The impact of C++ language features on the application of design patterns

The impact of features such as polymorphism, template programming and smart pointers in the C language on the application of design patterns include: Polymorphism: allowing different types of objects in design patterns such as strategy pattern and abstract factory pattern to respond differently to the same call. . Template programming: used to create a common event bus that handles different types of events (Observer pattern) and define an operation framework (Template Method pattern). Smart pointers: used to manage dynamically allocated memory in factory method mode and singleton mode.

The impact of C language features on the application of design patterns

C is a powerful object-oriented programming language with its unique There is an inseparable relationship between language features and the application of design patterns. This article will explore how the characteristics of the C language affect the application of design patterns and illustrate it through practical cases.

Polymorphism

Polymorphism is a crucial feature in object-oriented programming. It allows objects to respond differently to the same call based on their class inheritance hierarchy. In design patterns, polymorphism is widely used in:

• Strategy pattern: Allows the client to select and switch between different strategies without modifying the client code.
• Abstract Factory Pattern: Allows clients to create objects of different product families without specifying their concrete classes.

Example: Consider a program that provides functionality for converting different file formats. We can use the strategy pattern to design a Converter class, which provides several strategies, each strategy is responsible for the conversion of a file format. This way the client can dynamically select the desired strategy and convert it via the Converter class.

Code Example:

class Converter {
public:
    virtual void convert(const std::string& filename) = 0;
};

class TxtConverter : public Converter {
public:
    void convert(const std::string& filename) override {
        // 转换 txt 文件
    }
};

class PdfConverter : public Converter {
public:
    void convert(const std::string& filename) override {
        // 转换 pdf 文件
    }
};

// ...

int main() {
    Converter* converter = new TxtConverter();
    converter->convert("file.txt");

    converter = new PdfConverter();
    converter->convert("file.pdf");

    delete converter;
}

Template Programming

Template programming in C allows writing functions and classes with generic type parameters . It is mainly used in design patterns:

• Observer pattern: Allows the subject to maintain a list of observers to notify observers when the subject status changes.
• Template method pattern: Defines a framework of operations, allowing subclasses to override certain steps.

Example: Consider an event bus system that allows components to subscribe to and publish events. We can use template programming to create a general event bus class that can handle the subscription and publishing of different types of events.

Code example:

template <typename T>
class EventBus {
public:
    void subscribe(T subscriber) {
        subscribers.push_back(subscriber);
    }

    void publish(T event) {
        for (auto& subscriber : subscribers) {
            subscriber(event);
        }
    }

private:
    std::vector<T> subscribers;
};

// ...

int main() {
    EventBus<std::string> stringEventBus;
    auto subscriber1 = [](const std::string& event) { std::cout << "Received: " << event << '\n'; };
    auto subscriber2 = [](const std::string& event) { std::cout << "Received: " << event << ", again!\n"; };
    
    stringEventBus.subscribe(subscriber1);
    stringEventBus.subscribe(subscriber2);
    stringEventBus.publish("Hello, world!");

    return 0;
}

Smart pointers

Smart pointers are useful tools in C for managing dynamic memory allocation. They are used in design patterns:

• Factory Method Pattern: Allows the creation of multiple implementations of a product without specifying their concrete classes.
• Singleton pattern: Ensures that a unique instance of an object class is created.

Example: Consider an implementation of the Singleton pattern that ensures that only one Settings object is created and accessed.

Code example:

class Settings {
public:
    static std::shared_ptr<Settings> getInstance() {
        if (!instance) {
            instance = std::make_shared<Settings>();
        }
        return instance;
    }

private:
    Settings() = default;
    static std::shared_ptr<Settings> instance;
};

// ...

int main() {
    auto settings1 = Settings::getInstance();
    auto settings2 = Settings::getInstance();
    assert(settings1 == settings2);

    return 0;
}

In short, features of the C language, such as polymorphism, template programming, and smart pointers, have had a profound impact on the application of design patterns. . These features allow developers to create flexible, scalable, and maintainable code.

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