"John Kiro" <johnkirollos@yahoo.com> wrote in message news:en6pvm$23fk$1@digitaldaemon.com...
> Speaking about casting, there is usually a need to cast a reference to an
> integer & vice-versa; I'm specifically pointing to the case of using a
> function
> like the Win32 API function SetWindowLong(), in order to link a window
> with a
> corresponding object. Here is how I did it:
>
>  //Linking view window to view obj:
>  SetWindowLong(hwndView,0,cast(uint)(cast(CView*)this));
>
>  //retrieve the object given the window handle:
>  cast(CView)cast(CView*)GetWindowLong(hwndView,0);
>
> Casting to void* instead of CView* also compiled without errors.
>
> So is this the usual way of doing such thing? I mean double casting? Because casting an object to int or vice-versa is rejected by the compiler.

Yes.  Though you should use the

cast(uint)cast(void*)this

form, as this is the more generally accepted way.  It makes it obvious that you're getting the pointer value of the reference, compared to

cast(uint)cast(CView*)this

Since 'this' is of type CView, casting CView to CView* doesn't really make sense, but casting to void* does -- it says "I want a raw pointer."

Thanks guys for all your comments.. I've found them invaluable in this tricky part of my D language exploration :-)

As a summary:

- CObj obj2=obj1;

    obj2 is a reference to obj1 (both obj1 & obj2 refer to the same
object). So no new object is created.

- CObj* pRefObj1=&obj1;

    pRefObj1 is the address of the reference of the object, not a
pointer to the object itself.. TAKE CARE!

- void* pObj1=cast(void*)obj1;

    pObj1 is a pointer to the object itself (as object pointers in
C++)


Happy New Year
John

"John Kiro" <johnkirollos@yahoo.com> wrote in message news:enavsd$49l$1@digitaldaemon.com...

> As a summary:
>
> - CObj obj2=obj1;
>
>    obj2 is a reference to obj1 (both obj1 & obj2 refer to the same
> object). So no new object is created.
>
> - CObj* pRefObj1=&obj1;
>
>    pRefObj1 is the address of the reference of the object, not a
> pointer to the object itself.. TAKE CARE!
>
> - void* pObj1=cast(void*)obj1;
>
>    pObj1 is a pointer to the object itself (as object pointers in
> C++)

Right on all counts.