DIP 36: Rvalue References

[Diggory]

In that example you could make opOpAssign take a "const ref" and 
then the compiler could see that it could not return that 
parameter, but this is slightly hacky and I can see how there may 
be obscure corner cases where the rules are not sufficient.

Actually this could also be solved by using the (original) 
meaning of "scope" to mark parameters that are not going to be 
returned. (I still think both "ref" and "scope ref" should accept 
rvalues)