Call method if declared only

[Виталий Фадеев]

On Friday, 28 February 2020 at 06:12:37 UTC, Виталий Фадеев wrote:
> Searching solution for idea !
>
> Goal is to get System message, dispatch/route to method !
> If method implemented only !
>
> I dream on in future write clean code of a derived widgets like 
> this :
>
>     class Base
>     {
>        // dispatch
>        void On( message ... )
>        {
>            // call On<message>()
>            // example: call OnKeyUp() - if method OnKeyUp() is 
> exists only
>        }
>     }
>
>     class Derived : Base
>     {
>        // method implementation
>        void OnKeyUp( ... )
>        {
>            //
>        }
>     }
>
>
>
> I tryed code like this:
>
>     import core.sys.windows.windows;
>     import std.stdio;
>
>
>     class Base
>     {
>        LRESULT On( UINT message, WPARAM wParam, LPARAM lParam )
>        {
> 		switch ( message )
> 		{
> 			case WM_KEYDOWN:
>                                 OnWM_KEYDOWN( wParam, lParam );
>  //   <-- but it required declared OnWM_KEYDOWN(...) in base 
> class Base. How will be without declaring in Base ?
> 				break;
>
> 			default: 				
> 		}
>        }
>     }
>
>
>     class Button : Base
>     {
>         LRESULT OnWM_KEYDOWN( WPARAM wParam, LPARAM lParam )
>         {
>             writeln( "WM_KEYDOWN" );
>         }
>     }
>
>
> May be other than derived ? May be templating ?
> How to implement ?

Now I go in ths way:

     import std.stdio;
     import std.traits;


     class Base
     {
         void On( alias THIS )( int message )
         {
             static if (
                        __traits( hasMember, THIS, "OnKey" ) &&
                        isCallable!( __traits( getMember, THIS, 
"OnKey" ) )
                       )
             {
                 __traits( getMember, THIS, "OnKey" )();
             }
         }

         void run( alias THIS )()
         {
             On!THIS( 1 );
         }
     }

     class A : Base
     {
         void OnKey()
         {
             writeln( "A.OnKey()" );
         }
     }


     void main()
     {
         auto a = new A();
         a.run!a();
     }


Searching for beauty readable code...