const Error = error{
    unexpected_result,
};

const main = fn () Error!void {
    var buffer: [2]u8 = undefined;
    const expected = 'a';
    const index: usize = 1;
    foo(buffer.&, index, expected);
    const ch = buffer[index];
    const sub = expected - ch;
    const result: u32 = sub;
    if (result != 0) {
        return Error.unexpected_result;
    }
}

const foo = fn (buffer: &[2]u8, index: usize, ch: u8) void {
    buffer[index] = ch;
}