Consider we add a library slice type called RCSlice!T. It would have the same primitives as T[] but would use reference counting through and through. When the last reference count is gone, the buffer underlying the slice is freed. The underlying allocator will be the GC allocator.

Now, what if someone doesn't care about the whole RC thing and aims at convenience? There would be a method .toGC that just detaches the slice and disables the reference counter (e.g. by setting it to uint.max/2 or whatever).

Then people who want reference counting say

auto x = fun();

and those who don't care say:

auto x = fun().toGC();


Destroy.