CodeIgniter MY_Loader class

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class MY_Loader extends CI_Loader {

    private $_CI;

    /**
     * Constructor
     */
    public function __construct()
    {
        parent::__construct();
        $this->_CI =& get_instance();
        set_error_handler(array($this, '_error_handler'));
        spl_autoload_register(array($this, '_class_autoloader'));
        $this->class_file('Custom_exception', CORE_PATH);
    }

    /**
     * Custom error handler.
     *
     * @param $severity  PHP error code.
     * @param $message  Text of error.
     * @param $filename  File error occurred in.
     * @param $line  Line number of error.
     * @return void
     * @throws ErrorException
     * @access private
     */
    private function _error_handler($severity, $message, $filename, $line)
    {
        throw new ErrorException($message, 0, $severity, $filename, $line);
    }

    /**
     * @param $class_name  The class name.
     * @return void
     * @access private
     */
    private function _class_autoloader($class_name)
    {
        if (strpos($class_name, $this->_CI->config->item('native_prefix')) === FALSE AND
            strpos($class_name, $this->_CI->config->item('subclass_prefix')) === FALSE AND
            strpos($class_name, 'PEAR') === FALSE)
        {
            $this->class_file($class_name, NULL, 3);
        }
    }

    /**
     * @param $class_name  Class name.
     * @param $file_path  File path.
     * @return void
     */
    public function class_file($class_name, $file_path = NULL, $backtrace_level = 1)
    {
        if (is_null($file_path))
        {
            $backtrace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, $backtrace_level);
            $backtrace = array_pop($backtrace);
            $full_path = dirname($backtrace['file']) . '/' . $class_name . '.php';
        }
        else
        {
            $full_path = $file_path . $class_name . '.php';
        }

        if (in_array($full_path, $this->_ci_loaded_files))
        {
            log_message('debug', $class_name . ' class already loaded. Second attempt ignored.');
            return;
        }

        try
        {
            include_once $full_path;
        }
        catch (ErrorException $e)
        {
            $log = 'Unable to load the requested class: ' . $class_name;
            if (ENVIRONMENT === 'development')
            {
                $log .= '<br><b> Full Trace: </b>' . str_replace('#', '<br>#', $e->getTraceAsString());
            }

            log_message('error', $log);
            show_error($log);
        }

        if ( ! isset($e))
        {
            $this->_ci_loaded_files[] = $full_path;
        }
    }

    /**
     * Clean all cached variables.
     *
     * @return void
     */
    public function clean_cached_vars()
    {
        // sets this instance variable to its default value
        $this->_ci_cached_vars = array();
    }
}

// END MY_Loader class

/* End of file MY_Loader.php */
/* Location: ./application/core/MY_Loader.php */