#include <iostream>
#include <string>
using namespace std;

class Element { public:
   virtual ~Element() { }
};

class This : public Element { public:
   string thiss() { return "This"; }
};

class That : public Element { public:
   string that() { return "That"; }
};

class TheOther : public Element { public:
   string theOther() { return "TheOther"; }
};

void main( void ) {
   Element* list[] = { new This(), new That(), new TheOther() };
   That* ptr;
   for (int i=0; i < 3; i++)
      if (ptr = dynamic_cast<That*>(list[i]))
         cout << "do something on " + ptr->that() << '\n';
      else
         cout << "not a That object\n";
}

// not a That object
// do something on That
// not a That object


#if 0

class Visitor {
public:
   virtual void visit( class This* ) = 0;
   virtual void visit( class That* ) = 0;
   virtual void visit( class TheOther* ) = 0;
};

class Element { public:
   virtual ~Element() { }
   virtual void accept( Visitor& ) = 0;
};

class This : public Element { public:
   string thiss() { return "This"; }
   /*virtual*/ void accept( Visitor& v ) { v.visit( this ); }
};

class That : public Element { public:
   string that() { return "That"; }
   /*virtual*/ void accept( Visitor& v ) { v.visit( this ); }
};

class TheOther : public Element { public:
   string theOther() { return "TheOther"; }
   /*virtual*/ void accept( Visitor& v ) { v.visit( this ); }
};

class ThatVisitor : public Visitor {
   /*virtual*/ void visit( This* ptr ) {
      cout << "not a That object\n"; }
   /*virtual*/ void visit( That* ptr ) {
      cout << "do something on " + ptr->that() << '\n'; }
   /*virtual*/ void visit( TheOther* ptr ) {
      cout << "not a That object\n"; }
};

class EveryoneVisitor : public Visitor {
   /*virtual*/ void visit( This* e ) {
      cout << "do Everyone on " + e->thiss() << '\n'; }
   /*virtual*/ void visit( That* e ) {
      cout << "do Everyone on " + e->that() << '\n'; }
   /*virtual*/ void visit( TheOther* e ) {
      cout << "do Everyone on " + e->theOther() << '\n'; }
};

void main( void ) {
   Element* list[] = { new This(), new That(), new TheOther() };
   ThatVisitor that;
   for (int i=0; i < 3; i++)
      list[i]->accept( that );
   cout << '\n';

   EveryoneVisitor all;
   for (i=0; i < 3; i++)
      list[i]->accept( all );
}

// not a That object
// do something on That
// not a That object
//
// do Everyone on This
// do Everyone on That
// do Everyone on TheOther

#endif