Defining a custom *constructor* (not initializer!)

[Mehrdad]

> OK, I understand what you are saying now.
>
> What about using NVI?
>
> class Window
> {
>   protected void processMessage_impl(int message) // virtual 
> call
>   {}
>   final public void processMessage(int message)
>   {
>     if(message == WM_CREATE)
>     {
>        // handle specially
>     }
>     else if(message == WM_DELETE)
>     {
>        // handle specially
>     }
>     else
>     {
>         processMessage_impl(int message);
>     }
>   }
>   private HWND window;
>   this()
>   {
>     window = CreateWindow(&processMessage); // or whatever 
> mechanism, you get the idea
>   }
>   ~this()
>   {
>     DestroyWindow(window);
>   }
> }
>
> -Steve

The trouble is that if you "handle these specially", then your 
subclasses won't....
But your subclasses MUST still be able to handle these messages, 
because they might need to do something special when the messages 
are sent. (For example, you might need to calculate the size of 
the window when WM_CREATE or WM_NCCREATE is sent. Or something 
else... there are a ton of situations that can happen -- such as 
MDI window creation, etc. -- that don't happen too often, but 
happen often enough that you simply can't assume you can get by 
without allowing them to handle the messages.)