- [php.net/manual/en/language.types.callable.php](https://www.php.net/manual/en/language.types.callable.php) - https://github.com/mage2pro/core/issues/174#user-content-callable - [stackoverflow.com/questions/29730720](https://stackoverflow.com/questions/29730720) `callable` is **supported** by **PHP ≥ 5.4**: ``` function a(callable $f) {return $f();} a(function() {return 'TEST';}); ``` [3v4l.org/ZtdKu](https://3v4l.org/ZtdKu)
callableis supported by PHP ≥ 5.4:3v4l.org/ZtdKu