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__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. 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.

<?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 since PHP 7.4.0.

<?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. This method must return a string, as otherwise a fatal E_RECOVERABLE_ERROR level error is emitted.

<?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;
?>

Hello

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()

__invoke (  ...$values ) : 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.

<?php
class CallableClass
{
    public function __invoke($x)
    {
        var_dump($x);
    }
}
$obj = new CallableClass;
$obj(5);
var_dump(is_callable($obj));
?>

int(5)
bool(true)

__set_state()

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, ...).

<?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);

?>

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()

__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.

This feature was added in PHP 5.6.0.

<?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));
?>

object(C)#1 (1) {
  ["propSquared"]=>
  int(1764)
}