How to Correctly Invoke Closures Assigned to Object Properties in PHP?

Invoking Closures Assigned to Object Properties Directly

Assigning a closure to an object's property allows developers to associate functionality with the object. However, accessing the closure directly can be problematic.

The Problem:

When attempting to invoke a closure assigned to an object property directly, the following error occurs:

Fatal error: Call to undefined method stdClass::callback().

This is because the property is stored as a closure object, which does not have a __invoke() method.

Solution in PHP 7 and above:

In PHP 7 onwards, the following syntax is available:

$obj = new stdClass;
$obj->fn = function($arg) { return "Hello $arg"; };
echo ($obj->fn)('World');

Alternatively, Closure::call() can be used, although it does not work with StdClass:

Closure::call($obj->callback, ['World']);

Solution before PHP 7:

Before PHP 7, the __call magic method can be implemented to intercept closure invocations:

class Foo
{
    public function __call($method, $args)
    {
        if (is_callable(array($this, $method))) {
            return call_user_func_array($this->$method, $args);
        }
        // else throw exception
    }
}

$foo = new Foo;
$foo->cb = function($who) { return "Hello $who"; };
echo $foo->cb('World');

Note: The __call method cannot use call_user_func_array(array($this, $method), $args) as it would lead to an infinite loop.

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