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.
All magic methods MUST be declared as public
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.
<link linkend="object.sleep">__sleep()</link> and
<link linkend="object.wakeup">__wakeup()</link>
publicarray__sleeppublicvoid__wakeupserialize 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.
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.
Sleep and wakeup
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();
}
}?>
]]>
<link linkend="object.serialize">__serialize()</link> and
<link linkend="object.unserialize">__unserialize()</link>
publicarray__serializepublicvoid__unserializearraydataserialize 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.
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.
If both __unserialize() and __wakeup()
are defined in the same object, only __unserialize() will be called.
__wakeup() will be ignored.
This feature is available since PHP 7.4.0.
Serialize and unserialize
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();
}
}?>
]]>
<link linkend="object.tostring">__toString()</link>publicstring__toString
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.
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.
Simple example
foo = $foo;
}
public function __toString()
{
return $this->foo;
}
}
$class = new TestClass('Hello');
echo $class;
?>
]]>
&example.outputs;
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.
<link linkend="object.invoke">__invoke()</link>mixed__invokevalues
The __invoke() method is called when a script tries to
call an object as a function.
This feature is available since PHP 5.3.0.
Using <link linkend="object.invoke">__invoke()</link>
]]>
&example.outputs;
<link linkend="object.set-state">__set_state()</link>staticobject__set_statearrayproperties
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, ...).
Using <link linkend="object.set-state">__set_state()</link> (since PHP 5.1.0)
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);
?>
]]>
&example.outputs;
int(5)
["var2"]=>
string(3) "foo"
}
]]>
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().
<link linkend="object.debuginfo">__debugInfo()</link>array__debugInfo
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.
Using <link linkend="object.debuginfo">__debugInfo()</link>
prop = $val;
}
public function __debugInfo() {
return [
'propSquared' => $this->prop ** 2,
];
}
}
var_dump(new C(42));
?>
]]>
&example.outputs;
int(1764)
}
]]>