rvalue references

[Andrei Alexandrescu]

On 4/23/13 3:07 AM, Namespace wrote:
> On Tuesday, 23 April 2013 at 03:30:35 UTC, Walter Bright wrote:
>> Previous discussions:
>>
>> http://forum.dlang.org/thread/4F84D6DD.5090405@digitalmars.com#post-4F84D6DD.5090405:40digitalmars.com
>>
>>
>> http://d.puremagic.com/issues/show_bug.cgi?id=9238
>
> I still like the Idea of DIP 36 (http://wiki.dlang.org/DIP36) with scope
> ref / in ref. On this link we have also collected several other
> suggested syntaxes.
> But maybe we should discuss first, if auto ref could work for
> non-templates.
> This would mean that
> 1. auto ref generate code bloat for non-templates (doubled the function
> 2^n times)
> or
> 2. auto ref works like scope ref would do (create a temporary lvalue and
> pass this to the function). But that would mean that auto ref work
> differently for templates and non-templates (maybe a problem?). If we
> choose this we should also discuss about the lifetime of the temporary:
> ----
> foo(auto ref A a) { }
>
> foo(A());
> // should then converted to
> {
> A __temp = A();
> foo(__temp); // after this, __temp is destroyed
> }
> ----
> or
> 3. the compiler choose if an argument should be passed by ref, by value
> or should be moved.
> For example:
> ----
> A a = A(42);
> foo(a); // by ref
> foo(A(23)); // move
> ----

That's on the mark. We need to make auto ref work with non-templates as 
well as templates, safely. The implementation mechanics may be 
different. Lifetime of temporaries is an important detail. I discuss 
such in http://d.puremagic.com/issues/show_bug.cgi?id=9238 but I never 
had the time to finish it.

Andrei