Move construction from !is(T == typeof(this))

[Andrei Alexandrescu via Digitalmars-d]

On 04/24/2017 04:23 PM, ag0aep6g wrote:
> On 04/24/2017 08:48 PM, Stanislav Blinov wrote:
>> Speaking of const violation and UB, std.algorithm.mutation.move seems to
>> violate const without remorse:
>
> Yup. Even in @safe code, which is a bug.
> https://issues.dlang.org/show_bug.cgi?id=15315

Should fail in all situations, thanks for reporting.

The original code should work like this:

struct X {}

struct Y {
   private X _x;
   this()(auto ref X x)
   {
     static if (__traits(isRef, x))
     {
         _x = x;
     }
     else
     {
         import std.algorithm.mutation : move;
         _x = move(x);
     }
   }
}

Note how I made the ctor templated so it accepts auto ref. The less 
sophisticated version is simply:

struct X {}

struct Y {
   private X _x;
   this(ref X x)
   {
      _x = x;
   }
   this(X x)
   {
      import std.algorithm.mutation : move;
      _x = move(x);
   }
}

There should be ways to do this easier, i.e. add a forward() function to 
std.algorithm.mutation. Contributions are welcome!


Andrei