<?php
class MY_Service
{
    public function __construct()
    {
        log_message('debug', "Service Class Initialized");
    }
    function __get($key)
    {
        $CI = & get_instance();
        return $CI->$key;
    }
}

<?php
class MY_Loader extends CI_Loader
{
    /**
  * List of loaded sercices
  *
  * @var array
  * @access protected
  */
 protected $_ci_services = array();
 /**
  * List of paths to load sercices from
  *
  * @var array
  * @access protected
  */
 protected $_ci_service_paths  = array();
    /**
     * Constructor
     *
     * Set the path to the Service files
     */
    public function __construct()
    {
        parent::__construct();
        $this->_ci_service_paths = array(APPPATH);
    }
    /**
     * Service Loader
     *
     * This function lets users load and instantiate classes.
  * It is designed to be called from a user's app controllers.
  *
  * @param string the name of the class
  * @param mixed the optional parameters
  * @param string an optional object name
  * @return void
     */
    public function service($service = '', $params = NULL, $object_name = NULL)
    {
        if(is_array($service))
        {
            foreach($service as $class)
            {
                $this->service($class, $params);
            }
            return;
        }
        if($service == '' or isset($this->_ci_services[$service])) {
            return FALSE;
        }
        if(! is_null($params) && ! is_array($params)) {
            $params = NULL;
        }
        $subdir = '';
        // Is the service in a sub-folder? If so, parse out the filename and path.
        if (($last_slash = strrpos($service, '/')) !== FALSE)
        {
                // The path is in front of the last slash
                $subdir = substr($service, 0, $last_slash + 1);
                // And the service name behind it
                $service = substr($service, $last_slash + 1);
        }
        foreach($this->_ci_service_paths as $path)
        {
            $filepath = $path .'service/'.$subdir.$service.'.php';
            if ( ! file_exists($filepath))
            {
                continue;
            }
            include_once($filepath);
            $service = strtolower($service);
            if (empty($object_name))
            {
                $object_name = $service;
            }
            $service = ucfirst($service);
            $CI = &get_instance();
            if($params !== NULL)
            {
                $CI->$object_name = new $service($params);
            }
            else
            {
                $CI->$object_name = new $service();
            }
            $this->_ci_services[] = $object_name;
            return;
        }
    }
}

<?php
class User extends CI_Controller
{
    public function __construct()
    {
  
        parent::__construct();
        $this->load->service('user_service');
    }
    public function login()
    {
        $name = 'phpddt.com';
        $psw = 'password';
        print_r($this->user_service->login($name, $psw));
    }
}

<?php
class User_service extends MY_Service
{
    public function __construct()
    {
        parent::__construct();
        $this->load->model('user_model');
    }
    public function login($name, $password)
    {
        $user = $this->user_model->get_user_by_where($name, $password);
        //.....
        //.....
        //.....
        return $user;
    }
}

<?php
class User_model extends CI_Model
{
    public function __construct()
    {
        parent::__construct();
    }
    public function get_user_by_where($name, $password)
    {
        //$this->db
        //......
        //......
        return array('id' => 1, 'name' => 'mckee');
    }
}