Shared via Rust Playground

playground.rs

trait TR {
  type Assoc : Clone + Copy + Default;
}

#[derive(Clone, Copy, Default)]
struct Foo<T: TR> {
  thing : T::Assoc,
}

impl <T: TR> Foo<T> {
    fn bar() {
        // This works
        let _ : T::Assoc = Default::default();
        // This does not.
        let _ : Foo<T> = Default::default();
    }
}

fn main() {
}