//! returns: 0
//! Basic trait object dispatch test.
record Counter {
    value: i32,
}

trait Adder {
    fn (*mut Adder) add(n: i32) -> i32;
}

instance Adder for Counter {
    fn (c: *mut Counter) add(n: i32) -> i32 {
        set c.value = c.value + n;
        return c.value;
    }
}

@default fn main() -> i32 {
    let mut c = Counter { value: 10 };
    let a: *mut opaque Adder = &mut c;

    let result = a.add(5);
    // c.value should be 15 now.
    assert result == 15;
    let result2 = a.add(3);
    // c.value should be 18 now.
    assert result2 == 18;
    return 0;
}