C++ 言語機能がデザイン パターンの適用に及ぼす影響

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 <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;
}

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;
}