Behavioral Pattern

template_method.cpp

#include <ctime>
#include <assert.h>
#include <iostream>
 
namespace wikibooks_design_patterns
{
    /**
    * An abstract class that is common to several games in
    * which players play against the others, but only one is
    * playing at a given time.
    */
 
    class Game {
 
    public:
        Game(): playersCount(0), movesCount(0), playerWon(-1)
        {
            srand( (unsigned)time( NULL));
        }
 
        /* A template method : */
        void playOneGame(const int playersCount = 0) {
 
            if (playersCount)
                this->playersCount = playersCount;
 
            InitializeGame();
            assert(this->playersCount);
 
            int j = 0;
            while (!endOfGame()) {
                makePlay(j);
                j = (j + 1) % this->playersCount;
                if (!j) {
                    ++movesCount;
                }
            }
            printWinner();
        }
 
    protected:
        virtual void initializeGame() = 0;
        virtual void makePlay(int player) = 0;
        virtual bool endOfGame() = 0;
        virtual void printWinner() = 0;
 
    private:
        void InitializeGame()
        {
            movesCount = 0;
            playerWon = -1;
 
            initializeGame();
        }
 
    protected:
        int playersCount;
        int movesCount;
        int playerWon;
    };
 
    //Now we can extend this class in order 
    //to implement actual games:
 
    class Monopoly: public Game {
 
        /* Implementation of necessary concrete methods */
        void initializeGame() {
            // Initialize players
            playersCount = rand() * 7 / RAND_MAX + 2;
            // Initialize money
        }
        void makePlay(int player) {
            // Process one turn of player
 
            //  Decide winner
            if (movesCount < 20)
                return;
            const int chances = (movesCount > 199) ? 199 : movesCount;
            const int random = MOVES_WIN_CORRECTION * rand() * 200 / RAND_MAX;
            if (random < chances)
                playerWon = player;
        }
        bool endOfGame() {
            // Return true if game is over 
            // according to Monopoly rules
            return (-1 != playerWon);
        }
        void printWinner() {
            assert(playerWon >= 0);
            assert(playerWon < playersCount);
 
            // Display who won
            std::cout<<"Monopoly, player "<<playerWon<<" won in "<<movesCount<<" moves."<<std::endl;
        }
 
    private:
        enum
        {
            MOVES_WIN_CORRECTION = 20,
        };
    };
 
    class Chess: public Game {
 
        /* Implementation of necessary concrete methods */
        void initializeGame() {
            // Initialize players
            playersCount = 2;
            // Put the pieces on the board
        }
        void makePlay(int player) {
            assert(player < playersCount);
 
            // Process a turn for the player
 
            //  decide winner
            if (movesCount < 2)
                return;
            const int chances = (movesCount > 99) ? 99 : movesCount;
            const int random = MOVES_WIN_CORRECTION * rand() * 100 / RAND_MAX;
            //std::cout<<random<<" : "<<chances<<std::endl;
            if (random < chances)
                playerWon = player;
        }
        bool endOfGame() {
            // Return true if in Checkmate or 
            // Stalemate has been reached
            return (-1 != playerWon);
        }
        void printWinner() {
            assert(playerWon >= 0);
            assert(playerWon < playersCount);
 
            // Display the winning player
            std::cout<<"Player "<<playerWon<<" won in "<<movesCount<<" moves."<<std::endl;
        }
 
    private:
        enum
        {
            MOVES_WIN_CORRECTION = 7,
        };
    };
 
}
 
int main()
{
    using namespace wikibooks_design_patterns;
 
    Game* game = NULL;
 
    Chess chess;
    game = &chess;
    for (unsigned i = 0; i < 100; ++i)
        game->playOneGame();
 
    Monopoly monopoly;
    game = &monopoly;
    for (unsigned i = 0; i < 100; ++i)
        game->playOneGame();
 
    return 0;
}

http://en.wikibooks.org/wiki/C%2B%2B_Programming/Code/Design_Patterns#Template_Method