Rust 1.30.0

# Associated Types

There is a new edition of the book and this is an old link.

> Associated types are a way of associating a type placeholder with a trait such that the trait method definitions can use these placeholder types in their signatures.

    pub trait Iterator {
        type Item;
        fn next(&mut self) -> Option<Self::Item>;
    }Run

Here are the relevant sections in the new and old books:

- In the second edition: Ch 19.03 — Advanced Traits
- In the first edition: Ch 3.30 — Associated Types