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);
    }

}