Magic Methods

Magic methods are special methods which override PHP's default's action when certain actions are performed on an object.

Caution

All methods names starting with __ are reserved by PHP. Therefore, it is not recommended to use such method names unless overriding PHP's behavior.

The following method names are considered magical: __construct(), __destruct(), __call(), __callStatic(), __get(), __set(), __isset(), __unset(), __sleep(), __wakeup(), __serialize(), __unserialize(), __toString(), __invoke(), __set_state(), __clone(), and __debugInfo().

Warning

All magic methods, with the exception of __construct(), __destruct(), and __clone(), must be declared as public, otherwise an E_WARNING is emitted. Prior to PHP 8.0.0, no diagnostic was emitted for the magic methods __sleep(), __wakeup(), __serialize(), __unserialize(), and __set_state().

Warning

If type declarations are used in the definition of a magic method, they must be identical to the signature described in this document. Otherwise, a fatal error is emitted. Prior to PHP 8.0.0, no diagnostic was emitted. However, __construct() and __destruct() must not declare a return type; otherwise a fatal error is emitted.

__sleep() and __wakeup()

public __sleep(): array
public __wakeup(): 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. Use __serialize() instead.

The intended use of __sleep() is to commit pending data or perform similar cleanup tasks. Also, the function is useful if a very large object doesn't 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();
}
}?>

__serialize() and __unserialize()

public __serialize(): 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 as of 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();
}
}?>

__toString()

public __toString(): 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.

Warning

As of PHP 8.0.0, the return value follows standard PHP type semantics, meaning it will be coerced into a string if possible and if strict typing is disabled.

As of PHP 8.0.0, any class that contains a __toString() method will also implicitly implement the Stringable interface, and will thus pass type checks for that interface. Explicitly implementing the interface anyway is recommended.

In PHP 7.4, the returned value must be a string, otherwise an Error is thrown.

Prior to PHP 7.4.0, the returned value must be a string, otherwise a fatal E_RECOVERABLE_ERROR is emitted.

Warning

It was not possible to throw an exception from within a __toString() method prior to 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:

Hello

__invoke()

__invoke( ...$values): mixed

The __invoke() method is called when a script tries to call an object as a function.

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:

int(5)
bool(true)

Example #5 Using __invoke()

<?php
class Sort
{
private $key;

public function __construct(string $key)
{
$this->key = $key;
}

public function __invoke(array $a, array $b): int
{
return $a[$this->key] <=> $b[$this->key];
}
}

$customers = [
['id' => 1, 'first_name' => 'John', 'last_name' => 'Do'],
['id' => 3, 'first_name' => 'Alice', 'last_name' => 'Gustav'],
['id' => 2, 'first_name' => 'Bob', 'last_name' => 'Filipe']
];

// sort customers by first name
usort($customers, new Sort('first_name'));
print_r($customers);

// sort customers by last name
usort($customers, new Sort('last_name'));
print_r($customers);
?>

The above example will output:

Array
(
    [0] => Array
        (
            [id] => 3
            [first_name] => Alice
            [last_name] => Gustav
        )

    [1] => Array
        (
            [id] => 2
            [first_name] => Bob
            [last_name] => Filipe
        )

    [2] => Array
        (
            [id] => 1
            [first_name] => John
            [last_name] => Do
        )

)
Array
(
    [0] => Array
        (
            [id] => 1
            [first_name] => John
            [last_name] => Do
        )

    [1] => Array
        (
            [id] => 2
            [first_name] => Bob
            [last_name] => Filipe
        )

    [2] => Array
        (
            [id] => 3
            [first_name] => Alice
            [last_name] => Gustav
        )

)

__set_state()

static __set_state(array $properties): object

This static method is called for classes exported by var_export().

The only parameter of this method is an array containing exported properties in the form ['property' => value, ...].

Example #6 Using __set_state()

<?php

class A
{
public $var1;
public $var2;

public static function __set_state($an_array)
{
$obj = new A;
$obj->var1 = $an_array['var1'];
$obj->var2 = $an_array['var2'];
return $obj;
}
}

$a = new A;
$a->var1 = 5;
$a->var2 = 'foo';

$b = var_export($a, true);
var_dump($b);
eval('$c = ' . $b . ';');
var_dump($c);
?>

The above example will output:

string(60) "A::__set_state(array(
   'var1' => 5,
   'var2' => 'foo',
))"
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 objects will result in an Error exception, 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()

__debugInfo(): 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.

Example #7 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)
}