Array operations with array of structs

[Peter via Digitalmars-d-learn]

On Monday, 6 July 2015 at 15:48:28 UTC, anonymous wrote:

Ok, I disabled everything in the struct except what I posted and 
it ran.
I then uncommented stuff to isolate the cause. I've added in the 
bits that cause the error below (plus some constructors just for 
reference).

struct Vector3 {
     public double[3] _p;
     @nogc this(in double[] p)
     {
	switch ( p.length ) {
	case 0: _p[0] = _p[1] = _p[2] = 0.0; break;
	case 1: _p[0] = p[0]; _p[1] = _p[2] = 0.0; break;
	case 2: _p[0] = p[0]; _p[1] = p[1]; _p[2] = 0.0; break;
	default: _p[0] = p[0]; _p[1] = p[1]; _p[2] = p[2]; break;
	}
     }
     @nogc this(in double p0, in double p1=0.0, in double p2=0.0)
     {
  	_p[0] = p0;
	_p[1] = p1;
	_p[2] = p2;
     }
     @nogc this(in Vector3 other)
     {
	_p[] = other._p[];
     }
     //...
     Vector3 opBinary(string op)(in Vector3 rhs) const
     if (op == "+"){
         Vector3 result;
         result._p[] = this._p[] + rhs._p[];
         return result;
     }
     // The bits that cause the error:
     //... Enabling any one (or more) of the following causes the 
error
     this(this)
     {
	_p = _p.dup;
     }

     @nogc ref Vector3 opAssign(ref Vector3 rhs)
     {
	_p[] = rhs._p[];
	 return this;
     }

     @nogc ref Vector3 opAssign(Vector3 rhs)
     {
	_p[] = rhs._p[];
	return this;
     }
     //...
}

Any ideas about what's happening?