CODEWITHSUNDEEP
phpoopthis
openfrog
openfrog

Reputation: 40735

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

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

Example:

I've seen this code recently. 

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?

Upvotes: 22

Views: 25300

Answers (7)

Yacoby
Yacoby

Reputation: 55445

$this refers to the current object, self refers to the current class. The class is the blueprint of the object. So you define a class, but you construct objects.

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

Upvotes: 19

Ahmed Magdy
Ahmed Magdy

Reputation: 101

  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

Upvotes: 4

Tor Valamo
Tor Valamo

Reputation: 33749

$this refers 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.

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

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

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

Upvotes: 20

Nimatullah Razmjo
Nimatullah Razmjo

Reputation: 1961

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

Upvotes: 2

Pascal MARTIN
Pascal MARTIN

Reputation: 400952

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

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


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

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 ->.


And, from the page Properties (quoting) :

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

Upvotes: 2

Matchu
Matchu

Reputation: 85794

self refers to the calling object's class. $this refers to the object itself.

Upvotes: 2

jldupont
jldupont

Reputation: 96716

self is used at the class-level scope whereas $this is used at the instance-level scope.

Upvotes: 4

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