Code shared from the Rust Playground

playground.rs

#![feature(specialization)]

trait Foo<T: DefaultFooBehavior> {
    fn bar() {
        T::do_stuff();
    }
}

trait DefaultFooBehavior {
    fn do_stuff();
}

impl<T> DefaultFooBehavior for T {
    default fn do_stuff() {}
}

struct Baz;

impl DefaultFooBehavior for Baz {
    fn do_stuff() { println!("wooooooo!") }
}

fn main() {}