Not really. I've worked with rust for 4 years, systems side, and never had to write a custom drop implementation. That's the gotcha here, not the rigamarole with the static+Send option type (which _would_ be something you'd encounter in prod).
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.
This is the problem when a language advertises with “guarantees” and it turns out it never had any due to many false assumptions by their promoters.
So what other soundness bugs are there in the language that we need to know about?
For some reason this is controversial, but it remains true.
But not custom drops that are doing variadic type stuff like this, usually.
- you've never written a custom Drop
- "Not really". Implying that your experience generalizes
I've written a bunch of rust programs without custom Drop. I believe your first statement. There are large classes of programs that don't need it. There are also many that do. I think your statement says a lot more about what kind of programs you work on than about custom Drop not being common. People are downvoting the implication that custom Drop is not a common pattern.
That it took 11 years for someone to come across this is a fairly intense counterargument to your attempt to paint this as a language with dangerous footguns.