Re: 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