rust/src/test/run-pass/iface-generic.rs

iface to_str {
    fn to_str() -> str;
}
impl of to_str for int {
    fn to_str() -> str { int::str(self) }
}
impl of to_str for str {
    fn to_str() -> str { self }
}
impl of to_str for () {
    fn to_str() -> str { "()" }
}

iface map<T> {
    fn map<U>(f: fn(T) -> U) -> [U]/~;
}
impl <T> of map<T> for [T]/~ {
    fn map<U>(f: fn(T) -> U) -> [U]/~ {
        let mut r = []/~;
        for self.each {|x| r += [f(x)]/~; }
        r
    }
}

fn foo<U, T: map<U>>(x: T) -> [str]/~ {
    x.map({|_e| "hi" })
}
fn bar<U: to_str, T: map<U>>(x: T) -> [str]/~ {
    x.map({|_e| _e.to_str() })
}

fn main() {
    assert foo([1]/~) == ["hi"]/~;
    assert bar::<int, [int]/~>([4, 5]/~) == ["4", "5"]/~;
    assert bar::<str, [str]/~>(["x", "y"]/~) == ["x", "y"]/~;
    assert bar::<(), [()]/~>([()]/~) == ["()"]/~;
}