PHP closures are very simple

Closures seem like big magic but in PHP they are just syntactic sugar over the following construct:

<?php
class OurClosure {
  function __construct($add) {
    $this->add = $add;
  }
  function __invoke($x) {
    print $x + $this->add;
    print "\n";
  }
}
$print_add_2 = new OurClosure(2); // call __construct
$print_add_2(5); // when an object is called like a function it calls __invoke
?>

Now, closures use the following syntax:

<?php
function get_add_printer($add) {
  return function ($x) use ($add) {
    print $x + $add;
    print "\n";
  };
}
$print_add_2 = get_add_printer(2);
$print_add_2(5);
?>

This is the exact same -- it's internally implemented exactly like that: function ($ARG1_TO_BE_USED_WHEN_CALLING_INVOKE, $ARG2_TO_BE_USED_WHEN_CALLING_INVOKE, ...) use ($ARG1_TO_STORE_IN_CONSTRUCT, $ARG2_TO_STORE_IN_CONSTRUCT, ...)