What is the usage of self in php

Usage of self in php:

self points to the class itself, that is, the PHP self keyword does not point to anything that has been instantiated Object, generally self is used to point to static variables in the class.
1. Self can access static properties and static methods in this class, and can access static properties and static methods in the parent class.

Related recommendations: "PHP Getting Started Tutorial"

2. When using self, you don’t need to instantiate it.

< ?php   
class Counter   
{   
//定义属性，包括一个静态变量   
private static $firstCount = 0;   
private $lastCount;   
//构造函数   
function __construct()   
{   
$this->lastCount = selft
::$firstCount;
 //使用PHP self关键字来调用静态变量,使用self
调用必须使用::(域运算符号)   
}   
//打印最次数值   
function printLastCount()   
{   
print( $this->lastCount );   
}    
}   
//实例化对象   
$countObject = new Counter();   
$countObject->printLastCount();
 //输出 1   
?>

We only need to pay attention to two places here, lines 6 and 12.

We defined a static variable $firstCount in the second line, and the initial value is 0. Then we called this value on line 12, using self to call it, and using "::" in the middle. To connect,

is what we call a domain operator, so what we call at this time is the static variable $frestCount defined by the class itself. Our static variable has nothing to do with the instance of the following object, it is only related to the class.

Then if I call the class itself, then we cannot use this to reference, we can use self to reference.

Because self points to the class itself and has nothing to do with any object instance. In other words, if there are static members in our class, we must also use self to call them.

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