单例模式

线程安全的单例模式（C++11）,C++11 标准规定: static local 的变量会保证初始化一次，并且是多线程安全的。由此我们可以得到这样的单例实现。

class Singleton
{
public:
    static Singleton &get_instance()
    {
        static Singleton instance;
        return instance;
    }

private:
    Singleton() = default;
    ~Singleton() = default;
    Singleton(const Singleton &) = delete;
    Singleton(Singleton &&) = delete;
    Singleton &operator=(const Singleton &) = delete;
    Singleton &operator=(Singleton &&) = delete;
};

// 进行初始化的传参
#include <iostream>

class Singleton
{
public:
    static Singleton &get_instance()
    {
        static Singleton instance(param);
        return instance;
    }

    static int param;
    int storage;

private:
    Singleton(int m) : storage(m) {}
    ~Singleton() = default;
    Singleton(const Singleton &) = delete;
    Singleton(Singleton &&) = delete;
    Singleton &operator=(const Singleton &) = delete;
    Singleton &operator=(Singleton &&) = delete;
};


int Singleton::param = 0;


int main(int argc, char **arg)
{
    Singleton::param = 1;
    std::cout << Singleton::get_instance().storage;
    return 0;
}

观察者模式