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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.13 $ -->
<sect1 id="language.oop5.magic">
<title>Magic Methods</title>
<para>
The function names
<literal>__construct</literal>,
<literal>__destruct</literal>
(see <link linkend="language.oop5.decon">Constructors and Destructors</link>),
<literal>__call</literal>,
<literal>__get</literal>,
<literal>__set</literal>,
<literal>__isset</literal>,
<literal>__unset</literal>
(see <link linkend="language.oop5.overloading">Overloading</link>),
<literal>__sleep</literal>,
<literal>__wakeup</literal>,
<literal>__toString</literal>,
<literal>__set_state</literal>,
<link linkend="language.oop5.cloning">__clone</link> and
<link linkend="language.oop5.autoload">__autoload</link>
are magical in PHP classes. You
cannot have functions with these names in any of your
classes unless you want the magic functionality associated
with them.
</para>
<caution>
<simpara>
PHP reserves all function names starting with __ as magical.
It is recommended that you do not use function names with
__ in PHP unless you want some documented magic functionality.
</simpara>
</caution>
<sect2 id="language.oop5.magic.sleep">
<title><literal>__sleep</literal> and <literal>__wakeup</literal></title>
<para>
<function>serialize</function> checks if your class has a function with
the magic name <literal>__sleep</literal>. If so, that function is
executed prior to any serialization. It can clean up the object
and is supposed to return an array with the names of all variables
of that object that should be serialized.
</para>
<para>
The intended use of <literal>__sleep</literal> is to close any
database connections that the object may have, commit pending
data or perform similar cleanup tasks. Also, the function is
useful if you have very large objects which do not need to be
saved completely.
</para>
<para>
Conversely, <function>unserialize</function> checks for the
presence of a function with the magic name
<literal>__wakeup</literal>. If present, this function can
reconstruct any resources that the object may have.
</para>
<para>
The intended use of <literal>__wakeup</literal> is to
reestablish any database connections that may have been lost
during serialization and perform other reinitialization
tasks.
</para>
<example>
<title>Sleep and wakeup</title>
<programlisting role="php">
<![CDATA[
<?php
class Connection {
protected $link;
private $server, $username, $password, $db;
public function __construct($server, $username, $password, $db)
{
$this->server = $server;
$this->username = $username;
$this->password = $password;
$this->db = $db;
$this->connect();
}
private function connect()
{
$this->link = mysql_connect($this->server, $this->username, $this->password);
mysql_select_db($this->db, $this->link);
}
public function __sleep()
{
mysql_close($this->link);
}
public function __wakeup()
{
$this->connect();
}
}
?>
]]>
</programlisting>
</example>
</sect2>
<sect2 id="language.oop5.magic.tostring">
<title><literal>__toString</literal></title>
<para>
The <literal>__toString</literal> method allows a class to decide
how it will react when it is converted to a string.
</para>
<example>
<title>Simple example</title>
<programlisting role="php">
<![CDATA[
<?php
// Declare a simple class
class TestClass
{
public $foo;
public function __construct($foo) {
$this->foo = $foo;
}
public function __toString() {
return $this->foo;
}
}
$class = new TestClass('Hello');
echo $class;
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
Hello
]]>
</screen>
</example>
<para>
It is worth noting that before PHP 5.2.0 the <literal>__toString</literal>
method was only called when it was directly combined with
<function>echo</function> or <function>print</function>.
</para>
</sect2>
<sect2 id="language.oop5.magic.set-state">
<title><literal>__set_state</literal></title>
<para>
This <link linkend="language.oop5.static">static</link> method is called
for classes exported by <function>var_export</function> since PHP 5.1.0.
</para>
<para>
The only parameter of this method is an array containing exported
properties in the form <literal>array('property' => value, ...)</literal>.
</para>
</sect2>
</sect1>
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