抽象工厂模式

提供一个创建一系列相关或相互依赖对象的接口，而无须指定它们具体的类。

抽象工厂接口 IFactory 包含所有产品创建的抽象方法。而 ConcreteFactory* 就是具体的工厂。为创建不同的产品对象，客户端应使用不同的具体工厂。

#include <iostream>
#include <memory>
/* 抽象产品类A */
class VProductA {
public:
  virtual void showFeature() const = 0;
  virtual ~VProductA() = default;
};
/* 具体产品类 A1 */
class ConcreteProductA1 final : public VProductA {
public:
  void showFeature() const override {
    std::cout << "Concrete Product A1 here\n";
  }
  ~ConcreteProductA1() = default;
};
/* 具体产品类 A2 */
class ConcreteProductA2 final : public VProductA {
public:
  void showFeature() const override {
    std::cout << "Concrete Product A2 here\n";
  }
  ~ConcreteProductA2() = default;
};
/* 抽象产品类B */
class VProductB {
public:
  virtual void showFeature() const = 0;
  virtual ~VProductB() = default;
};
/* 具体产品类 B1 */
class ConcreteProductB1 final : public VProductB {
public:
  void showFeature() const override {
    std::cout << "Concrete Product B1 here\n";
  }
  ~ConcreteProductB1() = default;
};
/* 具体产品类 B2 */
class ConcreteProductB2 final : public VProductB {
public:
  void showFeature() const override {
    std::cout << "Concrete Product B2 here\n";
  }
  ~ConcreteProductB2() = default;
};
/* 抽象工厂 */
class VFactory {
public:
  virtual std::unique_ptr<VProductA> CreateProductA() = 0;
  virtual std::unique_ptr<VProductB> CreateProductB() = 0;
  ~VFactory() = default;
};
/* 具体工厂1 */
class Factory1 final : public VFactory {
public:
  std::unique_ptr<VProductA> CreateProductA() {
    return std::make_unique<ConcreteProductA1>();
  }
  std::unique_ptr<VProductB> CreateProductB() {
    return std::make_unique<ConcreteProductB1>();
  }
  ~Factory1() = default;
};
/* 具体工厂2 */
class Factory2 final : public VFactory {
public:
  std::unique_ptr<VProductA> CreateProductA() {
    return std::make_unique<ConcreteProductA2>();
  }
  std::unique_ptr<VProductB> CreateProductB() {
    return std::make_unique<ConcreteProductB2>();
  }
  ~Factory2() = default;
};
auto main() -> int {
  std::unique_ptr<VFactory> fac = std::make_unique<Factory1>();
  auto productA = fac->CreateProductA();
  auto productB = fac->CreateProductB();
  productA->showFeature();
  productB->showFeature();
  fac.reset(new Factory2);
  std::cout << '\n';
  productA = fac->CreateProductA();
  productB = fac->CreateProductB();
  productA->showFeature();
  productB->showFeature();
  return 0;
}