, return null.
< / p >
< p > C code< / p >
< pre > < code class = "c" > // malloc prototype included for reference
void *malloc(size_t size);
struct Foo *do_a_thing(void) {
char *ptr = malloc(1234);
if (!ptr) return NULL;
// ...
}< / code > < / pre >
< p > Zig code< / p >
< pre > < code class = "zig" > // malloc prototype included for reference
extern fn malloc(size: size_t) -> ?& u8;
fn doAThing() -> ?& Foo {
const ptr = malloc(1234) ?? return null;
// ...
}< / code > < / pre >
< p >
Here, Zig is at least as convenient, if not more, than C. And, the type of "ptr"
is < code > & u8< / code > < em > not< / em > < code > ?& u8< / code > . The < code > ??< / code > operator
unwrapped the nullable type and therefore < code > ptr< / code > is guaranteed to be non-null everywhere
it is used in the function.
< / p >
< p >
The other form of checking against NULL you might see looks like this:
< / p >
< pre > < code class = "c" > void do_a_thing(struct Foo *foo) {
// do some stuff
if (foo) {
do_something_with_foo(foo);
}
// do some stuff
}< / code > < / pre >
< p >
In Zig you can accomplish the same thing:
< / p >
< pre > < code class = "zig" > fn doAThing(nullable_foo: ?& Foo) {
// do some stuff
if (const foo ?= nullable_foo) {
doSomethingWithFoo(foo);
}
// do some stuff
}< / code > < / pre >
< p >
Once again, the notable thing here is that inside the if block,
< code > foo< / code > is no longer a nullable pointer, it is a pointer, which
cannot be null.
< / p >
< p >
One benefit to this is that functions which take pointers as arguments can
be annotated with the "nonnull" attribute - < code > __attribute__((nonnull))< / code > in
< a href = "https://gcc.gnu.org/onlinedocs/gcc-4.0.0/gcc/Function-Attributes.html" > GCC< / a > .
The optimizer can sometimes make better decisions knowing that pointer arguments
cannot be null.
< / p >
< h2 id = "casting" > Casting< / h2 >
< p > TODO: explain implicit vs explicit casting< / p >
< p > TODO: resolve peer types builtin< / p >
< p > TODO: truncate builtin< / p >
< p > TODO: bitcast builtin< / p >
< p > TODO: int to ptr builtin< / p >
< p > TODO: ptr to int builtin< / p >
< p > TODO: ptrcast builtin< / p >
< p > TODO: explain number literals vs concrete types< / p >
< h2 id = "void" > void< / h2 >
< p > TODO: assigning void has no codegen< / p >
< p > TODO: hashmap with void becomes a set< / p >
< p > TODO: difference between c_void and void< / p >
< p > TODO: void is the default return value of functions< / p >
< p > TODO: functions require assigning the return value< / p >
< h2 id = "this" > this< / h2 >
< p > TODO: example of this referring to Self struct< / p >
< p > TODO: example of this referring to recursion function< / p >
< p > TODO: example of this referring to basic block for @setDebugSafety< / p >
< h2 id = "comptime" > comptime< / h2 >
< p >
Zig places importance on the concept of whether an expression is known at compile-time.
There are a few different places this concept is used, and these building blocks are used
to keep the language small, readable, and powerful.
< / p >
< h3 id = "introducing-compile-time-concept" > Introducing the Compile-Time Concept< / h3 >
< h4 id = "compile-time-parameters" > Compile-Time Parameters< / h4 >
< p >
Compile-time parameters is how Zig implements generics. It is compile-time duck typing.
< / p >
< pre > < code class = "zig" > fn max(comptime T: type, a: T, b: T) -> T {
if (a > b) a else b
}
fn gimmeTheBiggerFloat(a: f32, b: f32) -> f32 {
max(f32, a, b)
}
fn gimmeTheBiggerInteger(a: u64, b: u64) -> u64 {
max(u64, a, b)
}< / code > < / pre >
< p >
In Zig, types are first-class citizens. They can be assigned to variables, passed as parameters to functions,
and returned from functions. However, they can only be used in expressions which are known at < em > compile-time< / em > ,
which is why the parameter < code > T< / code > in the above snippet must be marked with < code > comptime< / code > .
< / p >
< p >
A < code > comptime< / code > parameter means that:
< / p >
< ul >
< li > At the callsite, the value must be known at compile-time, or it is a compile error.< / li >
< li > In the function definition, the value is known at compile-time.< / li >
< / ul >
< p >
< / p >
< p >
For example, if we were to introduce another function to the above snippet:
< / p >
< pre > < code class = "zig" > fn max(comptime T: type, a: T, b: T) -> T {
if (a > b) a else b
}
fn letsTryToPassARuntimeType(condition: bool) {
const result = max(
if (condition) f32 else u64,
1234,
5678);
}< / code > < / pre >
< p >
Then we get this result from the compiler:
< / p >
< pre > < code class = "sh" > ./test.zig:6:9: error: unable to evaluate constant expression
if (condition) f32 else u64,
^< / code > < / pre >
< p >
This is an error because the programmer attempted to pass a value only known at run-time
to a function which expects a value known at compile-time.
< / p >
< p >
Another way to get an error is if we pass a type that violates the type checker when the
function is analyzed. This is what it means to have < em > compile-time duck typing< / em > .
< / p >
< p >
For example:
< / p >
< pre > < code class = "zig" > fn max(comptime T: type, a: T, b: T) -> T {
if (a > b) a else b
}
fn letsTryToCompareBools(a: bool, b: bool) -> bool {
max(bool, a, b)
}< / code > < / pre >
< p >
The code produces this error message:
< / p >
< pre > < code > ./test.zig:2:11: error: operator not allowed for type 'bool'
if (a > b) a else b
^
./test.zig:5:8: note: called from here
max(bool, a, b)
^< / code > < / pre >
< p >
On the flip side, inside the function definition with the < code > comptime< / code > parameter, the
value is known at compile-time. This means that we actually could make this work for the bool type
if we wanted to:
< / p >
< pre > < code class = "zig" > fn max(comptime T: type, a: T, b: T) -> T {
if (T == bool) {
return a or b;
} else if (a > b) {
return a;
} else {
return b;
}
}
fn letsTryToCompareBools(a: bool, b: bool) -> bool {
max(bool, a, b)
}< / code > < / pre >
< p >
This works because Zig implicitly inlines < code > if< / code > expressions when the condition
is known at compile-time, and the compiler guarantees that it will skip analysis of
the branch not taken.
< / p >
< p >
This means that the actual function generated for < code > max< / code > in this situation looks like
this:
< / p >
< pre > < code class = "zig" > fn max(a: bool, b: bool) -> bool {
return a or b;
}< / code > < / pre >
< p >
All the code that dealt with compile-time known values is eliminated and we are left with only
the necessary run-time code to accomplish the task.
< / p >
< p >
This works the same way for < code > switch< / code > expressions - they are implicitly inlined
when the target expression is compile-time known.
< / p >
< h4 id = "compile-time-variables" > Compile-Time Variables< / h4 >
< p >
In Zig, the programmer can label variables as < code > comptime< / code > . This guarantees to the compiler
that every load and store of the variable is performed at compile-time. Any violation of this results in a
compile error.
< / p >
< p >
This combined with the fact that we can < code > inline< / code > loops allows us to write
a function which is partially evaluated at compile-time and partially at run-time.
< / p >
< p >
For example:
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
const CmdFn = struct {
name: []const u8,
func: fn(i32) -> i32,
};
const cmd_fns = []CmdFn{
CmdFn {.name = "one", .func = one},
CmdFn {.name = "two", .func = two},
CmdFn {.name = "three", .func = three},
};
fn one(value: i32) -> i32 { value + 1 }
fn two(value: i32) -> i32 { value + 2 }
fn three(value: i32) -> i32 { value + 3 }
fn performFn(comptime prefix_char: u8, start_value: i32) -> i32 {
var result: i32 = start_value;
comptime var i = 0;
inline while (i < cmd_fns.len) : (i += 1) {
if (cmd_fns[i].name[0] == prefix_char) {
result = cmd_fns[i].func(result);
}
}
return result;
}
test "perform fn" {
assert(performFn('t', 1) == 6);
assert(performFn('o', 0) == 1);
assert(performFn('w', 99) == 99);
}< / code > < / pre >
< p >
This example is a bit contrived, because the compile-time evaluation component is unnecessary;
this code would work fine if it was all done at run-time. But it does end up generating
different code. In this example, the function < code > performFn< / code > is generated three different times,
for the different values of < code > prefix_char< / code > provided:
< / p >
< pre > < code class = "zig" > // From the line:
// assert(performFn('t', 1) == 6);
fn performFn(start_value: i32) -> i32 {
var result: i32 = start_value;
result = two(result);
result = three(result);
return result;
}
// From the line:
// assert(performFn('o', 0) == 1);
fn performFn(start_value: i32) -> i32 {
var result: i32 = start_value;
result = one(result);
return result;
}
// From the line:
// assert(performFn('w', 99) == 99);
fn performFn(start_value: i32) -> i32 {
var result: i32 = start_value;
return result;
}< / code > < / pre >
< p >
Note that this happens even in a debug build; in a release build these generated functions still
pass through rigorous LLVM optimizations. The important thing to note, however, is not that this
is a way to write more optimized code, but that it is a way to make sure that what < em > should< / em > happen
at compile-time, < em > does< / em > happen at compile-time. This catches more errors and as demonstrated
later in this article, allows expressiveness that in other languages requires using macros,
generated code, or a preprocessor to accomplish.
< / p >
< h4 id = "compile-time-expressions" > Compile-Time Expressions< / h4 >
< p >
In Zig, it matters whether a given expression is known at compile-time or run-time. A programmer can
use a < code > comptime< / code > expression to guarantee that the expression will be evaluated at compile-time.
If this cannot be accomplished, the compiler will emit an error. For example:
< / p >
< pre > < code class = "zig" > extern fn exit() -> unreachable;
fn foo() {
comptime {
exit();
}
}< / code > < / pre >
< pre > < code > ./test.zig:5:9: error: unable to evaluate constant expression
exit();
^< / code > < / pre >
< p >
It doesn't make sense that a program could call < code > exit()< / code > (or any other external function)
at compile-time, so this is a compile error. However, a < code > comptime< / code > expression does much
more than sometimes cause a compile error.
< / p >
< p >
Within a < code > comptime< / code > expression:
< / p >
< ul >
< li > All variables are < code > comptime< / code > variables.< / li >
< li > All < code > if< / code > , < code > while< / code > , < code > for< / code > , < code > switch< / code > , and < code > goto< / code >
expressions are evaluated at compile-time, or emit a compile error if this is not possible.< / li >
< li > All function calls cause the compiler to interpret the function at compile-time, emitting a
compile error if the function tries to do something that has global run-time side effects.< / li >
< / ul >
< p >
This means that a programmer can create a function which is called both at compile-time and run-time, with
no modification to the function required.
< / p >
< p >
Let's look at an example:
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
fn fibonacci(index: u32) -> u32 {
if (index < 2) return index;
return fibonacci(index - 1) + fibonacci(index - 2);
}
test "fibonacci" {
// test fibonacci at run-time
assert(fibonacci(7) == 13);
// test fibonacci at compile-time
comptime {
assert(fibonacci(7) == 13);
}
}< / code > < / pre >
< pre > < code > $ zig test test.zig
Test 1/1 testFibonacci...OK< / code > < / pre >
< p >
Imagine if we had forgotten the base case of the recursive function and tried to run the tests:
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
fn fibonacci(index: u32) -> u32 {
//if (index < 2) return index;
return fibonacci(index - 1) + fibonacci(index - 2);
}
test "fibonacci" {
comptime {
assert(fibonacci(7) == 13);
}
}< / code > < / pre >
< pre > < code > $ zig test test.zig
./test.zig:3:28: error: operation caused overflow
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:14:25: note: called from here
assert(fibonacci(7) == 13);
^< / code > < / pre >
< p >
The compiler produces an error which is a stack trace from trying to evaluate the
function at compile-time.
< / p >
< p >
Luckily, we used an unsigned integer, and so when we tried to subtract 1 from 0, it triggered
undefined behavior, which is always a compile error if the compiler knows it happened.
But what would have happened if we used a signed integer?
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
fn fibonacci(index: i32) -> i32 {
//if (index < 2) return index;
return fibonacci(index - 1) + fibonacci(index - 2);
}
test "fibonacci" {
comptime {
assert(fibonacci(7) == 13);
}
}< / code > < / pre >
< pre > < code > ./test.zig:3:21: error: evaluation exceeded 1000 backwards branches
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^
./test.zig:3:21: note: called from here
return fibonacci(index - 1) + fibonacci(index - 2);
^< / code > < / pre >
< p >
The compiler noticed that evaluating this function at compile-time took a long time,
and thus emitted a compile error and gave up. If the programmer wants to increase
the budget for compile-time computation, they can use a built-in function called
< a href = "#builtin-setEvalBranchQuota" > @setEvalBranchQuota< / a > to change the default number 1000 to something else.
< / p >
< p >
What if we fix the base case, but put the wrong value in the < code > assert< / code > line?
< / p >
< pre > < code class = "zig" > comptime {
assert(fibonacci(7) == 99999);
}< / code > < / pre >
< pre > < code > ./test.zig:15:14: error: unable to evaluate constant expression
if (!ok) unreachable;
^
./test.zig:10:15: note: called from here
assert(fibonacci(7) == 99999);
^< / code > < / pre >
< p >
What happened is Zig started interpreting the < code > assert< / code > function with the
parameter < code > ok< / code > set to < code > false< / code > . When the interpreter hit
< code > unreachable< / code > it emitted a compile error, because reaching unreachable
code is undefined behavior, and undefined behavior causes a compile error if it is detected
at compile-time.
< / p >
< p >
In the global scope (outside of any function), all expressions are implicitly
< code > comptime< / code > expressions. This means that we can use functions to
initialize complex static data. For example:
< / p >
< pre > < code class = "zig" > const first_25_primes = firstNPrimes(25);
const sum_of_first_25_primes = sum(first_25_primes);
fn firstNPrimes(comptime n: usize) -> [n]i32 {
var prime_list: [n]i32 = undefined;
var next_index: usize = 0;
var test_number: i32 = 2;
while (next_index < prime_list.len) : (test_number += 1) {
var test_prime_index: usize = 0;
var is_prime = true;
while (test_prime_index < next_index) : (test_prime_index += 1) {
if (test_number % prime_list[test_prime_index] == 0) {
is_prime = false;
break;
}
}
if (is_prime) {
prime_list[next_index] = test_number;
next_index += 1;
}
}
return prime_list;
}
fn sum(numbers: []i32) -> i32 {
var result: i32 = 0;
for (numbers) |x| {
result += x;
}
return result;
}< / code > < / pre >
< p >
When we compile this program, Zig generates the constants
with the answer pre-computed. Here are the lines from the generated LLVM IR:
< / p >
< pre > < code > @0 = internal unnamed_addr constant [25 x i32] [i32 2, i32 3, i32 5, i32 7, i32 11, i32 13, i32 17, i32 19, i32 23, i32 29, i32 31, i32 37, i32 41, i32 43, i32 47, i32 53, i32 59, i32 61, i32 67, i32 71, i32 73, i32 79, i32 83, i32 89, i32 97]
@1 = internal unnamed_addr constant i32 1060< / code > < / pre >
< p >
Note that we did not have to do anything special with the syntax of these functions. For example,
we could call the < code > sum< / code > function as is with a slice of numbers whose length and values were
only known at run-time.
< / p >
< h3 id = "generic-data-structures" > Generic Data Structures< / h3 >
< p >
Zig uses these capabilities to implement generic data structures without introducing any
special-case syntax. If you followed along so far, you may already know how to create a
generic data structure.
< / p >
< p >
Here is an example of a generic < code > List< / code > data structure, that we will instantiate with
the type < code > i32< / code > . In Zig we refer to the type as < code > List(i32)< / code > .
< / p >
< pre > < code class = "zig" > fn List(comptime T: type) -> type {
struct {
items: []T,
len: usize,
}
}< / code > < / pre >
< p >
That's it. It's a function that returns an anonymous < code > struct< / code > . For the purposes of error messages
and debugging, Zig infers the name < code > "List(i32)"< / code > from the function name and parameters invoked when creating
the anonymous struct.
< / p >
< p >
To keep the language small and uniform, all aggregate types in Zig are anonymous. To give a type
a name, we assign it to a constant:
< / p >
< pre > < code class = "zig" > const Node = struct {
next: & Node,
name: []u8,
};< / code > < / pre >
< p >
This works because all top level declarations are order-independent, and as long as there isn't
an actual infinite regression, values can refer to themselves, directly or indirectly. In this case,
< code > Node< / code > refers to itself as a pointer, which is not actually an infinite regression, so
it works fine.
< / p >
< h3 id = "case-study-printf" > Case Study: printf in Zig< / h3 >
< p >
Putting all of this together, let's seee how < code > printf< / code > works in Zig.
< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
const a_number: i32 = 1234;
const a_string = "foobar";
pub fn main(args: [][]u8) -> %void {
warn("here is a string: '{}' here is a number: {}\n", a_string, a_number);
}< / code > < / pre >
< pre > < code > here is a string: 'foobar' here is a number: 1234< / code > < / pre >
< p >
Let's crack open the implementation of this and see how it works:
< / p >
< pre > < code class = "zig" > /// Calls print and then flushes the buffer.
pub fn printf(self: & OutStream, comptime format: []const u8, args: ...) -> %void {
const State = enum {
Start,
OpenBrace,
CloseBrace,
};
comptime var start_index: usize = 0;
comptime var state = State.Start;
comptime var next_arg: usize = 0;
inline for (format) |c, i| {
switch (state) {
State.Start => switch (c) {
'{' => {
if (start_index < i) %return self.write(format[start_index...i]);
state = State.OpenBrace;
},
'}' => {
if (start_index < i) %return self.write(format[start_index...i]);
state = State.CloseBrace;
},
else => {},
},
State.OpenBrace => switch (c) {
'{' => {
state = State.Start;
start_index = i;
},
'}' => {
%return self.printValue(args[next_arg]);
next_arg += 1;
state = State.Start;
start_index = i + 1;
},
else => @compileError("Unknown format character: " ++ c),
},
State.CloseBrace => switch (c) {
'}' => {
state = State.Start;
start_index = i;
},
else => @compileError("Single '}' encountered in format string"),
},
}
}
comptime {
if (args.len != next_arg) {
@compileError("Unused arguments");
}
if (state != State.Start) {
@compileError("Incomplete format string: " ++ format);
}
}
if (start_index < format.len) {
%return self.write(format[start_index...format.len]);
}
%return self.flush();
}< / code > < / pre >
< p >
This is a proof of concept implementation; the actual function in the standard library has more
formatting capabilities.
< / p >
< p >
Note that this is not hard-coded into the Zig compiler; this is userland code in the standard library.
< / p >
< p >
When this function is analyzed from our example code above, Zig partially evaluates the function
and emits a function that actually looks like this:
< / p >
< pre > < code class = "zig" > pub fn printf(self: & OutStream, arg0: i32, arg1: []const u8) -> %void {
%return self.write("here is a string: '");
%return self.printValue(arg0);
%return self.write("' here is a number: ");
%return self.printValue(arg1);
%return self.write("\n");
%return self.flush();
}< / code > < / pre >
< p >
< code > printValue< / code > is a function that takes a parameter of any type, and does different things depending
on the type:
< / p >
< pre > < code class = "zig" > pub fn printValue(self: & OutStream, value: var) -> %void {
const T = @typeOf(value);
if (@isInteger(T)) {
return self.printInt(T, value);
} else if (@isFloat(T)) {
return self.printFloat(T, value);
} else if (@canImplicitCast([]const u8, value)) {
const casted_value = ([]const u8)(value);
return self.write(casted_value);
} else {
@compileError("Unable to print type '" ++ @typeName(T) ++ "'");
}
}< / code > < / pre >
< p >
And now, what happens if we give too many arguments to < code > printf< / code > ?
< / p >
< pre > < code class = "zig" > warn("here is a string: '{}' here is a number: {}\n",
a_string, a_number, a_number);< / code > < / pre >
< pre > < code > .../std/io.zig:147:17: error: Unused arguments
@compileError("Unused arguments");
^
./test.zig:7:23: note: called from here
warn("here is a number: {} and here is a string: {}\n",
^< / code > < / pre >
< p >
Zig gives programmers the tools needed to protect themselves against their own mistakes.
< / p >
< p >
Zig doesn't care whether the format argument is a string literal,
only that it is a compile-time known value that is implicitly castable to a < code > []const u8< / code > :
< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
const a_number: i32 = 1234;
const a_string = "foobar";
const fmt = "here is a string: '{}' here is a number: {}\n";
pub fn main(args: [][]u8) -> %void {
warn(fmt, a_string, a_number);
}< / code > < / pre >
< p >
This works fine.
< / p >
< p >
Zig does not special case string formatting in the compiler and instead exposes enough power to accomplish this
task in userland. It does so without introducing another language on top of Zig, such as
a macro language or a preprocessor language. It's Zig all the way down.
< / p >
< p > TODO: suggestion to not use inline unless necessary< / p >
< h2 id = "inline" > inline< / h2 >
< p > TODO: inline while< / p >
< p > TODO: inline for< / p >
< p > TODO: suggestion to not use inline unless necessary< / p >
< h2 id = "assembly" > Assembly< / h2 >
< p > TODO: example of inline assembly< / p >
< p > TODO: example of module level assembly< / p >
< p > TODO: example of using inline assembly return value< / p >
< p > TODO: example of using inline assembly assigning values to variables< / p >
< h2 id = "atomics" > Atomics< / h2 >
< p > TODO: @fence()< / p >
< p > TODO: @atomic rmw< / p >
< p > TODO: builtin atomic memory ordering enum< / p >
< h2 id = "builtin-functions" > Builtin Functions< / h2 >
< p >
Builtin functions are provided by the compiler and are prefixed with < code > @< / code > .
The < code > comptime< / code > keyword on a parameter means that the parameter must be known
at compile time.
< / p >
< h3 id = "builtin-addWithOverflow" > @addWithOverflow< / h3 >
< pre > < code class = "zig" > @addWithOverflow(comptime T: type, a: T, b: T, result: & T) -> bool< / code > < / pre >
< p >
Performs < code > *result = a + b< / code > . If overflow or underflow occurs,
stores the overflowed bits in < code > result< / code > and returns < code > true< / code > .
If no overflow or underflow occurs, returns < code > false< / code > .
< / p >
< h3 id = "builtin-ArgType" > @ArgType< / h3 >
< p > TODO< / p >
< h3 id = "builtin-bitCast" > @bitCast< / h3 >
< pre > < code class = "zig" > @bitCast(comptime DestType: type, value: var) -> DestType< / code > < / pre >
< p >
Converts a value of one type to another type.
< / p >
< p >
Asserts that < code > @sizeOf(@typeOf(value)) == @sizeOf(DestType)< / code > .
< / p >
< p >
Asserts that < code > @typeId(DestType) != @import("builtin").TypeId.Pointer< / code > . Use < code > @ptrCast< / code > or < code > @intToPtr< / code > if you need this.
< / p >
< p >
Can be used for these things for example:
< / p >
< ul >
< li > Convert < code > f32< / code > to < code > u32< / code > bits< / li >
< li > Convert < code > i32< / code > to < code > u32< / code > preserving twos complement< / li >
< / ul >
< p >
Works at compile-time if < code > value< / code > is known at compile time. It's a compile error to bitcast a struct to a scalar type of the same size since structs have undefined layout. However if the struct is packed then it works.
< / p >
< h3 id = "builtin-breakpoint" > @breakpoint< / h3 >
< pre > < code class = "zig" > @breakpoint()< / code > < / pre >
< p >
This function inserts a platform-specific debug trap instruction which causes
debuggers to break there.
< / p >
< p >
This function is only valid within function scope.
< / p >
< h3 id = "builtin-alignCast" > @alignCast< / h3 >
< pre > < code class = "zig" > @alignCast(comptime alignment: u29, ptr: var) -> var< / code > < / pre >
< p >
< code > ptr< / code > can be < code > & T< / code > , < code > fn()< / code > , < code > ?& T< / code > ,
< code > ?fn()< / code > , or < code > []T< / code > . It returns the same type as < code > ptr< / code >
except with the alignment adjusted to the new value.
< / p >
< p > A < a href = "#undef-incorrect-pointer-alignment" > pointer alignment safety check< / a > is added
to the generated code to make sure the pointer is aligned as promised.< / p >
< h3 id = "builtin-alignOf" > @alignOf< / h3 >
< pre > < code class = "zig" > @alignOf(comptime T: type) -> (number literal)< / code > < / pre >
< p >
This function returns the number of bytes that this type should be aligned to
for the current target to match the C ABI. When the child type of a pointer has
this alignment, the alignment can be omitted from the type.
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
comptime {
assert(& u32 == & align(@alignOf(u32)) u32);
}< / code > < / pre >
< p >
The result is a target-specific compile time constant. It is guaranteed to be
less than or equal to < a href = "#builtin-sizeOf" > @sizeOf(T)< / a > .
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#alignment" > Alignment< / a > < / li >
< / ul >
< h3 id = "builtin-cDefine" > @cDefine< / h3 >
< pre > < code class = "zig" > @cDefine(comptime name: []u8, value)< / code > < / pre >
< p >
This function can only occur inside < code > @cImport< / code > .
< / p >
< p >
This appends < code > #define $name $value< / code > to the < code > @cImport< / code >
temporary buffer.
< / p >
< p >
To define without a value, like this:
< / p >
< pre > < code class = "c" > #define _GNU_SOURCE< / code > < / pre >
< p >
Use the void value, like this:
< / p >
< pre > < code class = "zig" > @cDefine("_GNU_SOURCE", {})< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#c-import" > Import from C Header File< / a > < / li >
< li > < a href = "#builtin-cInclude" > @cInclude< / a > < / li >
< li > < a href = "#builtin-cImport" > @cImport< / a > < / li >
< li > < a href = "#builtin-cUndef" > @cUndef< / a > < / li >
< li > < a href = "#void" > void< / a > < / li >
< / ul >
< h3 id = "builtin-cImport" > @cImport< / h3 >
< pre > < code class = "zig" > @cImport(expression) -> (namespace)< / code > < / pre >
< p >
This function parses C code and imports the functions, types, variables, and
compatible macro definitions into the result namespace.
< / p >
< p >
< code > expression< / code > is interpreted at compile time. The builtin functions
< code > @cInclude< / code > , < code > @cDefine< / code > , and < code > @cUndef< / code > work
within this expression, appending to a temporary buffer which is then parsed as C code.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#c-import" > Import from C Header File< / a > < / li >
< li > < a href = "#builtin-cInclude" > @cInclude< / a > < / li >
< li > < a href = "#builtin-cDefine" > @cDefine< / a > < / li >
< li > < a href = "#builtin-cUndef" > @cUndef< / a > < / li >
< / ul >
< h3 id = "builtin-cInclude" > @cInclude< / h3 >
< pre > < code class = "zig" > @cInclude(comptime path: []u8)< / code > < / pre >
< p >
This function can only occur inside < code > @cImport< / code > .
< / p >
< p >
This appends < code > #include < $path>\n< / code > to the < code > c_import< / code >
temporary buffer.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#c-import" > Import from C Header File< / a > < / li >
< li > < a href = "#builtin-cImport" > @cImport< / a > < / li >
< li > < a href = "#builtin-cDefine" > @cDefine< / a > < / li >
< li > < a href = "#builtin-cUndef" > @cUndef< / a > < / li >
< / ul >
< h3 id = "builtin-cUndef" > @cUndef< / h3 >
< pre > < code class = "zig" > @cUndef(comptime name: []u8)< / code > < / pre >
< p >
This function can only occur inside < code > @cImport< / code > .
< / p >
< p >
This appends < code > #undef $name< / code > to the < code > @cImport< / code >
temporary buffer.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#c-import" > Import from C Header File< / a > < / li >
< li > < a href = "#builtin-cImport" > @cImport< / a > < / li >
< li > < a href = "#builtin-cDefine" > @cDefine< / a > < / li >
< li > < a href = "#builtin-cInclude" > @cInclude< / a > < / li >
< / ul >
< h3 id = "builtin-canImplicitCast" > @canImplicitCast< / h3 >
< pre > < code class = "zig" > @canImplicitCast(comptime T: type, value) -> bool< / code > < / pre >
< p >
Returns whether a value can be implicitly casted to a given type.
< / p >
< h3 id = "builtin-clz" > @clz< / h3 >
< pre > < code class = "zig" > @clz(x: T) -> U< / code > < / pre >
< p >
This function counts the number of leading zeroes in < code > x< / code > which is an integer
type < code > T< / code > .
< / p >
< p >
The return type < code > U< / code > is an unsigned integer with the minimum number
of bits that can represent the value < code > T.bit_count< / code > .
< / p >
< p >
If < code > x< / code > is zero, < code > @clz< / code > returns < code > T.bit_count< / code > .
< / p >
< h3 id = "builtin-cmpxchg" > @cmpxchg< / h3 >
< pre > < code class = "zig" > @cmpxchg(ptr: & T, cmp: T, new: T, success_order: AtomicOrder, fail_order: AtomicOrder) -> bool< / code > < / pre >
< p >
This function performs an atomic compare exchange operation.
< / p >
< p >
< code > AtomicOrder< / code > can be found with < code > @import("builtin").AtomicOrder< / code > .
< / p >
< p > < code > @typeOf(ptr).alignment< / code > must be < code > > = @sizeOf(T).< / code > < / p >
< p > See also:< / p >
< ul >
< li > < a href = "#compile-variables" > Compile Variables< / a > < / li >
< / ul >
< h3 id = "builtin-compileError" > @compileError< / h3 >
< pre > < code class = "zig" > @compileError(comptime msg: []u8)< / code > < / pre >
< p >
This function, when semantically analyzed, causes a compile error with the
message < code > msg< / code > .
< / p >
< p >
There are several ways that code avoids being semantically checked, such as
using < code > if< / code > or < code > switch< / code > with compile time constants,
and < code > comptime< / code > functions.
< / p >
< h3 id = "builtin-compileLog" > @compileLog< / h3 >
< pre > < code class = "zig" > @compileLog(args: ...)< / code > < / pre >
< p >
This function prints the arguments passed to it at compile-time.
< / p >
< p >
To prevent accidentally leaving compile log statements in a codebase,
a compilation error is added to the build, pointing to the compile
log statement. This error prevents code from being generated, but
does not otherwise interfere with analysis.
< / p >
< p >
This function can be used to do "printf debugging" on
compile-time executing code.
< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
const num1 = {
var val1: i32 = 99;
@compileLog("comptime val1 = ", val1);
val1 = val1 + 1;
val1
};
pub fn main() -> %void {
@compileLog("comptime in main");
warn("Runtime in main, num1 = {}.\n", num1);
}< / code > < / pre >
< / p >
< p >
will ouput:
< / p >
< pre > < code class = "sh" > $ zig build-exe test.zig
| "comptime in main"
| "comptime val1 = ", 99
test.zig:14:5: error: found compile log statement
@compileLog("comptime in main");
^
test.zig:6:2: error: found compile log statement
@compileLog("comptime val1 = ", val1);
^< / code > < / pre >
< p >
If all < code > @compileLog< / code > calls are removed or
not encountered by analysis, the
program compiles successfully and the generated executable prints:
< / p >
< pre > < code class = "sh" > Runtime in main, num1 = 100.< / code > < / pre >
< h3 id = "builtin-ctz" > @ctz< / h3 >
< pre > < code class = "zig" > @ctz(x: T) -> U< / code > < / pre >
< p >
This function counts the number of trailing zeroes in < code > x< / code > which is an integer
type < code > T< / code > .
< / p >
< p >
The return type < code > U< / code > is an unsigned integer with the minimum number
of bits that can represent the value < code > T.bit_count< / code > .
< / p >
< p >
If < code > x< / code > is zero, < code > @ctz< / code > returns < code > T.bit_count< / code > .
< / p >
< h3 id = "builtin-divExact" > @divExact< / h3 >
< pre > < code class = "zig" > @divExact(numerator: T, denominator: T) -> T< / code > < / pre >
< p >
Exact division. Caller guarantees < code > denominator != 0< / code > and
< code > @divTrunc(numerator, denominator) * denominator == numerator< / code > .
< / p >
< ul >
< li > < code > @divExact(6, 3) == 2< / code > < / li >
< li > < code > @divExact(a, b) * b == a< / code > < / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-divTrunc" > @divTrunc< / a > < / li >
< li > < a href = "#builtin-divFloor" > @divFloor< / a > < / li >
< li > < code > @import("std").math.divExact< / code > < / li >
< / ul >
< h3 id = "builtin-divFloor" > @divFloor< / h3 >
< pre > < code class = "zig" > @divFloor(numerator: T, denominator: T) -> T< / code > < / pre >
< p >
Floored division. Rounds toward negative infinity. For unsigned integers it is
the same as < code > numerator / denominator< / code > . Caller guarantees < code > denominator != 0< / code > and
< code > !(@typeId(T) == builtin.TypeId.Int and T.is_signed and numerator == @minValue(T) and denominator == -1)< / code > .
< / p >
< ul >
< li > < code > @divFloor(-5, 3) == -2< / code > < / li >
< li > < code > @divFloor(a, b) + @mod(a, b) == a< / code > < / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-divTrunc" > @divTrunc< / a > < / li >
< li > < a href = "#builtin-divExact" > @divExact< / a > < / li >
< li > < code > @import("std").math.divFloor< / code > < / li >
< / ul >
< h3 id = "builtin-divTrunc" > @divTrunc< / h3 >
< pre > < code class = "zig" > @divTrunc(numerator: T, denominator: T) -> T< / code > < / pre >
< p >
Truncated division. Rounds toward zero. For unsigned integers it is
the same as < code > numerator / denominator< / code > . Caller guarantees < code > denominator != 0< / code > and
< code > !(@typeId(T) == builtin.TypeId.Int and T.is_signed and numerator == @minValue(T) and denominator == -1)< / code > .
< / p >
< ul >
< li > < code > @divTrunc(-5, 3) == -1< / code > < / li >
< li > < code > @divTrunc(a, b) + @rem(a, b) == a< / code > < / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-divFloor" > @divFloor< / a > < / li >
< li > < a href = "#builtin-divExact" > @divExact< / a > < / li >
< li > < code > @import("std").math.divTrunc< / code > < / li >
< / ul >
< h3 id = "builtin-embedFile" > @embedFile< / h3 >
< pre > < code class = "zig" > @embedFile(comptime path: []const u8) -> [X]u8< / code > < / pre >
< p >
This function returns a compile time constant fixed-size array with length
equal to the byte count of the file given by < code > path< / code > . The contents of the array
are the contents of the file.
< / p >
< p >
< code > path< / code > is absolute or relative to the current file, just like < code > @import< / code > .
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-import" > @import< / a > < / li >
< / ul >
2017-12-19 15:39:43 +08:00
< h3 id = "builtin-export" > @export< / h3 >
< pre > < code class = "zig" > @export(comptime name: []const u8, target: var, linkage: builtin.GlobalLinkage) -> []const u8< / code > < / pre >
< p >
Creates a symbol in the output object file.
< / p >
2017-12-04 09:43:56 +08:00
< h3 id = "builtin-tagName" > @tagName< / h3 >
< pre > < code class = "zig" > @tagName(value: var) -> []const u8< / code > < / pre >
2017-11-07 16:22:27 +08:00
< p >
2017-12-04 09:43:56 +08:00
Converts an enum value or union value to a slice of bytes representing the name.
2017-11-07 16:22:27 +08:00
< / p >
2017-12-01 10:46:02 +08:00
< h3 id = "builtin-EnumTagType" > @EnumTagType< / h3 >
< pre > < code class = "zig" > @EnumTagType(T: type) -> type< / code > < / pre >
< p >
Returns the integer type that is used to store the enumeration value.
< / p >
2017-11-07 16:22:27 +08:00
< h3 id = "builtin-errorName" > @errorName< / h3 >
< pre > < code class = "zig" > @errorName(err: error) -> []u8< / code > < / pre >
< p >
This function returns the string representation of an error. If an error
declaration is:
< / p >
< pre > < code class = "zig" > error OutOfMem< / code > < / pre >
< p >
Then the string representation is < code > "OutOfMem"< / code > .
< / p >
< p >
If there are no calls to < code > @errorName< / code > in an entire application,
or all calls have a compile-time known value for < code > err< / code > , then no
error name table will be generated.
< / p >
< h3 id = "builtin-fence" > @fence< / h3 >
< pre > < code class = "zig" > @fence(order: AtomicOrder)< / code > < / pre >
< p >
The < code > fence< / code > function is used to introduce happens-before edges between operations.
< / p >
< p >
< code > AtomicOrder< / code > can be found with < code > @import("builtin").AtomicOrder< / code > .
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#compile-variables" > Compile Variables< / a > < / li >
< / ul >
< h3 id = "builtin-fieldParentPtr" > @fieldParentPtr< / h3 >
< pre > < code class = "zig" > @fieldParentPtr(comptime ParentType: type, comptime field_name: []const u8,
field_ptr: & T) -> & ParentType< / code > < / pre >
< p >
Given a pointer to a field, returns the base pointer of a struct.
< / p >
< h3 id = "builtin-frameAddress" > @frameAddress< / h3 >
< pre > < code class = "zig" > @frameAddress()< / code > < / pre >
< p >
This function returns the base pointer of the current stack frame.
< / p >
< p >
The implications of this are target specific and not consistent across all
platforms. The frame address may not be available in release mode due to
aggressive optimizations.
< / p >
< p >
This function is only valid within function scope.
< / p >
< h3 id = "builtin-import" > @import< / h3 >
< pre > < code class = "zig" > @import(comptime path: []u8) -> (namespace)< / code > < / pre >
< p >
This function finds a zig file corresponding to < code > path< / code > and imports all the
public top level declarations into the resulting namespace.
< / p >
< p >
< code > path< / code > can be a relative or absolute path, or it can be the name of a package.
If it is a relative path, it is relative to the file that contains the < code > @import< / code >
function call.
< / p >
< p >
The following packages are always available:
< / p >
< ul >
< li > < code > @import("std")< / code > - Zig Standard Library< / li >
< li > < code > @import("builtin")< / code > - Compiler-provided types and variables< / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#compile-variables" > Compile Variables< / a > < / li >
< li > < a href = "#builtin-embedFile" > @embedFile< / a > < / li >
< / ul >
< h3 id = "builtin-inlineCall" > @inlineCall< / h3 >
< pre > < code class = "zig" > @inlineCall(function: X, args: ...) -> Y< / code > < / pre >
< p >
This calls a function, in the same way that invoking an expression with parentheses does:
< / p >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "inline function call" {
assert(@inlineCall(add, 3, 9) == 12);
}
fn add(a: i32, b: i32) -> i32 { a + b }< / code > < / pre >
< p >
Unlike a normal function call, however, < code > @inlineCall< / code > guarantees that the call
will be inlined. If the call cannot be inlined, a compile error is emitted.
< / p >
< h3 id = "builtin-intToPtr" > @intToPtr< / h3 >
< pre > < code class = "zig" > @intToPtr(comptime DestType: type, int: usize) -> DestType< / code > < / pre >
< p >
Converts an integer to a pointer. To convert the other way, use < a href = "#builtin-ptrToInt" > @ptrToInt< / a > .
< / p >
< h3 id = "builtin-IntType" > @IntType< / h3 >
< pre > < code class = "zig" > @IntType(comptime is_signed: bool, comptime bit_count: u8) -> type< / code > < / pre >
< p >
This function returns an integer type with the given signness and bit count.
< / p >
< h3 id = "builtin-maxValue" > @maxValue< / h3 >
< pre > < code class = "zig" > @maxValue(comptime T: type) -> (number literal)< / code > < / pre >
< p >
This function returns the maximum value of the integer type < code > T< / code > .
< / p >
< p >
The result is a compile time constant.
< / p >
< h3 id = "builtin-memberCount" > @memberCount< / h3 >
< pre > < code class = "zig" > @memberCount(comptime T: type) -> (number literal)< / code > < / pre >
< p >
This function returns the number of enum values in an enum type.
< / p >
< p >
The result is a compile time constant.
< / p >
< h3 id = "builtin-memberName" > @memberName< / h3 >
< p > TODO< / p >
< h3 id = "builtin-memberType" > @memberType< / h3 >
< p > TODO< / p >
< h3 id = "builtin-memcpy" > @memcpy< / h3 >
< pre > < code class = "zig" > @memcpy(noalias dest: & u8, noalias source: & const u8, byte_count: usize)< / code > < / pre >
< p >
This function copies bytes from one region of memory to another. < code > dest< / code > and
< code > source< / code > are both pointers and must not overlap.
< / p >
< p >
This function is a low level intrinsic with no safety mechanisms. Most code
should not use this function, instead using something like this:
< / p >
< pre > < code class = "zig" > for (source[0...byte_count]) |b, i| dest[i] = b;< / code > < / pre >
< p >
The optimizer is intelligent enough to turn the above snippet into a memcpy.
< / p >
< p > There is also a standard library function for this:< / p >
< pre > < code class = "zig" > const mem = @import("std").mem;
mem.copy(u8, dest[0...byte_count], source[0...byte_count]);< / code > < / pre >
< h3 id = "builtin-memset" > @memset< / h3 >
< pre > < code class = "zig" > @memset(dest: & u8, c: u8, byte_count: usize)< / code > < / pre >
< p >
This function sets a region of memory to < code > c< / code > . < code > dest< / code > is a pointer.
< / p >
< p >
This function is a low level intrinsic with no safety mechanisms. Most
code should not use this function, instead using something like this:
< / p >
< pre > < code class = "zig" > for (dest[0...byte_count]) |*b| *b = c;< / code > < / pre >
< p >
The optimizer is intelligent enough to turn the above snippet into a memset.
< / p >
< p > There is also a standard library function for this:< / p >
< pre > < code > const mem = @import("std").mem;
mem.set(u8, dest, c);< / code > < / pre >
< h3 id = "builtin-minValue" > @minValue< / h3 >
< pre > < code class = "zig" > @minValue(comptime T: type) -> (number literal)< / code > < / pre >
< p >
This function returns the minimum value of the integer type T.
< / p >
< p >
The result is a compile time constant.
< / p >
< h3 id = "builtin-mod" > @mod< / h3 >
< pre > < code class = "zig" > @mod(numerator: T, denominator: T) -> T< / code > < / pre >
< p >
Modulus division. For unsigned integers this is the same as
< code > numerator % denominator< / code > . Caller guarantees < code > denominator > 0< / code > .
< / p >
< ul >
< li > < code > @mod(-5, 3) == 1< / code > < / li >
< li > < code > @divFloor(a, b) + @mod(a, b) == a< / code > < / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-rem" > @rem< / a > < / li >
< li > < code > @import("std").math.mod< / code > < / li >
< / ul >
< h3 id = "builtin-mulWithOverflow" > @mulWithOverflow< / h3 >
< pre > < code class = "zig" > @mulWithOverflow(comptime T: type, a: T, b: T, result: & T) -> bool< / code > < / pre >
< p >
Performs < code > *result = a * b< / code > . If overflow or underflow occurs,
stores the overflowed bits in < code > result< / code > and returns < code > true< / code > .
If no overflow or underflow occurs, returns < code > false< / code > .
< / p >
< h3 id = "builtin-offsetOf" > @offsetOf< / h3 >
< pre > < code class = "zig" > @offsetOf(comptime T: type, comptime field_name: [] const u8) -> (number literal)< / code > < / pre >
< p >
This function returns the byte offset of a field relative to its containing struct.
< / p >
< h3 id = "builtin-OpaqueType" > @OpaqueType< / h3 >
< pre > < code class = "zig" > @OpaqueType() -> type< / code > < / pre >
< p >
Creates a new type with an unknown size and alignment.
< / p >
< p >
This is typically used for type safety when interacting with C code that does not expose struct details.
Example:
< / p >
< pre > < code class = "zig" > const Derp = @OpaqueType();
const Wat = @OpaqueType();
extern fn bar(d: & Derp);
export fn foo(w: & Wat) {
bar(w);
}< / code > < / pre >
< pre > < code class = "sh" > $ ./zig build-obj test.zig
test.zig:5:9: error: expected type '& Derp', found '& Wat'
bar(w);
^< / code > < / pre >
< h3 id = "builtin-panic" > @panic< / h3 >
< pre > < code class = "zig" > @panic(message: []const u8) -> noreturn< / code > < / pre >
< p >
Invokes the panic handler function. By default the panic handler function
calls the public < code > panic< / code > function exposed in the root source file, or
if there is not one specified, invokes the one provided in < code > std/special/panic.zig< / code > .
< / p >
< p > Generally it is better to use < code > @import("std").debug.panic< / code > .
However, < code > @panic< / code > can be useful for 2 scenarios:
< / p >
< ul >
< li > From library code, calling the programmer's panic function if they exposed one in the root source file.< / li >
< li > When mixing C and Zig code, calling the canonical panic implementation across multiple .o files.< / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#root-source-file" > Root Source File< / a > < / li >
< / ul >
< h3 id = "builtin-ptrCast" > @ptrCast< / h3 >
< pre > < code class = "zig" > @ptrCast(comptime DestType: type, value: var) -> DestType< / code > < / pre >
< p >
Converts a pointer of one type to a pointer of another type.
< / p >
< h3 id = "builtin-ptrToInt" > @ptrToInt< / h3 >
< pre > < code class = "zig" > @ptrToInt(value: var) -> usize< / code > < / pre >
< p >
Converts < code > value< / code > to a < code > usize< / code > which is the address of the pointer. < code > value< / code > can be one of these types:
< / p >
< ul >
< li > < code > & T< / code > < / li >
< li > < code > ?& T< / code > < / li >
< li > < code > fn()< / code > < / li >
< li > < code > ?fn()< / code > < / li >
< / ul >
< p > To convert the other way, use < a href = "#builtin-intToPtr" > @intToPtr< / a > < / p >
< h3 id = "builtin-rem" > @rem< / h3 >
< pre > < code class = "zig" > @rem(numerator: T, denominator: T) -> T< / code > < / pre >
< p >
Remainder division. For unsigned integers this is the same as
< code > numerator % denominator< / code > . Caller guarantees < code > denominator > 0< / code > .
< / p >
< ul >
< li > < code > @rem(-5, 3) == -2< / code > < / li >
< li > < code > @divTrunc(a, b) + @rem(a, b) == a< / code > < / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-mod" > @mod< / a > < / li >
< li > < code > @import("std").math.rem< / code > < / li >
< / ul >
< h3 id = "builtin-returnAddress" > @returnAddress< / h3 >
< pre > < code class = "zig" > @returnAddress()< / code > < / pre >
< p >
This function returns a pointer to the return address of the current stack
frame.
< / p >
< p >
The implications of this are target specific and not consistent across
all platforms.
< / p >
< p >
This function is only valid within function scope.
< / p >
< h3 id = "builtin-setDebugSafety" > @setDebugSafety< / h3 >
< pre > < code class = "zig" > @setDebugSafety(scope, safety_on: bool)< / code > < / pre >
< p >
Sets whether debug safety checks are on for a given scope.
< / p >
< h3 id = "builtin-setEvalBranchQuota" > @setEvalBranchQuota< / h3 >
< pre > < code class = "zig" > @setEvalBranchQuota(new_quota: usize)< / code > < / pre >
< p >
Changes the maximum number of backwards branches that compile-time code
execution can use before giving up and making a compile error.
< / p >
< p >
If the < code > new_quota< / code > is smaller than the default quota (< code > 1000< / code > ) or
a previously explicitly set quota, it is ignored.
< / p >
< p >
Example:
< / p >
< pre > < code class = "zig" > comptime {
var i = 0;
while (i < 1001) : (i += 1) {}
}< / code > < / pre >
< pre > < code class = "sh" > $ ./zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:3:5: error: evaluation exceeded 1000 backwards branches
while (i < 1001) : (i += 1) {}
^< / code > < / pre >
< p > Now we use < code > @setEvalBranchQuota< / code > :< / p >
< pre > < code class = "zig" > comptime {
@setEvalBranchQuota(1001);
var i = 0;
while (i < 1001) : (i += 1) {}
}< / code > < / pre >
< pre > < code class = "sh" > $ ./zig build-obj test.zig< / code > < / pre >
< p > (no output because it worked fine)< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#comptime" > comptime< / a > < / li >
< / ul >
< h3 id = "builtin-setFloatMode" > @setFloatMode< / h3 >
< pre > < code class = "zig" > @setFloatMode(scope, mode: @import("builtin").FloatMode)< / code > < / pre >
< p >
Sets the floating point mode for a given scope. Possible values are:
< / p >
< pre > < code class = "zig" > pub const FloatMode = enum {
Optimized,
Strict,
};< / code > < / pre >
< ul >
< li >
< code > Optimized< / code > (default) - Floating point operations may do all of the following:
< ul >
< li > Assume the arguments and result are not NaN. Optimizations are required to retain defined behavior over NaNs, but the value of the result is undefined.< / li >
< li > Assume the arguments and result are not +/-Inf. Optimizations are required to retain defined behavior over +/-Inf, but the value of the result is undefined.< / li >
< li > Treat the sign of a zero argument or result as insignificant.< / li >
< li > Use the reciprocal of an argument rather than perform division.< / li >
< li > Perform floating-point contraction (e.g. fusing a multiply followed by an addition into a fused multiply-and-add).< / li >
< li > Perform algebraically equivalent transformations that may change results in floating point (e.g. reassociate).< / li >
< / ul >
This is equivalent to < code > -ffast-math< / code > in GCC.
< / li >
< li >
< code > Strict< / code > - Floating point operations follow strict IEEE compliance.
< / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#float-operations" > Floating Point Operations< / a > < / li >
< / ul >
< h3 id = "builtin-setGlobalLinkage" > @setGlobalLinkage< / h3 >
< pre > < code class = "zig" > @setGlobalLinkage(global_variable_name, comptime linkage: GlobalLinkage)< / code > < / pre >
< p >
< code > GlobalLinkage< / code > can be found with < code > @import("builtin").GlobalLinkage< / code > .
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#compile-variables" > Compile Variables< / a > < / li >
< / ul >
< h3 id = "builtin-setGlobalSection" > @setGlobalSection< / h3 >
< pre > < code class = "zig" > @setGlobalSection(global_variable_name, comptime section_name: []const u8) -> bool< / code > < / pre >
< p >
Puts the global variable in the specified section.
< / p >
< h3 id = "builtin-shlExact" > @shlExact< / h3 >
< pre > < code class = "zig" > @shlExact(value: T, shift_amt: Log2T) -> T< / code > < / pre >
< p >
Performs the left shift operation (< code > < < < / code > ). Caller guarantees
that the shift will not shift any 1 bits out.
< / p >
< p >
The type of < code > shift_amt< / code > is an unsigned integer with < code > log2(T.bit_count)< / code > bits.
This is because < code > shift_amt > = T.bit_count< / code > is undefined behavior.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-shrExact" > @shrExact< / a > < / li >
< li > < a href = "#builtin-shlWithOverflow" > @shlWithOverflow< / a > < / li >
< / ul >
< h3 id = "builtin-shlWithOverflow" > @shlWithOverflow< / h3 >
< pre > < code class = "zig" > @shlWithOverflow(comptime T: type, a: T, shift_amt: Log2T, result: & T) -> bool< / code > < / pre >
< p >
Performs < code > *result = a < < b< / code > . If overflow or underflow occurs,
stores the overflowed bits in < code > result< / code > and returns < code > true< / code > .
If no overflow or underflow occurs, returns < code > false< / code > .
< / p >
< p >
The type of < code > shift_amt< / code > is an unsigned integer with < code > log2(T.bit_count)< / code > bits.
This is because < code > shift_amt > = T.bit_count< / code > is undefined behavior.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-shlExact" > @shlExact< / a > < / li >
< li > < a href = "#builtin-shrExact" > @shrExact< / a > < / li >
< / ul >
< h3 id = "builtin-shrExact" > @shrExact< / h3 >
< pre > < code class = "zig" > @shrExact(value: T, shift_amt: Log2T) -> T< / code > < / pre >
< p >
Performs the right shift operation (< code > > > < / code > ). Caller guarantees
that the shift will not shift any 1 bits out.
< / p >
< p >
The type of < code > shift_amt< / code > is an unsigned integer with < code > log2(T.bit_count)< / code > bits.
This is because < code > shift_amt > = T.bit_count< / code > is undefined behavior.
< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-shlExact" > @shlExact< / a > < / li >
< / ul >
< h3 id = "builtin-sizeOf" > @sizeOf< / h3 >
< pre > < code class = "zig" > @sizeOf(comptime T: type) -> (number literal)< / code > < / pre >
< p >
This function returns the number of bytes it takes to store < code > T< / code > in memory.
< / p >
< p >
The result is a target-specific compile time constant.
< / p >
< h3 id = "builtin-subWithOverflow" > @subWithOverflow< / h3 >
< pre > < code class = "zig" > @subWithOverflow(comptime T: type, a: T, b: T, result: & T) -> bool< / code > < / pre >
< p >
Performs < code > *result = a - b< / code > . If overflow or underflow occurs,
stores the overflowed bits in < code > result< / code > and returns < code > true< / code > .
If no overflow or underflow occurs, returns < code > false< / code > .
< / p >
< h3 id = "builtin-truncate" > @truncate< / h3 >
< pre > < code class = "zig" > @truncate(comptime T: type, integer) -> T< / code > < / pre >
< p >
This function truncates bits from an integer type, resulting in a smaller
integer type.
< / p >
< p >
The following produces a crash in debug mode and undefined behavior in
release mode:
< / p >
< pre > < code class = "zig" > const a: u16 = 0xabcd;
const b: u8 = u8(a);< / code > < / pre >
< p >
However this is well defined and working code:
< / p >
< pre > < code class = "zig" > const a: u16 = 0xabcd;
const b: u8 = @truncate(u8, a);
// b is now 0xcd< / code > < / pre >
< p >
This function always truncates the significant bits of the integer, regardless
of endianness on the target platform.
< / p >
< h3 id = "builtin-typeId" > @typeId< / h3 >
< pre > < code class = "zig" > @typeId(comptime T: type) -> @import("builtin").TypeId< / code > < / pre >
< p >
Returns which kind of type something is. Possible values:
< / p >
< pre > < code class = "zig" > pub const TypeId = enum {
Type,
Void,
Bool,
NoReturn,
Int,
Float,
Pointer,
Array,
Struct,
FloatLiteral,
IntLiteral,
UndefinedLiteral,
NullLiteral,
Nullable,
ErrorUnion,
Error,
Enum,
EnumTag,
Union,
Fn,
Namespace,
Block,
BoundFn,
ArgTuple,
Opaque,
};< / code > < / pre >
< h3 id = "builtin-typeName" > @typeName< / h3 >
< pre > < code class = "zig" > @typeName(T: type) -> []u8< / code > < / pre >
< p >
This function returns the string representation of a type.
< / p >
< h3 id = "builtin-typeOf" > @typeOf< / h3 >
< pre > < code class = "zig" > @typeOf(expression) -> type< / code > < / pre >
< p >
This function returns a compile-time constant, which is the type of the
expression passed as an argument. The expression is evaluated.
< / p >
< h2 id = "build-mode" > Build Mode< / h2 >
< p >
Zig has three build modes:
< / p >
< ul >
< li > < a href = "#build-mode-debug" > Debug< / a > (default)< / li >
< li > < a href = "#build-mode-release-fast" > ReleaseFast< / a > < / li >
< li > < a href = "#build-mode-release-safe" > ReleaseSafe< / a > < / li >
< / ul >
< p >
To add standard build options to a < code > build.zig< / code > file:
< / p >
< pre > < code class = "sh" > const Builder = @import("std").build.Builder;
pub fn build(b: & Builder) {
const exe = b.addExecutable("example", "example.zig");
exe.setBuildMode(b.standardReleaseOptions());
b.default_step.dependOn(& exe.step);
}< / code > < / pre >
< p >
This causes these options to be available:
< / p >
< pre > < code class = "sh" > -Drelease-safe=(bool) optimizations on and safety on
-Drelease-fast=(bool) optimizations on and safety off< / code > < / pre >
< h3 id = "build-mode-debug" > Debug< / h2 >
< pre > < code class = "sh" > $ zig build-exe example.zig< / code > < / pre >
< ul >
< li > Fast compilation speed< / li >
< li > Safety checks enabled< / li >
< li > Slow runtime performance< / li >
< / ul >
< h3 id = "build-mode-release-fast" > ReleaseFast< / h2 >
< pre > < code class = "sh" > $ zig build-exe example.zig --release-fast< / code > < / pre >
< ul >
< li > Fast runtime performance< / li >
< li > Safety checks disabled< / li >
< li > Slow compilation speed< / li >
< / ul >
< h3 id = "build-mode-release-safe" > ReleaseSafe< / h2 >
< pre > < code class = "sh" > $ zig build-exe example.zig --release-safe< / code > < / pre >
< ul >
< li > Medium runtime performance< / li >
< li > Safety checks enabled< / li >
< li > Slow compilation speed< / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#compile-variables" > Compile Variables< / a > < / li >
< li > < a href = "#zig-build-system" > Zig Build System< / a > < / li >
< li > < a href = "#undefined-behavior" > Undefined Behavior< / a > < / li >
< / ul >
< h2 id = "undefined-behavior" > Undefined Behavior< / h2 >
< p >
Zig has many instances of undefined behavior. If undefined behavior is
detected at compile-time, Zig emits an error. Most undefined behavior that
cannot be detected at compile-time can be detected at runtime. In these cases,
Zig has safety checks. Safety checks can be disabled on a per-block basis
with < code > @setDebugSafety< / code > . The < a href = "#build-mode-release-fast" > ReleaseFast< / a >
build mode disables all safety checks in order to facilitate optimizations.
< / p >
< p >
When a safety check fails, Zig crashes with a stack trace, like this:
< / p >
< pre > < code class = "zig" > test "safety check" {
unreachable;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig test test.zig
Test 1/1 safety check...reached unreachable code
/home/andy/dev/zig/build/lib/zig/std/special/zigrt.zig:16:35: 0x000000000020331c in ??? (test)
@import("std").debug.panic("{}", message_ptr[0...message_len]);
^
/home/andy/dev/zig/build/test.zig:2:5: 0x0000000000203297 in ??? (test)
unreachable;
^
/home/andy/dev/zig/build/lib/zig/std/special/test_runner.zig:9:21: 0x0000000000214b0a in ??? (test)
test_fn.func();
^
/home/andy/dev/zig/build/lib/zig/std/special/bootstrap.zig:50:21: 0x0000000000214a17 in ??? (test)
return root.main();
^
/home/andy/dev/zig/build/lib/zig/std/special/bootstrap.zig:37:13: 0x00000000002148d0 in ??? (test)
callMain(argc, argv, envp) %% exit(1);
^
/home/andy/dev/zig/build/lib/zig/std/special/bootstrap.zig:30:20: 0x0000000000214820 in ??? (test)
callMainAndExit()
^
Tests failed. Use the following command to reproduce the failure:
./test< / code > < / pre >
< h3 id = "undef-unreachable" > Reaching Unreachable Code< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
assert(false);
}
fn assert(ok: bool) {
if (!ok) unreachable; // assertion failure
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:5:14: error: unable to evaluate constant expression
if (!ok) unreachable; // assertion failure
^
/home/andy/dev/zig/build/test.zig:2:11: note: called from here
assert(false);
^
/home/andy/dev/zig/build/test.zig:1:10: note: called from here
comptime {
^< / code > < / pre >
< p > At runtime crashes with the message < code > reached unreachable code< / code > and a stack trace.< / p >
< h3 id = "undef-index-out-of-bounds" > Index out of Bounds< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const array = "hello";
const garbage = array[5];
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:3:26: error: index 5 outside array of size 5
const garbage = array[5];
^< / code > < / pre >
< p > At runtime crashes with the message < code > index out of bounds< / code > and a stack trace.< / p >
< h3 id = "undef-cast-negative-unsigned" > Cast Negative Number to Unsigned Integer< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const value: i32 = -1;
const unsigned = u32(value);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig test.zig:3:25: error: attempt to cast negative value to unsigned integer
const unsigned = u32(value);
^< / code > < / pre >
< p > At runtime crashes with the message < code > attempt to cast negative value to unsigned integer< / code > and a stack trace.< / p >
< p >
If you are trying to obtain the maximum value of an unsigned integer, use < code > @maxValue(T)< / code > ,
where < code > T< / code > is the integer type, such as < code > u32< / code > .
< / p >
< h3 id = "undef-cast-truncates-data" > Cast Truncates Data< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const spartan_count: u16 = 300;
const byte = u8(spartan_count);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
test.zig:3:20: error: cast from 'u16' to 'u8' truncates bits
const byte = u8(spartan_count);
^< / code > < / pre >
< p > At runtime crashes with the message < code > integer cast truncated bits< / code > and a stack trace.< / p >
< p >
If you are trying to truncate bits, use < code > @truncate(T, value)< / code > ,
where < code > T< / code > is the integer type, such as < code > u32< / code > , and < code > value< / code >
is the value you want to truncate.
< / p >
< h3 id = "undef-integer-overflow" > Integer Overflow< / h3 >
< h4 id = "undef-int-overflow-default" > Default Operations< / h4 >
< p > The following operators can cause integer overflow:< / p >
< ul >
< li > < code > +< / code > (addition)< / li >
< li > < code > -< / code > (subtraction)< / li >
< li > < code > -< / code > (negation)< / li >
< li > < code > *< / code > (multiplication)< / li >
< li > < code > /< / code > (division)< / li >
< li > < code > @divTrunc< / code > (division)< / li >
< li > < code > @divFloor< / code > (division)< / li >
< li > < code > @divExact< / code > (division)< / li >
< / ul >
< p > Example with addition at compile-time:< / p >
< pre > < code class = "zig" > comptime {
var byte: u8 = 255;
byte += 1;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:3:10: error: operation caused overflow
byte += 1;
^< / code > < / pre >
< p > At runtime crashes with the message < code > integer overflow< / code > and a stack trace.< / p >
< h4 id = "undef-int-overflow-std" > Standard Library Math Functions< / h4 >
< p > These functions provided by the standard library return possible errors.< / p >
< ul >
< li > < code > @import("std").math.add< / code > < / li >
< li > < code > @import("std").math.sub< / code > < / li >
< li > < code > @import("std").math.mul< / code > < / li >
< li > < code > @import("std").math.divTrunc< / code > < / li >
< li > < code > @import("std").math.divFloor< / code > < / li >
< li > < code > @import("std").math.divExact< / code > < / li >
< li > < code > @import("std").math.shl< / code > < / li >
< / ul >
< p > Example of catching an overflow for addition:< / p >
< pre > < code class = "zig" > const math = @import("std").math;
const warn = @import("std").debug.warn;
pub fn main() -> %void {
var byte: u8 = 255;
byte = if (math.add(u8, byte, 1)) |result| {
result
} else |err| {
warn("unable to add one: {}\n", @errorName(err));
return err;
};
warn("result: {}\n", byte);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-exe test.zig
$ ./test
unable to add one: Overflow< / code > < / pre >
< h4 id = "undef-int-overflow-builtin" > Builtin Overflow Functions< / h4 >
< p >
These builtins return a < code > bool< / code > of whether or not overflow
occurred, as well as returning the overflowed bits:
< / p >
< ul >
< li > < code > @addWithOverflow< / code > < / li >
< li > < code > @subWithOverflow< / code > < / li >
< li > < code > @mulWithOverflow< / code > < / li >
< li > < code > @shlWithOverflow< / code > < / li >
< / ul >
< p >
Example of < code > @addWithOverflow< / code > :
< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
pub fn main() -> %void {
var byte: u8 = 255;
var result: u8 = undefined;
if (@addWithOverflow(u8, byte, 10, & result)) {
warn("overflowed result: {}\n", result);
} else {
warn("result: {}\n", result);
}
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-exe test.zig
$ ./test
overflowed result: 9< / code > < / pre >
< h4 id = "undef-int-overflow-wrap" > Wrapping Operations< / h4 >
< p >
These operations have guaranteed wraparound semantics.
< / p >
< ul >
< li > < code > +%< / code > (wraparound addition)< / li >
< li > < code > -%< / code > (wraparound subtraction)< / li >
< li > < code > -%< / code > (wraparound negation)< / li >
< li > < code > *%< / code > (wraparound multiplication)< / li >
< / ul >
< pre > < code class = "zig" > const assert = @import("std").debug.assert;
test "wraparound addition and subtraction" {
const x: i32 = @maxValue(i32);
const min_val = x +% 1;
assert(min_val == @minValue(i32));
const max_val = min_val -% 1;
assert(max_val == @maxValue(i32));
}< / code > < / pre >
< h3 id = "undef-shl-overflow" > Exact Left Shift Overflow< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const x = @shlExact(u8(0b01010101), 2);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:2:15: error: operation caused overflow
const x = @shlExact(u8(0b01010101), 2);
^< / code > < / pre >
< p > At runtime crashes with the message < code > left shift overflowed bits< / code > and a stack trace.< / p >
< h3 id = "undef-shr-overflow" > Exact Right Shift Overflow< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const x = @shrExact(u8(0b10101010), 2);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:2:15: error: exact shift shifted out 1 bits
const x = @shrExact(u8(0b10101010), 2);
^< / code > < / pre >
< p > At runtime crashes with the message < code > right shift overflowed bits< / code > and a stack trace.< / p >
< h3 id = "undef-division-by-zero" > Division by Zero< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const a: i32 = 1;
const b: i32 = 0;
const c = a / b;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:4:17: error: division by zero is undefined
const c = a / b;
^< / code > < / pre >
< p > At runtime crashes with the message < code > division by zero< / code > and a stack trace.< / p >
< h3 id = "undef-remainder-division-by-zero" > Remainder Division by Zero< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const a: i32 = 10;
const b: i32 = 0;
const c = a % b;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:4:17: error: division by zero is undefined
const c = a % b;
^< / code > < / pre >
< p > At runtime crashes with the message < code > remainder division by zero< / code > and a stack trace.< / p >
< h3 id = "undef-exact-division-remainder" > Exact Division Remainder< / h3 >
< p > TODO< / p >
< h3 id = "undef-slice-widen-remainder" > Slice Widen Remainder< / h3 >
< p > TODO< / p >
< h3 id = "undef-attempt-unwrap-null" > Attempt to Unwrap Null< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const nullable_number: ?i32 = null;
const number = ??nullable_number;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:3:20: error: unable to unwrap null
const number = ??nullable_number;
^< / code > < / pre >
< p > At runtime crashes with the message < code > attempt to unwrap null< / code > and a stack trace.< / p >
< p > One way to avoid this crash is to test for null instead of assuming non-null, with
the < code > if< / code > expression:< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
pub fn main() -> %void {
const nullable_number: ?i32 = null;
if (nullable_number) |number| {
warn("got number: {}\n", number);
} else {
warn("it's null\n");
}
}< / code > < / pre >
< pre > < code class = "sh" > % zig build-exe test.zig
$ ./test
it's null< / code > < / pre >
< h3 id = "undef-attempt-unwrap-error" > Attempt to Unwrap Error< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > comptime {
const number = %%getNumberOrFail();
}
error UnableToReturnNumber;
fn getNumberOrFail() -> %i32 {
return error.UnableToReturnNumber;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:2:20: error: unable to unwrap error 'UnableToReturnNumber'
const number = %%getNumberOrFail();
^< / code > < / pre >
< p > At runtime crashes with the message < code > attempt to unwrap error: ErrorCode< / code > and a stack trace.< / p >
< p > One way to avoid this crash is to test for an error instead of assuming a successful result, with
the < code > if< / code > expression:< / p >
< pre > < code class = "zig" > const warn = @import("std").debug.warn;
pub fn main() -> %void {
const result = getNumberOrFail();
if (result) |number| {
warn("got number: {}\n", number);
} else |err| {
warn("got error: {}\n", @errorName(err));
}
}
error UnableToReturnNumber;
fn getNumberOrFail() -> %i32 {
return error.UnableToReturnNumber;
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-exe test.zig
$ ./test
got error: UnableToReturnNumber< / code > < / pre >
< h3 id = "undef-invalid-error-code" > Invalid Error Code< / h3 >
< p > At compile-time:< / p >
< pre > < code class = "zig" > error AnError;
comptime {
const err = error.AnError;
const number = u32(err) + 10;
const invalid_err = error(number);
}< / code > < / pre >
< pre > < code class = "sh" > $ zig build-obj test.zig
/home/andy/dev/zig/build/test.zig:5:30: error: integer value 11 represents no error
const invalid_err = error(number);
^< / code > < / pre >
< p > At runtime crashes with the message < code > invalid error code< / code > and a stack trace.< / p >
< h3 id = "undef-invalid-enum-cast" > Invalid Enum Cast< / h3 >
< p > TODO< / p >
< h3 id = "undef-incorrect-pointer-alignment" > Incorrect Pointer Alignment< / h3 >
< p > TODO< / p >
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< h3 id = "undef-bad-union-field" > Wrong Union Field Access< / h3 >
< p > TODO< / p >
2017-11-07 16:22:27 +08:00
< h2 id = "memory" > Memory< / h2 >
< p > TODO: explain no default allocator in zig< / p >
< p > TODO: show how to use the allocator interface< / p >
< p > TODO: mention debug allocator< / p >
< p > TODO: importance of checking for allocation failure< / p >
< p > TODO: mention overcommit and the OOM Killer< / p >
< p > TODO: mention recursion< / p >
< p > See also:< / p >
< ul >
< li > < a href = "#pointers" > Pointers< / a > < / li >
< / ul >
< h2 id = "compile-variables" > Compile Variables< / h2 >
< p >
Compile variables are accessible by importing the < code > "builtin"< / code > package,
which the compiler makes available to every Zig source file. It contains
compile-time constants such as the current target, endianness, and release mode.
< / p >
< pre > < code class = "zig" > const builtin = @import("builtin");
const separator = if (builtin.os == builtin.Os.windows) '\\' else '/';< / code > < / pre >
< p >
Example of what is imported with < code > @import("builtin")< / code > :
< / p >
< pre > < code class = "zig" > pub const Os = enum {
freestanding,
cloudabi,
darwin,
dragonfly,
freebsd,
ios,
kfreebsd,
linux,
lv2,
macosx,
netbsd,
openbsd,
solaris,
windows,
haiku,
minix,
rtems,
nacl,
cnk,
bitrig,
aix,
cuda,
nvcl,
amdhsa,
ps4,
elfiamcu,
tvos,
watchos,
mesa3d,
};
pub const Arch = enum {
armv8_2a,
armv8_1a,
armv8,
armv8m_baseline,
armv8m_mainline,
armv7,
armv7em,
armv7m,
armv7s,
armv7k,
armv6,
armv6m,
armv6k,
armv6t2,
armv5,
armv5te,
armv4t,
armeb,
aarch64,
aarch64_be,
avr,
bpfel,
bpfeb,
hexagon,
mips,
mipsel,
mips64,
mips64el,
msp430,
powerpc,
powerpc64,
powerpc64le,
r600,
amdgcn,
sparc,
sparcv9,
sparcel,
s390x,
tce,
thumb,
thumbeb,
i386,
x86_64,
xcore,
nvptx,
nvptx64,
le32,
le64,
amdil,
amdil64,
hsail,
hsail64,
spir,
spir64,
kalimbav3,
kalimbav4,
kalimbav5,
shave,
lanai,
wasm32,
wasm64,
renderscript32,
renderscript64,
};
pub const Environ = enum {
gnu,
gnuabi64,
gnueabi,
gnueabihf,
gnux32,
code16,
eabi,
eabihf,
android,
musl,
musleabi,
musleabihf,
msvc,
itanium,
cygnus,
amdopencl,
coreclr,
};
pub const ObjectFormat = enum {
unknown,
coff,
elf,
macho,
};
pub const GlobalLinkage = enum {
Internal,
Strong,
Weak,
LinkOnce,
};
pub const AtomicOrder = enum {
Unordered,
Monotonic,
Acquire,
Release,
AcqRel,
SeqCst,
};
pub const Mode = enum {
Debug,
ReleaseSafe,
ReleaseFast,
};
pub const is_big_endian = false;
pub const is_test = false;
pub const os = Os.linux;
pub const arch = Arch.x86_64;
pub const environ = Environ.gnu;
pub const object_format = ObjectFormat.elf;
pub const mode = Mode.ReleaseFast;
pub const link_libs = [][]const u8 {
};< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#build-mode" > Build Mode< / a > < / li >
< / ul >
< h2 id = "root-source-file" > Root Source File< / h2 >
< p > TODO: explain how root source file finds other files< / p >
< p > TODO: pub fn main< / p >
< p > TODO: pub fn panic< / p >
< p > TODO: if linking with libc you can use export fn main< / p >
< p > TODO: order independent top level declarations< / p >
< p > TODO: lazy analysis< / p >
< p > TODO: using comptime { _ = @import() }< / p >
< h2 id = "zig-test" > Zig Test< / h2 >
< p > TODO: basic usage< / p >
< p > TODO: lazy analysis< / p >
< p > TODO: --test-filter< / p >
< p > TODO: --test-name-prefix< / p >
< p > TODO: testing in releasefast and releasesafe mode. assert still works< / p >
< h2 id = "zig-build-system" > Zig Build System< / h2 >
< p > TODO: explain purpose, it's supposed to replace make/cmake< / p >
< p > TODO: example of building a zig executable< / p >
< p > TODO: example of building a C library< / p >
< h2 id = "c" > C< / h2 >
< p >
Although Zig is independent of C, and, unlike most other languages, does not depend on libc,
Zig acknowledges the importance of interacting with existing C code.
< / p >
< p >
There are a few ways that Zig facilitates C interop.
< / p >
< h3 id = "c-type-primitives" > C Type Primitives< / h3 >
< p >
These have guaranteed C ABI compatibility and can be used like any other type.
< / p >
< ul >
< li > < code > c_short< / code > < / li >
< li > < code > c_ushort< / code > < / li >
< li > < code > c_int< / code > < / li >
< li > < code > c_uint< / code > < / li >
< li > < code > c_long< / code > < / li >
< li > < code > c_ulong< / code > < / li >
< li > < code > c_longlong< / code > < / li >
< li > < code > c_ulonglong< / code > < / li >
< li > < code > c_longdouble< / code > < / li >
< li > < code > c_void< / code > < / li >
< / ul >
< p > See also:< / p >
< ul >
< li > < a href = "#primitive-types" > Primitive Types< / a > < / li >
< / ul >
< h3 id = "c-string-literals" > C String Literals< / h3 >
< pre > < code class = "zig" > extern fn puts(& const u8);
pub fn main() -> %void {
puts(c"this has a null terminator");
puts(
c\\and so
c\\does this
c\\multiline C string literal
);
}< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#string-literals" > String Literals< / a > < / li >
< / ul >
< h3 id = "c-import" > Import from C Header File< / h3 >
< p >
The < code > @cImport< / code > builtin function can be used
to directly import symbols from .h files:
< / p >
< pre > < code class = "zig" > const c = @cImport(@cInclude("stdio.h"));
pub fn main() -> %void {
c.printf("hello\n");
}< / code > < / pre >
< p >
The < code > @cImport< / code > function takes an expression as a parameter.
This expression is evaluated at compile-time and is used to control
preprocessor directives and include multiple .h files:
< / p >
< pre > < code class = "zig" > const builtin = @import("builtin");
const c = @cImport({
@cDefine("NDEBUG", builtin.mode == builtin.Mode.ReleaseFast);
if (something) {
@cDefine("_GNU_SOURCE", {});
}
@cInclude("stdlib.h")
if (something) {
@cUndef("_GNU_SOURCE");
}
@cInclude("soundio.h");
});< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#builtin-cImport" > @cImport< / a > < / li >
< li > < a href = "#builtin-cInclude" > @cInclude< / a > < / li >
< li > < a href = "#builtin-cDefine" > @cDefine< / a > < / li >
< li > < a href = "#builtin-cUndef" > @cUndef< / a > < / li >
< li > < a href = "#builtin-import" > @import< / a > < / li >
< / ul >
< h3 id = "mixing-object-files" > Mixing Object Files< / h3 >
< p >
You can mix Zig object files with any other object files that respect the C ABI. Example:
< / p >
< h4 > base64.zig< / h4 >
< pre > < code class = "zig" > const base64 = @import("std").base64;
export fn decode_base_64(dest_ptr: & u8, dest_len: usize,
source_ptr: & const u8, source_len: usize) -> usize
{
2017-11-18 14:42:21 +08:00
const src = source_ptr[0..source_len];
const dest = dest_ptr[0..dest_len];
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const base64_decoder = base64.standard_decoder_unsafe;
const decoded_size = base64_decoder.calcSize(src);
base64_decoder.decode(dest[0..decoded_size], src);
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return decoded_size;
}
< / code > < / pre >
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< h4 > test.c< / h4 >
< pre > < code class = "c" > // This header is generated by zig from base64.zig
#include "base64.h"
#include < string.h>
#include < stdio.h>
int main(int argc, char **argv) {
const char *encoded = "YWxsIHlvdXIgYmFzZSBhcmUgYmVsb25nIHRvIHVz";
char buf[200];
size_t len = decode_base_64(buf, 200, encoded, strlen(encoded));
buf[len] = 0;
puts(buf);
return 0;
}< / code > < / pre >
< h4 > build.zig< / h4 >
< pre > < code class = "zig" > const Builder = @import("std").build.Builder;
pub fn build(b: & Builder) {
const obj = b.addObject("base64", "base64.zig");
const exe = b.addCExecutable("test");
exe.addCompileFlags([][]const u8 {
"-std=c99",
});
exe.addSourceFile("test.c");
exe.addObject(obj);
exe.setOutputPath(".");
b.default_step.dependOn(& exe.step);
}< / code > < / pre >
< h4 > Terminal< / h4 >
< pre > < code class = "sh" > $ zig build
$ ./test
all your base are belong to us< / code > < / pre >
< p > See also:< / p >
< ul >
< li > < a href = "#targets" > Targets< / a > < / li >
< li > < a href = "#zig-build-system" > Zig Build System< / a > < / li >
< / ul >
< h2 id = "targets" > Targets< / h2 >
< p >
Zig supports generating code for all targets that LLVM supports. Here is
what it looks like to execute < code > zig targets< / code > on a Linux x86_64
computer:
< / p >
< pre > < code class = "sh" > $ zig targets
Architectures:
armv8_2a
armv8_1a
armv8
armv8m_baseline
armv8m_mainline
armv7
armv7em
armv7m
armv7s
armv7k
armv6
armv6m
armv6k
armv6t2
armv5
armv5te
armv4t
armeb
aarch64
aarch64_be
avr
bpfel
bpfeb
hexagon
mips
mipsel
mips64
mips64el
msp430
powerpc
powerpc64
powerpc64le
r600
amdgcn
sparc
sparcv9
sparcel
s390x
tce
thumb
thumbeb
i386
x86_64 (native)
xcore
nvptx
nvptx64
le32
le64
amdil
amdil64
hsail
hsail64
spir64
kalimbav3
kalimbav4
kalimbav5
shave
lanai
wasm32
wasm64
renderscript32
renderscript64
Operating Systems:
freestanding
cloudabi
darwin
dragonfly
freebsd
ios
kfreebsd
linux (native)
lv2
macosx
netbsd
openbsd
solaris
windows
haiku
minix
rtems
nacl
cnk
bitrig
aix
cuda
nvcl
amdhsa
ps4
elfiamcu
tvos
watchos
mesa3d
Environments:
gnu (native)
gnuabi64
gnueabi
gnueabihf
gnux32
code16
eabi
eabihf
android
musl
musleabi
musleabihf
msvc
itanium
cygnus
amdopencl
coreclr< / code > < / pre >
< p >
The Zig Standard Library (< code > @import("std")< / code > ) has architecture, environment, and operating sytsem
abstractions, and thus takes additional work to support more platforms. It currently supports
Linux x86_64. Not all standard library code requires operating system abstractions, however,
so things such as generic data structures work an all above platforms.
< / p >
< h2 id = "style-guide" > Style Guide< / h2 >
< p >
These coding conventions are not enforced by the compiler, but they are shipped in
this documentation along with the compiler in order to provide a point of
reference, should anyone wish to point to an authority on agreed upon Zig
coding style.
< / p >
< h3 id = "style-guide-whitespace" > Whitespace< / h3 >
< ul >
< li >
4 space indentation
< / li >
< li >
Open braces on same line, unless you need to wrap.
< / li >
< li > If a list of things is longer than 2, put each item on its own line and
exercise the abilty to put an extra comma at the end.
< / li >
< li >
Line length: aim for 100; use common sense.
< / li >
< / ul >
< h3 id = "style-guide-names" > Names< / h3 >
< p >
Roughly speaking: < code > camelCaseFunctionName< / code > , < code > TitleCaseTypeName< / code > ,
< code > snake_case_variable_name< / code > . More precisely:
< / p >
< ul >
< li >
If < code > x< / code > is a < code > struct< / code > (or an alias of a < code > struct< / code > ),
then < code > x< / code > should be < code > TitleCase< / code > .
< / li >
< li >
If < code > x< / code > otherwise identifies a type, < code > x< / code > should have < code > snake_case< / code > .
< / li >
< li >
If < code > x< / code > is callable, and < code > x< / code > 's return type is < code > type< / code > , then < code > x< / code > should be < code > TitleCase< / code > .
< / li >
< li >
If < code > x< / code > is otherwise callable, then < code > x< / code > should be < code > camelCase< / code > .
< / li >
< li >
Otherwise, < code > x< / code > should be < code > snake_case< / code > .
< / li >
< / ul >
< p >
Acronyms, initialisms, proper nouns, or any other word that has capitalization
rules in written English are subject to naming conventions just like any other
word. Even acronyms that are only 2 letters long are subject to these
conventions.
< / p >
< p >
These are general rules of thumb; if it makes sense to do something different,
do what makes sense. For example, if there is an established convention such as
< code > ENOENT< / code > , follow the established convention.
< / p >
< h3 id = "style-guide-examples" > Examples< / h3 >
< pre > < code class = "zig" > const namespace_name = @import("dir_name/file_name.zig");
var global_var: i32 = undefined;
const const_name = 42;
const primitive_type_alias = f32;
const string_alias = []u8;
const StructName = struct {};
const StructAlias = StructName;
fn functionName(param_name: TypeName) {
var functionPointer = functionName;
functionPointer();
functionPointer = otherFunction;
functionPointer();
}
const functionAlias = functionName;
fn ListTemplateFunction(comptime ChildType: type, comptime fixed_size: usize) -> type {
return List(ChildType, fixed_size);
}
fn ShortList(comptime T: type, comptime n: usize) -> type {
struct {
field_name: [n]T,
fn methodName() {}
}
}
// The word XML loses its casing when used in Zig identifiers.
const xml_document =
\\< ?xml version="1.0" encoding="UTF-8"?>
\\< document>
\\< /document>
;
const XmlParser = struct {};
// The initials BE (Big Endian) are just another word in Zig identifier names.
fn readU32Be() -> u32 {}< / code > < / pre >
< p >
See the Zig Standard Library for more examples.
< / p >
< h2 id = "grammar" > Grammar< / h2 >
< pre > < code > Root = many(TopLevelItem) EOF
TopLevelItem = ErrorValueDecl | CompTimeExpression(Block) | TopLevelDecl | TestDecl
TestDecl = "test" String Block
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TopLevelDecl = option("pub") (FnDef | ExternDecl | GlobalVarDecl | UseDecl)
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ErrorValueDecl = "error" Symbol ";"
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GlobalVarDecl = option("export") VariableDeclaration ";"
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2017-12-19 14:19:49 +08:00
LocalVarDecl = option("comptime") VariableDeclaration
VariableDeclaration = ("var" | "const") Symbol option(":" TypeExpr) option("align" "(" Expression ")") option("section" "(" Expression ")") "=" Expression
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ContainerMember = (ContainerField | FnDef | GlobalVarDecl)
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ContainerField = Symbol option(":" PrefixOpExpression option("=" PrefixOpExpression ","
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UseDecl = "use" Expression ";"
ExternDecl = "extern" option(String) (FnProto | VariableDeclaration) ";"
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FnProto = option("coldcc" | "nakedcc" | "stdcallcc" | "extern") "fn" option(Symbol) ParamDeclList option("align" "(" Expression ")") option("section" "(" Expression ")") option("-> " TypeExpr)
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FnDef = option("inline" | "export") FnProto Block
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ParamDeclList = "(" list(ParamDecl, ",") ")"
ParamDecl = option("noalias" | "comptime") option(Symbol ":") (TypeExpr | "...")
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Block = option(Symbol ":") "{" many(Statement) "}"
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Statement = LocalVarDecl ";" | Defer(Block) | Defer(Expression) ";" | BlockExpression(Block) | Expression ";" | ";"
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TypeExpr = PrefixOpExpression | "var"
BlockOrExpression = Block | Expression
Expression = ReturnExpression | BreakExpression | AssignmentExpression
AsmExpression = "asm" option("volatile") "(" String option(AsmOutput) ")"
AsmOutput = ":" list(AsmOutputItem, ",") option(AsmInput)
AsmInput = ":" list(AsmInputItem, ",") option(AsmClobbers)
AsmOutputItem = "[" Symbol "]" String "(" (Symbol | "-> " TypeExpr) ")"
AsmInputItem = "[" Symbol "]" String "(" Expression ")"
AsmClobbers= ":" list(String, ",")
UnwrapExpression = BoolOrExpression (UnwrapNullable | UnwrapError) | BoolOrExpression
UnwrapNullable = "??" Expression
UnwrapError = "%%" option("|" Symbol "|") Expression
AssignmentExpression = UnwrapExpression AssignmentOperator UnwrapExpression | UnwrapExpression
AssignmentOperator = "=" | "*=" | "/=" | "%=" | "+=" | "-=" | "< < =" | "> > =" | "& =" | "^=" | "|=" | "*%=" | "+%=" | "-%="
BlockExpression(body) = Block | IfExpression(body) | TryExpression(body) | TestExpression(body) | WhileExpression(body) | ForExpression(body) | SwitchExpression | CompTimeExpression(body)
CompTimeExpression(body) = "comptime" body
SwitchExpression = "switch" "(" Expression ")" "{" many(SwitchProng) "}"
SwitchProng = (list(SwitchItem, ",") | "else") "=> " option("|" option("*") Symbol "|") Expression ","
SwitchItem = Expression | (Expression "..." Expression)
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ForExpression(body) = option(Symbol ":") option("inline") "for" "(" Expression ")" option("|" option("*") Symbol option("," Symbol) "|") body option("else" BlockExpression(body))
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BoolOrExpression = BoolAndExpression "or" BoolOrExpression | BoolAndExpression
ReturnExpression = option("%") "return" option(Expression)
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BreakExpression = "break" option(":" Symbol) option(Expression)
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Defer(body) = option("%") "defer" body
IfExpression(body) = "if" "(" Expression ")" body option("else" BlockExpression(body))
TryExpression(body) = "if" "(" Expression ")" option("|" option("*") Symbol "|") body "else" "|" Symbol "|" BlockExpression(body)
TestExpression(body) = "if" "(" Expression ")" option("|" option("*") Symbol "|") body option("else" BlockExpression(body))
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WhileExpression(body) = option(Symbol ":") option("inline") "while" "(" Expression ")" option("|" option("*") Symbol "|") option(":" "(" Expression ")") body option("else" option("|" Symbol "|") BlockExpression(body))
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BoolAndExpression = ComparisonExpression "and" BoolAndExpression | ComparisonExpression
ComparisonExpression = BinaryOrExpression ComparisonOperator BinaryOrExpression | BinaryOrExpression
ComparisonOperator = "==" | "!=" | "< " | "> " | "< =" | "> ="
BinaryOrExpression = BinaryXorExpression "|" BinaryOrExpression | BinaryXorExpression
BinaryXorExpression = BinaryAndExpression "^" BinaryXorExpression | BinaryAndExpression
BinaryAndExpression = BitShiftExpression "& " BinaryAndExpression | BitShiftExpression
BitShiftExpression = AdditionExpression BitShiftOperator BitShiftExpression | AdditionExpression
BitShiftOperator = "< < " | "> > " | "< < "
AdditionExpression = MultiplyExpression AdditionOperator AdditionExpression | MultiplyExpression
AdditionOperator = "+" | "-" | "++" | "+%" | "-%"
MultiplyExpression = CurlySuffixExpression MultiplyOperator MultiplyExpression | CurlySuffixExpression
CurlySuffixExpression = TypeExpr option(ContainerInitExpression)
MultiplyOperator = "*" | "/" | "%" | "**" | "*%"
PrefixOpExpression = PrefixOp PrefixOpExpression | SuffixOpExpression
SuffixOpExpression = PrimaryExpression option(FnCallExpression | ArrayAccessExpression | FieldAccessExpression | SliceExpression)
FieldAccessExpression = "." Symbol
FnCallExpression = "(" list(Expression, ",") ")"
ArrayAccessExpression = "[" Expression "]"
SliceExpression = "[" Expression ".." option(Expression) "]"
ContainerInitExpression = "{" ContainerInitBody "}"
ContainerInitBody = list(StructLiteralField, ",") | list(Expression, ",")
StructLiteralField = "." Symbol "=" Expression
PrefixOp = "!" | "-" | "~" | "*" | ("& " option("align" "(" Expression option(":" Integer ":" Integer) ")" ) option("const") option("volatile")) | "?" | "%" | "%%" | "??" | "-%"
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PrimaryExpression = Integer | Float | String | CharLiteral | KeywordLiteral | GroupedExpression | BlockExpression(BlockOrExpression) | Symbol | ("@" Symbol FnCallExpression) | ArrayType | FnProto | AsmExpression | ("error" "." Symbol) | ContainerDecl | ("continue" option(":" Symbol))
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ArrayType : "[" option(Expression) "]" option("align" "(" Expression option(":" Integer ":" Integer) ")")) option("const") option("volatile") TypeExpr
GroupedExpression = "(" Expression ")"
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KeywordLiteral = "true" | "false" | "null" | "undefined" | "error" | "this" | "unreachable"
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ContainerDecl = option("extern" | "packed")
("struct" option(GroupedExpression) | "union" option("enum" option(GroupedExpression) | GroupedExpression) | ("enum" option(GroupedExpression)))
"{" many(ContainerMember) "}"< / code > < / pre >
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< h2 id = "zen" > Zen< / h2 >
< ul >
< li > Communicate intent precisely.< / li >
< li > Edge cases matter.< / li >
< li > Favor reading code over writing code.< / li >
< li > Only one obvious way to do things.< / li >
< li > Runtime crashes are better than bugs.< / li >
< li > Compile errors are better than runtime crashes.< / li >
< li > Incremental improvements.< / li >
< li > Avoid local maximums.< / li >
< li > Reduce the amount one must remember.< / li >
< li > Minimize energy spent on coding style.< / li >
< li > Together we serve end users.< / li >
< / ul >
< h2 > TODO< / h2 >
< p > TODO: document changes from a31b23c46ba2a8c28df01adc1aa0b4d878b9a5cf (compile time reflection additions)< / p >
< / div >
< script src = "highlight/highlight.pack.js" > < / script >
< script > hljs . initHighlightingOnLoad ( ) ; < / script >
< / body >
< / html >
