Re: Copy-assignment and C++0x move-assignment operator ambiguous?
On Sep 17, 12:26 am, "Niels Dekker - no return address"
<nore...@this.is.invalid> 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
obj2,
even though operator= has a "by value" argument, 'f'. So in this case,
'f'
isn't really destroyed at the end of operator=.
//////////////////////////////////////////////////
class foo {
public:
int data;
foo & operator=(foo f);
foo(const foo & arg): data(arg.data) {}
explicit foo(int arg = 0): data(arg) {}
void swap(foo& arg) {
int temp = data;
data = arg.data;
arg.data = temp;
}
};
foo && move(foo & arg) { return arg; }
int main() {
foo obj1(1);
foo obj2(2);
obj1 = move(obj2);
return obj2.data; // Returns zero!
}
After I took care of the link error by changing op= to:
foo & operator=(foo f)
{
swap( f );
return *this;
}
obj2.data 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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