const std = #import("std");
const expect = std.testing.expect;
const assert = std.assert;

const Foo = struct(.{ .sliceable = true }) {
    pointer: [&]u8, 
    length: u32,
    capacity: u32,

    const add = fn (foo: &Foo, item: u8) void {
        const index = foo.length;
        assert(index < foo.capacity);
        foo.length += 1;
        foo[index] = item;
    }
};

const main = fn () *!void {
    var foo = [1]u8{0}; 
    var s = Foo{
        .pointer = foo.&,
        .length = 0,
        .capacity = 1,
    };

    s.add(5);

    try expect(s.length == 1);
    try expect(foo[0] == 5);
    try expect(s[0] == 5);
}