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How to Extend a Class without Using Inheritance

2.8 version

How to Extend a Class without Using InheritanceΒΆ

To allow multiple classes to add methods to another one, you can define the magic __call() method in the class you want to be extended like this:

class Foo
    // ...

    public function __call($method, $arguments)
        // creates an event named 'foo.method_is_not_found'
        $event = new HandleUndefinedMethodEvent($this, $method, $arguments);
        $this->dispatcher->dispatch('foo.method_is_not_found', $event);

        // no listener was able to process the event? The method does not exist
        if (!$event->isProcessed()) {
            throw new \Exception(sprintf('Call to undefined method %s::%s.', get_class($this), $method));

        // returns the listener returned value
        return $event->getReturnValue();

This uses a special HandleUndefinedMethodEvent that should also be created. This is a generic class that could be reused each time you need to use this pattern of class extension:

use Symfony\Component\EventDispatcher\Event;

class HandleUndefinedMethodEvent extends Event
    protected $subject;
    protected $method;
    protected $arguments;
    protected $returnValue;
    protected $isProcessed = false;

    public function __construct($subject, $method, $arguments)
        $this->subject = $subject;
        $this->method = $method;
        $this->arguments = $arguments;

    public function getSubject()
        return $this->subject;

    public function getMethod()
        return $this->method;

    public function getArguments()
        return $this->arguments;

     * Sets the value to return and stops other listeners from being notified
    public function setReturnValue($returnValue)
        $this->returnValue = $returnValue;
        $this->isProcessed = true;

    public function getReturnValue()
        return $this->returnValue;

    public function isProcessed()
        return $this->isProcessed;

Next, create a class that will listen to the foo.method_is_not_found event and add the method bar():

class Bar
    public function onFooMethodIsNotFound(HandleUndefinedMethodEvent $event)
        // only respond to the calls to the 'bar' method
        if ('bar' != $event->getMethod()) {
            // allow another listener to take care of this unknown method

        // the subject object (the foo instance)
        $foo = $event->getSubject();

        // the bar method arguments
        $arguments = $event->getArguments();

        // ... do something

        // set the return value

Finally, add the new bar() method to the Foo class by registering an instance of Bar with the foo.method_is_not_found event:

$bar = new Bar();
$dispatcher->addListener('foo.method_is_not_found', array($bar, 'onFooMethodIsNotFound'));

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.