需要私有化单例类中的赋值运算符 [英] Need of privatizing assignment operator in a Singleton class

问题描述

有人可以证明在单例类实现中私有化赋值运算符的必要性吗?

Can someone justify the need of privatizing the assignment operator in a Singleton class implementation?

制作Singleton&它解决了什么问题operator=(Singleton const&); private?

What problem does it solve by making Singleton& operator=(Singleton const&); private?

class Singleton {
public:
  static Singleton& Instance() {
    static Singleton theSingleton;
    return theSingleton;
  }

private:
  Singleton(); // ctor hidden
  Singleton(Singleton const&); // copy ctor hidden
  Singleton& operator=(Singleton const&); // assign op. hidden
  ~Singleton(); // dtor hidden
};

推荐答案

在单例上赋值只是一种无意义的操作，因为它应该只存在一个对象.

Assignment on a singleton is simply a nonsense operation since only one object of it should ever exist.

将赋值运算符设为私有有助于诊断如下无意义代码:

Making the assignment operator private helps diagnose nonsense code such as the following:

Singleton& a = Singleton::Instance();
Singleton& b = Singleton::Instance();
a = b; // Oops, accidental assignment.

这篇关于需要私有化单例类中的赋值运算符的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！