Daniel Frey:
The attached patch optimizes the current implementation of enable_shared_from_this, it saves one plain pointer. That might not be very much, but it's a start. It is 100% compatible for the users, no features are dropped. Further improvements might be possible, but I think the attached patch is a good base.
Peter, do you see any chance for it? If not, please tell me why and (if possible) what needs to be improved.
Your patch (still) contains a number of changes, some of which are unrelated to its purpose (to save one pointer in esft). To break it down: 1. Changes esft.hpp to use the shared_count constructor to eliminate the circular initialization instead of sp_accept_owner overload( sp_deleter_wrapper* ). Stylistic change, not necessary, avoids testing a possible use of the sp_accept_owner mechanism. 2. Changes shared_count(weak_count) to not throw. Arbitrary change, not necessary, makes shared_count:weak_count inconsistent with shared_ptr:weak_ptr. 3. Adds a move constructor to shared_count. OK, not essential, but desirable. 4. Adds if( tmp != pi_ ) optimizations. OK, but a separate issue. 5. Adds shared_ptr(shared_count, p). OK, essential. The && overload is not guarded, BTW. 6. Adds _internal_shared_count. OK, essential. Should probably be called get_shared_count. You may commit #4 right away; as for the rest, I'd really like to see the patch without #1 and #2.