fn main() {
    auto s = "a";
    s += "b";
    assert (s.(0) == 'a' as u8);
    assert (s.(1) == 'b' as u8);
    s += "c";
    s += "d";
    assert (s.(0) == 'a' as u8);
    assert (s.(1) == 'b' as u8);
    assert (s.(2) == 'c' as u8);
    assert (s.(3) == 'd' as u8);
}