Macro frame_support::match_types

macro_rules! match_types {
    (
		pub type $n:ident: impl Contains<$t:ty> = {
			$phead:pat_param $( | $ptail:pat )*
		};
		$( $rest:tt )*
	) => { ... };
    (
		pub type $n:ident: impl ContainsPair<$a:ty, $b:ty> = {
			$phead:pat_param $( | $ptail:pat )*
		};
		$( $rest:tt )*
	) => { ... };
    () => { ... };
}

Create a type which implements the Contains trait for a particular type with syntax similar to matches!.