Efficiently exchange the value of this object with the value of the specified other object. This method provides the no‐throw exception‐safety guarantee if *this and other allocators compare equal. The behavior is undefined unless either *this and other allocators compare equal or propagate_on_container_swap is true. Note that this function is only available for C++11 (and later) language standards because it requires that swap be provided on the (platform supplied) base class for this type.