cpp/memory/allocator traits/select on container copy construction

If possible, obtains the copy-constructed version of the allocator, by calling. If the above is not possible (e.g. does not have the member function ), then returns, unmodified.

This function is called by the copy constructors of all standard library containers. It allows the allocator used by the constructor's argument to become aware that the container is being copied and modify state if necessary.

Return value
The allocator to use by the copy-constructed standard containers.