7 impl Variable<'_> for () {
13 F: Fn(T), // <- if removed, all fn_* then require type annotations
14 F: for<'a> Fn(<T as Variable<'a>>::Type),
15 T: for<'a> Variable<'a>,
19 fn test(arg: impl Fn(())) {
21 let fn_2 = |_: ()| ();
22 let fn_3 = |a| fn_1(a);