Php namespaces in subfolders issue

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PHP

I have very simple web app. Learning how to use namespaces.

Structure of directories is:
www (root)
class (application directory)
index.php
payment (sub-directory for namespace)
card.php (separate class, namespace)
gameplay (sub-directory for namespace)
card.php (separate class, namespace)


Code is as follows:

index.php

<?php 
	function my_autoload_function($c)
	{
		require_once "class/".str_replace("\\","/",$c).".php";		
	}

	spl_autoload_register('my_autoload_function');

	$gpcard=new \gameplay\card;
	$gpcard->play();
?>

card.php (subfolder payment)

<?php 
	namespace payment;
	class Card
	{
		public function pay()
		{
			echo "Plaćanje Visa karticom";
		}
	}
?>

card.php (subfolder gameplay)

<?php 
	namespace gameplay;
	class Card
	{
		public function play()
		{
			echo "Igra Dama crvena";
		}
	}
?>

Error messages which I get are:
1)

Quote:

Warning: require_once(class/gameplay/card.php): failed to open stream: No such file or directory in C:\wamp64\www\class\index.php on line 4

2)

Quote:

Fatal error: require_once(): Failed opening required 'class/gameplay/card.php' (include_path='.;C:\php\pear') in C:\wamp64\www\class\index.php on line 4

Can somebody help with this?

What I have tried:

I tried different solutions with paths but without success.