Every application consists of a large number of classes in many different locations.
The framework provides classes for core functionality. Your application will have a
number of libraries, models, and other entities to make it work. You might have third-party
classes that your project is using. Keeping track of where every single file is, and
hard-coding that location into your files in a series of
requires() is a massive
headache and very error-prone. That’s where autoloaders come in.
CodeIgniter provides a very flexible autoloader that can be used with very little configuration. It can locate individual namespaced classes that adhere to PSR-4 autoloading directory structures.
The autoloader works great by itself, but can also work with other autoloaders, like Composer, or even your own custom autoloaders, if needed. Because they’re all registered through spl_autoload_register, they work in sequence and don’t get in each other’s way.
The autoloader is always active, being registered with
spl_autoload_register() at the
beginning of the framework’s execution.
Initial configuration is done in app/Config/Autoload.php. This file contains two primary arrays: one for the classmap, and one for PSR-4 compatible namespaces.
The recommended method for organizing your classes is to create one or more namespaces for your
application’s files. This is most important for any business-logic related classes, entity classes,
psr4 array in the configuration file allows you to map the namespace to the directory
those classes can be found in:
<?php $psr4 = [ 'App' => APPPATH, 'CodeIgniter' => SYSTEMPATH, ];
The key of each row is the namespace itself. This does not need a trailing back slash. The value is the location to the directory the classes can be found in. They should have a trailing slash.
By default, the application folder is namespace to the
App namespace. While you are not forced to namespace the controllers,
libraries, or models in the application directory, if you do, they will be found under the
You may change this namespace by editing the app/Config/Constants.php file and setting the
new namespace value under the
<?php define('APP_NAMESPACE', 'App');
You will need to modify any existing files that are referencing the current namespace.
Config files are namespaced in the
Config namespace, not in
App\Config as you might
expect. This allows the core system files to always be able to locate them, even when the application
namespace has changed.
The classmap is used extensively by CodeIgniter to eke the last ounces of performance out of the system
by not hitting the file-system with extra
is_file() calls. You can use the classmap to link to
third-party libraries that are not namespaced:
<?php $classmap = [ 'Markdown' => APPPATH . 'third_party/markdown.php', ];
The key of each row is the name of the class that you want to locate. The value is the path to locate it at.
Composer support is automatically initialized by default. By default, it looks for Composer’s autoload file at
ROOTPATH . 'vendor/autoload.php'. If you need to change the location of that file for any reason, you can modify
the value defined in app/Config/Constants.php.
If the same namespace is defined in both CodeIgniter and Composer, CodeIgniter’s autoloader will be the first one to get a chance to locate the file.