Source of: /manual/en/language.oop5.paamayim-nekudotayim.php
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<div id="language.oop5.paamayim-nekudotayim" class="sect1">
<h2 class="title">Scope Resolution Operator (::)</h2>
<p class="para">
The Scope Resolution Operator (also called Paamayim Nekudotayim) or in
simpler terms, the double colon, is a token that allows access to
<a href="language.oop5.static.php" class="link">static</a>,
<a href="language.oop5.constants.php" class="link">constant</a>, and overridden
properties or methods of a class.
</p>
<p class="para">
When referencing these items from outside the class definition, use
the name of the class.
</p>
<p class="para">
As of PHP 5.3.0, it's possible to reference the class using a variable.
The variable's value can not be a keyword (e.g. <i>self</i>,
<i>parent</i> and <i>static</i>).
</p>
<p class="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!
</p>
<div class="example">
<p><b>Example #1 :: from outside the class definition</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">MyClass </span><span style="color: #007700">{<br /> const </span><span style="color: #0000BB">CONST_VALUE </span><span style="color: #007700">= </span><span style="color: #DD0000">'A constant value'</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">$classname </span><span style="color: #007700">= </span><span style="color: #DD0000">'MyClass'</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">$classname</span><span style="color: #007700">::</span><span style="color: #0000BB">CONST_VALUE</span><span style="color: #007700">; </span><span style="color: #FF8000">// As of PHP 5.3.0<br /><br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">MyClass</span><span style="color: #007700">::</span><span style="color: #0000BB">CONST_VALUE</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
Two special keywords <var class="varname">self</var> and <var class="varname">parent</var>
are used to access properties or methods from inside the class definition.
</p>
<div class="example">
<p><b>Example #2 :: from inside the class definition</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">OtherClass </span><span style="color: #007700">extends </span><span style="color: #0000BB">MyClass<br /></span><span style="color: #007700">{<br /> public static </span><span style="color: #0000BB">$my_static </span><span style="color: #007700">= </span><span style="color: #DD0000">'static var'</span><span style="color: #007700">;<br /><br /> public static function </span><span style="color: #0000BB">doubleColon</span><span style="color: #007700">() {<br /> echo </span><span style="color: #0000BB">parent</span><span style="color: #007700">::</span><span style="color: #0000BB">CONST_VALUE </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> echo </span><span style="color: #0000BB">self</span><span style="color: #007700">::</span><span style="color: #0000BB">$my_static </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$classname </span><span style="color: #007700">= </span><span style="color: #DD0000">'OtherClass'</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">$classname</span><span style="color: #007700">::</span><span style="color: #0000BB">doubleColon</span><span style="color: #007700">(); </span><span style="color: #FF8000">// As of PHP 5.3.0<br /><br /></span><span style="color: #0000BB">OtherClass</span><span style="color: #007700">::</span><span style="color: #0000BB">doubleColon</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
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 <a href="language.oop5.decon.php" class="link">Constructors and Destructors</a>, <a href="language.oop5.overloading.php" class="link">Overloading</a>, and <a href="language.oop5.magic.php" class="link">Magic</a> method definitions.
</p>
<div class="example">
<p><b>Example #3 Calling a parent's method</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">MyClass<br /></span><span style="color: #007700">{<br /> protected function </span><span style="color: #0000BB">myFunc</span><span style="color: #007700">() {<br /> echo </span><span style="color: #DD0000">"MyClass::myFunc()\n"</span><span style="color: #007700">;<br /> }<br />}<br /><br />class </span><span style="color: #0000BB">OtherClass </span><span style="color: #007700">extends </span><span style="color: #0000BB">MyClass<br /></span><span style="color: #007700">{<br /> </span><span style="color: #FF8000">// Override parent's definition<br /> </span><span style="color: #007700">public function </span><span style="color: #0000BB">myFunc</span><span style="color: #007700">()<br /> {<br /> </span><span style="color: #FF8000">// But still call the parent function<br /> </span><span style="color: #0000BB">parent</span><span style="color: #007700">::</span><span style="color: #0000BB">myFunc</span><span style="color: #007700">();<br /> echo </span><span style="color: #DD0000">"OtherClass::myFunc()\n"</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$class </span><span style="color: #007700">= new </span><span style="color: #0000BB">OtherClass</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$class</span><span style="color: #007700">-></span><span style="color: #0000BB">myFunc</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
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