Description of magic methods in php

* Magic method:

* 1. Methods in the class that start with double underscores are built-in by the system. User methods should not start with double underscores;

* 2. Magic The method is automatically triggered by the system under certain conditions and cannot be called directly by the user;

* Note: It is a good habit to add a single underscore in front of the private members in the class;

* For example: private $_salary; private function _listUsers(){...}

* Use magic methods to implement several object access interceptors

* The so-called interceptor: it is some errors or illegal access to users Perform detection and control.

* We have learned __get($fieldName) and __set() before, which are the two most commonly used interceptors

* Now we will learn another set: __isset($fieldName) and __unset($fieldName)

* 1. __isset(): It will be automatically called when checking whether a class attribute exists outside the class

* 2. __unset(): When checking whether a class attribute exists outside the class When a class attribute is destroyed externally, it will be automatically called.

class Demo 
{
    private $name = 'peter';
    private $email = 'peter@php.cn';
    
    //当在类外使用isset()检测某个属性是否存在时自动调用
    public function __isset($name)
    {
        //对访问进行过滤:如果属性名是'name',返回false,否则允许访问
        //即除了'name'属性外的其它属性允许外部进行isset()检测
        return ($name=='name') ? false : true;
    }
}
//实例化 Demo 类
$obj = new Demo;
//检测$obj中是否有name属性,返回 
echo isset($obj->name)?'存在':'不存在';
echo &#39;<hr>&#39;;

Detects whether the email attribute exists in $obj and returns that it exists because __isset() in the class returns true

echo isset($obj->email)?'存在':'不存在';

Use unset() externally To destroy class attributes

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