/**/class Product {};#ifdef Implementation1class MyProduct : public Product {};class YourProduct : public Product {};class TheirProduct : public Product {};typedef int ProductId;const int MINE = 1;const int YOURS = 2;const int THEIRS = 2;/**/class Creator {public:    virtual Product* Create(ProductId);};/**/Product* Creator::Create (ProductId id) {    if (id == MINE)  return new MyProduct;    if (id == YOURS) return new YourProduct;    // repeat for remaining products...    return 0;}/**/class MyCreator : public Creator {public:    virtual Product* Create(ProductId);};/**/Product* MyCreator::Create (ProductId id) {    if (id == YOURS)  return new MyProduct;    if (id == MINE)   return new YourProduct;        // N.B.: switched YOURS and MINE    if (id == THEIRS) return new TheirProduct;    return Creator::Create(id); // called if all others fail}/**/#endif#ifdef Implementation2/**/class Creator {public:    Product* GetProduct();protected:    virtual Product* CreateProduct();private:    Product* _product;};/**/Product* Creator::GetProduct () {    if (_product == 0) {        _product = CreateProduct();    }    return _product;}/**/#endif#ifdef Implementation3/**/class Creator {public:    virtual Product* CreateProduct() = 0;};/**/template <class TheProduct>class StandardCreator: public Creator {public:    virtual Product* CreateProduct();};/**/template <class TheProduct>Product* StandardCreator<TheProduct>::CreateProduct () {    return new TheProduct;}/**/class MyProduct : public Product {public:    MyProduct();    // ...};StandardCreator<MyProduct> myCreator;/**/#endif/**/#include "C++/MazeParts.H"/**/class MazeGame {public:    Maze* CreateMaze();/**/// factory methods:/**/    virtual Maze* MakeMaze() const        { return new Maze; }    virtual Room* MakeRoom(int n) const        { return new Room(n); }    virtual Wall* MakeWall() const        { return new Wall; }    virtual Door* MakeDoor(Room* r1, Room* r2) const        { return new Door(r1, r2); }};/**/Maze* MazeGame::CreateMaze () {    Maze* aMaze = MakeMaze();/**/    Room* r1 = MakeRoom(1);    Room* r2 = MakeRoom(2);    Door* theDoor = MakeDoor(r1, r2);/**/    aMaze->AddRoom(r1);    aMaze->AddRoom(r2);/**/    r1->SetSide(North, MakeWall());    r1->SetSide(East, theDoor);    r1->SetSide(South, MakeWall());    r1->SetSide(West, MakeWall());/**/    r2->SetSide(North, MakeWall());    r2->SetSide(East, MakeWall());    r2->SetSide(South, MakeWall());    r2->SetSide(West, theDoor);/**/    return aMaze;}/**/class BombedMazeGame : public MazeGame {public:    BombedMazeGame();/**/    virtual Wall* MakeWall() const        { return new BombedWall; }/**/    virtual Room* MakeRoom(int n) const        { return new RoomWithABomb(n); }};/**/class EnchantedMazeGame : public MazeGame {public:    EnchantedMazeGame();/**/    virtual Room* MakeRoom(int n) const        { return new EnchantedRoom(n, CastSpell()); }/**/    virtual Door* MakeDoor(Room* r1, Room* r2) const        { return new DoorNeedingSpell(r1, r2); }protected:    Spell* CastSpell() const;};/**/