config.yml

services:
  mailer:
    class:     Mailer
  newsletter_manager:
    class:     NewsletterManager
    dependencies:
      mailer: Mailer

main.php

$newsletter = InjectionSingleton::inject('newsletter_manager');
$newsletter->doStuff();

super.php

class NewsletterManager {

  public function __construct() {
    InjectionSingleton::inject($this);
  }
  
  public function doStuff() {
    $this->mailer->doOtherStuff();
  }
}