[Bug libstdc++/59872] Cannot move std::map with move-only mapped_type

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59872

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, the branch that copies needs to be a separate function.

http://cplusplus.github.io/LWG/lwg-active.html#2108 might answer your last
question