Why does r-value reference to object generator call require copy constructor?

Question

I'm getting trouble with the following code with Visual Studio 2010 C++.

makeA() is just an object generator idiom in C++ (like std::make_pair)

#include <stdio.h>

struct A{ // 7th line
    A() {}
    A(A &&) {printf("move\n");}
    ~A() {printf("~A();\n");}
private:
    A(const A &) {printf("copy\n");} // 12th line
};

A makeA()
{
    return A();
}

int main()
{
    A &&rrefA(makeA()); // 22nd line
    return 0;
}

Error message

2>d:\test.cpp(22): error C2248: 'A::A' : cannot access private member declared in class 'A'
2>          d:\test.cpp(12) : see declaration of 'A::A'
2>          d:\test.cpp(7) : see declaration of 'A'
2>

I expect makeA() to call both A() constructor and A(A &&) constructor, and 22nd line to call makeA() and nothing else. (If without RVO) The compiler should not require A(const A &) constructor to be accessible, am I right?

Can you tell me what's wrong with the code?

With recent version of g++, 'g++ -std=c++0x' and 'g++ -std=c++0x -fno-elide-constructors' compiles the code without any error.

Answer 1

It's a bug in the optimizer. The compiler attempts to ellide the move, but is only programmed to ellide a copy constructor- which requires a copy constructor to exist to be ellided in the first place.

I don't recall what (if any) the fix for this error is, but it might have been fixed in SP1.