// 'static` and not `Fn(isize) -> (isize + 'static)`. The latter would
// cause a compilation error. Issue #18772.
-fn adder(y: isize) -> Box<Fn(isize) -> isize + 'static> {
+fn adder(y: isize) -> Box<dyn Fn(isize) -> isize + 'static> {
Box::new(move |x| y + x)
}