rvalue references

[Manu]

On 27 April 2013 12:26, Jonathan M Davis <jmdavisProg at gmx.com> wrote:

> On Saturday, April 27, 2013 10:21:32 Manu wrote:
> > > > Why bother with 'auto'? Why not just make this default behaviour?
> > >
> > > For the same reason that T& doesn't take rvalues in C++ while const T&
> > > does.
> > > There's a big difference between wanting an argument to be passed as
> > > efficiently
> > > as possible and specifically wanting to alter the argument being passed
> > > in.
> > > Plain ref is for cases where you explicitly want to mutate the
> argument.
> > > You're just asking for bugs if you allow ref to accept rvalues. We've
> had
> > > problems like this before when some literals were treated as lvalues.
> The
> > > behavior of a function which takes its argument by ref and the
> behavior of
> > > one
> > > which takes its argument by auto ref are fundamentally different.
> >
> > So you're saying it should be const ref instead of auto ref...
> > I agree.
>
> Not at all. const is so much more restrictive in D that it really doesn't
> make
> sense to have const be required in order to be able to pass an argument to
> a
> function efficiently without caring whether it's an rvalue or an lvalue.
> auto
> ref permits const but doesn't require it - which is what we need - whereas
> const ref is always const.
>
> I'm arguing that we need an attribute which differs from naked ref which
> indicates that the function doesn't care whether it's given an lvalue or an
> rvalue - it just wants it to be passed as efficiently as possible. auto
> ref is
> supposed to serve this purpose. Naked ref on the other hand is
> specifically for
> when the function needs to alter the argument and not a copy of the
> argument.
> const ref is ultimately kind of useless IMHO.
>
> The only real hangup with that at this point is that templated functions
> should be able to use the auto ref solution that non-templated functions
> should use (invisibly creating a variable when an rvalue is passed so that
> an
> lvalue can be passed), but we also need the current auto ref functionality
> that we have for templated functions. So, either we need a new attribute,
> or
> we need to do what Timon suggested and make the compiler smart enough to
> figure
> out when it can get away with using the non-templated auto ref solution
> with a
> templated function without changing the function's semantics.
>

I don't see myself ever getting on board with this auto-ref idea. I just
think it's crazy. It makes no sense to me, they are completely unrelated
concepts. It will only lead to confusion.

I'm back at scope-ref. Kenji is right as far as I'm concerned. Not to
mention, he actually did the work.
It makes perfect sense, and I can't see any reason why auto-ref should be
used instead of something that actually makes intuitive sense, and people
will eventually want to use anyway...
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