import std.stdio;

interface SupportsTag {
}

interface HelloWorld {
   void helloWorld ();
}

class X : HelloWorld {
   void helloWorld () {
      writefln ("X: Hello World");
   }
}

class Y : HelloWorld, SupportsTag {
   void helloWorld () {
      writefln ("Y: Hello World");
   }
}

void main () {
   auto x = new X ();
   auto y = new Y ();
   
   if (cast(SupportsTag)(x)) {
      x.helloWorld ();
   }
   
   if (cast(SupportsTag)(y)) {
      y.helloWorld ();
   }
   
   HelloWorld hw;
   
   hw = x;
   if (cast(X)(hw)) {
      writefln ("1: HW is X");
   }
   if (cast(Y)(hw)) {
      writefln ("1: HW is Y");
   }
   if (cast(SupportsTag)(hw)) {
      hw.helloWorld ();
   }
   
   hw = y;
   if (cast(X)(hw)) {
      writefln ("2: HW is X");
   }
   if (cast(Y)(hw)) {
      writefln ("2: HW is Y");
   }
   if (cast(SupportsTag)(hw)) {
      hw.helloWorld ();
   }
}