[Bug libstdc++/65978] New: missing constexpr on std::forward_as_tuple and std::tie (LWG issues 2275 and 2301)

[rhalbersma at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65978

            Bug ID: 65978
           Summary: missing constexpr on std::forward_as_tuple and
                    std::tie (LWG issues 2275 and 2301)
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rhalbersma at gmail dot com
  Target Milestone: ---

Neither libstdc++ 5.1.0 nor the trunk version implement LWG defect reports 2275
and 2301 that make std::tuple utilities std::forward_as_tuple and std::tie
constexpr 

http://wg21.cmeerw.net/lwg/issue2275
http://wg21.cmeerw.net/lwg/issue2301

Both of these have been implemented in libc++ for a while now:
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20131007/090369.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20140224/099936.html

Since both resolutions only require C++11 style constexpr support, they could
also be backported to earlier versions in -std=c++1y mode.