PHP - calling class that implements interface without knowing class name

Question

I'm trying to create a PHP file that calls a function in another file. Some sample code:

Interface code:

interface AJAXDispatcher {
    static function dispatch($action);
}

Implementation:

class myAJAX implements AJAXDispatcher {

static function dispatch($action) {
    if ($action === "action1") {
        do_something();
}

This seems ok to me. I try to call it by first importing the file that it's in. I'm trying to make it independent of the name of the class so that I can do something like this:

AJAXDispatcher::dispatch($action);

Thought this would work as myAJAX would inherit from AJAXDispatcher, but I get the following error:

Fatal error: Cannot call abstract method AJAXDispatcher::dispatch() in ....

Anyone know what I'm doing wrong?

The fatal error seems to explain pretty well. You can't call an abstract method. You could call myAJAX::dispatch($action) because its an actual implementation... — thetaiko
– thetaiko, Commented Jul 19, 2010 at 13:54

igorw · Accepted Answer · 2010-07-19 14:00:45Z

5

Interfaces with static methods don't make any sense, because to call a static method you (usually) need to know the class name.

Instead, you should make the method non-static and create an instance of myAJAX somewhere. The code that calls the AJAXDispatcher receives the instance and calls it. You can use type hinting to ensure you are getting the right instance.

interface AJAXDispatcher {
  public function dispatch($action);
}

class myAJAX implements AJAXDispatcher {
  public function dispatch($action) {
    do_something();
  }
}

class Controller {
  private $dispatcher;

  public function __construct(AJAXDispatcher $dispatcher) {
    $this->dispatcher = $dispatcher;
  }

  public function action($action) {
    $this->dispatcher->dispatch($action);
  }
}

$dispatcher = new myAJAX();

$controller = new Controller($dispatcher);
$controller->action('index');

This example uses the Dependency Injection design pattern.

answered Jul 19, 2010 at 14:00

igorw

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2 Comments

bcoughlan Over a year ago

So any way I do it I'll have to explicitly reference the class?

igorw Over a year ago

Well, you could probably pass the class name and then do call_user_func(array($class_name, 'dispatch', $action)); php.net/call_user_func But I would advise against this approach.

Community · Accepted Answer · 2023-11-17 19:32:19Z

2

An interface has no method implementation. It only defines a public API that classes have to implement. How they implement it, is up to the concrete classes. Thus, you cannot call methods of an interface directly, because there is no code to call. You have to call the method on the implementing class.

Have a look at the PHP Manual on Interfaces.

edited Nov 17, 2023 at 19:32

CommunityBot

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answered Jul 19, 2010 at 13:56

Gordon

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Comments

Peter Bailey · Accepted Answer · 2010-07-19 13:57:27Z

1

No, you can't do that. There are several things wrong here

That's now how inheritance works. Method chaining goes up the class hierarchy, now down.
Static methods are connected to the class. If you override a static method in a subclass, and want to invoke the subclass' version, you must reference the subclass explicitly.
Interfaces have no implementation. Even if the language allowed the type of call you're making, nothing would happen. AJAXDispatcher::dispatch() has no body.

You're going to have to re-think your strategy here.

answered Jul 19, 2010 at 13:57

Peter Bailey

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