const ref rvalues

[Denis Koroskin]

On Mon, 14 Dec 2009 23:38:34 +0300, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> Denis Koroskin wrote:
>> On Mon, 14 Dec 2009 21:06:20 +0300, dsimcha <dsimcha at yahoo.com> 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);
>>  I agree it hurts a lot. I faced the same problem implementing  
>> RefCounted: you can't return RefCounted object from one function and  
>> pass it by reference to another one. Passing it by value is not a good  
>> option.
>
> The compiler will optimize that case.
>
> Andrei

How can it optimize away a function with a side effect (RefCounted  
ctor/dtor invokes an interlocked increment/decrement that theoretically  
may destroy an object, but wouldn't in practice)? Make it special for  
compiler?