Copying and cloning objects in php

* Copying and cloning of objects

* 1. By default, objects are passed by reference (actually a copy of the object identifier, which will be discussed in detail later)

* 2. In other words, the two object variables actually refer to the same object

* 3. If you want to create a new object, you must use the clone keyword to clone the current object

* 4 .When using the clone keyword, if there is __clone() in the class, it will be automatically called

* 5. The __clone() method runs on the newly created object

* 6.__clone( ) method can control what we copy and the basic operations to be completed when cloning

class Member
{
    //声明三个私有属性
    private $name;  //会员名
    private $email; //会员邮箱
    private $score; //会员积分
    
    //构造方法
    public function __construct($name='',$email='',$score=0)
    {
        $this->name = $name;
        $this->email = $email;
        $this->score = $score;
    }
    
    //查询器(暂时省略访问控制)
    public function __get($name)
    {
        return $this->$name;
    }
    
    //设置器(暂时省略访问控制)
    public function __set($name,$value)
    {
        $this->$name = $value;
    }
    
    //克隆魔术方法在对象克隆时自动调用,针对新对象进行初始化操作
    public function __clone()
    {
        $this->score = 0;
    }
    
}

//Instantiate the member class Member and create the member object $member

$member = new Member('peter','peter@php.cn',1000);

//Access test

echo $member->score;

//Copy the member object

$member1 = $member;

//Use the new variable name $member1 to update the object information

$member1->score = 2000;

//Use the new object variable name $member1 to access

echo $member1->score;
echo &#39;<hr>&#39;;

//Use the original object name $member to access

echo $member->score;

* Conclusion:

* 1. The result of the new variable modification is reflected in the original object variable

* 2 .Explain that these two variables actually point to the same object

* 3. That is, the object is passed by reference by default

* 4. In other words, the second variable name $member1 It is just an alias of the original variable, and no new object is created

* 5. It can be understood that it is just a new name for the identifier of the original object

var_dump($member1);  //对象id=1
var_dump($member);   //对象id=1

//Explanation$ member1 and $member are two identical objects, just with different names

//What should you do if you want to completely create a brand new object? You need to use the keyword: clone

$member2 = clone $member;

//Let’s first check the score attribute value of the object variable $member2

echo $member2->score; //目前是原始值2000

//Modify the score value

$member2->score = 5000;
echo &#39;<hr>&#39;;

//Check the score in $member2 again

echo $member2->score; //新值5000
echo &#39;<hr>&#39;;

//Think about it, will my modification affect the score attribute value of the original $member variable?

echo $member->score; //发现原对象的score属性值仍为2000,未发生变化

//Why is this? Because we used cloning technology to create Two completely different object variables

//Verification below

var_dump($member); //变量id是1
var_dump($member2); //变量id是2

//The IDs of these two object variables are different, indicating that they are two completely different objects

//The following is a task to complete: When creating a new member object, clear the member's points to zero? What should be done?

//Create a __clone() clone in the Member class Magic method, preprocess the cloned new object

//Demonstrate it again

//View the current points

echo $member->score;

//Clone to create a brand new object $member3

$member3 = clone $member;

//Check the score value of the new object $member3 to verify whether __clone() in the class is effective?

echo &#39;<hr>&#39;;
echo $member3->score; //0,说明克隆魔术方法已经生效

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