const Error = error{
    unexpected_result,
};

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