🚀 go-pugleaf

Fergus Henderson wrote:
> 
> In comp.lang.c++.moderated, kanze@gabi-soft.fr (J. Kanze) writes:
> 
> >"Nathan Myers" <ncm@cantrip.org> writes:
> >
> >|> The Draft standard requires that your compiler not try to generate
> >|> auto_ptr::operator->() unless you use it.
> [...]
> >The requirement in the draft that Nathan is referring to (and which *is*
> >new, and not supported by many compilers) is that they not check the
> >return type of operator-> *unless* they actual have to generate the
> >function.  (I'm not sure of the exact words, but that is more or less
> >the meaning.)
> 
> I'm sure you're right, but when I had a look for this in the draft
> standard, I couldn't find it.  Could anyone please direct me to the
> appropriate place?

Actually, the language is a lot broader than James suggests. The WP
places no restrictions on the return type of operator->, as such; it 
only defines the meaning of the expression -> in terms of that return 
type.  This implies that it is at the call site that an error has 
occurred, if you try to apply "a->b" where a.operator->() returns 
something that doesn't have a member b. 

(In fact, it doesn't say that, if you do use it, it needs to return
a pointer.  That is, if X::operator->() returned a Y&, and Y defines
Y::operator->(), then x->m could mean x.operator->().operator->m.
I don't know of any compilers that support this (yet).)

The language in the post-Santa Cruz mailing is in 14.7.1, paragraph 6:
"An implementation shall not implicitly instantiate a ... non-virtual
member function ... that does not require instantiation."

Many current compilers generate the code for all member functions when
the class is instantiated, and then report an error if some unused member
uses an operation not defined for the template argument instantiated on.

So if your compiler doesn't support auto_ptr<int>::operator->(), it's
broken on several counts even before we start talking about template
constructors.  But that's life before the Standard.

Nathan Myers
ncm@cantrip.org  http://www.cantrip.org/
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