Macro generate_tuple_impls 

macro_rules! generate_tuple_impls {
    (
        $( $u:ident ),* ;
        $( $t:ident ),* ;
    ) => { ... };
    (@__recur__
        [ ] [ ];
        [ ] [ ];
    ) => { ... };
    (@__recur__
        [ $( $uhead:ident )* ] [ $u:ident $( $utail:ident )+ ];
        [ $( $thead:ident )* ] [ $t:ident $( $ttail:ident )+ ];
    ) => { ... };
    (@__recur__
        [ $( $uhead:ident )* ] [ $u:ident ];
        [ $( $thead:ident )* ] [ $t:ident ];
    ) => { ... };
    (@__expand_at__
        [ $( $uhead:ident )* ] [ $u:ident $( $utail:ident )* ];
        [ $( $thead:ident )* ] [ $t:ident $( $ttail:ident )* ];
    ) => { ... };
}