抽象工廠（C）

抽象工廠模式提供了一種通過工廠函式集合獲取物件的連貫集合的方法。對於每個模式，通過抽象建立一組物件的方式來減少耦合，這樣使用者程式碼就不會意識到他需要的物件的許多細節。

以下 C++示例說明了如何獲取相同（假設）GUI 系列的不同型別的物件：

#include <iostream>

/* Abstract definitions */
class GUIComponent {
public:
  virtual ~GUIComponent() = default;
  virtual void draw() const = 0;
};
class Frame  : public GUIComponent {};
class Button : public GUIComponent {};
class Label  : public GUIComponent {};

class GUIFactory {
public:
  virtual ~GUIFactory() = default;
  virtual std::unique_ptr<Frame> createFrame() = 0;
  virtual std::unique_ptr<Button> createButton() = 0;
  virtual std::unique_ptr<Label> createLabel() = 0;
  static std::unique_ptr<GUIFactory> create(const std::string& type);
};

/* Windows support */
class WindowsFactory : public GUIFactory {
private:
    class WindowsFrame : public Frame {
    public:
      void draw() const override { std::cout << "I'm a Windows-like frame" << std::endl; }
    };
    class WindowsButton : public Button {
    public:
      void draw() const override { std::cout << "I'm a Windows-like button" << std::endl; }
    };
    class WindowsLabel : public Label {
    public:
      void draw() const override { std::cout << "I'm a Windows-like label" << std::endl; }
    };
public:
  std::unique_ptr<Frame> createFrame() override { return std::make_unique<WindowsFrame>(); }
  std::unique_ptr<Button> createButton() override { return std::make_unique<WindowsButton>(); }
  std::unique_ptr<Label> createLabel() override { return std::make_unique<WindowsLabel>(); }
};

/* Linux support */
class LinuxFactory : public GUIFactory {
private:
    class LinuxFrame : public Frame {
    public:
      void draw() const override { std::cout << "I'm a Linux-like frame" << std::endl; }
    };
    class LinuxButton : public Button {
    public:
      void draw() const override { std::cout << "I'm a Linux-like button" << std::endl; }
    };
    class LinuxLabel : public Label {
    public:
      void draw() const override { std::cout << "I'm a Linux-like label" << std::endl; }
    };
public:
  std::unique_ptr<Frame> createFrame() override { return std::make_unique<LinuxFrame>(); }
  std::unique_ptr<Button> createButton() override { return std::make_unique<LinuxButton>(); }
  std::unique_ptr<Label> createLabel() override { return std::make_unique<LinuxLabel>(); }
};

std::unique_ptr<GUIFactory> GUIFactory::create(const string& type) {
  if (type == "windows") return std::make_unique<WindowsFactory>();
  return std::make_unique<LinuxFactory>();
}

/* User code */
void buildInterface(GUIFactory& factory) {
  auto frame = factory.createFrame();
  auto button = factory.createButton();
  auto label = factory.createLabel();

  frame->draw();
  button->draw();
  label->draw();
}

int main(int argc, char *argv[]) {
  if (argc < 2) return 1;
  auto guiFactory = GUIFactory::create(argv[1]);
  buildInterface(*guiFactory);
}

如果生成的可執行檔名為 abstractfactory，那麼輸出可能會給出：

$ ./abstractfactory windows
I'm a Windows-like frame
I'm a Windows-like button
I'm a Windows-like label
$ ./abstractfactory linux  
I'm a Linux-like frame
I'm a Linux-like button
I'm a Linux-like label