rust/src/test/compile-fail/ambig_impl_unify.rs

trait foo {
    fn foo() -> int;
}

impl methods of foo for ~[uint] {
    fn foo() -> int {1} //~ NOTE candidate #1 is `methods::foo`
}

impl methods of foo for ~[int] {
    fn foo() -> int {2} //~ NOTE candidate #2 is `methods::foo`
}

fn main() {
    let x = ~[];
    x.foo(); //~ ERROR multiple applicable methods in scope
}