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

<?xml version="1.0" encoding="utf-8"?>
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<sect1 xml:id="language.oop5.paamayim-nekudotayim" xmlns="http://docbook.org/ns/docbook">
 <title>Scope Resolution Operator (::)</title>

 <para>
  The Scope Resolution Operator (also called Paamayim Nekudotayim) or in
  simpler terms, the double colon, is a token that allows access to
  <link linkend="language.oop5.static">static</link>,
  <link linkend="language.oop5.constants">constant</link>, and overridden
  properties or methods of a class.
 </para>

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

 <para>
  It's possible to reference the class using a variable.
  The variable's value can not be a keyword (e.g. <literal>self</literal>,
  <literal>parent</literal> and <literal>static</literal>).
 </para>

 <para>
  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!
 </para>

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

$classname = 'MyClass';
echo $classname::CONST_VALUE;

echo MyClass::CONST_VALUE;
?>
]]>
  </programlisting>
 </example>

 <para>
  Three special keywords <varname>self</varname>, <varname>parent</varname> and
  <varname>static</varname> are used to access properties 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";
    }
}

$classname = 'OtherClass';
$classname::doubleColon();

OtherClass::doubleColon();
?>
]]>
  </programlisting>
 </example>

 <para>
  When an extending class overrides the parent's 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 <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 definitions.
 </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>
 <para>
  See also <link linkend="language.oop5.basic.class.this">some examples of
  static call trickery</link>.
 </para>

</sect1>
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