By Jeremy Lindblom on January 28th, 2010
Anonymous functions, also known as closures, allow the creation of functions which have no specified name. They are most useful as the value of callback parameters, but they have many other uses. Closures can also be used as the values of variables; PHP automatically converts such expressions into instances of the Closure internal class.
PHP has very few predefined classes that are part of the core language, so naturally I was intrigued by the Closure class. The PHP Manual has this to say about the class:
The predefined final class Closure was introduced in PHP 5.3.0. It is used for internal implementation of anonymous functions. The class has a constructor forbidding the manual creation of the object (issues
E_RECOVERABLE_ERROR) and the
__invoke()method with the calling magic.
The invoke magic method is also a new feature in PHP 5.3. It is called when an object is used in the context of a function (e.g.
$object($parameter);). Since Closure objects will be used like functions, this is a critical feature of the Closure object. The Closure class may be perfectly equipped to act like an anonymous function, but it does not provide any extra utility beyond that. A
var_dump() of a closure will reveal the functions parameters, but there is no way to get any other information about the Closure (like the actual code of the function). Trying to serialize the Closure throws an Exception and
json_encode() just returns an empty JSON string. To make matters worse, the Closure class is final, so there is no way to extend it.
That simply wasn’t going to cut it for me. I wanted to make my own Closure class that was at least able to do the following: Read More »