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</div><hr /><div id="oop4.object-comparison" class="sect1">
   <h2 class="title">Comparing objects</h2>
  <p class="para">
   In PHP 4, objects are compared in a very simple manner, namely: Two object
   instances are equal if they have the same attributes and values, and are
   instances of the same class. Similar rules are applied when comparing two
   objects using the identity operator (<em>===</em>).
  </p>
  <p class="para">
   If we were to execute the code in the example below:
   <div class="example" id="example-5623">
    <p><strong>Example #1 Example of object comparison in PHP 4</strong></p>
    <div class="example-contents">
<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">$bool</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(</span><span style="color: #0000BB">$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;&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;&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">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">'o1&nbsp;==&nbsp;o2&nbsp;:&nbsp;'</span><span style="color: #007700">.</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">).</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;'</span><span style="color: #007700">.</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">).</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;'</span><span style="color: #007700">.</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">).</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;'</span><span style="color: #007700">.</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">).</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />}<br /><br />class&nbsp;</span><span style="color: #0000BB">Flag&nbsp;</span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;var&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</span><span style="color: #007700">=</span><span style="color: #0000BB">true</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&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">SwitchableFlag&nbsp;</span><span style="color: #007700">extends&nbsp;</span><span style="color: #0000BB">Flag&nbsp;</span><span style="color: #007700">{<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">turnOn</span><span style="color: #007700">()&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">flag&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">true</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">turnOff</span><span style="color: #007700">()&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$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">false</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">(</span><span style="color: #0000BB">false</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$q&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">Flag</span><span style="color: #007700">();<br /><br /></span><span style="color: #0000BB">$r&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">SwitchableFlag</span><span style="color: #007700">();<br /><br />echo&nbsp;</span><span style="color: #DD0000">"Compare&nbsp;instances&nbsp;created&nbsp;with&nbsp;the&nbsp;same&nbsp;parameters\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">"\nCompare&nbsp;instances&nbsp;created&nbsp;with&nbsp;different&nbsp;parameters\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">"\nCompare&nbsp;an&nbsp;instance&nbsp;of&nbsp;a&nbsp;parent&nbsp;class&nbsp;with&nbsp;one&nbsp;from&nbsp;a&nbsp;subclass\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"><p>The above example will output:</p></div>
    <div class="example-contents screen">
<div class="cdata"><pre>    
Compare instances created with the same parameters
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : TRUE
o1 !== o2 : FALSE

Compare instances created with different parameters
o1 == o2 : FALSE
o1 != o2 : TRUE
o1 === o2 : FALSE
o1 !== o2 : TRUE

Compare an instance of a parent class with one from a subclass
o1 == o2 : FALSE
o1 != o2 : TRUE
o1 === o2 : FALSE
o1 !== o2 : TRUE
</pre></div>
    </div>
   </div>   
   Which is the output we will expect to obtain given the comparison rules
   above. Only instances with the same values for their attributes 
   and from the same class are considered equal and identical.
  </p>
  <p class="para">
   Even in the cases where we have object composition, the same comparison
   rules apply. In the example below we create a container class that stores
   an associative array of <strong class="classname">Flag</strong> objects.
   <div class="example" id="example-5624">
    <p><strong>Example #2 Compound object comparisons in PHP 4</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">class&nbsp;</span><span style="color: #0000BB">FlagSet&nbsp;</span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;var&nbsp;</span><span style="color: #0000BB">$set</span><span style="color: #007700">;<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">FlagSet</span><span style="color: #007700">(</span><span style="color: #0000BB">$flagArr&nbsp;</span><span style="color: #007700">=&nbsp;array())&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">set&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$flagArr</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">addFlag</span><span style="color: #007700">(</span><span style="color: #0000BB">$name</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$flag</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">set</span><span style="color: #007700">[</span><span style="color: #0000BB">$name</span><span style="color: #007700">]&nbsp;=&nbsp;</span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">removeFlag</span><span style="color: #007700">(</span><span style="color: #0000BB">$name</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(</span><span style="color: #0000BB">array_key_exists</span><span style="color: #007700">(</span><span style="color: #0000BB">$name</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">set</span><span style="color: #007700">))&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;unset(</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">set</span><span style="color: #007700">[</span><span style="color: #0000BB">$name</span><span style="color: #007700">]);<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br /><br /></span><span style="color: #0000BB">$u&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">FlagSet</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$u</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">addFlag</span><span style="color: #007700">(</span><span style="color: #DD0000">'flag1'</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$o</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$u</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">addFlag</span><span style="color: #007700">(</span><span style="color: #DD0000">'flag2'</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$p</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$v&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">FlagSet</span><span style="color: #007700">(array(</span><span style="color: #DD0000">'flag1'</span><span style="color: #007700">=&gt;</span><span style="color: #0000BB">$q</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">'flag2'</span><span style="color: #007700">=&gt;</span><span style="color: #0000BB">$p</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">$w&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">FlagSet</span><span style="color: #007700">(array(</span><span style="color: #DD0000">'flag1'</span><span style="color: #007700">=&gt;</span><span style="color: #0000BB">$q</span><span style="color: #007700">));<br /><br />echo&nbsp;</span><span style="color: #DD0000">"\nComposite&nbsp;objects&nbsp;u(o,p)&nbsp;and&nbsp;v(q,p)\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$u</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$v</span><span style="color: #007700">);<br /><br />echo&nbsp;</span><span style="color: #DD0000">"\nu(o,p)&nbsp;and&nbsp;w(q)\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$u</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$w</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</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>
Composite objects u(o,p) and v(q,p)
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : TRUE
o1 !== o2 : FALSE

u(o,p) and w(q)
o1 == o2 : FALSE
o1 != o2 : TRUE
o1 === o2 : FALSE
o1 !== o2 : TRUE
</pre></div>
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