//! returns: 0
//! Test trait dispatch inside control flow.
//!
//! Exercises: trait method calls inside loops and conditionals,
//! verifying that vtable dispatch works correctly when interleaved
//! with branching and iteration.

record Counter: Copy {
    value: i32,
}

trait Stepper {
    unsafe fn (*unsafe mut Stepper) step() -> i32;
    unsafe fn (*unsafe Stepper) current() -> i32;
}

instance Stepper for Counter {
    unsafe fn (c: *unsafe mut Counter) step() -> i32 {
        set c.value = c.value + 1;
        return c.value;
    }

    unsafe fn (c: *unsafe Counter) current() -> i32 {
        return c.value;
    }
}

@default unsafe fn main() -> i32 {
    let mut c = Counter { value: 0 };
    let s: *unsafe mut opaque Stepper = &mut c;

    // Dispatch in a while loop.
    let mut i: i32 = 0;
    while i < 5 {
        s.step();
        set i = i + 1;
    }
    assert s.current() == 5;

    // Dispatch in a conditional.
    if s.current() > 3 {
        s.step();
    }
    assert s.current() == 6;

    // Dispatch result used as loop condition.
    while s.current() < 10 {
        s.step();
    }
    assert s.current() == 10;

    // Dispatch result used in conditional expression.
    let v = s.current();
    assert v == 10;
    return 0;
}