https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100667
--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #6) > (In reply to Piotr Nycz from comment #0) > > It looks that std library code start requiring this to pass: > > std::is_nothrow_constructible<A&&, A>... > > Indeed, that's what the standard requires (Clang and MSVC reject this the > same way). The standard also says that using traits like is_constructible > requires complete types. > > However, that's clearly silly for is_constructible<A&&, A> because we know > that reference binding is valid for any A whether it's complete or not. > > This is the subject of: > https://cplusplus.github.io/LWG/issue2939 We can fix this in std::tuple by adding && to the source objects in all is_constructible and is_convertible conditions. Or we could fix it in the type traits themselves. But I think it would be best to fix it in the compiler, so that we always allow directly binding T&& or const T& to T, even if T is incomplete. Otherwise we'll be playing whackamole all over the library.
