Scope Resolution Operator (::)

The Scope Resolution Operator (also called Paamayim Nekudotayim) or in simpler terms, the double colon, is a token that allows access to static , constant , and overridden members or methods of a class.

When referencing these items from outside the class definition, use the name of the class.

Paamayim Nekudotayim would, at first, seem like a strange choice for naming a double-colon. However, while writing the Zend Engine 0.5 (which powers PHP 3), that's what the Zend team decided to call it. It actually does mean double-colon - in Hebrew!

例子 19-10. :: from outside the class definition <?php class MyClass {     const CONST_VALUE = 'A constant value' ; } echo MyClass :: CONST_VALUE ; ?>

Two special keywords self and parent are used to access members or methods from inside the class definition.

例子 19-11. :: from inside the class definition <?php class OtherClass extends MyClass {      public static $my_static = 'static var' ;      public static function doubleColon () {         echo parent :: CONST_VALUE . "\n" ;         echo self :: $my_static . "\n" ;     } } OtherClass :: doubleColon (); ?>

When an extending class overrides the parents definition of a method, PHP will not call the parent's method. It's up to the extended class on whether or not the parent's method is called. This also applies to Constructors and Destructors , Overloading , and Magic method definitions.

例子 19-12. Calling a parent's method <?php class MyClass {      protected function myFunc () {         echo "MyClass::myFunc()\n" ;     } } class OtherClass extends MyClass {      // Override parent's definition      public function myFunc ()     {          // But still call the parent function          parent :: myFunc ();         echo "OtherClass::myFunc()\n" ;     } } $class = new OtherClass (); $class -> myFunc (); ?>