[PATCH] D49317: Move __construct_forward (etc.) out of std::allocator_traits.

Marshall Clow via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Mon Jul 30 11:15:49 PDT 2018

mclow.lists added a comment.

> I don't think it makes sense to pessimize existing (non-constexpr) users in C++03-through-C++17 just because someone hypothetically might in C++2a-or-later want to mutate a std::vector in a constexpr context.

That's not the right (implied) question.

The correct question is:

> Will libc++pessimize existing (non-constexpr) users in C++03-through-C++17 ***who are using old compilers*** in order to support new constexpr features that come down the pike?

And the answer to that is yes - eventually. 
I don't know when that will be, since the //new compilers// don't yet exist.
That's the point of https://bugs.llvm.org/show_bug.cgi?id=25165.

  rCXX libc++


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