rvalue references

[Namespace via Digitalmars-d]

On Wednesday, 3 June 2015 at 03:57:38 UTC, bitwise wrote:
> I forgot to mention, in terms of this statement I made:
>
>> I can't remember right now what the reasoning was for 'const 
>> ref' not to take
>> rvalues in the first place. I think it was that you could 
>> escape the reference,
>> but this isn't true anymore with DIP25 right?
>
> I think someone brought this up about a weeks ago,
That was me.
> and this was Andrei's response:
>
>> Knee-jerk response: if no "return" attribute on a function it 
>> should be safeto bind rvalues to ref parameters. Of course 
>> that's impractical as a default
>> so explicit "auto ref" would be needed. -- Andrei
>
> What's impractical?

It's dangerous. If rvalues could be passed to normal ref 
parameter we would have a problem. Consider this:

----
struct Sprite {
     private Texture* _tex;

     this(ref Texture tex) {
         _tex = &tex;
     }
}
----

This works because we accept a valid lvalue and store a pointer 
to it. If the CTor would accept also rvalues, then the pointer 
would be invalid, since the texture was just a temporary 
variable. Not the best example, but I think you understand what I 
mean.