class LinkRelationTypeManager

class LinkRelationTypeManager extends DefaultPluginManager {
    
    /**
     * {@inheritdoc}
     */
    protected $defaults = [
        'class' => LinkRelationType::class,
    ];
    
    /**
     * The app root.
     *
     * @var string
     */
    protected $root;
    
    /**
     * Constructs a new LinkRelationTypeManager.
     *
     * @param string $root
     *   The app root.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache
     *   The cache backend.
     */
    public function __construct($root, ModuleHandlerInterface $module_handler, CacheBackendInterface $cache) {
        $this->root = $root;
        $this->pluginInterface = LinkRelationTypeInterface::class;
        $this->moduleHandler = $module_handler;
        $this->setCacheBackend($cache, 'link_relation_type_plugins', [
            'link_relation_type',
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getDiscovery() {
        if (!$this->discovery) {
            $directories = [
                'core' => $this->root . '/core',
            ];
            $directories += array_map(function (Extension $extension) {
                return $this->root . '/' . $extension->getPath();
            }, $this->moduleHandler
                ->getModuleList());
            $this->discovery = new YamlDiscovery('link_relation_types', $directories);
        }
        return $this->discovery;
    }

}