Discussion: Rvalue refs and a Move construtor for D

[Suleyman]

On Wednesday, 4 September 2019 at 17:41:02 UTC, Suleyman wrote:
> [...]

I expanded rvalue ref in the POC. It is now possible to have a 
implementation of `forward` based on rvalue ref.

Example:
```
template forward(alias arg)
{
     // rvalue ref
     enum isRvalue = __traits(isRvalueRef, arg) ||
                     !(__traits(isRef,  arg) ||
                       __traits(isOut,  arg) ||
                       __traits(isLazy, arg));
     static if (isRvalue)
         @property @rvalue ref forward() { return __move(arg); }
     else
         alias forward = arg;
}

unittest
{
     class C
     {
         import core.stdc.stdio : puts;

         static void foo(int n)     { puts("foo value"); }
         static void foo(ref int n) { puts("foo ref"); }

         static void bar(@rvalue ref int n)  { puts("bar rvalue 
ref"); }
         static void bar(ref int n)          { puts("bar ref"); }
     }

     void foo()(auto ref int x) { C.foo(forward!x); }
     void bar()(auto ref int x) { C.bar(forward!x); }

     int i;
     foo(1);
     foo(i);

     bar(1);
     bar(i);
}
```

I don't see how we can achieve the same efficiency without rvalue 
ref.