ConditionalWeakTable return ref

[Thaina]

As of now we have return ref in C#. So I wish we would have more of it support on collection. And ConditionalWeakTable is one I think needed

It could be new class such as ConditionalWeakTableRef<TKey,TValue>. Just have it return reference when index. So we could attach struct to hold extension value

[stephentoub]

Returning ref from collections can be dangerous if the storage for that ref might get removed or replaced, e.g. if a ref is returned to an array in the a list, and then the list grows and replaces the array such that the ref is now effectively invalidated, pointing into an array no longer associated with the list. That could happen implicitly as part of a conditional weak table, with the data getting dropped automatically when the key is no longer kept alive. Plus conditional weak tables are often used in a concurrent environment, where the underlying storage could get invalidated by other threads interacting with the collection. In short, I don't think this is something we should do.

So we could attach struct to hold extension value

If your concern is being able to store a struct in a conditional weak table, you can just wrap it in an object, e,.g. instead of making it a ConditionalWeakTable<TKey, TValue>, make it a ConditionalWeakTable<TKey, StrongBox<TValue>>.

[Thaina]

Understandable. Thank you for your clarification