Re: Internal move vs. copy in std::vector

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<iostream>
   #include<vector>

   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<elem> 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.