src/CI_Base_Model.php
private function getCallableFunction($method)
    {
        if (is_callable($method)) {
            return $method;
        }

        if (is_string($method) && is_callable(array($this, $method))) {
            return array($this, $method);
        }

        return FALSE;
    }
private function getCallableFunction($method)
    {
        if (is_callable($method)) {
            return $method;
        }

        if (is_string($method) && is_callable(array($this, $method))) {
            return array($this, $method);
        }

        return FALSE;
    }
Get callable as per given method

@param $method
@return array|bool|callable