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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>Object cloning</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.final.html">Final Keyword</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.object-comparison.html">Comparing objects</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.cloning" class="sect1"> <h2 class="title">Object cloning</h2> <p class="para"> Creating a copy of an object with fully replicated properties is not always the wanted behavior. A good example of the need for copy constructors, is if you have an object which represents a GTK window and the object holds the resource of this GTK window, when you create a duplicate you might want to create a new window with the same properties and have the new object hold the resource of the new window. Another example is if your object holds a reference to another object which it uses and when you replicate the parent object you want to create a new instance of this other object so that the replica has its own separate copy. </p> <p class="para"> An object copy is created by using the clone keyword (which calls the object's __clone() method if possible). An object's __clone() method cannot be called directly. </p> <div class="informalexample"> <div class="example-contents"><div class="cdata"><pre>$copy_of_object = clone $object;</pre></div> </div> </div> <p class="para"> When an object is cloned, PHP 5 will perform a shallow copy of all of the object's properties. Any properties that are references to other variables, will remain references. If a __clone() method is defined, then the newly created object's __clone() method will be called, to allow any necessary properties that need to be changed. </p> <div class="example"> <p><b>Example #1 Cloning an object</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">SubObject<br /></span><span style="color: #007700">{<br /> static </span><span style="color: #0000BB">$instances </span><span style="color: #007700">= </span><span style="color: #0000BB">0</span><span style="color: #007700">;<br /> public </span><span style="color: #0000BB">$instance</span><span style="color: #007700">;<br /><br /> public function </span><span style="color: #0000BB">__construct</span><span style="color: #007700">() {<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">instance </span><span style="color: #007700">= ++</span><span style="color: #0000BB">self</span><span style="color: #007700">::</span><span style="color: #0000BB">$instances</span><span style="color: #007700">;<br /> }<br /><br /> public function </span><span style="color: #0000BB">__clone</span><span style="color: #007700">() {<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">instance </span><span style="color: #007700">= ++</span><span style="color: #0000BB">self</span><span style="color: #007700">::</span><span style="color: #0000BB">$instances</span><span style="color: #007700">;<br /> }<br />}<br /><br />class </span><span style="color: #0000BB">MyCloneable<br /></span><span style="color: #007700">{<br /> public </span><span style="color: #0000BB">$object1</span><span style="color: #007700">;<br /> public </span><span style="color: #0000BB">$object2</span><span style="color: #007700">;<br /><br /> function </span><span style="color: #0000BB">__clone</span><span style="color: #007700">()<br /> {<br /> </span><span style="color: #FF8000">// Force a copy of this->object, otherwise<br /> // it will point to same object.<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">object1 </span><span style="color: #007700">= clone </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">object1</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$obj </span><span style="color: #007700">= new </span><span style="color: #0000BB">MyCloneable</span><span style="color: #007700">();<br /><br /></span><span style="color: #0000BB">$obj</span><span style="color: #007700">-></span><span style="color: #0000BB">object1 </span><span style="color: #007700">= new </span><span style="color: #0000BB">SubObject</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$obj</span><span style="color: #007700">-></span><span style="color: #0000BB">object2 </span><span style="color: #007700">= new </span><span style="color: #0000BB">SubObject</span><span style="color: #007700">();<br /><br /></span><span style="color: #0000BB">$obj2 </span><span style="color: #007700">= clone </span><span style="color: #0000BB">$obj</span><span style="color: #007700">;<br /><br /><br />print(</span><span style="color: #DD0000">"Original Object:\n"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">$obj</span><span style="color: #007700">);<br /><br />print(</span><span style="color: #DD0000">"Cloned Object:\n"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">$obj2</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">?></span></span></code></div> </div> <div class="example-contents"><p>The above example will output:</p></div> <div class="example-contents"><pre><div class="cdata"><pre>Original Object:MyCloneable Object( [object1] => SubObject Object ( [instance] => 1 ) [object2] => SubObject Object ( [instance] => 2 ))Cloned Object:MyCloneable Object( [object1] => SubObject Object ( [instance] => 3 ) [object2] => SubObject Object ( [instance] => 2 ))</pre></div> </pre></div> </div> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.oop5.final.html">Final Keyword</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.object-comparison.html">Comparing objects</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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