Class Not found when autoloading with namespace (no Composer)

Question

I have been checking for answers but with no success. I'm not using composer autoload function.

I'm trying to test some classes, Collections and traits in a index.php. The problem is when i'm including a namespace, I'have created the _autoload function (No composer) to load a class when needed. If I execute php index.php i'm getting the class not found error.

I have tried the use command, but with no success as well.

It solves when I include each class one by one like this:

include_once __DIR__ . '/Collection.php';
include_once __DIR__ . '/User.php';
include_once __DIR__ . '/Tweet.php';
include_once __DIR__ . '/UserCollection.php';
include_once __DIR__ . '/TweetCollection.php';

Thats my index.php:

<?php

namespace phpexercises\entregableT3;

error_reporting(E_ALL);
ini_set( "display_errors", "on" );
/*
include_once __DIR__ . '/Collection.php';
include_once __DIR__ . '/User.php';
include_once __DIR__ . '/Tweet.php';
include_once __DIR__ . '/UserCollection.php';
include_once __DIR__ . '/TweetCollection.php';
*/
use phpexercises\entregableT3\User;

function __autoload($classname){
   require __DIR__ . "/" . $classname . ".php";

}

//UserCollection pruebas

$alex = new User();
$jumbo = new User();

$users = new UserCollection();
$alex->phone = "682383";
$alex->email = "[email protected]";
$alex->city = "BCN";
$alex->gender = "Male";


$jumbo->phone = "54534535";
$jumbo->email = "[email protected]";
$jumbo->city = "elche";
$jumbo->gender = "Male";

$users->add($alex);
$users->add($jumbo);



print_r($users->findByEmail("[email protected]"));
print_r($users->findByGender("Female"));

//Tweet Collection pruebas

$tweet = new Tweet();
$tweet->email  = "[email protected]";
$tweet->text = "This is a tweet";
$tweet->date = date("D:M:Y");

$tweet1 = new Tweet();
$tweet1->email  = "[email protected]";
$tweet1->text = "This is a tweet";
$tweet1->date = date("D:M:Y");

When I uncomment the requires, everything works fine, but it is not the way to load all classes...Any idea for this behaviour? How should I load the classes at same time? Thanks