php-doc-en/functions/overload.xml

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 <reference id="ref.overload">
  <title>Object property and method call overloading</title>
  <titleabbrev>Object overloading</titleabbrev>

  <partintro id="overload.partintro">
   &warn.experimental;
   <para>
    The purpose of this extension is to allow overloading of object
    property access and method calls. Only one function is defined
    in this extension, <function>overload</function> which
    takes the name of the class that should have this functionality
    enabled. The class named has to define appropriate methods if
    it wants to have this functionality: <literal>__get()</literal>,
    <literal>__set()</literal> and <literal>__call()</literal>
    respectively for getting/setting a property, or calling a method.
    This way overloading can be selective. Inside these handler
    functions the overloading is disabled so you can access object
    properties normally.
   </para>
   <para>
    Some simple examples on using the <function>overload</function>
    function:
    <example>
     <title>Overloading a PHP class</title>
     <programlisting role="php">
<![CDATA[
<?php

class OO
{
    var $a = 111;
    var $elem = array('b' => 9, 'c' => 42);

    // Callback method for getting a property
    function __get($prop_name, &$prop_value)
    {
        if (isset($this->elem[$prop_name])) {
            $prop_value = $this->elem[$prop_name];
            return true;
        } else {
            return false;
        }
    }

    // Callback method for setting a property
    function __set($prop_name, $prop_value)
    {
        $this->elem[$prop_name] = $prop_value;
        return true;
    }
}

// Here we overload the OO object
overload('OO');

$o = new OO;
print "\$o->a: $o->a\n"; // print: $o->a:
print "\$o->b: $o->b\n"; // print: $o->b: 9
print "\$o->c: $o->c\n"; // print: $o->c: 42
print "\$o->d: $o->d\n"; // print: $o->d:

// add a new item to the $elem array in OO
$o->x = 56; 

// instantiate stdclass (it is built-in in PHP 4)
// $val is not overloaded!
$val = new stdclass;
$val->prop = 555;

// Set "a" to be an array with the $val object in it
// But __set() will put this in the $elem array
$o->a = array($val);
var_dump($o->a[0]->prop);

?>
]]>
     </programlisting>
    </example>
   </para>
   <warning>
    <para>
     As this is an experimental extension, not all things
     work. There is no <literal>__call()</literal> support
     currently, you can only overload the get and set
     operations for properties. You cannot invoke the
     original overloading handlers of the class, and
     <literal>__set()</literal> only works to one level
     of property access.
    </para>
   </warning>
  </partintro>

  <refentry id="function.overload">
   <refnamediv>
    <refname>overload</refname>
    <refpurpose>Enable property and method call overloading for a class</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>void</type><methodname>overload</methodname>
      <methodparam choice="opt"><type>string</type><parameter>class_name</parameter></methodparam>
     </methodsynopsis>
    <para>
     The <function>overload</function> function will enable
     property and method call overloading for a class identified
     by <parameter>class_name</parameter>.
     <link linkend="overload.partintro">See an example
     in the introductory section of this part</link>.
    </para>
   </refsect1>
  </refentry>
 </reference>

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