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Source of: /manual/en/language.oop5.object-comparison.php

<?php
include_once $_SERVER['DOCUMENT_ROOT'] . '/include/shared-manual.inc';
$TOC = array();
$PARENTS = array();
include_once dirname(__FILE__) ."/toc/language.oop5.inc";
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    1 => 'en',
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  'this' =>
  array (
    0 => 'language.oop5.object-comparison.php',
    1 => 'Comparing Objects',
  ),
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    1 => 'Classes and Objects',
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?>
<div id="language.oop5.object-comparison" class="sect1">
   <h2 class="title">Comparing Objects</h2>
   <p class="para">
    In PHP 5, object comparison is more complicated than in PHP 4 and more
    in accordance to what one will expect from an Object Oriented Language
    (not that PHP 5 is such a language).
   </p>
   <p class="para">
    When using the comparison operator (<i>==</i>),
    object variables are compared in a simple manner, namely: Two object
    instances are equal if they have the same attributes and values, and are
    instances of the same class.
   </p>
   <p class="para">
    On the other hand, when using the identity operator (<i>===</i>),
    object variables are identical if and only if they refer to the same
    instance of the same class.
   </p>
   <p class="para">
    An example will clarify these rules.
    </p><div class="example">
     <p><b>Example #1 Example of object comparison in PHP 5</b></p>
     <div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">function&nbsp;</span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$bool</span><span style="color: #007700">)<br />{<br />&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(</span><span style="color: #0000BB">$bool&nbsp;</span><span style="color: #007700">===&nbsp;</span><span style="color: #0000BB">false</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;</span><span style="color: #DD0000">'FALSE'</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;else&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;</span><span style="color: #DD0000">'TRUE'</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br />function&nbsp;</span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(&amp;</span><span style="color: #0000BB">$o1</span><span style="color: #007700">,&nbsp;&amp;</span><span style="color: #0000BB">$o2</span><span style="color: #007700">)<br />{<br />&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">'o1&nbsp;==&nbsp;o2&nbsp;:&nbsp;'&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1&nbsp;</span><span style="color: #007700">==&nbsp;</span><span style="color: #0000BB">$o2</span><span style="color: #007700">)&nbsp;.&nbsp;</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">'o1&nbsp;!=&nbsp;o2&nbsp;:&nbsp;'&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1&nbsp;</span><span style="color: #007700">!=&nbsp;</span><span style="color: #0000BB">$o2</span><span style="color: #007700">)&nbsp;.&nbsp;</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">'o1&nbsp;===&nbsp;o2&nbsp;:&nbsp;'&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1&nbsp;</span><span style="color: #007700">===&nbsp;</span><span style="color: #0000BB">$o2</span><span style="color: #007700">)&nbsp;.&nbsp;</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">'o1&nbsp;!==&nbsp;o2&nbsp;:&nbsp;'&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1&nbsp;</span><span style="color: #007700">!==&nbsp;</span><span style="color: #0000BB">$o2</span><span style="color: #007700">)&nbsp;.&nbsp;</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />}<br /><br />class&nbsp;</span><span style="color: #0000BB">Flag<br /></span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;</span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">Flag</span><span style="color: #007700">(</span><span style="color: #0000BB">$flag&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">true</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">flag&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br />class&nbsp;</span><span style="color: #0000BB">OtherFlag<br /></span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;</span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">OtherFlag</span><span style="color: #007700">(</span><span style="color: #0000BB">$flag&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">true</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">flag&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br /></span><span style="color: #0000BB">$o&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">Flag</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$p&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">Flag</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$q&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$o</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$r&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">OtherFlag</span><span style="color: #007700">();<br /><br />echo&nbsp;</span><span style="color: #DD0000">"Two&nbsp;instances&nbsp;of&nbsp;the&nbsp;same&nbsp;class\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$p</span><span style="color: #007700">);<br /><br />echo&nbsp;</span><span style="color: #DD0000">"\nTwo&nbsp;references&nbsp;to&nbsp;the&nbsp;same&nbsp;instance\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$q</span><span style="color: #007700">);<br /><br />echo&nbsp;</span><span style="color: #DD0000">"\nInstances&nbsp;of&nbsp;two&nbsp;different&nbsp;classes\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$r</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
     </div>

     <div class="example-contents para"><p>The above example will output:</p></div>
     <div class="example-contents screen">
<div class="cdata"><pre>
Two instances of the same class
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : FALSE
o1 !== o2 : TRUE

Two references to the same instance
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : TRUE
o1 !== o2 : FALSE

Instances of two different classes
o1 == o2 : FALSE
o1 != o2 : TRUE
o1 === o2 : FALSE
o1 !== o2 : TRUE
</pre></div>
     </div>
    </div><p>
   </p>
   <blockquote><p><b class="note">Note</b>:
   
     Extensions can define own rules for their objects comparison.
    <br />
   </p></blockquote>
  </div><?php manual_footer(); ?>
 
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