PHP: oop5 language - Overloading

Overloading

Overloading in PHP provides means to dynamically "create" members 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 members 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 members" 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 "overloading" is 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
5.1.0	Added __isset() and __unset().
5.3.0	Added __callStatic(). Added warning to enforce public visibility and non-static declaration.

Member overloading

void __set ( string $name , mixed $value )

mixed __get ( string $name )

bool __isset ( string $name )

void __unset ( string $name )

__set() is run when writing data to inaccessible members.

__get() is utilized for reading data from inaccessible members.

__isset() is triggered by calling isset() or empty() on inaccessible members.

__unset() is invoked when unset() is used on inaccessible members.

The $name argument is the name of the member being interacted with. The __set() method's $value argument specifies the value the $name'ed member should be set to.

Member overloading only works in object context. These magic methods will not be triggered in static context. Therefore these methods can not be declared static.

Example #1 overloading with __get, __set, __isset and __unset example


<?php
class MemberTest {
    /**  Location for overloaded data.  */
    private $data = array();

    /**  Overloading not used on declared members.  */
    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 MemberTest;

$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

mixed __call ( string $name , array $arguments )

mixed __callStatic ( string $name , array $arguments )

__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 instantiated methods with __call and ___callStatic


<?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