Overloading
Overloading in PHP provides means to dynamically
create
properties and methods.
These dynamic entities are processed via magic methods
one can establish in a class for various action types.
The overloading methods are invoked when interacting with
properties or methods that have not been declared or are not
visible in
the current scope. The rest of this section will use the terms
inaccessible properties
and inaccessible
methods
to refer to this combination of declaration
and visibility.
All overloading methods must be defined as public.
Note:
None of the arguments of these magic methods can be passed by reference.
Note:
PHP's interpretation of
overloadingis different than most object oriented languages. Overloading traditionally provides the ability to have multiple methods with the same name but different quantities and types of arguments.
Changelog
| Version | Description |
|---|---|
| 5.3.0 | Added __callStatic(). Added warning to enforce public visibility and non-static declaration. |
| 5.1.0 | Added __isset() and __unset(). Added support for __get() for overloading of private properties. |
| 5.0.0 | Added __get(). |
Property overloading
$name
) : bool$name
) : void__set() is run when writing data to inaccessible (protected or private) or non-existing properties.
__get() is utilized for reading data from inaccessible (protected or private) or non-existing properties.
__isset() is triggered by calling isset() or empty() on inaccessible (protected or private) or non-existing properties.
__unset() is invoked when unset() is used on inaccessible (protected or private) or non-existing properties.
The $name argument is the name of the property being interacted with. The __set() method's $value argument specifies the value the $name'ed property should be set to.
Property overloading only works in object context. These magic methods will not be triggered in static context. Therefore these methods should not be declared static. As of PHP 5.3.0, a warning is issued if one of the magic overloading methods is declared static.
Note:
The return value of __set() is ignored because of the way PHP processes the assignment operator. Similarly, __get() is never called when chaining assignments together like this:
$a = $obj->b = 8;
Example #1 Overloading properties via the __get(), __set(), __isset() and __unset() methods
<?php
class PropertyTest
{
/** Location for overloaded data. */
private $data = array();
/** Overloading not used on declared properties. */
public $declared = 1;
/** Overloading only used on this when accessed outside the class. */
private $hidden = 2;
public function __set($name, $value)
{
echo "Setting '$name' to '$value'\n";
$this->data[$name] = $value;
}
public function __get($name)
{
echo "Getting '$name'\n";
if (array_key_exists($name, $this->data)) {
return $this->data[$name];
}
$trace = debug_backtrace();
trigger_error(
'Undefined property via __get(): ' . $name .
' in ' . $trace[0]['file'] .
' on line ' . $trace[0]['line'],
E_USER_NOTICE);
return null;
}
/** As of PHP 5.1.0 */
public function __isset($name)
{
echo "Is '$name' set?\n";
return isset($this->data[$name]);
}
/** As of PHP 5.1.0 */
public function __unset($name)
{
echo "Unsetting '$name'\n";
unset($this->data[$name]);
}
/** Not a magic method, just here for example. */
public function getHidden()
{
return $this->hidden;
}
}
echo "<pre>\n";
$obj = new PropertyTest;
$obj->a = 1;
echo $obj->a . "\n\n";
var_dump(isset($obj->a));
unset($obj->a);
var_dump(isset($obj->a));
echo "\n";
echo $obj->declared . "\n\n";
echo "Let's experiment with the private property named 'hidden':\n";
echo "Privates are visible inside the class, so __get() not used...\n";
echo $obj->getHidden() . "\n";
echo "Privates not visible outside of class, so __get() is used...\n";
echo $obj->hidden . "\n";
?>
The above example will output:
Setting 'a' to '1' Getting 'a' 1 Is 'a' set? bool(true) Unsetting 'a' Is 'a' set? bool(false) 1 Let's experiment with the private property named 'hidden': Privates are visible inside the class, so __get() not used... 2 Privates not visible outside of class, so __get() is used... Getting 'hidden' Notice: Undefined property via __get(): hidden in <file> on line 70 in <file> on line 29
Method overloading
__call() is triggered when invoking inaccessible methods in an object context.
__callStatic() is triggered when invoking inaccessible methods in a static context.
The $name argument is the name of the method being called. The $arguments argument is an enumerated array containing the parameters passed to the $name'ed method.
Example #2 Overloading methods via the __call() and __callStatic() methods
<?php
class MethodTest
{
public function __call($name, $arguments)
{
// Note: value of $name is case sensitive.
echo "Calling object method '$name' "
. implode(', ', $arguments). "\n";
}
/** As of PHP 5.3.0 */
public static function __callStatic($name, $arguments)
{
// Note: value of $name is case sensitive.
echo "Calling static method '$name' "
. implode(', ', $arguments). "\n";
}
}
$obj = new MethodTest;
$obj->runTest('in object context');
MethodTest::runTest('in static context'); // As of PHP 5.3.0
?>
The above example will output:
Calling object method 'runTest' in object context Calling static method 'runTest' in static context
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Document created the 30/01/2003, last modified the 26/10/2018
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References
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