1 // Coherence error results because we do not know whether `T: Foo<P>` or not
2 // for the second impl.
4 use std::marker::PhantomData;
6 pub trait Foo<P> { fn foo() {} }
8 impl <P, T: Foo<P>> Foo<P> for Option<T> {}
10 impl<T, U> Foo<T> for Option<U> { }