// Purpose.  Template Method design pattern demo.
// 
// Discussion.  The "template method" establishes the steps to be
// performed.  All standard, or invariant, steps have their implementation
// provided by the abstract base class.  All variable steps are not
// defined in the base class, but must be defined by concrete derived
// classes.  "stepFour" below is an embellishment on the design pattern
// where the base class provides a default implementation, and then the
// derived class may extend that method by: overriding the method,
// "calling-back" to the base class to leverage its implementation, and
// then adding its own peculiar behavior.

#include <iostream.h>

class IncompleteAlgorithm {
public:
   void doIt() {       // this is the Template Method
      stepOne();       // invariant, standard
      stepTwo();       // invariant, standard
      stepThree();     // variable,  supplied by subclass
      stepFour(); }    // variable,  default provided
private:
   void stepOne() {
      cout << "IncompleteAlgorithm::stepOne" << endl; }
   void stepTwo() {
      cout << "IncompleteAlgorithm::stepTwo" << endl; }
   virtual void stepThree() = 0;
protected:
   virtual void stepFour() {
      cout << "IncompleteAlgorithm::stepFour" << endl; }
};

class FillInTheTemplate : public IncompleteAlgorithm {
   /* virtual */ void stepThree() {
      cout << "FillInTheTemplate::stepThree" << endl; }
   /* virtual */ void stepFour() {
      IncompleteAlgorithm::stepFour();
      cout << "FillInTheTemplate::stepFour" << endl; }
};

int main()
{
   FillInTheTemplate  theThingToDo;

   theThingToDo.doIt();
}

// IncompleteAlgorithm::stepOne
// IncompleteAlgorithm::stepTwo
// FillInTheTemplate::stepThree
// IncompleteAlgorithm::stepFour
// FillInTheTemplate::stepFour