How to constrain the element type of an iterator?

Question

I’m converting some older Rust code to work on 1.0.0. I need to convert a function that takes an iterator over characters, which used to be written like this:

Answer 1

Okay, I was able to figure this out from reading some RFC discussions, and the answer is that you can instantiate associated types in the trait (like signature fibration in ML):

fn f>(char_iter: I)

Soon it should be possible to use equality constraints in where clauses, but this doesn’t work in 1.0.0-alpha:

fn f(char_iter: I) where I::Item == char