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// check-pass
trait Variable<'a> {
type Type;
}
impl Variable<'_> for () {
type Type = ();
}
fn check<F, T>(_: F)
where
F: Fn(T), // <- if removed, all fn_* then require type annotations
F: for<'a> Fn(<T as Variable<'a>>::Type),
T: for<'a> Variable<'a>,
{
}
fn test(arg: impl Fn(())) {
fn fn_1(_: ()) {}
let fn_2 = |_: ()| ();
let fn_3 = |a| fn_1(a);
let fn_4 = arg;
check(fn_1); // Error
check(fn_2); // Ok
check(fn_3); // Ok
check(fn_4); // Error
}
fn main() {}
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