I'm having second thoughts on this... the set datatype would be useful for reducing repeat calls for when a user changes the same property multiple times in one update cycle (which is around twice a second, I don't know the specific number). For example when playing an animation in the editor, numeric properties can be interpolated every process frame, while the inspector is only updated every ten or twenty. Unless I'm missing something this is probably the reason why the pending variable is a HashSet.

@KoBeWi thoughts on whether the tradeoff is important?

I checked and not sure if there is a way to trigger duplicate property updates. pending is only used for properties changed within the inspector, external changes (animation, tool scripts) don't use it. Quickly changing a property results in a single update per frame.

Although the main improvement in this PR is getting rid of this weird stack-like usage, which makes no sense. That change is independent from the type of pending, so you could revert it back to HashSet, while keeping the new loop (HashSet can be iterated too AFAIK).

I reduced the PR to just remove the stack-like pattern for pending. I'm more happy with it now, although I didn't realize that pending was only for changes within the inspector. It also seems to be called with notify_property_list_changed, which can be determined by the user.

Thanks!