Re: Binding a temporary to a const reference

[Jason Merrill <jason at cygnus dot com>]

>>>>> Branko Cibej <brane@cthulhu.engr.sgi.com> writes:

 > Joe Buck wrote:
 >> 
 >> While I believe you are correct in saying that g++ is wrong in this case,
 >> the protection rule is independent of whether or not the copy constructor
 >> is actually called.

 > Yes, I'm aware of that. (Seems to me there used to be a bug in g++
 > regarding that, didn't there?)

g++ started enforcing this rule recently, but then the rule itself is
somewhat recent.

 > Alexandre Oliva wrote:
 >> 
 >> [dcl.init.ref]/8 says that, if the initializer expression is an rvalue
 >> and the reference is of class type, an implementation is allowed (but
 >> not required) to copy-construct another temporary and bind the
 >> refenrence to it.  In any case, the copy constructor must be
 >> accessible [dcl.init.ref]/9.  So g++ is right.

 > Hmm. So what about the following? G++ accepts it without a diagnostic:

 >     class A {
 >         A (A const&);
 >         A operator = (A const&);

 >       public:
 >         A() {}
 >     };

 >     A const a;
 >     A const& ra = a;

Here, 'a' is an lvalue, so Alexandre's quote doesn't apply.

Jason