<?php

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

class Mailer
{
    public function mail($recipient, $content)
    {
        echo 'mail sent';
    }
}

class UserManager
{
    private $mailer;

    public function __construct(Mailer $mailer)
    {
        $this->mailer = $mailer;
    }

    public function register($email, $password)
    {
        $this->mailer->mail($email, 'Hello and welcome!');
    }
}

$container = new DI\Container();
$userManager = $container->get('UserManager');
$userManager->register('john@gmail.com', 'password');