抽象工厂（C）

抽象工厂模式提供了一种通过工厂函数集合获取对象的连贯集合的方法。对于每个模式，通过抽象创建一组对象的方式来减少耦合，这样用户代码就不会意识到他需要的对象的许多细节。

以下 C++示例说明了如何获取相同（假设）GUI 系列的不同类型的对象：

#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);
}

如果生成的可执行文件名为 abstractfactory，那么输出可能会给出：

$ ./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