Autoloading and PSR-0/PSR-4 - php

Question

I, like many others it seems, am having trouble getting my head around when and how to use auto-loading. I think I understand the concept of composer and PSR-0/PSR-4 and directory structure that this requires. But if I'm building my own project using my own MVC framework
Should I now put all my class files in a src folder inside the vendor folder
Do I then edit the composer autoload file?
Or do I still keep the original structure and just use my own autoloader?
-project
-app
-core /Main.php
-controllers /Controller.php
-models /User.php
/index.php
Since composer comes with its own autoloader which will load all dependenies that I may want to include with my project and if I'm not going to make my website into a distributed project do I even need my own namespacing? Why don't I just stick with includes/requires?
And finally, if I do adopt namespacing using a closure like this
function __autoload($class){
require $class .'.php';
});
do I need to require the autoload.php file in all pages where I load my classes as I do with the old include/require of the past. Is the above file correct? I think the namespace would be
<?php
namespace app\core; //for Main.php
namespace app\controllers; //for Controller.php
use app\controllers\Controller; //if I call the class

Answer 1

At the beginning of your main file (maybe /var/www/dist/index.php) you just include the Composer or whatever autoloader you use.
<?php
if ( file_exists( __DIR__.'/path/to/vendor/autoload.php' ) )
require __DIR__.'/path/to/vendor/autoload.php';
Then you can either add shortcuts to the classes that you use in a file by making use of the use statement
use MyNamespace\Controller\Index,
MyNamespace\Service\FooService;
use Zend\Foo\Bar;
use Symfony\Baz\Biz;
use Etc\Etc\Etc;
// Refers to \Zend\Foo\Bar
$bar = new Bar;
or just use the full path when instantiating a class
$bar = new \Zend\Foo\Bar;
To add your own namespace, just add it to your composer.json file
"autoload" : {
"psr-4" : {
"MyNamespace\\" : "src/"
}
}
and open your command line interface/terminal/console and add the namespace to the autoloader
# local install of Composer in your project
php composer.php dump-autoload
# or global install and `composer` is in your $PATH
composer dump-autoload
There is a rule:
One class per file
And if your project really is (PSR-0 deprecated or) PSR-4 compatible, then you don't use more than one namespace in one file. A class name gets (in the PSR-4 FIG standard) defined as
A fully qualified class name has the following form:
\<NamespaceName>(\<SubNamespaceNames>)*\<ClassName>
The contiguous sub-namespace names after the "namespace prefix" [note: \ is the "root") correspond to a subdirectory within a "base directory", in which the namespace separators represent directory separators.
with the following example:
+------------------------------+------------------+------------------------+---------------------------------------+
| Fully Qualified Class Name | Namespace Prefix | Base Directory | Resulting File Path |
+------------------------------+------------------+------------------------+---------------------------------------+
| \Acme\Log\Writer\File_Writer | Acme\Log\Writer | ./acme-log-writer/lib/ | ./acme-log-writer/lib/File_Writer.php |
+------------------------------+------------------+------------------------+---------------------------------------+