PHP 类或 PHP 方法中的 self 和 $this-> 之间的区别在哪里？

Where's the difference between self and $this-> in a PHP class or PHP method?

提问by openfrog

Where's the difference between selfand $this->in a PHP class or PHP method?

PHP 类或 PHP 方法之间self和$this->中的区别在哪里？

Example:

例子：

I've seen this code recently.

我最近看到了这段代码。

public static function getInstance() {

    if (!self::$instance) {
        self::$instance = new PDO("mysql:host='localhost';dbname='animals'", 'username', 'password');;
        self::$instance-> setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }
    return self::$instance;
}

But I remember that $this->refers to the current instance (object) of a class (might also be wrong). However, what's the difference?

但是我记得那个$this->是指一个类的当前实例（对象）（也可能是错误的）。然而，有什么区别呢？

回答by Tor Valamo

$thisrefers to the instance of the class, that is correct. However, there is also something called static state, which is the same for all instances of that class. self::is the accessor for those attributes and functions.

$this指的是类的实例，这是正确的。然而，还有一种叫做静态的东西，对于那个类的所有实例都是一样的。self::是这些属性和函数的访问器。

Also, you cannot normally access an instance member from a static method. Meaning, you cannot do

此外，您通常无法从静态方法访问实例成员。意思是，你不能做

static function something($x) {
  $this->that = $x;
}

because the static method would not know which instance you are referring to.

因为静态方法不知道您指的是哪个实例。

回答by Yacoby

$thisrefers to the current object, selfrefers to the current class. The class is the blueprint of the object. So you define a class, but you construct objects.

$this指当前对象，self指当前类。类是对象的蓝图。所以你定义了一个类，但你构造了对象。

So in other words, use self for static and this for non-static members or methods.

因此，换句话说，将 self 用于静态，将 this 用于非静态成员或方法。

回答by Ahmed Magdy

1. this-> can't access static method or static attribute , we use self to access them.

2. $this-> when dealing with extended class will refer to the current scope that u extended , self will always refer to the parent class because its doesn't need instance to access class method or attr its access the class directly.

   <?php
   class FirstClass{
     function selfTest(){
       $this->classCheck();
       self::classCheck();
     } 
     function classCheck(){
       echo "First Class";
     }
   }
   class SecondClass extends FirstClass{
       function classCheck(){
         echo "Second Class";
       }
   }
   $var = new SecondClass();
   $var->selfTest(); //this-> will refer to Second Class , where self refer to the parent class
   

1. this-> 不能访问静态方法或静态属性，我们使用 self 来访问它们。

2. $this-> 在处理扩展类时将引用您扩展的当前范围，self 将始终引用父类，因为它不需要实例来访问类方法或直接访问类。

   <?php
   class FirstClass{
     function selfTest(){
       $this->classCheck();
       self::classCheck();
     } 
     function classCheck(){
       echo "First Class";
     }
   }
   class SecondClass extends FirstClass{
       function classCheck(){
         echo "Second Class";
       }
   }
   $var = new SecondClass();
   $var->selfTest(); //this-> will refer to Second Class , where self refer to the parent class
   

回答by jldupont

selfis used at the class-level scope whereas $thisis used at the instance-level scope.

self在类级别范围内$this使用，而在实例级别范围内使用。

回答by Pascal MARTIN

$thisis used to reference methods and properties of the current instance of a class.

$this用于引用类的当前实例的方法和属性。

selfus used to reference static methods and properties, shared by all instances (and even accessible outside of any instance)of a class.

self我们过去常常引用静态方法和属性，由类的所有实例（甚至可以在任何实例之外访问）共享。

You can take a look at Static Keyword(quoting a few lines):

你可以看看静态关键字（引用几行）：

Declaring class properties or methods as static makes them accessible without needing an instantiation of the class. A property declared as static can not be accessed with an instantiated class object (though a static method can)

...

Static properties cannot be accessed through the object using the arrow operator ->.

将类属性或方法声明为静态使它们无需实例化即可访问。声明为静态的属性不能被实例化的类对象访问（尽管静态方法可以）

...

无法使用箭头运算符 -> 通过对象访问静态属性。

And, from the page Properties(quoting):

并且，从页面属性（引用）：

Within class methods the properties, constants, and methods may be accessed by using the form $this->property(where propertyis the name of the property)unless the access is to a static property within the context of a static class method, in which case it is accessed using the form self::$property.

在类方法中，可以使用表单$this->property（其中property是属性的名称）访问属性、常量和方法，除非访问是在静态类方法的上下文中访问静态属性，在这种情况下，可以使用形式 self::$property。

回答by Nimatullah Razmjo

$thisis use to call the instance of class, where self::is mostly used to call the constant variable within class.

$this用于调用类的实例，其中self::主要用于调用类内的常量变量。

回答by Matchu

selfrefers to the calling object's class. $thisrefers to the object itself.

self指的是调用对象的类。$this指对象本身。