php-doc-en/language/oop5/paamayim-nekudotayim.xml

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 <sect1 id="language.oop5.paamayim-nekudotayim">
  <title>::</title>

  <para>
   The Paamayim Nekudotayim, or in simpler terms, the double colon.
   This token provides a way to access <link
   linkend="language.oop5.static">static</link>, <link
   linkend="language.oop5.constants">constant</link> or overridden members
   or methods of a class. 
  </para>

  <para>
   When referencing these items from outside the class definition, you use
   name of the class.
  </para>

  <para>
   Paamayim Nekudotayim would, at first, seem a strange choice for a
   double-colon. However, at the time of writing of Zend Engine 0.5
   (which powered PHP3), that is what Andi and Zeev decided to call it.
   It actually does mean double-colon - in Hebrew! As PHP has progressed
   with its development it has just never changed.
  </para>

  <example>
   <title>:: from outside class definition</title>
   <programlisting role="php">
<![CDATA[
<?php
class MyClass {
  const CONST_VALUE = 'A constant value';
}
echo MyClass::CONST_VALUE;
?>
]]>
   </programlisting>
  </example>

  <para>
   Two special keywords <varname>self</varname> and <varname>parent</varname>
   are used to access members or methods from inside the class definition.
  </para>

  <example>
   <title>:: from inside the class definition</title>
   <programlisting role="php">
<![CDATA[
<?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();
?>
]]>
   </programlisting>
  </example>

  <para>
   When an extending class overrides the parents definition of a method,
   php will not call the parent's method.  It is up to the extending class
   to call the parent method or not, this also applies to <link
   linkend="language.oop5.decon">Constructors and Destructors</link>, <link
   linkend="language.oop5.overloading">Overloading</link> and <link
   linkend="language.oop5.magic">Magic</link> method defintions as well.
  </para>

  <example>
   <title>Calling a parent's method</title>
   <programlisting role="php">
<![CDATA[
<?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();
?>
]]>
   </programlisting>
  </example>

 </sect1>
 
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