diff --git a/core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotatedClassDiscovery.php
index a073665..11ed449 100644
--- a/core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Component/Annotation/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -51,7 +51,7 @@ class AnnotatedClassDiscovery implements DiscoveryInterface {
    *
    * @var string[]
    */
-  protected $annotationNamespaces = array();
+  protected $annotationNamespaces = [];
 
   /**
    * Constructs a new instance.
@@ -65,7 +65,7 @@ class AnnotatedClassDiscovery implements DiscoveryInterface {
    * @param string[] $annotation_namespaces
    *   (optional) Additional namespaces to be scanned for annotation classes.
    */
-  function __construct($plugin_namespaces = array(), $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin', array $annotation_namespaces = array()) {
+  function __construct($plugin_namespaces = array(), $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin', array $annotation_namespaces = []) {
     $this->pluginNamespaces = $plugin_namespaces;
     $this->pluginDefinitionAnnotationName = $plugin_definition_annotation_name;
     $this->annotationNamespaces = $annotation_namespaces;
@@ -84,8 +84,11 @@ protected function getAnnotationReader() {
       // Add the namespaces from the main plugin annotation, like @EntityType.
       $namespace = substr($this->pluginDefinitionAnnotationName, 0, strrpos($this->pluginDefinitionAnnotationName, '\\'));
       $this->annotationReader->addNamespace($namespace);
+
       // Register additional namespaces to be scanned for annotations.
-      array_walk($this->annotationNamespaces, [$this->annotationReader, 'addNamespace']);
+      foreach ($this->annotationNamespaces as $namespace) {
+        $this->annotationReader->addNamespace($namespace);
+      }
     }
     return $this->annotationReader;
   }
diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index 065e99a..0232fbe 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -42,7 +42,7 @@ class DefaultPluginManager extends PluginManagerBase implements PluginManagerInt
    *
    * @var array
    */
-  protected $cacheTags = array();
+  protected $cacheTags = [];
 
   /**
    * Name of the alter hook if one should be invoked.
@@ -73,7 +73,7 @@ class DefaultPluginManager extends PluginManagerBase implements PluginManagerInt
    *
    * @var array
    */
-  protected $defaults = array();
+  protected $defaults = [];
 
   /**
    * The name of the annotation that contains the plugin definition.
@@ -103,7 +103,7 @@ class DefaultPluginManager extends PluginManagerBase implements PluginManagerInt
    *
    * @var string[]
    */
-  protected $annotationNamespaces = array();
+  protected $annotationNamespaces = [];
 
   /**
    * Creates the discovery object.
@@ -123,7 +123,7 @@ class DefaultPluginManager extends PluginManagerBase implements PluginManagerInt
    * @param string[] $annotation_namespaces
    *   (optional) Additional namespaces to scan for annotation definitions.
    */
-  public function __construct($subdir, \Traversable $namespaces, ModuleHandlerInterface $module_handler, $plugin_interface = NULL, $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin', array $annotation_namespaces = array()) {
+  public function __construct($subdir, \Traversable $namespaces, ModuleHandlerInterface $module_handler, $plugin_interface = NULL, $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin', array $annotation_namespaces = []) {
     $this->subdir = $subdir;
     $this->namespaces = $namespaces;
     $this->pluginDefinitionAnnotationName = $plugin_definition_annotation_name;
@@ -248,29 +248,6 @@ public function useCaches($use_caches = FALSE) {
   }
 
   /**
-   * Fetches from the cache backend, respecting the use caches flag.
-   *
-   * @see \Drupal\Core\Cache\CacheBackendInterface::get()
-   */
-  protected function cacheGet($cid) {
-    if ($this->useCaches && $this->cacheBackend) {
-      return $this->cacheBackend->get($cid);
-    }
-    return FALSE;
-  }
-
-  /**
-   * Stores data in the persistent cache, respecting the use caches flag.
-   *
-   * @see \Drupal\Core\Cache\CacheBackendInterface::set()
-   */
-  protected function cacheSet($cid, $data, $expire = Cache::PERMANENT, array $tags = array()) {
-    if ($this->cacheBackend && $this->useCaches) {
-      $this->cacheBackend->set($cid, $data, $expire, $tags);
-    }
-  }
-
-  /**
    * Performs extra processing on plugin definitions.
    *
    * By default we add defaults for the type to the definition. If a type has