CODEWITHSUNDEEP
phpoopcallback
SmxCde
SmxCde

Reputation: 5403

How to use class methods as callbacks

I have a class with methods that I want to use as callbacks.
How can I pass them as arguments?

Class MyClass {
    
    public function myMethod() {
        // How should these be called?
        $this->processSomething(this->myCallback);
        $this->processSomething(self::myStaticCallback);
    }

    private function processSomething(callable $callback) {
        // Process something...
        $callback();
    }

    private function myCallback() {
        // Do something...
    }

    private static function myStaticCallback() {
        // Do something...
    }   
    
}

Upvotes: 153

Views: 129554

Answers (5)

Geovani Santos
Geovani Santos

Reputation: 391

You can also to use call_user_func() to specify a callback:

public function myMethod() {
    call_user_func(array($this, 'myCallback'));
}

private function myCallback() {
    // do something...
}

Upvotes: 14

Bankzilla
Bankzilla

Reputation: 2096

Since 5.4 there is a more elegant way you can write it, I'm still trying to find out if it can be reduced more

$this->processSomething(function() {
    $this->myCallback();
});

Since 8.1 PHP has the first class callable syntax:

$this->processSomething(
    $this->myCallback(...);
);

Upvotes: 17

Dharman
Dharman

Reputation: 33238

As of PHP 8.1, we now have first-class callables. They use the syntax $callable = functionName(...). The three dots are part of the syntax and not an omission.

You can use the new syntax to create callable class methods.

Class MyClass {
    
    public function myMethod() {
        // first-class callables
        $this->processSomething($this->myCallback(...));
        $this->processSomething(self::myStaticCallback(...));
    }

    private function processSomething(callable $callback) {
        // Process something...
        $callback();
    }

    private function myCallback() {
        // Do something...
    }

    private static function myStaticCallback() {
        // Do something...
    }   
    
}

The three dots are not an omission/placeholder for parameters. They are a special syntax for creating a callable. If the method accepts no parameters, the syntax remains the same.

Upvotes: 45

Pax Exterminatus
Pax Exterminatus

Reputation: 550

You can set the method return type to callable. It works for PHP 7.1

protected function myMethod(): callable
{
    return function (int $j) {
    };
}

Then call it like this:

someFunction($this->myMethod());

Upvotes: -1

MikO
MikO

Reputation: 18741

Check the callable manual to see all the different ways to pass a function as a callback. I copied that manual here and added some examples of each approach based on your scenario.

Callable

  • A PHP function is passed by its name as a string. Any built-in or user-defined function can be used, except language constructs such as: array(), echo, empty(), eval(), exit(), isset(), list(), print or unset().
  // Not applicable in your scenario
  $this->processSomething('some_global_php_function');
  • A method of an instantiated object is passed as an array containing an object at index 0 and the method name at index 1.
  // Only from inside the same class
  $this->processSomething([$this, 'myCallback']);
  $this->processSomething([$this, 'myStaticCallback']);
  // From either inside or outside the same class
  $myObject->processSomething([new MyClass(), 'myCallback']);
  $myObject->processSomething([new MyClass(), 'myStaticCallback']);
  • Static class methods can also be passed without instantiating an object of that class by passing the class name instead of an object at index 0.
  // Only from inside the same class
  $this->processSomething([__CLASS__, 'myStaticCallback']);
  // From either inside or outside the same class
  $myObject->processSomething(['\Namespace\MyClass', 'myStaticCallback']);
  $myObject->processSomething(['\Namespace\MyClass::myStaticCallback']); // PHP 5.2.3+
  $myObject->processSomething([MyClass::class, 'myStaticCallback']); // PHP 5.5.0+
  • Apart from common user-defined function, anonymous functions can also be passed to a callback parameter. 
  // Not applicable in your scenario unless you modify the structure
  $this->processSomething(function() {
      // process something directly here...
  });

Upvotes: 251

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