In Section 6.5 (“Iter”), the return type is hard to infer

[evelon]

The issue introduced in #189 still persists.

The return type of into_iter is shown like this in the standard library documentation:

fn into_iter(self) -> <&'a Vec<T, A> as IntoIterator>::IntoIter ⓘ Creates an iterator from a value. Read more

It is simply impossible to infer the concrete return type std::slice::Iter from this signature for a learner working through these exercises.

This exercise, possibly including section 6.4 (“Iterators”), should probably be moved to a later stage.