basic_stringbuf& operator=(basic_stringbuf&& rhs);
void swap(basic_stringbuf& rhs) noexcept(see below);
template<class charT, class traits, class Allocator>
void swap(basic_stringbuf<charT, traits, Allocator>& x,
basic_stringbuf<charT, traits, Allocator>& y) noexcept(noexcept(x.swap(y)));