The liabilities of binding rvalues to ref

[Timon Gehr]

On 05/09/2013 11:06 PM, Jonathan M Davis wrote:
> On Thursday, May 09, 2013 21:39:14 Rob T wrote:
>> So, if I understand correctly, auto ref for templates will end up
>> doing exactly the same thing as auto ref for non-template
>> functions? That would be perfect, otherwise it'll be terribly
>> confusing.
>
> auto ref on templates would be essentially unchanged from what it is now (the
> fact that it forwards the refness of its arguments is actually very useful for
> some situations, and we don't want to lose that). However, what we might be
> able to do as an optimization would be to make it so that auto ref on
> templates acts the same as auto ref on non-templated functions when the
> compiler is able to determine that there's no real semantic difference - i.e.
> when the fact that the refness is being forwarded is irrelevant.
>
> So, with a function like
>
> auto foo(T)(auto ref T t)
> {
>   return t;
> }
>
> the non-templated solution could be used, whereas in a function like
>
> auto ref foo(T)(auto ref T t)
> {
>   return t;
> }
>
> or
>

Yes.

> auto foo(T)(auto ref T t)
> {
>   return anotherFuncWhichTakesByAutoRef(t);
> }
>
> the compiler would have to use the normal templated solution, because the
> refness of the arguments would have an effect on the code.
>
> ...

Actually, no. This would instantiate the ref version in any case, hence 
only one instantiation is necessarily required.