Magic Methods
The function names
__construct,
__destruct,
__call,
__callStatic,
__get,
__set,
__isset,
__unset,
__sleep,
__wakeup,
__toString,
__invoke,
__set_state and
__clone
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.
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.
<literal>__sleep</literal> and <literal>__wakeup</literal>serialize checks if your class has a function with
the magic name __sleep. 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.
If the method doesn't return anything then &null; is serialized and
E_NOTICE is issued.
The intended use of __sleep is to 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.
Conversely, unserialize checks for the
presence of a function with the magic name
__wakeup. If present, this function can
reconstruct any resources that the object may have.
The intended use of __wakeup is to
reestablish any database connections that may have been lost
during serialization and perform other reinitialization
tasks.
Sleep and wakeup
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()
{
return array('server', 'username', 'password', 'db');
}
public function __wakeup()
{
$this->connect();
}
}
?>
]]>
<literal>__toString</literal>
The __toString method allows a class to decide
how it will react when it is converted to a string.
Simple example
foo = $foo;
}
public function __toString() {
return $this->foo;
}
}
$class = new TestClass('Hello');
echo $class;
?>
]]>
&example.outputs;
It is worth noting that before PHP 5.2.0 the __toString
method was only called when it was directly combined with
echo or print.
Since PHP 5.2.0, it is called in any string context (e.g. in
printf with %s modifier) but not
in other types contexts (e.g. with %d modifier).
Since PHP 5.2.0, converting objects without __toString
method to string would cause E_RECOVERABLE_ERROR.
<literal>__invoke</literal>
The __invoke method is called when a script tries to
call an object as a function.
This feature is available since PHP 5.3.0.
Using <literal>__invoke</literal>
]]>
&example.outputs;
<literal>__set_state</literal>
This static method is called
for classes exported by var_export since PHP 5.1.0.
The only parameter of this method is an array containing exported
properties in the form array('property' => value, ...).
Using <literal>__set_state</literal> (since PHP 5.1.0)
var1 = $an_array['var1'];
$obj->var2 = $an_array['var2'];
return $obj;
}
}
$a = new A;
$a->var1 = 5;
$a->var2 = 'foo';
eval('$b = ' . var_export($a, true) . ';'); // $b = A::__set_state(array(
// 'var1' => 5,
// 'var2' => 'foo',
// ));
var_dump($b);
?>
]]>
&example.outputs;
int(5)
["var2"]=>
string(3) "foo"
}
]]>