From: daniel.kruegler@googlemail.com   
      
   On 2012-05-07 02:03, Wil Evers wrote:   
   > I experimented a little bit with gcc-4.7.0, and FWIW, I did run into a   
   > surprise when adding move semantics to a C++-98-style noncopyable   
   > type.  This is what I tried:   
   >   
   >    #include   
   >    #include   
   >   
   >    class elem {   
   >    public :   
   >      elem() { }   
   >      elem(elem&&) { std::cout<<  "elem(elem&&)"<<  std::endl; }   
   >   
   >    private :   
   >      // Disable copying (C++98 style)   
   >      elem(const elem&); // not defined   
   >    };   
   >   
   >    int main()   
   >    {   
   >      std::vector  vec;   
   >      vec.emplace_back();   
   >      vec.reserve(vec.capacity() + 1);   
   >   
   >      return 0;   
   >    }   
   >   
   > This caused the compiler to complain that elem's copy constructor is   
   > not accessible. (The actual instantiation traceback is quite   
   > interesting, but I'll leave that out for now.)  Because elem's move   
   > constructor may throw, the compiler insists on using the copy   
   > constructor - even though it is inaccessible.   
   >   
   > To get the code to compile, one has to either decorate the move   
   > constructor with 'nothrow', or the copy constructor with '= delete'.   
   > I wonder how many C++ users will understand which of these to pick,   
   > and when.   
      
   Note that this observation is based on a compiler that still does not   
   completely implement the C++11 standard. As of C++11 access "violations"   
   will be considered as part of "sfinae" conditions, that is a private   
   copy constructor of type X *should* have the effect that   
   std::is_copy_consructible::value evaluates to false. For gcc 4.8 this   
   does currently not yet happen, because access control is not yet part of   
   sfiane. I do not know the corresponding state of other compilers, though.   
      
   Greetings from Bremen,   
      
   - Daniel   
      
      
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