068-单例模式

单例模式是一种设计模式，确保一个类只有一个实例，并提供一个全局访问点。

懒汉模式(Meyers’ Singleton)

class Singleton{
public:
    static Singleton& getInstance(){
        static Singleton obj;  // 静态局部变量
        return obj;
    }
    Singleton(const Singleton&) = delete; // 显示拒绝拷贝构造和复制构造
    Singleton& operator=(const Singleton&) = delete;
private:
    Singleton() = default;
    ~Singleton() = default;
};

通用化

template<typename T>
class Singleton
{
public:
    static T& getInstance() {
        static T t;
        return t;
    }
    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;
private:
    Singleton() = default;
    ~Singleton() = default;
};

饿汉模式

class Singleton
{
public:
    static Singleton& getInstance()
    {
        return instance;
    }
    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;
private:
    Singleton() = default;
    ~Singleton() = default;
private:
    static Singleton instance;
};
Singleton Singleton::instance;