Macro define_for_tuples 

macro_rules! define_for_tuples {
    { $( $A:ident )* - $B:ident $( $C:ident )* } => { ... };
    { $( $A:ident )* - } => { ... };
}

impl Resolvable for (A,B..) where A: Resolvable, B: Resolvable ...

The implementation simply calls Resolvable::resolve for each output tuple member.

define_for_tuples!{ A B - C D.. }

expands to

1. define_for_tuples!{ A B - }: defines for tuple (A,B,)
2. define_for_tuples!{ A B C - D.. }: recurses to generate longer tuples