[Bug c++/14823] the copy constructor is called unnecessarily/incorrectly when passing an arg by reference to the base class

["robert dot schweikert at abaqus dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Additional Comments From robert dot schweikert at abaqus dot com  2004-04-07 13:57 -------
Subject: Re:  the copy constructor is called
	unnecessarily/incorrectly when passing an arg by reference to the base class

OK,

One more message on this subject. I have conferred with a few more
people and I was obviously confused. 

Sorry for taking up your time. Thanks for the clarifications you
provided and for your patience.

There is no bug, I will fix the code.

Thanks,
Robert

On Mon, 2004-04-05 at 09:49, giovannibajo at libero dot it wrote:
> ------- Additional Comments From giovannibajo at libero dot it  2004-04-05 13:49 -------
> Subject: Re:  the copy constructor is called unnecessarily/incorrectly when passing an arg by reference to the base class
> 
> robert dot schweikert at abaqus dot com wrote:
> 
> >> Where exactly does the standard speak of a rvalue-to-lvalue
> >> conversion?
> >
> > That would be on page 147 in the [dcl.init.ref] section (8.5.3) bullet
> > 5.
> >  [...]
> > "
> > - has a class type (i.e. T2 is a class type) and can be implicitly
> > converted to an lvalue ....
> > "
> >
> > So T2 in this case would be the rvalue and the reference would be
> > bound to the result of the conversion (lvalue).
> 
> It says: "**IF** the initializer expression [...] has a class type and can be
> implicitly converted to an lvalue [...] then the reference is bound directly"
> (my stress). So we have an if-then clause. A temporary created by the explicit
> function notation is a rvalue. How can it be converted to an lvalue? This is
> what I asked. You didn't show me where the standard says that a rvalue of that
> kind (or any kind) can be implicitly converted to a lvalue. There is no default
> conversion to do so. So the "if" condition is false.
> 
> > At the end of the page one can find the following note:
> > "
> > [Note the usual lvalue-to-rvalue (4.1), array-to-pointer (4.2), and
> > function-to-pointer (4.3) standard conversions are not needed, and
> > therefore are suppressed, when such direct bindings to lvalues are
> > done.]
> 
> Yes, but we're speaking of binding to *lvalues*. Your initializer expression is
> a rvalue. And there is no way it can be converted.
> 
> > Lets consider the following simple example:
> > [...] yet this simple example compiles just fine.
> 
> I don't have time to analyze it properly, but by the looks of it it shouldn't
> compile. If it does, it's a bug. Please, file a different bug report for this.
> 
> Giovanni Bajo


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14823