<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="splobjectstorage.gethash" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>SplObjectStorage::getHash</refname>
  <refpurpose>
   Calculate a unique identifier for the contained objects
  </refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis role="SplObjectStorage">
   <modifier>public</modifier> <type>string</type><methodname>SplObjectStorage::getHash</methodname>
   <methodparam><type>object</type><parameter>object</parameter></methodparam>
  </methodsynopsis>
  <para>
   This method calculates an identifier for the objects added to an
   <classname>SplObjectStorage</classname> object.
  </para>
  <para>
   The implementation in <classname>SplObjectStorage</classname> returns
   the same value as <function>spl_object_hash</function>.
  </para>
  <para>
   The storage object will never contain more than one object with the same identifier.
   As such, it can be used to implement a set (a collection of unique values)
   where the quality of an object being unique is determined by the value
   returned by this function being unique.
  </para>

 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>object</parameter></term>
    <listitem>
     <para>
      The object whose identifier is to be calculated.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   A <type>string</type> with the calculated identifier.
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   A <classname>RuntimeException</classname> is thrown when the returned
   value is not a <type>string</type>.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>SplObjectStorage::getHash</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
class OneSpecimenPerClassStorage extends SplObjectStorage {
    public function getHash($o) {
        return get_class($o);
    }
}
class A {}

$s = new OneSpecimenPerClassStorage;
$o1 = new stdClass;
$o2 = new stdClass;
$o3 = new A;

$s[$o1] = 1;
//$o2 is considered equal to $o1 so the value is replaced
$s[$o2] = 2;
$s[$o3] = 3;

//these are considered equal to the objects before
//so they can be used to access the values stored under them
$p1 = new stdClass;
$p2 = new A;
echo $s[$p1], "\n";
echo $s[$p2], "\n";
?>
]]>
    </programlisting>
    &example.outputs.similar;
    <screen>
<![CDATA[
2
3
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>spl_object_hash</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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