Not able to infer equality in some special cases

[bvssvni]

Example:

 error: type mismatch resolving `<<F as device::backend::Associated>::Backend as device::backend::Backend>::Resources == <F as device::backend::OfBackend>::Resources`:
 expected trait `device::backend::Backend`,
    found trait `device::backend::OfBackend`

[bvssvni]

A similar error can be replicated in the_simpsons example:

fn foo<T: HasChildren>(a: T) -> T::Father { a.cutest().father() }

examples/the_simpsons.rs:59:45: 59:64 error: mismatched types:
 expected `<T as OfBackend>::Father`,
    found `<<T as OfBackend>::Kids as OfBackend>::Father`
(expected type parameter,
    found associated type) [E0308]
examples/the_simpsons.rs:59 fn foo<T: HasChildren>(a: T) -> T::Father { a.cutest().father() }
                                                                        ^~~~~~~~~~~~~~~~~~~
examples/the_simpsons.rs:59:45: 59:64 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to previous error
Could not compile `backend`.

[bvssvni]

One solution could be to generate methods on the backend that converts the type safely.

[bvssvni]

It is possible to create an unsafe trait like this:

pub unsafe trait Cast<T, U> {
    fn cast(a: T) -> U  {
        unsafe { ::std::mem::transmute_copy(&a) }
    }
}

unsafe impl<T> Cast<<<T as OfBackend>::Kids as OfBackend>::Father, T::Father> for T
    where T: OfBackend
{}

fn foo<T: HasChildren>(a: T) -> T::Father { T::cast(a.cutest().father()) }

However, this does not work for T::cast(a.cutest().father().cutest().father()).

The impls will conflict, preventing one from supporting more than one cast method.