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</div><hr /><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 (<em>==</em>),
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 (<em>===</em>),
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.
<div class="example" id="example-226">
<p><strong>Example #1 Example of object comparison in PHP 5</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$bool</span><span style="color: #007700">)<br />{<br /> if (</span><span style="color: #0000BB">$bool </span><span style="color: #007700">=== </span><span style="color: #0000BB">false</span><span style="color: #007700">) {<br /> return </span><span style="color: #DD0000">'FALSE'</span><span style="color: #007700">;<br /> } else {<br /> return </span><span style="color: #DD0000">'TRUE'</span><span style="color: #007700">;<br /> }<br />}<br /><br />function </span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(&</span><span style="color: #0000BB">$o1</span><span style="color: #007700">, &</span><span style="color: #0000BB">$o2</span><span style="color: #007700">)<br />{<br /> echo </span><span style="color: #DD0000">'o1 == o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">== </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> echo </span><span style="color: #DD0000">'o1 != o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">!= </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> echo </span><span style="color: #DD0000">'o1 === o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">=== </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> echo </span><span style="color: #DD0000">'o1 !== o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">!== </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />}<br /><br />class </span><span style="color: #0000BB">Flag<br /></span><span style="color: #007700">{<br /> public </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /><br /> function </span><span style="color: #0000BB">Flag</span><span style="color: #007700">(</span><span style="color: #0000BB">$flag </span><span style="color: #007700">= </span><span style="color: #0000BB">true</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">flag </span><span style="color: #007700">= </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /> }<br />}<br /><br />class </span><span style="color: #0000BB">OtherFlag<br /></span><span style="color: #007700">{<br /> public </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /><br /> function </span><span style="color: #0000BB">OtherFlag</span><span style="color: #007700">(</span><span style="color: #0000BB">$flag </span><span style="color: #007700">= </span><span style="color: #0000BB">true</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">flag </span><span style="color: #007700">= </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$o </span><span style="color: #007700">= new </span><span style="color: #0000BB">Flag</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$p </span><span style="color: #007700">= new </span><span style="color: #0000BB">Flag</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$q </span><span style="color: #007700">= </span><span style="color: #0000BB">$o</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$r </span><span style="color: #007700">= new </span><span style="color: #0000BB">OtherFlag</span><span style="color: #007700">();<br /><br />echo </span><span style="color: #DD0000">"Two instances of the same class\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">, </span><span style="color: #0000BB">$p</span><span style="color: #007700">);<br /><br />echo </span><span style="color: #DD0000">"\nTwo references to the same instance\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">, </span><span style="color: #0000BB">$q</span><span style="color: #007700">);<br /><br />echo </span><span style="color: #DD0000">"\nInstances of two different classes\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">, </span><span style="color: #0000BB">$r</span><span style="color: #007700">);<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 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>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Extensions can define own rules for their objects comparison
(<em>==</em>).
</p>
</p></blockquote>
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