Daniel Frey:
My new version even allows one more use case:
When the refactored implementation reaches line 130, the weak_count.use_count() == 0 is true, thus init_weak_once() initializes a fresh _shared_count/_weak_count pair and expects someone else to take over ownership later as if the object was just created.
Yes. What is the motivation for this use case? Given the sequence: 1. Object is created 2. A shared_ptr takes ownership 3. Owner dies 4. Another shared_ptr takes ownership the original esft allowed shared_from_this calls after 2 and 4, but not after 1 or 3. The new esft allows shared_from_this after 1 as well with the motivation to support calls from within the object constructor. But the constructor only runs once, so this motivation doesn't extend to 3.