Webmozart\Assert\Assert::isCallable PHP Method

    public static function isCallable($value, $message = '')
    {
        if (!is_callable($value)) {
            static::reportInvalidArgument(sprintf($message ?: 'Expected a callable. Got: %s', static::typeToString($value)));
        }
    }

 /**
  * Handle the callback.
  *
  * @param array|callable $callback  Callback as Contao array notation or as PHP callable.
  * @param array          $arguments List of arguments being passed to the callback.
  *
  * @return mixed
  * @throws InvalidArgumentException On callback is not callable.
  */
 public function invoke($callback, array $arguments = [])
 {
     if (is_array($callback)) {
         $callback[0] = \System::importStatic($callback[0]);
     }
     Assert::isCallable($callback);
     return call_user_func_array($callback, $arguments);
 }