From: Greg Colvin (gcolvin_at_[hidden])
Date: 2001-04-06 11:01:18
From: Stephen C. Gilardi <squeegee_at_[hidden]>
> > > The caveat about temporary smart pointer objects still applies. My rule is
> > > "never create an unnamed temporary smart pointer." The non-const reference
> > > idiom tries to enforce this rule... although I have another reason for
> > > preferring pass by non-const reference:
> > >
> >> void f(T arg);
> > >
> > > T t;
> >>
> >> f(t);
> > >
> > > // now t is unchanged, right?
> >
> >Wrong, of course. Usually, the declaration of f isn't visible near the call,
> >so you can't assume much about what's changed. But this case could be seen
> >as an argument for using the unnamed temporary... then there's no object
> >hanging around with a confusing value.
>
> I don't see how t's value could be changed in the above example.
> Could you please explain?
If f() is declared as
void f(T&);
then t is not passed by value.
> It seems to me that t was passed by value. My understanding is that
> an unnamed temporary of type T is constructed using T's copy
> constructor and sent to the body of f. This leaves t completely
> unmolested.
>
> If my understanding is incorrect, I'll be very happy to learn what
> really happens.
>
> Thanks,
>
> --Steve
>
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