Service.php

<?php

namespace Drupal\new_dependency_test;


/**
 * A service that can decorated itself.
 *
 * @see new_dependency_test.services.yml
 */
class Service {
    
    /**
     * The decorated service.
     *
     * @var \Drupal\new_dependency_test\Service
     */
    protected $inner;
    
    /**
     * Service constructor.
     *
     * @param \Drupal\new_dependency_test\Service|null $inner
     *   The service to decorate.
     */
    public function __construct(?Service $inner = NULL) {
        $this->inner = $inner;
    }
    
    /**
     * Determines if the service is decorated.
     *
     * @return bool
     *   TRUE if the services is decorated, FALSE if not.
     */
    public function isDecorated() {
        return isset($this->inner);
    }

}