Re: Copy-assignment and C++0x move-assignment operator ambiguous?

Peter Dimov <>
Sat, 20 Sep 2008 00:24:45 CST
On Sep 17, 12:26 am, "Niels Dekker - no return address"
<> wrote:

I just ran the following little C++0x program (compiled by GCC 4.3 -
ConceptGCC, BoostCon Edition), and it returned zero, indicating that the
assignment, "obj1 = move(obj2)", has effectively cleared the value of


even though operator= has a "by value" argument, 'f'. So in this case,


isn't really destroyed at the end of operator=.

   class foo {
       int data;

       foo & operator=(foo f);
       foo(const foo & arg): data( {}
       explicit foo(int arg = 0): data(arg) {}

       void swap(foo& arg) {
         int temp = data;
         data =; = temp;

   foo && move(foo & arg) { return arg; }

   int main() {
     foo obj1(1);
     foo obj2(2);
     obj1 = move(obj2);
     return; // Returns zero!

After I took care of the link error by changing op= to:

    foo & operator=(foo f)
        swap( f );
        return *this;
    } was 1. (I'm using ConceptGCC alpha 6 though.) Adding some
std::cout statements confirmed that g++ has indeed allocated f and
obj2 at the same address. But I do not believe that it is within its
rights to do so.

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