auto ref is on the docket

[Jonathan M Davis via Digitalmars-d]

On Monday, 22 June 2015 at 13:23:47 UTC, Marc Schütz wrote:
> On Monday, 22 June 2015 at 04:11:41 UTC, Andrei Alexandrescu 
> wrote:
>> Walter and I discussed what auto ref for templates should look 
>> like and reached the conclusion that an approach based on 
>> lowering would be best. I added a proposed lowering to 
>> https://github.com/D-Programming-Language/dmd/pull/4717.
>
> I have to concur with Manu's statement in the PR. IMO `auto 
> ref` (i.e. the status quo) is a hack introduced because of the 
> lack of usable `scope`. We shouldn't spread it to other parts 
> of the language, at least not for rvalue references. `scope 
> ref` is the perfect fit for those.
>
> (There may still be a use for `auto ref` with the meaning "pass 
> this as efficiently as possible, I don't care whether it's a 
> reference or not", but I'm not convinced of that either.)

I'm afraid that I don't understand this. What on earth does scope 
have to do with this issue? We need a way to indicate that a 
parameter should accept both lvalues and rvalues. auto ref was 
supposed to do that originally, but Walter misunderstood what 
Andrei was proposing and implemented what we have now, which is 
great for forwarding, but it doesn't solve the general case, 
because it only works with templates. That means that if we want 
that functionality we then need to either implement auto ref for 
non-templated functions as originally intended, or we need to 
come up with a new attribute which does that and which could be 
used with both templated and non-templated functions (thus not 
requiring the extra template bloat of the current auto ref 
implementation with templates if all you want is to accept both 
lvalues and rvalues, not have the refness of the argument 
forwarded).

What on earth does _any_ of that have to do with scope? 
Theoretically, scope indicates that a variable isn't supposed to 
escape the function - whatever that really means (it's never 
actually been defined outside of delegates, and even there, I'm 
not sure that it's defined all that well). What does that have to 
do with accepting lvalues or rvalues?

- Jonathan M Davis