[RFC] 403. basic_string::swap should not throw exceptions (Ready)

[Paolo Carlini]

Hi,

according to the resolution of this DR (now Ready)

  http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-active.html#403

a throw clause should be added: "Throws: Shall not throw exceptions."
However, is also clarified that:

Note: There remains long standing concern over whether or not it
is possible to reasonably meet the 23.1 [lib.container.requirements]
paragraph 10 swap requirements when allocators are unequal. The
specification of basic_string::swap exception requirements is in no
way intended to address, prejudice, or otherwise impact that concern.

So, which are the implication for our implementation which reads:

  template<typename _CharT, typename _Traits, typename _Alloc>
    void basic_string<_CharT, _Traits, _Alloc>::swap(basic_string& __s)
    {
      if (_M_rep()->_M_is_leaked())
        _M_rep()->_M_set_sharable();
      if (__s._M_rep()->_M_is_leaked())
        __s._M_rep()->_M_set_sharable();
      if (this->get_allocator() == __s.get_allocator())
        {
          _CharT* __tmp = _M_data();
          _M_data(__s._M_data());
          __s._M_data(__tmp);
        }
      // The code below can usually be optimized away.
      else
        {
          basic_string __tmp1(_M_ibegin(), _M_iend(), __s.get_allocator());
          basic_string __tmp2(__s._M_ibegin(), __s._M_iend(),
                              this->get_allocator());
          *this = __tmp2;
          __s = __tmp1;
        }
    }

???

Looks ok to me, in that when the allocators are equal cannot throw. Do you
concur?

Thanks,
Paolo.