I'd just like to make sure a reference to my concern about hidden implicit allocations that I made in the comments thread is present here.

I would strongly appeal to amend the DIP to only apply to `scope` delegates, such that they may (should? must?) stack allocate. Non-scope delegates require typical `() =>` syntax, which is important because it is possible to SEE the allocation.

Potential for invisible closure allocations at every argument to every function call in D is terrifying to me.

Otherwise, I like this DIP.