BoundedArray from a slice?

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1

Is there an API in the standard library similar to bounded array but for a slice?
Kind of like fixedBufferStream but for types other than u8.

For example,

I have been given a slice and I would like to append() to the slice starting from index zero in the slice.

2

In order to append, you need to have free space at the end of the slice. If the space comes from a pre-determined array, that’s BoundedArray. If the space needs to be allocated from the heap, it’s ArrayList. How would like to obtain the space for appending?

3

Append may have been unclear.

Something like this:

pub fn SliceBoundedArray(comptime T: type, slice: []T) type {
    return struct {
        slice: []T = slice,
        len: usize,

        fn append(self: @This(), item: T) error{NoSpaceLeft}!void {
            if (self.len == self.slice.len) return error.NoSpaceLeft;
            slice[self.len] = item;
            self.len += 1;
        }
    };
}
4

This looks good to me. If you want to reuse code from the std library, you could just initialize an array list with your slice, and give it a failing allocator. Then append is forced to only use the space you provided.

5

ArrayListUnmanaged(T).initBuffer(slice): Zig Documentation

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6

This, by itself, doesn’t work, because you can’t call append or any other allocating function. You’d have to provide a failing allocator to make this legal again.

7

True, my mistake.

8

It’s a bit footgun-y, but this is the intended use-case for initBuffer

Context: std: use BoundedArray less by andrewrk · Pull Request #18067 · ziglang/zig · GitHub

The use-case would be improved by std.array_list: Add *NoResize functions to ArrayListUnmanaged by notcancername · Pull Request #18361 · ziglang/zig · GitHub (and this PR is on my list of PRs to revive)

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