Problem with Point property

[Chris Nicholson-Sauls]

Henning Hasemann wrote:
> I found a 'solution' myself which is aahh.. 'tricky'.
> I extend the struct to be able to call the setter method
> whenever its value changes.
> To stop behaving it like a pointer, I misuse opCast as
> a 'copy constructor'. So
> 
> Point p = (new Foo).position;
> p.x = 5;
> 
> wont change the Foo's position, as it where when position was
> a real member. 
> 
> Look here:
> 
> struct Point {
>   private {
>     int mX, mY;
>     void delegate(Point) setter;
>   }
>   
>   Point opCast() {
>     Point p;
>     p.setter = null;
>     p.mX = x; p.mY = y;
>     return p;
>   }
> 
>   int x() {
>     return mX;
>   }
>   void x(int x1) {
>     mX = x1;
>     if(setter !is null)
>       setter(*this);
>   }
>   // skipped the same for y
> }
> 
> To be used like:
> 
> class Bar {
>   private Point mPosition;
>   this() {
>     mPosition.setter = &position;
>   }
>   Point position() {
>     return mPosition;
>   }
>   void position(Point p) {
>     mPosition = p;
>   }
> }
> 
>   Bar b;
> 
>   // This actually changes the object
>   b.position.x = 7;
>   writefln(b.position.x); // 7
> 
>   // This as before, does not
>   Point p = b.position; // here opCast is being called
>   p.x = 5;
>   writefln(b.position.x); // still 7
> 
> 
> The only thing is Im not quite sure if using opCast this way is
> portable across versions and compiler manufracturers,
> anyone knowing something about that?
> 
> Henning
> 

Actually, that's rather slick, and worth studying, even if it turns out not to be optimal. 
  (Which with a significant number of such properties, it couldn't possibly be.)  I really 
can't offer anything better off hand.

-- Chris Nicholson-Sauls