Why would you ever conditionally custom impl Drop? I don't think I've ever seen that pattern, and I can't think of a use case.
impl<T: 'static + Send> Drop for Q<T> {
fn drop(&mut self) { if let Some(t) = self.0.take() { KEPT.lock().unwrap().push(Box::new(t)); } }
}
struct Q<T>(Option<T>);
impl<T: 'static> Drop for Q<T> {
fn drop(&mut self) {}
}
error[E0367]: `Drop` impl requires `T: 'static` but the struct it is implemented for does not
--> src/main.rs:3:9
|
3 | impl<T: 'static> Drop for Q<T> {
| ^^^^^^^
|
note: the implementor must specify the same requirement
--> src/main.rs:1:1
|
1 | struct Q<T>(Option<T>);
| ^^^^^^^^^^^You also don't have to place those bounds on the Drop impl just because they're on Q, that's not an error.
And I'm still not any closer to understanding what the bug is about.
It doesn't even have to be less constrained than the containing types definition. You can provide an impl with more constraints; for example, a type Q<T: Read + Write>, but impl Seek for Q<T: Read + Seek>
Do you happen to know the specific rules of when it's an error and when it's not?
That said I was wrong earlier.