问题
According to http://flamingdangerzone.com/cxx11/2012/07/06/optimal-tuple-i.html, with regards to std::tuple...
libstdc++ always places the members in reverse order, and libc++ always places the members in the order given
Assuming that's true, is there a reason (historical or otherwise) why libstdc++ uses reverse order?
Bonus: Has either implementation ever changed its std::tuple ordering for any reason?
回答1:
See this answer for why libc++ chose forward order. As for why libstdc++ chose reverse order, that is probably because that's how it was demonstrated in the variadics template proposal, and is the more obvious implementation.
Bonus: No. These orderings have been stable in both libraries.
Update
libc++ chose forward storage order because:
- It is implementable.
- The implementation has good compile-time performance.
- It gives clients of libc++ something that is intuitive and controllable, should they care about the order of the storage, and are willing to depend on it while using libc++, despite its being unspecified.
In short, the implementor of the libc++ tuple merely felt that storing the objects in the order the client (implicitly) specified was the quality thing to do.
来源：https://stackoverflow.com/questions/27663641/why-does-libstdc-store-stdtuple-elements-in-reverse-order