工厂模式

C++工厂模式的模板，包含简单工厂、工厂方法和抽象工厂三种常见的实现方式。

1. 简单工厂模式模板

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#include <iostream>
#include <memory>
#include <string>

// 产品基类
class Product {
public:
    virtual ~Product() = default;
    virtual void operation() = 0;
};

// 具体产品A
class ConcreteProductA : public Product {
public:
    void operation() override {
        std::cout << "ConcreteProductA operation" << std::endl;
    }
};

// 具体产品B
class ConcreteProductB : public Product {
public:
    void operation() override {
        std::cout << "ConcreteProductB operation" << std::endl;
    }
};

// 简单工厂类
class SimpleFactory {
public:
    enum class ProductType {
        TYPE_A,
        TYPE_B
    };
    
    static std::unique_ptr<Product> createProduct(ProductType type) {
        switch (type) {
            case ProductType::TYPE_A:
                return std::make_unique<ConcreteProductA>();
            case ProductType::TYPE_B:
                return std::make_unique<ConcreteProductB>();
            default:
                return nullptr;
        }
    }
};

// 使用示例
int main_simple_factory() {
    auto productA = SimpleFactory::createProduct(SimpleFactory::ProductType::TYPE_A);
    auto productB = SimpleFactory::createProduct(SimpleFactory::ProductType::TYPE_B);
    
    if (productA) productA->operation();
    if (productB) productB->operation();
    
    return 0;
}

2. 工厂方法模式模板

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#include <iostream>
#include <memory>
#include <string>

// 产品基类
class Product {
public:
    virtual ~Product() = default;
    virtual void operation() = 0;
};

// 具体产品A
class ConcreteProductA : public Product {
public:
    void operation() override {
        std::cout << "ConcreteProductA operation" << std::endl;
    }
};

// 具体产品B
class ConcreteProductB : public Product {
public:
    void operation() override {
        std::cout << "ConcreteProductB operation" << std::endl;
    }
};

// 工厂基类
class Factory {
public:
    virtual ~Factory() = default;
    virtual std::unique_ptr<Product> createProduct() = 0;
};

// 具体工厂A
class ConcreteFactoryA : public Factory {
public:
    std::unique_ptr<Product> createProduct() override {
        return std::make_unique<ConcreteProductA>();
    }
};

// 具体工厂B
class ConcreteFactoryB : public Factory {
public:
    std::unique_ptr<Product> createProduct() override {
        return std::make_unique<ConcreteProductB>();
    }
};

// 使用示例
int main_factory_method() {
    std::unique_ptr<Factory> factoryA = std::make_unique<ConcreteFactoryA>();
    std::unique_ptr<Factory> factoryB = std::make_unique<ConcreteFactoryB>();
    
    auto productA = factoryA->createProduct();
    auto productB = factoryB->createProduct();
    
    productA->operation();
    productB->operation();
    
    return 0;
}

3. 抽象工厂模式模板

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#include <iostream>
#include <memory>
#include <string>

// 抽象产品族A
class AbstractProductA {
public:
    virtual ~AbstractProductA() = default;
    virtual void operationA() = 0;
};

// 抽象产品族B
class AbstractProductB {
public:
    virtual ~AbstractProductB() = default;
    virtual void operationB() = 0;
};

// 具体产品A1
class ConcreteProductA1 : public AbstractProductA {
public:
    void operationA() override {
        std::cout << "ConcreteProductA1 operation" << std::endl;
    }
};

// 具体产品A2
class ConcreteProductA2 : public AbstractProductA {
public:
    void operationA() override {
        std::cout << "ConcreteProductA2 operation" << std::endl;
    }
};

// 具体产品B1
class ConcreteProductB1 : public AbstractProductB {
public:
    void operationB() override {
        std::cout << "ConcreteProductB1 operation" << std::endl;
    }
};

// 具体产品B2
class ConcreteProductB2 : public AbstractProductB {
public:
    void operationB() override {
        std::cout << "ConcreteProductB2 operation" << std::endl;
    }
};

// 抽象工厂
class AbstractFactory {
public:
    virtual ~AbstractFactory() = default;
    virtual std::unique_ptr<AbstractProductA> createProductA() = 0;
    virtual std::unique_ptr<AbstractProductB> createProductB() = 0;
};

// 具体工厂1
class ConcreteFactory1 : public AbstractFactory {
public:
    std::unique_ptr<AbstractProductA> createProductA() override {
        return std::make_unique<ConcreteProductA1>();
    }
    
    std::unique_ptr<AbstractProductB> createProductB() override {
        return std::make_unique<ConcreteProductB1>();
    }
};

// 具体工厂2
class ConcreteFactory2 : public AbstractFactory {
public:
    std::unique_ptr<AbstractProductA> createProductA() override {
        return std::make_unique<ConcreteProductA2>();
    }
    
    std::unique_ptr<AbstractProductB> createProductB() override {
        return std::make_unique<ConcreteProductB2>();
    }
};

// 使用示例
int main_abstract_factory() {
    std::unique_ptr<AbstractFactory> factory1 = std::make_unique<ConcreteFactory1>();
    std::unique_ptr<AbstractFactory> factory2 = std::make_unique<ConcreteFactory2>();
    
    auto productA1 = factory1->createProductA();
    auto productB1 = factory1->createProductB();
    
    auto productA2 = factory2->createProductA();
    auto productB2 = factory2->createProductB();
    
    productA1->operationA();
    productB1->operationB();
    
    productA2->operationA();
    productB2->operationB();
    
    return 0;
}

4. 模板工厂模式（使用模板）

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#include <iostream>
#include <memory>

// 基类
class BaseProduct {
public:
    virtual ~BaseProduct() = default;
    virtual void operation() = 0;
};

// 具体产品
class ProductA : public BaseProduct {
public:
    void operation() override {
        std::cout << "ProductA operation" << std::endl;
    }
};

class ProductB : public BaseProduct {
public:
    void operation() override {
        std::cout << "ProductB operation" << std::endl;
    }
};

// 模板工厂类
template<typename T>
class TemplateFactory {
public:
    static std::unique_ptr<T> create() {
        return std::make_unique<T>();
    }
};

// 使用示例
int main_template_factory() {
    auto productA = TemplateFactory<ProductA>::create();
    auto productB = TemplateFactory<ProductB>::create();
    
    productA->operation();
    productB->operation();
    
    return 0;
}

各种工厂模式的特点

  1. 简单工厂模式：

    • 优点：客户端不需要知道具体类的实现细节，只需传入参数即可
    • 缺点：违背开闭原则，新增产品需要修改工厂类

  2. 工厂方法模式：

    • 优点：符合开闭原则，新增产品只需新增对应的工厂类
    • 缺点：类的数量增加，系统更复杂

  3. 抽象工厂模式：

    • 优点：保证产品族的一致性，易于交换产品系列
    • 缺点：不易扩展产品等级结构

  4. 模板工厂模式：

    • 优点：代码简洁，类型安全
    • 缺点：编译时确定类型，灵活性较低