Copy constructor with non const rhs arg

[llewelly@xmission.com]

"paul moore" <paulmoore100@hotmail.com> writes:

> This code does not compile on gcc (3.2.2 on rh9 - 3.3 on suse 9)
>  
> class test
> {
> public:
> int x;
> test(test &rhs)
> {
> 	x = rhx.x;
> }
> };
> 
> test foo();
> int main(int argc, char* argv[])
> {
> 	test dd = foo();

C++ does not allow binding a temporary to a reference to non-const.

> 	return 0;
> }
> 
> The test dd line gets hit saying there is no match for test::test(test), the
> candidates are test::test(test&)
> If I change the copy constructor to 'test(const test&)' it compiles fine.
> 
> What am I trying to do? In real life the class contains an auto_ptr - since
> the auto_ptr copy constructor updates the rhs you cannot pass it in with
> const. (Note the auto_ptr copy constructor itself is declared with a non
> const rhs - and code using it compiles fine - this is really
> puzzling)

auto_ptr uses a truly hideous trick involving a sort of proxy class
    called auto_ptr_ref. You are probably better off not tryiing to
    emulate it. If you *need* to emulate it, you'll have to look at
    the sources; I can't explain it.

> 
> Also if I change foo to 'test &foo()' it compiles fine (but of course this
> is totally different semantics)
> Note also that MSFT vs 2003 compiles this code quite happily.

M$ supports binding a temporary to a reference to non-const as an extension.