trait Foo {
    fn foo();
}

impl Foo for Vec<u8> {
    fn foo() { println!("u8"); }
}

impl Foo for Vec<usize> {
    fn foo() { println!("usize"); }
}

fn main() {
    // Error: Rust doesn't konw the type.
    // Vec::foo();
    Vec::<u8>::foo();
    Vec::<usize>::foo();
}