How do I remove a Weak<T> value from a BinaryHeap if it fails to upgrade to a strong reference?

Question

I would like to use a BinaryHeap with elements of type MyWrapperStruct(Weak<MyStruct>), where I implement Ord for MyWrapperStruct. In this implementation, I need to upgrade the weak references, which might fail. If they fail, I want the element to be removed from the heap.

How could I implement this in a way that doesn't require me to traverse the entire heap first to remove all the non-upgradable weak references? There will be a large amount of data in this heap, while only very few of these will become invalid. For the sake of performance, I would like to avoid traversal of all data.

Answer 1

You can't remove an item while you are comparing something.

Also, from my point of view, implementing Ord would be wrong for the same reason why Ord is not implemented for floating-point values in Rust. If you have two non-upgradable Weak structures, there is no order between them and that's the reason why PartialOrd exists.

If you really want to make your example work, implement Ord for your type and order non-upgradable Weaks at the very top (e.g. it is always the biggest element), then use peek on your BinaryHeap to check if it is upgradable; if not, remove it and take the next one.
This is a nasty hack but probably your best solution if you want your thing to work.