CODEWITHSUNDEEP
c++c++11libstdc++libc++
Ixrec
Ixrec

Reputation: 976

Why does libstdc++ store std::tuple elements in reverse order?

According to Link, 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?

Upvotes: 10

Views: 979

Answers (1)

Howard Hinnant
Howard Hinnant

Reputation: 218830

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:

  1. It is implementable.
  2. The implementation has good compile-time performance.
  3. 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.

Upvotes: 12

Related Questions