How to Pass Class Methods as Callbacks in PHP?

Using Class Methods as Callbacks in PHP

Background:

Often, you may need to pass class methods as callbacks to be executed in external contexts. This guide explores the techniques to accomplish this in PHP.

Passing Class Methods as Callbacks

There are several approaches to pass class methods as callbacks:

1. Using an Array:

• For non-static methods, create an array with the object at index 0 and the method name at index 1.
• Example: $this->processSomething([$this, 'myCallback']);

2. Using Static Class Names:

• For static methods, use the class name instead of an object in the array.
• Example: $this->processSomething([__CLASS__, 'myStaticCallback']);

3. Using Class Constants and PHP 5.2.3 :

• From PHP 5.2.3 onwards, you can use the class constant self followed by the static method name without an array.
• Example: $this->processSomething(self::myStaticCallback);

4. Using PHP 5.5.0 Class References:

• In PHP 5.5.0 and later, you can use MyClass::class syntax to reference the class and its methods.
• Example: $this->processSomething([MyClass::class, 'myStaticCallback']);

5. Passing Global PHP Functions (Not Applicable):

• Global PHP functions can be passed directly as strings.
• Example: $this->processSomething('some_global_php_function');

Note on Static and Instance Methods:

• Only instance methods require an object instance in the array. Static methods can be used without an object and passed directly as a class reference.
• For non-static methods, you can also pass an array with an object_id key instead of the object instance. This is useful when serializing callbacks.

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