[Bug libstdc++/86127] STL containers do not satisfy container.requirements.general clause 8

[fidget324 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86127

--- Comment #7 from Scott Constable <fidget324 at gmail dot com> ---
(In reply to Jonathan Wakely from comment #1)
> The allocator requirements say that move construction must be equivalent to
> copy construction, and allocators should be cheap to copy anyway. I don't
> consider this a bug.

To be nitpicky, it looks like this equivalence requirement was introduced
recently in the C++20 draft. I'm compiling using C++14.

I agree that allocators should be cheap to copy, but as a general principle I
think that all objects should be copied only when necessary. This is the
behavior I have observed in STL containers in libc++, as shown in my example
above. It just makes sense to me that when an STL container is moved, its
allocator should be moved, and no copying should be performed.