bsl::basic_string<char32_t>::swap

Exchange the value of this object with that of the specified other object; also exchange the allocator of this object with that of other if the (template parameter) type ALLOCATOR has the propagate_on_container_swap trait, and do not modify either allocator otherwise. This method provides the no-throw exception-safety guarantee. This operation has O[1] complexity if either this object was created with the same allocator as other or ALLOCATOR has the propagate_on_container_swap trait; otherwise, it has O[n + m] complexity, where n and m are the lengths of this object and other, respectively. Note that this method`s support for swapping objects created with different allocators when ALLOCATOR does not have the propagate_on_container_swap trait is a departure from the C++ Standard.