DIP 1016--ref T accepts r-values--Formal Assessment

[Olivier FAURE]

On Thursday, 31 January 2019 at 02:10:05 UTC, Manu wrote:
> I still can't see a truck-sized hole.

I don't know if it's truck-sized, but here's another corner case:

     int doubleMyValue(ref int x) {
         x *= 2;
         return x;
     }

     Point pt;
     pt.x = 5;
     pt.y = foobar();

     doubleMyValue(pt.x);
     assert(pt.x == 10);

Question: in the above code, will the assertion pass?

Answer: it depends on Point's implementation. If x is a member 
variable, then yes. If it's a getter, then doubleMyValue will 
take a rvalue and x won't be mutated and the assertion will fail.

I think this is a non-trivial conceptual problem.