Rvalue references - The resolution

[Rob T]

On Monday, 6 May 2013 at 14:05:48 UTC, Andrei Alexandrescu wrote:
> template <class T> const T& min(const T& a, const T& b) {
>     return b < a ? b : a;
> }
> ...
> int x = ...;
> auto & weird = min(x, 100);
>

What I see going on is an attempt to double up on the use of ref 
for twp conflicting purposes. Perhaps part of the solution is to 
use a new variation of ref that allows rvalues and lvalues, while 
normal ref continues to disallow rvalues, eg ref vs refr.


void foo(ref b)
{
...
}

ref T min(ref T a, refr T b) {
      ++b; // error refr cannot be modified
      foo(b); // error, cannot pass refr to normal ref
      return b < a ? b : a; // error cannot return refr
  }

The "auto ref" system can then be extended to determine if normal 
ref or refr is required, and refuse to compile when the rules are 
violated rather than try and fake a real ref with a temporary, 
since I would think that's something you'd normally never want 
done anyway.

A runtime safety check will still be needed for returns of normal 
ref that may escape.

I can definitely agree on the runtime safety check, but I have 
doubts about the idea of faking a real ref.

--rt