The function names
__construct,
__destruct
(see Constructors and Destructors),
__call,
__get,
__set,
__isset,
__unset
(see Overloading),
__sleep,
__wakeup,
__toString,
__set_state,
__clone and
__autoload
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.
| Caution |
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.
|
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.
The intended use of __sleep 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.
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.
Example 19-26. Sleep and wakeup
<?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();
}
}
?>
|
|
The __toString method allows a class to decide
how it will react when it is converted to a string.
Example 19-27. Simple example
<?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;
?>
|
The above example will output: |
It is worth noting that the __toString method
will only be called when it is directly combined with
echo() or print().
Example 19-28. Cases where __toString is called
<?php
// __toString called
echo $class;
// __toString called (still a normal parameter for echo)
echo 'text', $class;
// __toString not called (concatenation operator used first)
echo 'text' . $class;
// __toString not called (cast to string first)
echo (string) $class;
// __toString not called (cast to string first)
echo "text $class";
?>
|
|
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, ...).
