Magic Methods
The function names
__construct(),
__destruct(),
__call(),
__callStatic(),
__get(),
__set(),
__isset(),
__unset(),
__sleep(),
__wakeup(),
__serialize(),
__unserialize(),
__toString(),
__invoke(),
__set_state(),
__clone() and
__debugInfo()
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.
Note:
All magic methods MUST be declared as public
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.
public __sleep
( void
) : array
public __wakeup
( void
) : void
serialize() checks if the 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.
Note:
It is not possible for __sleep() to return names of
private properties in parent classes. Doing this will result in an
E_NOTICE level error. Instead you may use the
Serializable interface.
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.
Example #1 Sleep and wakeup
<?php
class Connection
{
protected $link;
private $dsn, $username, $password;
public function __construct($dsn, $username, $password)
{
$this->dsn = $dsn;
$this->username = $username;
$this->password = $password;
$this->connect();
}
private function connect()
{
$this->link = new PDO($this->dsn, $this->username, $this->password);
}
public function __sleep()
{
return array('dsn', 'username', 'password');
}
public function __wakeup()
{
$this->connect();
}
}?>
public __serialize
( void
) : array
public __unserialize
( array $data
) : void
serialize() checks if the class has a function with
the magic name __serialize(). If so, that function is
executed prior to any serialization. It must construct and return an associative array of key/value pairs
that represent the serialized form of the object. If no array is returned a TypeError
will be thrown.
Note:
If both __serialize() and __sleep()
are defined in the same object, only __serialize() will be called.
__sleep() will be ignored. If the object implements the Serializable
interface, the interface's serialize() method will be ignored and __serialize()
used instead.
The intended use of __serialize() is to define a serialization-friendly
arbitrary representation of the object. Elements of the array may correspond to properties of the object but
that is not required.
Conversely, unserialize() checks for the
presence of a function with the magic name
__unserialize(). If present, this function will be passed the
restored array that was returned from __serialize(). It may
then restore the properties of the object from that array as appropriate.
Note:
If both __unserialize() and __wakeup()
are defined in the same object, only __unserialize() will be called.
__wakeup() will be ignored.
Note:
This feature is available since PHP 7.4.0.
Example #2 Serialize and unserialize
<?php
class Connection
{
protected $link;
private $dsn, $username, $password;
public function __construct($dsn, $username, $password)
{
$this->dsn = $dsn;
$this->username = $username;
$this->password = $password;
$this->connect();
}
private function connect()
{
$this->link = new PDO($this->dsn, $this->username, $this->password);
}
public function __serialize(): array
{
return [
'dsn' => $this->dsn,
'user' => $this->username,
'pass' => $this->password,
];
}
public function __unserialize(array $data): void
{
$this->dsn = $data['dsn'];
$this->username = $data['user'];
$this->password = $data['pass'];
$this->connect();
}
}?>
public __toString
( void
) : string
The __toString() method allows a class to decide
how it will react when it is treated like a string. For example,
what echo $obj; will print. This method must
return a string, as otherwise a fatal E_RECOVERABLE_ERROR
level error is emitted.
Warning
It was not possible to throw an exception from within a
__toString() method before PHP 7.4.0. Doing so will
result in a fatal error.
Example #3 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 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.
__invoke
([
$...
] ) :
mixed
The __invoke() method is called when a script tries to
call an object as a function.
Note:
This feature is available since PHP 5.3.0.
Example #4 Using __invoke()
<?php
class CallableClass
{
public function __invoke($x)
{
var_dump($x);
}
}
$obj = new CallableClass;
$obj(5);
var_dump(is_callable($obj));
?>
The above example will output:
static __set_state
( array $properties
) : object
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, ...).
Example #5 Using __set_state() (since PHP 5.1.0)
<?php
class A
{
public $var1;
public $var2;
public static function __set_state($an_array) // As of PHP 5.1.0
{
$obj = new A;
$obj->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);
?>
The above example will output:
object(A)#2 (2) {
["var1"]=>
int(5)
["var2"]=>
string(3) "foo"
}
Note:
When exporting an object, var_export() does not check
whether __set_state() is
implemented by the object's class, so re-importing such objects will fail,
if __set_state() is not implemented. Particularly, this affects some
internal classes.
It is the responsibility of the programmer to verify that only objects will
be re-imported, whose class implements __set_state().
__debugInfo
( void
) : array
This method is called by var_dump() when dumping an
object to get the properties that should be shown. If the method isn't
defined on an object, then all public, protected and private properties
will be shown.
This feature was added in PHP 5.6.0.
Example #6 Using __debugInfo()
<?php
class C {
private $prop;
public function __construct($val) {
$this->prop = $val;
}
public function __debugInfo() {
return [
'propSquared' => $this->prop ** 2,
];
}
}
var_dump(new C(42));
?>
The above example will output:
object(C)#1 (1) {
["propSquared"]=>
int(1764)
}
add a note