Kohana 3 :: Loading Classes

Kohana takes advantage of PHP autoloading. This removes the need to call include or require before using a class. For instance, when you want to use the Cookie::set method, you just call:
Cookie::set('mycookie', 'any string value');
Or to load an Encrypt instance, just call Encrypt::instance:

$encrypt = Encrypt::instance();
Classes are loaded via the Kohana::auto_load method, which makes a simple conversion from class name to file name:
  1. Classes are placed in the classes/ directory of the filesystem
  2. Any underscore characters are converted to slashes
  3. The filename is lowercase
When calling a class that has not been loaded (eg: Session_Cookie), Kohana will search the filesystem usingKohana::find_file for a file named classes/session/cookie.php.

Custom Autoloaders

The default autoloader is enabled in application/bootstrap.php using spl_autoload_register:
spl_autoload_register(array('Kohana', 'auto_load'));
This allows Kohana::auto_load to attempt to load any class that does not yet exist when the class is first used.

Transparent Class Extension

The cascading filesystem allows transparent class extension. For instance, the class Cookie is defined inSYSPATH/classes/cookie.php as:
class Cookie extends Kohana_Cookie {}
The default Kohana classes, and many extensions, use this definition so that almost all classes can be extended. You extend any class transparently, by defining your own class in APPPATH/classes/cookie.php to add your own methods.
You should never modify any of the files that are distributed with Kohana. Always make modifications to classes using extensions to prevent upgrade issues.
For instance, if you wanted to create method that sets encrypted cookies using the Encrypt class:
<?php defined('SYSPATH') or die('No direct script access.');
class Cookie extends Kohana_Cookie {
     * @var  mixed  default encryption instance
    public static $encryption = 'default';
     * Sets an encrypted cookie.
     * @uses  Cookie::set
     * @uses  Encrypt::encode
     public static function encrypt($name, $value, $expiration = NULL)
         $value = Encrypt::instance(Cookie::$encrpytion)->encode((string) $value);
         parent::set($name, $value, $expiration);
      * Gets an encrypted cookie.
      * @uses  Cookie::get
      * @uses  Encrypt::decode
      public static function decrypt($name, $default = NULL)
          if ($value = parent::get($name, NULL))
              $value = Encrypt::instance(Cookie::$encryption)->decode($value);
          return isset($value) ? $value : $default;
} // End Cookie
Now calling Cookie::encrypt('secret', $data) will create an encrypted cookie which we can decrypt with $data = Cookie::decrypt('secret').

Multiple Levels of Extension

If you are extending a Kohana class in a module, you should maintain transparent extensions. Instead of making theCookie extension extend Kohana, you can create MODPATH/mymod/encrypted/cookie.php:
class Encrypted_Cookie extends Kohana_Cookie {
    // Use the same encrypt() and decrypt() methods as above
And create MODPATH/mymod/cookie.php:
class Cookie extends Encrypted_Cookie {}
This will still allow users to add their own extension to Cookie with your extensions intact. However, the next extension ofCookie will have to extend Encrypted_Cookie instead of Kohana_Cookie.


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