<?php

// An example callback function
function my_callback_function() { echo 'hello world!'; }

// An example callback method
class MyClass {
    static function myCallbackMethod() { echo 'Hello World!'; }
}

// Type 1: Simple callback
call_user_func('my_callback_function');

// Type 2: Static class method call
call_user_func(array('MyClass', 'myCallbackMethod'));

// Type 3: Object method call
$obj = new MyClass();
call_user_func(array($obj, 'myCallbackMethod'));

// Type 4: Static class method call (As of PHP 5.2.3)
call_user_func('MyClass::myCallbackMethod');

// Type 5: Relative static class method call (As of PHP 5.3.0)
class A {
    public static function who() { echo "A\n"; }
}
class B extends A {
    public static function who() { echo "B\n"; }
}
call_user_func(array('B', 'parent::who')); // A

// Type 6: Objects implementing __invoke can be used as callables (since PHP 5.3)
class C {
    public function __invoke($name) { echo 'Hello ', $name, "\n"; }
}
$c = new C();
call_user_func($c, 'PHP!');

// Error case
call_user_func(500, 100);

