class ForumBreadcrumbBuilderBase

abstract class ForumBreadcrumbBuilderBase implements BreadcrumbBuilderInterface {
  use StringTranslationTrait;
  
  /**
   * Configuration object for this builder.
   *
   * @var \Drupal\Core\Config\Config
   */
  protected $config;
  
  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;
  
  /**
   * The forum manager service.
   *
   * @var \Drupal\forum\ForumManagerInterface
   */
  protected $forumManager;
  
  /**
   * The taxonomy term storage.
   *
   * @var \Drupal\taxonomy\TermStorageInterface
   */
  protected $termStorage;
  
  /**
   * Constructs a forum breadcrumb builder object.
   *
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
   *   The configuration factory.
   * @param \Drupal\forum\ForumManagerInterface $forum_manager
   *   The forum manager service.
   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
   *   The string translation service.
   */
  public function __construct(EntityTypeManagerInterface $entity_type_manager, ConfigFactoryInterface $config_factory, ForumManagerInterface $forum_manager, TranslationInterface $string_translation) {
    $this->entityTypeManager = $entity_type_manager;
    $this->config = $config_factory->get('forum.settings');
    $this->forumManager = $forum_manager;
    $this->setStringTranslation($string_translation);
    $this->termStorage = $entity_type_manager->getStorage('taxonomy_term');
  }
  
  /**
   * {@inheritdoc}
   */
  public function build(RouteMatchInterface $route_match) {
    $breadcrumb = new Breadcrumb();
    $breadcrumb->addCacheContexts([
      'route',
    ]);
    $links[] = Link::createFromRoute($this->t('Home'), '<front>');
    $vocabulary = $this->entityTypeManager
      ->getStorage('taxonomy_vocabulary')
      ->load($this->config
      ->get('vocabulary'));
    $breadcrumb->addCacheableDependency($vocabulary);
    $links[] = Link::createFromRoute($vocabulary->label(), 'forum.index');
    return $breadcrumb->setLinks($links);
  }

}