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

[Paolo Carlini <pcarlini at suse dot de>]

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.