Delicious Bookmark this on Delicious Share on Facebook SlashdotSlashdot It! Digg! Digg



PHP : Language Reference : Classes and Objects (PHP 5) : Late Static Bindings

Late Static Bindings

As of PHP 5.3.0, PHP implements a feature called late static bindings which can be used to reference the called class in a context of static inheritance.

This feature was named "late static bindings" with an internal perspective in mind. "Late binding" comes from the fact that static:: will no longer be resolved using the class where the method is defined but it will rather be computed using runtime information. It was also called a "static binding" as it can be used for (but is not limited to) static method calls.

Limitations of self::

Static references to the current class like self:: or __CLASS__ are resolved using the class in which the function belongs, as in where it was defined:

Example 10.42. self:: usage

copy to clipboard
<?php
class A {
   public static function who() {
       echo __CLASS__;
   }
   public static function test() {
       self::who();      
   }  
}  

class B extends A {      
   public static function who() {
        echo __CLASS__;
   }  
}  

B::test();
?>

The above example will output:

copy to clipboard
A


Late Static Bindings' usage

Late static bindings tries to solve that limitation by introducing a keyword that references the class that was initially called at runtime. Basically, a keyword that would allow you to reference B from test() in the previous example. It was decided not to introduce a new keyword but rather use static that was already reserved.

Example 10.43. static:: simple usage

copy to clipboard
<?php
class A {
   public static function who() {
       echo __CLASS__;
   }
   public static function test() {
       static::who(); // Here comes Late Static Bindings    
   }  
}  

class B extends A {      
   public static function who() {
        echo __CLASS__;
   }  
}  

B::test();
?>

The above example will output:

copy to clipboard
B


Note:

static:: does not work like $this for static methods! $this-> follows the rules of inheritance while static:: doesn't. This difference is detailed later on this manual page.

Example 10.44. static:: usage in a non-static context

copy to clipboard
<?php
class TestChild extends TestParent {
   public function __construct() {
       static::who();
   }

   public function test() {
       $o = new TestParent();
   }

   public static function who() {
       echo __CLASS__."\n";
   }
}

class TestParent {
   public function __construct() {
       static::who();
   }

   public static function who() {
       echo __CLASS__."\n";
   }
}
$o = new TestChild;
$o->test();

?>

The above example will output:

copy to clipboard
TestChild
TestParent


Note:

Late static bindings' reslution will stop at a fully resolved static call with no fallback.

Example 10.45. Fully resolved static calls

copy to clipboard
<?php
class A {
   public static function foo() {
       static::who();
   }
       
   public static function who() {
       echo __CLASS__."\n";
   }
}

class B extends A {
   public static function test() {
       A::foo();
   }

   public static function who() {
       echo __CLASS__."\n";
   }
}

B::test();
?>

The above example will output:

copy to clipboard
A


Edge cases

There are lots of different ways to trigger a method call in PHP, like callbacks or magic methods. As late static bindings base their resolution on runtime information, it might give unexpected results in so-called edge cases.

Example 10.46. Late static bindings inside magic methods

copy to clipboard
<?php
class A {

  protected static function who() {
       echo __CLASS__."\n";
  }

  public function __get($var) {
      return static::who();
  }
}

class B extends A {

  protected static function who() {
       echo __CLASS__."\n";
  }
}

$b = new B;
$b->foo;
?>

The above example will output:

copy to clipboard
B

Change Language


Follow Navioo On Twitter
Introduction
The Basics
Autoloading Objects
Constructors and Destructors
Visibility
Scope Resolution Operator (::)
Static Keyword
Class Constants
Class Abstraction
Object Interfaces
Overloading
Object Iteration
Patterns
Magic Methods
Final Keyword
Object cloning
Comparing objects
Reflection
Type Hinting
Late Static Bindings
Terms of Service Privacy Policy Sitemap

©2024 -EPSILONSYS SOFTWARE inc

Other EPSILONSYS SOFTWARE Web Sites : Programming Resources | News Headline | Free local classifieds

eXTReMe Tracker