https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62318
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3905.html which proposes adding it to the C++ standard library as a separate API. The new components are part of the Library Fundamentals TS: http://cplusplus.github.io/fundamentals-ts/main.html#func That part of the TS has not yet been implemented in libstdc++.
