Magic Methods
Magic methods are special methods which override PHP's default's action
when certain actions are performed on an object.
Attenzione
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().
Avviso
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().
Avviso
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.
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.
Nota:
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.
Nota:
As of PHP 8.0.0, returning a value which is not an array from __sleep() generates a warning. Previously, it generated a notice.
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();
}
}?>
public __serialize():
array
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.
Nota:
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.
Nota:
If both __unserialize() and __wakeup()
are defined in the same object, only __unserialize() will be called.
__wakeup() will be ignored.
Nota:
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();
}
}?>
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.
Avviso
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.
A Stringable object will
not be accepted by a string type declaration if
strict typing
is enabled. If such behaviour is wanted the type declaration must accept
Stringable and string via a union type.
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.
Avviso
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 $class;
?>
Il precedente esempio visualizzerà:
__invoke(
...$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));
?>
Il precedente esempio visualizzerà:
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);
?>
Il precedente esempio visualizzerà:
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
)
)
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);
?>
Il precedente esempio visualizzerà:
string(60) "A::__set_state(array(
'var1' => 5,
'var2' => 'foo',
))"
object(A)#2 (2) {
["var1"]=>
int(5)
["var2"]=>
string(3) "foo"
}
Nota:
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().
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));
?>
Il precedente esempio visualizzerà:
object(C)#1 (1) {
["propSquared"]=>
int(1764)
}
