Editing Prototype pattern (section)

== Example ==
=== C++11 Example ===
This [[C++23]] implementation is based on the pre-C++98 implementation in the book. Discussion of the design pattern along with a complete illustrative example implementation using polymorphic class design are provided in the [https://fbb-git.gitlab.io/cppannotations/cppannotations/html/cplusplus14.html#l318 C++ Annotations].

<syntaxhighlight lang="c++">
import std;

enum class Direction {North, South, East, West};

class MapSite {
public:
  virtual void enter() = 0;
  virtual MapSite* clone() const = 0;
  virtual ~MapSite() = default;
};

class Room : public MapSite {
public:
  Room(): roomNumber(0) {}
  Room(int n): roomNumber(n) {}
  void setSide(Direction d, MapSite* ms) {
    std::println("Room::setSide {} ms", d);
  }
  virtual void enter() {}
  virtual Room* clone() const { // implements an operation for cloning itself.
    return new Room(*this);
  }
  Room& operator=(const Room&) = delete;
private:
  int roomNumber;
};

class Wall: public MapSite {
public:
  Wall() {}
  virtual void enter() {}
  virtual Wall* clone() const {
    return new Wall(*this);
  }
};

class Door: public MapSite {
public:
  Door(Room* r1 = nullptr, Room* r2 = nullptr)
    :room1(r1), room2(r2) {}
  Door(const Door& other)
    :room1(other.room1), room2(other.room2) {}
  virtual void enter() {}
  virtual Door* clone() const {
    return new Door(*this);
  }
  virtual void initialize(Room* r1, Room* r2) {
    room1 = r1;
    room2 = r2;
  }
  Door& operator=(const Door&) = delete;
private:
  Room* room1;
  Room* room2;
};

class Maze {
public:
  void addRoom(Room* r) {
    std::println("Maze::addRoom {}", r);
  }
  Room* roomNo(int) const {
    return nullptr;
  }
  virtual Maze* clone() const {
    return new Maze(*this);
  }
  virtual ~Maze() = default;
};

class MazeFactory {
public:
  MazeFactory() = default;
  virtual ~MazeFactory() = default;

  virtual Maze* makeMaze() const {
    return new Maze;
  }
  virtual Wall* makeWall() const {
    return new Wall;
  }
  virtual Room* makeRoom(int n) const {
    return new Room(n);
  }
  virtual Door* makeDoor(Room* r1, Room* r2) const {
    return new Door(r1, r2);
  }
};

class MazePrototypeFactory: public MazeFactory {
public:
  MazePrototypeFactory(Maze* m, Wall* w, Room* r, Door* d):
prototypeMaze(m), prototypeRoom(r), prototypeWall(w), prototypeDoor(d) 
    {}
  virtual Maze* makeMaze() const {
    // creates a new object by asking a prototype to clone itself.
    return prototypeMaze->clone();
  }
  virtual Room* makeRoom(int) const {
    return prototypeRoom->clone();
  }
  virtual Wall* makeWall() const {
    return prototypeWall->clone();
  }
  virtual Door* makeDoor(Room* r1, Room* r2) const {
    Door* door = prototypeDoor->clone();
    door->initialize(r1, r2);
    return door;
  }
  MazePrototypeFactory(const MazePrototypeFactory&) = delete;
  MazePrototypeFactory& operator=(const MazePrototypeFactory&) = delete;
private:
  Maze* prototypeMaze;
  Room* prototypeRoom;
  Wall* prototypeWall;
  Door* prototypeDoor;
};

// If createMaze is parameterized by various prototypical room, door, and wall objects, which it then copies and adds to the maze, then you can change the maze's composition by replacing these prototypical objects with different ones. This is an example of the Prototype (133) pattern.

class MazeGame {
public:
  Maze* createMaze(MazePrototypeFactory& m) {
    Maze* aMaze = m.makeMaze();
    Room* r1 = m.makeRoom(1);
    Room* r2 = m.makeRoom(2);
    Door* theDoor = m.makeDoor(r1, r2);
    aMaze->addRoom(r1);
    aMaze->addRoom(r2);
    r1->setSide(Direction::North, m.makeWall());
    r1->setSide(Direction::East, theDoor);
    r1->setSide(Direction::South, m.makeWall());
    r1->setSide(Direction::West, m.makeWall());
    r2->setSide(Direction::North, m.makeWall());
    r2->setSide(Direction::East, m.makeWall());
    r2->setSide(Direction::South, m.makeWall());
    r2->setSide(Direction::West, theDoor);
    return aMaze;
  }
};

int main() {
  MazeGame game;
  MazePrototypeFactory simpleMazeFactory(new Maze, new Wall, new Room, new Door);
  game.createMaze(simpleMazeFactory);
}
</syntaxhighlight>

The program output is:

<syntaxhighlight lang="c++">
Maze::addRoom 0x1160f50
Maze::addRoom 0x1160f70
Room::setSide 0 0x11613c0
Room::setSide 2 0x1160f90
Room::setSide 1 0x11613e0
Room::setSide 3 0x1161400
Room::setSide 0 0x1161420
Room::setSide 2 0x1161440
Room::setSide 1 0x1161460
Room::setSide 3 0x1160f90
</syntaxhighlight>