LL | | Self: Sized;
| |__________________________- definition of `foo` from trait
...
-LL | / fn foo<F>(&mut self, f: F) //~ ERROR impl has stricter
+LL | / fn foo<F>(&mut self, f: F)
LL | | where F: fmt::Debug + 'static,
LL | | {
LL | | self.list.push(Box::new(f));