No more anonymous parameters - The Edition Guide

# No more anonymous trait parameters

In accordance with RFC #1685, parameters in trait method declarations are no longer allowed to be anonymous.

For example, in the 2015 edition, this was allowed:

    # #![allow(unused_variables)]
    #fn main() {
    trait Foo {
        fn foo(&self, u8);
    }
    #}

In the 2018 edition, all parameters must be given an argument name (even if it's just `_`):

    # #![allow(unused_variables)]
    #fn main() {
    trait Foo {
        fn foo(&self, baz: u8);
    }
    #}