What are the applications of combining C++ templates with design patterns?

The combination of templates and design patterns creates powerful code: Templates create reusable code while maintaining type safety. The factory pattern separates object creation through interfaces, and templates create universal factories. The Builder pattern handles complex objects through step-by-step construction, and templates create universal builders. The publish-subscribe pattern uses events to achieve loose coupling and templates to create generic publishers and subscribers. A practical case demonstrates the factory mode's application of dynamically creating user types in the user account management system.

The powerful combination of C++ templates and design patterns

Introduction

C++ templates are a powerful tool. It allows developers to create reusable code while retaining type safety. Design patterns provide common solutions for creating flexible and extensible code. When used together, templates and design patterns can produce impressive results.

Template and Factory Pattern

The factory pattern separates object creation from the actual construction of the object by creating an interface. By using templates, we can create generic factories that generate objects:

template<typename T>
class Factory {
public:
    T* create() {
        // 实际对象的创建逻辑
        return new T;
    }
};

Templates and Builder Pattern

The Builder pattern allows for the gradual construction of complex objects, where each stage Handled by different builders. We can write a generic builder using templates:

template<typename T>
class Builder {
public:
    Builder() {}
    T* build() {
        // 复杂的构建逻辑
        return new T;
    }

    void step1() {
        // 构建步骤 1
    }
    void step2() {
        // 构建步骤 2
    }
};

Templates and publish-subscribe pattern

The publish-subscribe pattern allows loosely coupled components to communicate through events. We can use templates to create generic implementations of publishers and subscribers:

template<typename T>
class Publisher {
public:
    void subscribe(T* subscriber) {
        subscribers.push_back(subscriber);
    }
    void publish(const std::string& message) {
        for (auto subscriber : subscribers) {
            subscriber->notify(message);
        }
    }
private:
    std::vector<T*> subscribers;
};

template<typename T>
class Subscriber {
public:
    void notify(const std::string& message) {
        // 处理消息
    }
};

Practical case: Managing user accounts using factory pattern

Suppose we have a user account management system , we need to create different user types, such as:

class User {
    // 用户基类
};

class AdminUser : public User {
    // 管理员用户
};

class StandardUser : public User {
    // 标准用户
};

We can use the factory pattern to dynamically create specific user types:

class UserFactory {
public:
    static User* createUser(const std::string& type) {
        if (type == "Admin") {
            return new AdminUser;
        } else if (type == "Standard") {
            return new StandardUser;
        } else {
            throw std::invalid_argument("Invalid user type");
        }
    }
};

Conclusion

C++ Templates combined with design patterns provide a powerful way to create flexible, scalable, and efficient code. By using templates to create a common infrastructure, we can focus on the implementation of specific business logic, simplifying development and improving code quality.

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