PSR-4 Standard of Autoloader and Usage with Composer

I don't know that but have you ever heard php-fig.org ? This guys trying to be standard for people who set the PHP structure. So they are saying, if you are going to set a structure, do it according to standards to it will be a thing :) ı will explain to easiest  PSR-4 Autoloading deal.

If you are new with classes namespaces can be meaningless for you. Why should i use it?  Now projects that used a lot of classes, you should think the namespaces liek a nickname if you don't they will clash it.

Assume that my name is phpExample and there are 2 more phpExample. To not get confused the namespaces I am phpExample designed for group A ,other phpExample is designed for group B.

If it happens like that nobody mix phpExample if they have a nickname. That's why we are using namespaces. Now you may say what is about, actually I don't know either I just wanted to inform you :) Our subject is how can we upload automatically our classes.

Usually we do

We were using _autoload() function. now with PHP 7.2 it's not recommended any more. Now we are using spl_autoload_register() function. How do we use it;

spl_autoload_register(function($class){
    $file = __DIR__ . '/src/classes/' . strtolower($class) . '.php';
    if (file_exists($file))
        require $file;
});

But this not enough now. Actually it is not logical. I might have other classes in my other files. That's why we didn'T think this as a problem.This FIG they indicated a autoloading standard that they all PSR-4. According to them these things should be;

\<NamespaceName>(\<SubNamespaceNames>)*\<ClassName>

So classes should have a top-level namespace. Also it is knowns as vendor namespace. In addition it should have 1 or more subspacename. And also class name.

If we do operation according to logic of this guys :)

spl_autoload_register(function($class){

    // top-level namespace
    $prefix = 'phpExample\';

    // home directory for namespace
    $base_dir = __DIR__ . '/src/libraries/';

    // If the class being called does not contain the prefix, move on to the next install.
    $len = strlen($prefix);
    if (strncmp($prefix, $class, $len) !== 0){
        return;
    }

    // remainder of class except prefix
    $relative_class = substr($class, $len);

    // combine them all to create directory path
    $file = $base_dir . str_replace('\', '/', $relative_class) . '.php';

    // If there is a class file, upload it
    if (file_exists($file)){
       require $file;
    }
});

// Actually this class is in
// src/libraries/validators/testvalidator.php
$test = new phpExample\Validators\TestValidator();

// src/libraries/database/testdatabase.php
$db = new phpExample\Database\TestDatabase();

Usage with Composer

{
  "autoload": {
    "psr-4": {
      "phpExample\": "src/libraries"
    }
  }
}

Here we indicated the top-level namespace and the array that includes namespace.If we run the update command of composer on the terminal, you will see a vendor folder that contains autoload.php in main array. Also there is a Composer folder. Here we do operations and  we called the autoload.php in our index file. And we try to use our classes.

<?php
require __DIR__ . '/vendor/autoload.php';

$test = new phpExample\Validators\TestValidator();
$db = new phpExample\Database\TestDatabase();

Result ? Yes it is working. Congrats, we achieved to use first standard :)