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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Scope Resolution Operator (::)</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.oop5.visibility.html">Visibility</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.static.html">Static Keyword</a></div> <div class="up"><a href="language.oop5.html">Classes and Objects (PHP 5)</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><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.html" class="link">static</a>, <a href="language.oop5.constants.html" class="link">constant</a>, and overridden members 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"><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 members 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"><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.html" class="link">Constructors and Destructors</a>, <a href="language.oop5.overloading.html" class="link">Overloading</a>, and <a href="language.oop5.magic.html" 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"><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> </div> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.oop5.visibility.html">Visibility</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.static.html">Static Keyword</a></div> <div class="up"><a href="language.oop5.html">Classes and Objects (PHP 5)</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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