[C++-sig] Re: [Implementation] Calling wrapped functions, converters, policies

[Niall Douglas]

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On 19 Sep 2003 at 10:57, David Abrahams wrote:

> > My main bugbear with GCC is it forces const temporaries. This makes
> > destructive copy construction semantics severely castrated, so much
> > so you usually must #ifdef hack in a copy constructor taking a const
> > reference just on GCC :(
> >
> > I know all the usual arguments about temporaries should be const. I
> > strongly disagree. 
> 
> Disagree all you want.  A C++ compiler should conform to the standard
> or it isn't C++.  Which compiler is correct in this regard is not open
> to debate.

My 1996 draft (which is all I can afford) doesn't say all temporaries 
are const. I take it this has changed?

I don't get why this was done. Sure making temporaries created from a 
conversion cast const is a good idea but temporaries returned from a 
function or produced through the action of an operator are quite 
different beasts - there is no danger of state changes getting lost 
in an unintended way. And besides, some objects you use clearly can 
have only one instance.

> > where that rope /could/ be used for something useful and no other
> > better way is available for doing it. And destructive copy
> > construction is clearly implied when it takes a non-const reference.
> 
> Maybe you would be interested in a proposal I co-authored:
> http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1377.htm

I support that document. My only concern is that using && as the 
token is a bad idea because if the proposed extension to permit 
taking references of references goes through, this might cause 
confusion in the debugger.

I would suggest ~& is much better. The ~ says it's destructive/move 
and the & denotes a reference. Much clearer.

Cheers,
Niall





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