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...
}
    

}
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最佳答案

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...
});
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Since 5.3 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();
});
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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...
}
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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...
}
    

}
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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());

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