The rule of three/five/zero

一、首先要知道rule of three、five、zero分别是什么含义，指代的什么，然后考虑如何来高效的实现它们。

二、另外需要注意的是，首先需要指定Copyable and movable，然后进行实现，不能够死板的套用"Rule of three/five/zero"

What is rule of three/five/zero？

一、Rule of three

cppreference The rule of three/five/zero # Rule of three

If a class requires a user-defined destructor, a user-defined copy constructor, or a user-defined copy assignment operator, it almost certainly requires all three.

支持copyable

二、Rule of five

cppreference The rule of three/five/zero # Rule of five

Because the presence of a user-defined destructor, copy-constructor, or copy-assignment operator prevents implicit definition of the move constructor and the move assignment operator, any class for which move semantics are desirable, has to declare all five special member functions

支持copyable and movable

三、rule of zero

feabhas The Rule of Zero

“The Rule of Zero” basically states:

You should NEVER implement a destructor, copy constructor, move constructor or assignment operators in your code.

With the (very important) corollary to this:

You should NEVER use a raw pointer to manage a resource.

需要注意的是，是"NEVER implement a destructor, copy constructor, move constructor or assignment operators"，constructor还是要实现的。

从 "automatic/manual resource management" 的角度来分析rule of three/five/zero

参见 florianwolters The Rule of Zero ，其中对此进行了非常深入的分析。

How to implementation

1、C++11 move constructor=default constructor+swap

2、assignment operator=[copy move] constructor+swap

3、Rule of Four (and a half)

stackoverflow Rule of Four (and a half)?

I've also seen references to the Rule of Four (and a half), which is a combination of the Rule of Five and the copy-and-swap idiom.

Copy and swap idiom

参见 Copy-and-swap-idiom 章节。

TODO

stackoverflow Rule-of-Three becomes Rule-of-Five with C++11?