Okay, so this is cool....

generic_impls.rust

pub struct Foo {
    x: usize
}

pub struct Baz {}

pub trait Derp<Foo> {
    fn foo_it(&self);
}

impl Derp<Foo> for Foo {
    fn foo_it(&self){
        println!("{}", self.x)
    }

}

impl Derp<Foo> for Baz {
    fn foo_it(&self){
        println!("OINK");
    }

}

pub trait Bar: Derp<Foo> {
    fn do_other_thing_with_foo(&mut self) {
        self.foo_it();
        self.foo_it();
    }
}

impl<T> Bar for T where T: Derp<Foo> {}

fn main() {
    let mut x = Foo{x:123};
    x.do_other_thing_with_foo();
    let mut z = Baz{};
    z.do_other_thing_with_foo();
}