Question

In PHP 5, what is the difference between using self and $this?

When is each appropriate?

Answer 1

Short Answer

Use $this to refer to the current object. Use self to refer to the current class. In other words, use $this->member for non-static members, use self::$member for static members.

Full Answer

Here is an example of correct usage of $this and self for non-static and static member variables:

<?php class X {     private $non_static_member = 1;     private static $static_member = 2;      function __construct() {         echo $this->non_static_member . ' '            . self::$static_member;     } }  new X(); ?> 

Here is an example of incorrect usage of $this and self for non-static and static member variables:

<?php class X {     private $non_static_member = 1;     private static $static_member = 2;      function __construct() {         echo self::$non_static_member . ' '            . $this->static_member;     } }  new X(); ?> 

Here is an example of polymorphism with $this for member functions:

<?php class X {     function foo() {         echo 'X::foo()';     }      function bar() {         $this->foo();     } }  class Y extends X {     function foo() {         echo 'Y::foo()';     } }  $x = new Y(); $x->bar(); ?> 

Here is an example of suppressing polymorphic behaviour by using self for member functions:

<?php class X {     function foo() {         echo 'X::foo()';     }      function bar() {         self::foo();     } }  class Y extends X {     function foo() {         echo 'Y::foo()';     } }  $x = new Y(); $x->bar(); ?> 

The idea is that $this->foo() calls the foo() member function of whatever is the exact type of the current object. If the object is of type X, it thus calls X::foo(). If the object is of type Y, it calls Y::foo(). But with self::foo(), X::foo() is always called.

From http://www.phpbuilder.com/board/showthread.php?t=10354489:

By http://board.phpbuilder.com/member.php?145249-laserlight