macro_rules! for_each_tuple_ {
 ( $m:ident !! ) => (
 $m! { }
 );
 ( $m:ident !! $h:ident, $($t:ident,)* ) => (
 $m! { $h $($t)* }
 for_each_tuple_! { $m !! $($t,)* }
 );
}
#[macro_export]
macro_rules! for_each_tuple {
 ( $m:ident ) => (
 for_each_tuple_! { $m !! A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, }
 );
}