const ref rvalues

[Denis Koroskin]

On Mon, 14 Dec 2009 22:15:06 +0300, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> Eldar Insafutdinov wrote:
>> dsimcha Wrote:
>>
>>> I mentioned this deep in another thread, but I think it deserves its  
>>> own
>>> thread.  Can we get something like:
>>>
>>> void doStuff(T)(const ref T val) {
>>>     // do stuff.
>>> }
>>>
>>> T getVal() {
>>>     return someValue;
>>> }
>>>
>>> void main() {
>>>     doStuff(getVal());  // Doesn't currently work.
>>> }
>>>
>>> For non-const ref parameters, it's understandable that passing rvalues  
>>> in
>>> doesn't work because this is likely a bug that the compiler should  
>>> catch.
>>> However, for const ref parameters, can't the compiler just implicitly  
>>> put the
>>> value on the caller's stack frame and convert it to an lvalue rather  
>>> than
>>> forcing the programmer to write the boilerplate to do this manually?   
>>> This
>>> would result in:
>>>
>>> doStuff(getVal()); -->
>>>
>>> auto __temp = getVal();
>>> doStuff(__temp);
>>  My vote for it.
>
> Binding rvalues to const references was probably the single most hurtful  
> design decisions for C++. I don't have time to explain now, but in short  
> I think all of the problems that were addressed by rvalue references,  
> and most of the aggravation within the design of rvalue references, are  
> owed by that one particular conversion.
>
> If we ever allow automatic conversion of an rvalue to a ref, we should  
> know very well what we're doing.
>
>
> Andrei

What about allowing binding rvalue to final ref const(T) (final would mean  
tail-const and wouldn't allow taking address of that variable)?

Wouldn't that allow the feature while side-stepping all the issues?