364 lines
13 KiB
Zig
364 lines
13 KiB
Zig
const std = @import("std.zig");
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const assert = std.debug.assert;
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const mem = std.mem;
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const testing = std.testing;
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/// A structure with an array and a length, that can be used as a slice.
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///
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/// Useful to pass around small arrays whose exact size is only known at
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/// runtime, but whose maximum size is known at comptime, without requiring
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/// an `Allocator`.
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///
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/// ```zig
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/// var actual_size = 32;
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/// var a = try BoundedArray(u8, 64).init(actual_size);
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/// var slice = a.slice(); // a slice of the 64-byte array
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/// var a_clone = a; // creates a copy - the structure doesn't use any internal pointers
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/// ```
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pub fn BoundedArray(comptime T: type, comptime buffer_capacity: usize) type {
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return struct {
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const Self = @This();
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buffer: [buffer_capacity]T = undefined,
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len: usize = 0,
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/// Set the actual length of the slice.
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/// Returns error.Overflow if it exceeds the length of the backing array.
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pub fn init(len: usize) error{Overflow}!Self {
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if (len > buffer_capacity) return error.Overflow;
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return Self{ .len = len };
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}
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/// View the internal array as a slice whose size was previously set.
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pub fn slice(self: anytype) mem.Span(@TypeOf(&self.buffer)) {
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return self.buffer[0..self.len];
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}
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/// View the internal array as a constant slice whose size was previously set.
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pub fn constSlice(self: *const Self) []const T {
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return self.slice();
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}
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/// Adjust the slice's length to `len`.
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/// Does not initialize added items if any.
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pub fn resize(self: *Self, len: usize) error{Overflow}!void {
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if (len > buffer_capacity) return error.Overflow;
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self.len = len;
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}
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/// Copy the content of an existing slice.
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pub fn fromSlice(m: []const T) error{Overflow}!Self {
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var list = try init(m.len);
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std.mem.copy(T, list.slice(), m);
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return list;
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}
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/// Return the element at index `i` of the slice.
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pub fn get(self: Self, i: usize) T {
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return self.constSlice()[i];
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}
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/// Set the value of the element at index `i` of the slice.
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pub fn set(self: *Self, i: usize, item: T) void {
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self.slice()[i] = item;
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}
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/// Return the maximum length of a slice.
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pub fn capacity(self: Self) usize {
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return self.buffer.len;
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}
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/// Check that the slice can hold at least `additional_count` items.
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pub fn ensureUnusedCapacity(self: Self, additional_count: usize) error{Overflow}!void {
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if (self.len + additional_count > buffer_capacity) {
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return error.Overflow;
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}
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}
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/// Increase length by 1, returning a pointer to the new item.
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pub fn addOne(self: *Self) error{Overflow}!*T {
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try self.ensureUnusedCapacity(1);
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return self.addOneAssumeCapacity();
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}
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/// Increase length by 1, returning pointer to the new item.
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/// Asserts that there is space for the new item.
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pub fn addOneAssumeCapacity(self: *Self) *T {
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assert(self.len < buffer_capacity);
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self.len += 1;
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return &self.slice()[self.len - 1];
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}
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/// Resize the slice, adding `n` new elements, which have `undefined` values.
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/// The return value is a slice pointing to the uninitialized elements.
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pub fn addManyAsArray(self: *Self, comptime n: usize) error{Overflow}!*[n]T {
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const prev_len = self.len;
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try self.resize(self.len + n);
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return self.slice()[prev_len..][0..n];
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}
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/// Remove and return the last element from the slice.
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/// Asserts the slice has at least one item.
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pub fn pop(self: *Self) T {
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const item = self.get(self.len - 1);
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self.len -= 1;
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return item;
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}
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/// Remove and return the last element from the slice, or
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/// return `null` if the slice is empty.
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pub fn popOrNull(self: *Self) ?T {
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return if (self.len == 0) null else self.pop();
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}
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/// Return a slice of only the extra capacity after items.
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/// This can be useful for writing directly into it.
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/// Note that such an operation must be followed up with a
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/// call to `resize()`
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pub fn unusedCapacitySlice(self: *Self) []T {
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return self.buffer[self.len..];
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}
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/// Insert `item` at index `i` by moving `slice[n .. slice.len]` to make room.
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/// This operation is O(N).
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pub fn insert(
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self: *Self,
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i: usize,
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item: T,
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) error{Overflow}!void {
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if (i > self.len) {
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return error.Overflow;
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}
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_ = try self.addOne();
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var s = self.slice();
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mem.copyBackwards(T, s[i + 1 .. s.len], s[i .. s.len - 1]);
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self.buffer[i] = item;
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}
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/// Insert slice `items` at index `i` by moving `slice[i .. slice.len]` to make room.
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/// This operation is O(N).
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pub fn insertSlice(self: *Self, i: usize, items: []const T) error{Overflow}!void {
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try self.ensureUnusedCapacity(items.len);
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self.len += items.len;
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mem.copyBackwards(T, self.slice()[i + items.len .. self.len], self.constSlice()[i .. self.len - items.len]);
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mem.copy(T, self.slice()[i .. i + items.len], items);
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}
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/// Replace range of elements `slice[start..start+len]` with `new_items`.
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/// Grows slice if `len < new_items.len`.
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/// Shrinks slice if `len > new_items.len`.
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pub fn replaceRange(
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self: *Self,
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start: usize,
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len: usize,
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new_items: []const T,
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) error{Overflow}!void {
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const after_range = start + len;
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var range = self.slice()[start..after_range];
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if (range.len == new_items.len) {
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mem.copy(T, range, new_items);
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} else if (range.len < new_items.len) {
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const first = new_items[0..range.len];
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const rest = new_items[range.len..];
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mem.copy(T, range, first);
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try self.insertSlice(after_range, rest);
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} else {
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mem.copy(T, range, new_items);
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const after_subrange = start + new_items.len;
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for (self.constSlice()[after_range..]) |item, i| {
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self.slice()[after_subrange..][i] = item;
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}
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self.len -= len - new_items.len;
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}
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}
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/// Extend the slice by 1 element.
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pub fn append(self: *Self, item: T) error{Overflow}!void {
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const new_item_ptr = try self.addOne();
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new_item_ptr.* = item;
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}
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/// Extend the slice by 1 element, asserting the capacity is already
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/// enough to store the new item.
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pub fn appendAssumeCapacity(self: *Self, item: T) void {
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const new_item_ptr = self.addOneAssumeCapacity();
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new_item_ptr.* = item;
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}
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/// Remove the element at index `i`, shift elements after index
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/// `i` forward, and return the removed element.
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/// Asserts the slice has at least one item.
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/// This operation is O(N).
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pub fn orderedRemove(self: *Self, i: usize) T {
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const newlen = self.len - 1;
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if (newlen == i) return self.pop();
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const old_item = self.get(i);
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for (self.slice()[i..newlen]) |*b, j| b.* = self.get(i + 1 + j);
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self.set(newlen, undefined);
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self.len = newlen;
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return old_item;
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}
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/// Remove the element at the specified index and return it.
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/// The empty slot is filled from the end of the slice.
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/// This operation is O(1).
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pub fn swapRemove(self: *Self, i: usize) T {
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if (self.len - 1 == i) return self.pop();
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const old_item = self.get(i);
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self.set(i, self.pop());
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return old_item;
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}
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/// Append the slice of items to the slice.
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pub fn appendSlice(self: *Self, items: []const T) error{Overflow}!void {
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try self.ensureUnusedCapacity(items.len);
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self.appendSliceAssumeCapacity(items);
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}
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/// Append the slice of items to the slice, asserting the capacity is already
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/// enough to store the new items.
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pub fn appendSliceAssumeCapacity(self: *Self, items: []const T) void {
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const oldlen = self.len;
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self.len += items.len;
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mem.copy(T, self.slice()[oldlen..], items);
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}
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/// Append a value to the slice `n` times.
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/// Allocates more memory as necessary.
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pub fn appendNTimes(self: *Self, value: T, n: usize) error{Overflow}!void {
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const old_len = self.len;
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try self.resize(old_len + n);
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mem.set(T, self.slice()[old_len..self.len], value);
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}
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/// Append a value to the slice `n` times.
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/// Asserts the capacity is enough.
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pub fn appendNTimesAssumeCapacity(self: *Self, value: T, n: usize) void {
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const old_len = self.len;
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self.len += n;
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assert(self.len <= buffer_capacity);
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mem.set(T, self.slice()[old_len..self.len], value);
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}
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pub const Writer = if (T != u8)
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@compileError("The Writer interface is only defined for BoundedArray(u8, ...) " ++
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"but the given type is BoundedArray(" ++ @typeName(T) ++ ", ...)")
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else
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std.io.Writer(*Self, error{Overflow}, appendWrite);
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/// Initializes a writer which will write into the array.
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pub fn writer(self: *Self) Writer {
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return .{ .context = self };
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}
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/// Same as `appendSlice` except it returns the number of bytes written, which is always the same
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/// as `m.len`. The purpose of this function existing is to match `std.io.Writer` API.
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fn appendWrite(self: *Self, m: []const u8) error{Overflow}!usize {
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try self.appendSlice(m);
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return m.len;
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}
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};
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}
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test "BoundedArray" {
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var a = try BoundedArray(u8, 64).init(32);
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try testing.expectEqual(a.capacity(), 64);
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try testing.expectEqual(a.slice().len, 32);
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try testing.expectEqual(a.constSlice().len, 32);
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try a.resize(48);
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try testing.expectEqual(a.len, 48);
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const x = [_]u8{1} ** 10;
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a = try BoundedArray(u8, 64).fromSlice(&x);
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try testing.expectEqualSlices(u8, &x, a.constSlice());
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var a2 = a;
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try testing.expectEqualSlices(u8, a.constSlice(), a2.constSlice());
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a2.set(0, 0);
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try testing.expect(a.get(0) != a2.get(0));
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try testing.expectError(error.Overflow, a.resize(100));
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try testing.expectError(error.Overflow, BoundedArray(u8, x.len - 1).fromSlice(&x));
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try a.resize(0);
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try a.ensureUnusedCapacity(a.capacity());
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(try a.addOne()).* = 0;
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try a.ensureUnusedCapacity(a.capacity() - 1);
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try testing.expectEqual(a.len, 1);
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const uninitialized = try a.addManyAsArray(4);
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try testing.expectEqual(uninitialized.len, 4);
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try testing.expectEqual(a.len, 5);
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try a.append(0xff);
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try testing.expectEqual(a.len, 6);
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try testing.expectEqual(a.pop(), 0xff);
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a.appendAssumeCapacity(0xff);
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try testing.expectEqual(a.len, 6);
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try testing.expectEqual(a.pop(), 0xff);
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try a.resize(1);
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try testing.expectEqual(a.popOrNull(), 0);
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try testing.expectEqual(a.popOrNull(), null);
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var unused = a.unusedCapacitySlice();
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mem.set(u8, unused[0..8], 2);
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unused[8] = 3;
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unused[9] = 4;
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try testing.expectEqual(unused.len, a.capacity());
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try a.resize(10);
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try a.insert(5, 0xaa);
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try testing.expectEqual(a.len, 11);
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try testing.expectEqual(a.get(5), 0xaa);
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try testing.expectEqual(a.get(9), 3);
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try testing.expectEqual(a.get(10), 4);
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try a.insert(11, 0xbb);
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try testing.expectEqual(a.len, 12);
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try testing.expectEqual(a.pop(), 0xbb);
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try a.appendSlice(&x);
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try testing.expectEqual(a.len, 11 + x.len);
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try a.appendNTimes(0xbb, 5);
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try testing.expectEqual(a.len, 11 + x.len + 5);
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try testing.expectEqual(a.pop(), 0xbb);
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a.appendNTimesAssumeCapacity(0xcc, 5);
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try testing.expectEqual(a.len, 11 + x.len + 5 - 1 + 5);
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try testing.expectEqual(a.pop(), 0xcc);
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try testing.expectEqual(a.len, 29);
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try a.replaceRange(1, 20, &x);
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try testing.expectEqual(a.len, 29 + x.len - 20);
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try a.insertSlice(0, &x);
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try testing.expectEqual(a.len, 29 + x.len - 20 + x.len);
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try a.replaceRange(1, 5, &x);
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try testing.expectEqual(a.len, 29 + x.len - 20 + x.len + x.len - 5);
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try a.append(10);
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try testing.expectEqual(a.pop(), 10);
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try a.append(20);
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const removed = a.orderedRemove(5);
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try testing.expectEqual(removed, 1);
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try testing.expectEqual(a.len, 34);
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a.set(0, 0xdd);
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a.set(a.len - 1, 0xee);
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const swapped = a.swapRemove(0);
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try testing.expectEqual(swapped, 0xdd);
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try testing.expectEqual(a.get(0), 0xee);
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while (a.popOrNull()) |_| {}
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const w = a.writer();
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const s = "hello, this is a test string";
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try w.writeAll(s);
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try testing.expectEqualStrings(s, a.constSlice());
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}
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