diff --git a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimeDefaultFormatter.php b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimeDefaultFormatter.php
index 729c44e..4ec311b 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimeDefaultFormatter.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimeDefaultFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Template\Attribute;
 
@@ -34,7 +35,7 @@ class DateTimeDefaultFormatter extends FormatterBase {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
 
     $elements = array();
 
diff --git a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimePlainFormatter.php b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimePlainFormatter.php
index 7c59dda..beff128 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimePlainFormatter.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/formatter/DatetimePlainFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
 
 /**
@@ -30,7 +31,7 @@ class DateTimePlainFormatter extends FormatterBase {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
 
     $elements = array();
 
diff --git a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDatelistWidget.php b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDatelistWidget.php
index 610f6fd..93e61b6 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDatelistWidget.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDatelistWidget.php
@@ -12,6 +12,7 @@
 use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\PluginSettingsBase;
 use Drupal\field\FieldInstanceInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
@@ -62,7 +63,7 @@ public function defaultValueFunction() {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $date_order = $this->getSetting('date_order');
     $time_type = $this->getSetting('time_type');
     $increment = $this->getSetting('increment');
diff --git a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDefaultWidget.php b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDefaultWidget.php
index 79f12bc..1566558 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDefaultWidget.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/widget/DatetimeDefaultWidget.php
@@ -12,6 +12,7 @@
 use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\PluginSettingsBase;
 use Drupal\field\FieldInstanceInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
@@ -56,7 +57,7 @@ public function defaultValueFunction() {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $format_type = datetime_default_format_type();
 
     // We are nesting some sub-elements inside the parent, so we need a wrapper.
diff --git a/core/modules/email/lib/Drupal/email/Plugin/field/formatter/MailToFormatter.php b/core/modules/email/lib/Drupal/email/Plugin/field/formatter/MailToFormatter.php
index 33e5920..002a684 100644
--- a/core/modules/email/lib/Drupal/email/Plugin/field/formatter/MailToFormatter.php
+++ b/core/modules/email/lib/Drupal/email/Plugin/field/formatter/MailToFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'email_mailto' formatter.
@@ -29,7 +30,7 @@ class MailToFormatter extends FormatterBase {
   /**
    * Implements Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/email/lib/Drupal/email/Plugin/field/widget/EmailDefaultWidget.php b/core/modules/email/lib/Drupal/email/Plugin/field/widget/EmailDefaultWidget.php
index 9cd6a99..fea0987 100644
--- a/core/modules/email/lib/Drupal/email/Plugin/field/widget/EmailDefaultWidget.php
+++ b/core/modules/email/lib/Drupal/email/Plugin/field/widget/EmailDefaultWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -44,7 +45,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * Implements Drupal\field\Plugin\Type\Widget\WidgetInterface::formElement().
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element['value'] = $element + array(
       '#type' => 'email',
       '#default_value' => isset($items[$delta]['value']) ? $items[$delta]['value'] : NULL,
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceEntityFormatter.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceEntityFormatter.php
index 51d48b9..a6e8418 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceEntityFormatter.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceEntityFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\entity_reference\RecursiveRenderingException;
 use Drupal\entity_reference\Plugin\field\formatter\EntityReferenceFormatterBase;
 
@@ -76,7 +77,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     // Remove un-accessible items.
     parent::viewElements($entity, $langcode, $items);
 
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceFormatterBase.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceFormatterBase.php
index 51f5285..15dd466 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceFormatterBase.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceFormatterBase.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 
 /**
@@ -99,7 +100,7 @@ public function prepareView(array $entities, $langcode, array &$items) {
    *
    * @see \Drupal\entity_reference\Plugin\field\formatter\EntityReferenceFormatterBase::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     // Remove un-accessible items.
     foreach ($items as $delta => $item) {
       if (empty($item['access'])) {
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceIdFormatter.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceIdFormatter.php
index 3de34ee..306438c 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceIdFormatter.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceIdFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\entity_reference\Plugin\field\formatter\EntityReferenceFormatterBase;
 
 /**
@@ -30,7 +31,7 @@ class EntityReferenceIdFormatter extends EntityReferenceFormatterBase {
   /**
    * Overrides \Drupal\entity_reference\Plugin\field\formatter\EntityReferenceFormatterBase::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceLabelFormatter.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceLabelFormatter.php
index 568d3d8..f308e29 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceLabelFormatter.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/formatter/EntityReferenceLabelFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\entity_reference\Plugin\field\formatter\EntityReferenceFormatterBase;
 
 /**
@@ -55,7 +56,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     // Remove un-accessible items.
     parent::viewElements($entity, $langcode, $items);
 
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidget.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidget.php
index ee98bfe..b68d344 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidget.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\entity_reference\Plugin\field\widget\AutocompleteWidgetBase;
 
 /**
@@ -40,7 +41,7 @@ class AutocompleteWidget extends AutocompleteWidgetBase {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     // We let the Field API handles multiple values for us, only take care of
     // the one matching our delta.
     if (isset($items[$delta])) {
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php
index 440b626..a279175 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -52,7 +53,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     global $user;
     $entity = $element['#entity'];
 
@@ -98,7 +99,7 @@ public function elementValidate($element, &$form_state, $form) { }
   /**
    * Gets the entity labels.
    */
-  protected function getLabels(array $items) {
+  protected function getLabels(FieldInterface $items) {
     $entity_ids = array();
     $entity_labels = array();
 
diff --git a/core/modules/field/field.attach.inc b/core/modules/field/field.attach.inc
index 7965679..49ca553 100644
--- a/core/modules/field/field.attach.inc
+++ b/core/modules/field/field.attach.inc
@@ -179,7 +179,7 @@ function field_invoke_method($method, $target_function, EntityInterface $entity,
       $langcodes = _field_language_suggestion($available_langcodes, $options['langcode'], $field_name);
 
       foreach ($langcodes as $langcode) {
-        $items = isset($entity->{$field_name}[$langcode]) ? $entity->{$field_name}[$langcode] : array();
+        $items = $entity->getTranslation($langcode)->get($field_name);
 
         $result = $target->$method($entity, $langcode, $items, $a, $b);
 
@@ -193,12 +193,6 @@ function field_invoke_method($method, $target_function, EntityInterface $entity,
             $return[] = $result;
           }
         }
-
-        // Populate $items back in the field values, but avoid replacing missing
-        // fields with an empty array (those are not equivalent on update).
-        if ($items !== array() || isset($entity->{$field_name}[$langcode])) {
-          $entity->{$field_name}[$langcode] = $items;
-        }
       }
     }
   }
@@ -290,7 +284,7 @@ function field_invoke_method_multiple($method, $target_function, array $entities
         foreach ($langcodes as $langcode) {
           // Group the entities and items corresponding to the current field.
           $grouped_entities[$instance_id][$langcode][$id] = $entities[$id];
-          $grouped_items[$instance_id][$langcode][$id] = isset($entity->{$field_name}[$langcode]) ? $entity->{$field_name}[$langcode] : array();
+          $grouped_items[$instance_id][$langcode][$id] = $entity->getTranslation($langcode)->get($field_name);
         }
       }
     }
@@ -303,7 +297,7 @@ function field_invoke_method_multiple($method, $target_function, array $entities
     $field_name = $instance['field_name'];
 
     // Iterate over all the field translations.
-    foreach ($grouped_items[$instance_id] as $langcode => &$items) {
+    foreach ($grouped_items[$instance_id] as $langcode => $items) {
       $entities = $grouped_entities[$instance_id][$langcode];
       $results = $grouped_targets[$instance_id]->$method($entities, $langcode, $items, $a, $b);
 
@@ -321,16 +315,6 @@ function field_invoke_method_multiple($method, $target_function, array $entities
         }
       }
     }
-
-    // Populate field values back in the entities, but avoid replacing missing
-    // fields with an empty array (those are not equivalent on update).
-    foreach ($grouped_entities[$instance_id] as $langcode => $entities) {
-      foreach ($entities as $id => $entity) {
-        if ($grouped_items[$instance_id][$langcode][$id] !== array() || isset($entity->{$field_name}[$langcode])) {
-          $entity->{$field_name}[$langcode] = $grouped_items[$instance_id][$langcode][$id];
-        }
-      }
-    }
   }
 
   return $return;
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterBase.php
index fa780a5..ac3c10c 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterBase.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\FieldInstanceInterface;
 use Drupal\field\Plugin\PluginSettingsBase;
 
@@ -73,7 +74,7 @@ public function __construct($plugin_id, array $plugin_definition, FieldDefinitio
   /**
    * {@inheritdoc}
    */
-  public function view(EntityInterface $entity, $langcode, array $items) {
+  public function view(EntityInterface $entity, $langcode, FieldInterface $items) {
     $addition = array();
 
     $elements = $this->viewElements($entity, $langcode, $items);
@@ -93,7 +94,8 @@ public function view(EntityInterface $entity, $langcode, array $items) {
         '#entity_type' => $entity_type,
         '#bundle' => $entity->bundle(),
         '#object' => $entity,
-        '#items' => $items,
+        // @todo Anything that uses #items should be converted as well...
+        '#items' => $items->getValue(),
         '#formatter' => $this->getPluginId(),
       );
 
@@ -120,7 +122,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function prepareView(array $entities, $langcode, array &$items) { }
+  public function prepareView(array $entities, $langcode, FieldInterface $items) { }
 
   /**
    * Returns whether the currently logged in user has access to the field.
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterInterface.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterInterface.php
index 8f7f3df..5d371e5 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterInterface.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterInterface.php
@@ -8,7 +8,7 @@
 namespace Drupal\field\Plugin\Type\Formatter;
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\field\Plugin\Core\Entity\FieldInstance;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\PluginSettingsInterface;
 
 /**
@@ -72,7 +72,7 @@ public function settingsSummary();
    * @param array $items
    *   Array of field values for the entities, keyed by entity ID.
    */
-  public function prepareView(array $entities, $langcode, array &$items);
+  public function prepareView(array $entities, $langcode, array $items);
 
   /**
    * Builds a renderable array for one field on one entity instance.
@@ -81,13 +81,13 @@ public function prepareView(array $entities, $langcode, array &$items);
    *   The entity being displayed.
    * @param string $langcode
    *   The language associated with $items.
-   * @param array $items
-   *   Array of field values already loaded for the entities, keyed by entity id.
+   * @param Drupal\Core\Entity\Field\FieldInterface $items
+   *   The field value for the entity for the language.
    *
    * @return array
    *   A renderable array for a themed field with its label and all its values.
    */
-  public function view(EntityInterface $entity, $langcode, array $items);
+  public function view(EntityInterface $entity, $langcode, FieldInterface $items);
 
   /**
    * Builds a renderable array for a field value.
@@ -103,6 +103,6 @@ public function view(EntityInterface $entity, $langcode, array $items);
    *   A renderable array for $items, as an array of child elements keyed by
    *   numeric indexes starting from 0.
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items);
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items);
 
 }
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
index 5cf902b..4ee0daf 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
@@ -10,6 +10,7 @@
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\FieldInstanceInterface;
 use Drupal\field\Plugin\PluginSettingsBase;
 
@@ -54,7 +55,7 @@ public function __construct($plugin_id, array $plugin_definition, FieldDefinitio
   /**
    * {@inheritdoc}
    */
-  public function form(EntityInterface $entity, $langcode, array $items, array &$form, array &$form_state, $get_delta = NULL) {
+  public function form(EntityInterface $entity, $langcode, FieldInterface $items, array &$form, array &$form_state, $get_delta = NULL) {
     $field_name = $this->fieldDefinition->getFieldName();
 
     $parents = $form['#parents'];
@@ -149,7 +150,7 @@ public function form(EntityInterface $entity, $langcode, array $items, array &$f
    * - AHAH-'add more' button
    * - table display and drag-n-drop value reordering
    */
-  protected function formMultipleElements(EntityInterface $entity, array $items, $langcode, array &$form, array &$form_state) {
+  protected function formMultipleElements(EntityInterface $entity, FieldInterface $items, $langcode, array &$form, array &$form_state) {
     $field_name = $this->fieldDefinition->getFieldName();
     $cardinality = $this->fieldDefinition->getFieldCardinality();
     $parents = $form['#parents'];
@@ -242,7 +243,7 @@ protected function formMultipleElements(EntityInterface $entity, array $items, $
   /**
    * Generates the form element for a single copy of the widget.
    */
-  protected function formSingleElement(EntityInterface $entity, array $items, $delta, $langcode, array $element, array &$form, array &$form_state) {
+  protected function formSingleElement(EntityInterface $entity, FieldInterface $items, $delta, $langcode, array $element, array &$form, array &$form_state) {
     $element += array(
       '#entity_type' => $entity->entityType(),
       '#bundle' => $entity->bundle(),
@@ -330,7 +331,7 @@ public function extractFormValues(EntityInterface $entity, $langcode, array &$it
   /**
    * {@inheritdoc}
    */
-  public function flagErrors(EntityInterface $entity, $langcode, array $items, array $form, array &$form_state) {
+  public function flagErrors(EntityInterface $entity, $langcode, FieldInterface $items, array $form, array &$form_state) {
     $field_name = $this->fieldDefinition->getFieldName();
 
     $field_state = field_form_get_state($form['#parents'], $field_name, $langcode, $form_state);
@@ -390,7 +391,7 @@ public function massageFormValues(array $values, array $form, array &$form_state
   /**
    * Sorts submitted field values according to drag-n-drop reordering.
    *
-   * @param array $items
+   * @param FieldInterface $items
    *   The field values.
    */
   protected function sortItems(array &$items) {
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBaseInterface.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBaseInterface.php
index ae107c9..5b3e673 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBaseInterface.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBaseInterface.php
@@ -8,6 +8,7 @@
 namespace Drupal\field\Plugin\Type\Widget;
 
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\PluginSettingsInterface;
 
 /**
@@ -31,7 +32,7 @@
    *   The entity for which the widget is being built.
    * @param string $langcode
    *   The language associated with the field.
-   * @param array $items
+   * @param FieldInterface $items
    *   An array of the field values. When creating a new entity this may be NULL
    *   or an empty array to use default values.
    * @param array $form
@@ -45,7 +46,7 @@
    * @return array
    *   The form element array created for this field.
    */
-  public function form(EntityInterface $entity, $langcode, array $items, array &$form, array &$form_state, $get_delta = NULL);
+  public function form(EntityInterface $entity, $langcode, FieldInterface $items, array &$form, array &$form_state, $get_delta = NULL);
 
   /**
    * Extracts field values from submitted form values.
@@ -54,7 +55,7 @@ public function form(EntityInterface $entity, $langcode, array $items, array &$f
    *   The entity for which the widget is being submitted.
    * @param string $langcode
    *   The language associated to $items.
-   * @param array $items
+   * @param FieldInterface $items
    *   The field values. This parameter is altered by reference to receive the
    *   incoming form values.
    * @param array $form
@@ -72,7 +73,7 @@ public function extractFormValues(EntityInterface $entity, $langcode, array &$it
    *   The entity for which the widget is being submitted.
    * @param string $langcode
    *   The language associated to $items.
-   * @param array $items
+   * @param FieldInterface $items
    *   The field values.
    * @param array $form
    *   The form structure where field elements are attached to. This might be a
@@ -80,6 +81,6 @@ public function extractFormValues(EntityInterface $entity, $langcode, array &$it
    * @param array $form_state
    *   The form state.
    */
-  public function flagErrors(EntityInterface $entity, $langcode, array $items, array $form, array &$form_state);
+  public function flagErrors(EntityInterface $entity, $langcode, FieldInterface $items, array $form, array &$form_state);
 
 }
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetInterface.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetInterface.php
index e00005b..1e28bea 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetInterface.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetInterface.php
@@ -8,7 +8,7 @@
 namespace Drupal\field\Plugin\Type\Widget;
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\field\Plugin\Core\Entity\FieldInstance;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Interface definition for field widget plugins.
@@ -61,7 +61,7 @@ public function settingsForm(array $form, array &$form_state);
    * definition and set them as ad-hoc $element['#custom'] properties, for later
    * use by its element callbacks.
    *
-   * @param array $items
+   * @param FieldInterface $items
    *   Array of default values for this field.
    * @param int $delta
    *   The order of this item in the array of subelements (0, 1, 2, etc).
@@ -101,7 +101,7 @@ public function settingsForm(array $form, array &$form_state);
    * @see hook_field_widget_form_alter()
    * @see hook_field_widget_WIDGET_TYPE_form_alter()
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state);
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state);
 
   /**
    * Assigns a field-level validation error to the right widget sub-element.
diff --git a/core/modules/field/lib/Drupal/field/Plugin/field/widget/HiddenWidget.php b/core/modules/field/lib/Drupal/field/Plugin/field/widget/HiddenWidget.php
index d2ff3cb..43cc435 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/field/widget/HiddenWidget.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/field/widget/HiddenWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -27,7 +28,7 @@ class HiddenWidget extends WidgetBase {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     // The purpose of this widget is to be hidden, so nothing to do here.
     return array();
   }
diff --git a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldDefaultFormatter.php b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldDefaultFormatter.php
index 4e1f59a..ea55105 100644
--- a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldDefaultFormatter.php
+++ b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldDefaultFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'field_test_default' formatter.
@@ -56,7 +57,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldEmptyFormatter.php b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldEmptyFormatter.php
index df71b16..cc00e2f 100644
--- a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldEmptyFormatter.php
+++ b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldEmptyFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 
 /**
@@ -44,7 +45,7 @@ public function prepareView(array $entities, $langcode, array &$items) {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     if (!empty($items)) {
diff --git a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldMultipleFormatter.php b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldMultipleFormatter.php
index 2810e09..0df2b73 100644
--- a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldMultipleFormatter.php
+++ b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldMultipleFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'field_test_multiple' formatter.
@@ -56,7 +57,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     if (!empty($items)) {
diff --git a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldPrepareViewFormatter.php b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldPrepareViewFormatter.php
index ad0ea47..59575b5 100644
--- a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldPrepareViewFormatter.php
+++ b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/formatter/TestFieldPrepareViewFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'field_test_with_prepare_view' formatter.
@@ -70,7 +71,7 @@ public function prepareView(array $entities, $langcode, array &$items) {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidget.php b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidget.php
index 293ef18..3ef5c0d 100644
--- a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidget.php
+++ b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -46,7 +47,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * Implements Drupal\field\Plugin\Type\Widget\WidgetInterface::formElement().
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element += array(
       '#type' => 'textfield',
       '#default_value' => isset($items[$delta]['value']) ? $items[$delta]['value'] : '',
diff --git a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidgetMultiple.php b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidgetMultiple.php
index 95b3cf2..401942e 100644
--- a/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidgetMultiple.php
+++ b/core/modules/field/tests/modules/field_test/lib/Drupal/field_test/Plugin/field/widget/TestFieldWidgetMultiple.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -47,7 +48,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * Implements Drupal\field\Plugin\Type\Widget\WidgetInterface::formElement().
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $values = array();
     foreach ($items as $delta => $value) {
       $values[] = $value['value'];
diff --git a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/GenericFileFormatter.php b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/GenericFileFormatter.php
index bc0d16e..01444aa 100644
--- a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/GenericFileFormatter.php
+++ b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/GenericFileFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'file_default' formatter.
@@ -29,7 +30,7 @@ class GenericFileFormatter extends FormatterBase {
   /**
    * Implements \Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/RSSEnclosureFormatter.php b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/RSSEnclosureFormatter.php
index ecbba24..c1d3bb6 100644
--- a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/RSSEnclosureFormatter.php
+++ b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/RSSEnclosureFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'file_rss_enclosure' formatter.
@@ -29,7 +30,7 @@ class RSSEnclosureFormatter extends FormatterBase {
   /**
    * Implements \Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
 
     // Add the first file as an enclosure to the RSS item. RSS allows only one
     // enclosure per item. See: http://en.wikipedia.org/wiki/RSS_enclosure
diff --git a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/TableFormatter.php b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/TableFormatter.php
index cc7a57d..8022d18 100644
--- a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/TableFormatter.php
+++ b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/TableFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'file_table' formatter.
@@ -29,7 +30,7 @@ class TableFormatter extends FormatterBase {
   /**
    * Implements \Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     if (!empty($items)) {
diff --git a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/UrlPlainFormatter.php b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/UrlPlainFormatter.php
index 507d86f..8555f81 100644
--- a/core/modules/file/lib/Drupal/file/Plugin/field/formatter/UrlPlainFormatter.php
+++ b/core/modules/file/lib/Drupal/file/Plugin/field/formatter/UrlPlainFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'file_url_plain' formatter.
@@ -29,7 +30,7 @@ class UrlPlainFormatter extends FormatterBase {
   /**
    * Implements \Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php b/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
index 4603288..7be47e0 100644
--- a/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
+++ b/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'file_generic' widget.
@@ -54,7 +55,7 @@ public function settingsForm(array $form, array &$form_state) {
    *
    * Special handling for draggable multiple widgets and 'add more' button.
    */
-  protected function formMultipleElements(EntityInterface $entity, array $items, $langcode, array &$form, array &$form_state) {
+  protected function formMultipleElements(EntityInterface $entity, FieldInterface $items, $langcode, array &$form, array &$form_state) {
     $field_name = $this->fieldDefinition->getFieldName();
 
     $parents = $form['#parents'];
@@ -164,7 +165,7 @@ protected function formMultipleElements(EntityInterface $entity, array $items, $
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $field_settings = $this->getFieldSettings();
 
     // The field settings include defaults for the field type. However, this
diff --git a/core/modules/image/lib/Drupal/image/Plugin/field/formatter/ImageFormatter.php b/core/modules/image/lib/Drupal/image/Plugin/field/formatter/ImageFormatter.php
index a5078a2..f21fc7a 100644
--- a/core/modules/image/lib/Drupal/image/Plugin/field/formatter/ImageFormatter.php
+++ b/core/modules/image/lib/Drupal/image/Plugin/field/formatter/ImageFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'image' formatter.
@@ -93,7 +94,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     $image_link_setting = $this->getSetting('image_link');
diff --git a/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php b/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php
index 3ad6e0f..79d0835 100644
--- a/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php
+++ b/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php
@@ -12,6 +12,7 @@
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 use Drupal\file\Plugin\field\widget\FileWidget;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'image_image' widget.
@@ -56,7 +57,7 @@ public function settingsForm(array $form, array &$form_state) {
    *
    * Special handling for draggable multiple widgets and 'add more' button.
    */
-  protected function formMultipleElements(EntityInterface $entity, array $items, $langcode, array &$form, array &$form_state) {
+  protected function formMultipleElements(EntityInterface $entity, FieldInterface $items, $langcode, array &$form, array &$form_state) {
     $elements = parent::formMultipleElements($entity, $items, $langcode, $form, $form_state);
 
     $cardinality = $this->fieldDefinition->getFieldCardinality();
@@ -76,7 +77,7 @@ protected function formMultipleElements(EntityInterface $entity, array $items, $
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element = parent::formElement($items, $delta, $element, $langcode, $form, $form_state);
 
     $field_settings = $this->getFieldSettings();
diff --git a/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkFormatter.php b/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkFormatter.php
index fe18bbe..014c883 100644
--- a/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkFormatter.php
+++ b/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 
 /**
@@ -145,7 +146,7 @@ public function prepareView(array $entities, $langcode, array &$items) {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $element = array();
     $settings = $this->getSettings();
 
diff --git a/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkSeparateFormatter.php b/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkSeparateFormatter.php
index 61e0417..6a039b3 100644
--- a/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkSeparateFormatter.php
+++ b/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkSeparateFormatter.php
@@ -15,6 +15,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 
 /**
@@ -39,7 +40,7 @@ class LinkSeparateFormatter extends LinkFormatter {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $element = array();
     $settings = $this->getSettings();
 
diff --git a/core/modules/link/lib/Drupal/link/Plugin/field/widget/LinkWidget.php b/core/modules/link/lib/Drupal/link/Plugin/field/widget/LinkWidget.php
index f960613..6a35cdf 100644
--- a/core/modules/link/lib/Drupal/link/Plugin/field/widget/LinkWidget.php
+++ b/core/modules/link/lib/Drupal/link/Plugin/field/widget/LinkWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -32,7 +33,7 @@ class LinkWidget extends WidgetBase {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element['url'] = array(
       '#type' => 'url',
       '#title' => t('URL'),
diff --git a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/DefaultNumberFormatter.php b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/DefaultNumberFormatter.php
index 8188dc1..e6ed084 100644
--- a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/DefaultNumberFormatter.php
+++ b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/DefaultNumberFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Parent plugin for decimal and integer formatters
@@ -64,7 +65,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberDecimalFormatter.php b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberDecimalFormatter.php
index 41f075d..21fe5c0 100644
--- a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberDecimalFormatter.php
+++ b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberDecimalFormatter.php
@@ -12,6 +12,7 @@
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\number\Plugin\field\formatter\DefaultNumberFormatter;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'number_decimal' formatter.
diff --git a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberIntegerFormatter.php b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberIntegerFormatter.php
index 16f36ad..446f226 100644
--- a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberIntegerFormatter.php
+++ b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberIntegerFormatter.php
@@ -12,6 +12,7 @@
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\number\Plugin\field\formatter\DefaultNumberFormatter;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'number_integer' formatter.
diff --git a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberUnformattedFormatter.php b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberUnformattedFormatter.php
index b8a3653..aed55f5 100644
--- a/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberUnformattedFormatter.php
+++ b/core/modules/number/lib/Drupal/number/Plugin/field/formatter/NumberUnformattedFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'number_unformatted' formatter.
@@ -31,7 +32,7 @@ class NumberUnformattedFormatter extends FormatterBase {
   /**
    * Implements Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/number/lib/Drupal/number/Plugin/field/widget/NumberWidget.php b/core/modules/number/lib/Drupal/number/Plugin/field/widget/NumberWidget.php
index 7cca027..cecbed4 100644
--- a/core/modules/number/lib/Drupal/number/Plugin/field/widget/NumberWidget.php
+++ b/core/modules/number/lib/Drupal/number/Plugin/field/widget/NumberWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -46,7 +47,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $value = isset($items[$delta]['value']) ? $items[$delta]['value'] : NULL;
     $field_settings = $this->getFieldSettings();
 
diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsDefaultFormatter.php b/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsDefaultFormatter.php
index 3da3b64..d0d7b5f 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsDefaultFormatter.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsDefaultFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'list_default' formatter.
@@ -32,7 +33,7 @@ class OptionsDefaultFormatter extends FormatterBase {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     $allowed_values = options_allowed_values($this->fieldDefinition, $entity);
diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsKeyFormatter.php b/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsKeyFormatter.php
index de62b57..89c42ea 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsKeyFormatter.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/formatter/OptionsKeyFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'list_key' formatter.
@@ -32,7 +33,7 @@ class OptionsKeyFormatter extends FormatterBase {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php
index 163f46c..02f719b 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'options_buttons' widget.
@@ -31,7 +32,7 @@ class ButtonsWidget extends OptionsWidgetBase {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element = parent::formElement($items, $delta, $element, $langcode, $form, $form_state);
 
     $options = $this->getOptions();
diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/widget/OnOffWidget.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OnOffWidget.php
index fd0d230..3bdc632 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/widget/OnOffWidget.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OnOffWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'options_onoff' widget.
@@ -44,7 +45,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element = parent::formElement($items, $delta, $element, $langcode, $form, $form_state);
 
     $options = $this->getOptions();
diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
index f6801c0..558aa48 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
@@ -8,6 +8,7 @@
 namespace Drupal\options\Plugin\field\widget;
 
 use Drupal\Core\Entity\Field\FieldDefinitionInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -45,7 +46,7 @@ public function __construct($plugin_id, array $plugin_definition, FieldDefinitio
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     // Prepare some properties for the child methods to build the actual form
     // element.
     $this->entity = $element['#entity'];
@@ -155,13 +156,13 @@ protected function getOptions() {
   /**
    * Determines selected options from the incoming field values.
    *
-   * @param array $items
+   * @param FieldInterface $items
    *   The field values.
    *
    * @return array
    *   The array of corresponding selected options.
    */
-  protected function getSelectedOptions(array $items) {
+  protected function getSelectedOptions(FieldInterface $items) {
     // We need to check against a flat list of options.
     $flat_options = $this->flattenOptions($this->getOptions());
 
diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php
index b17a448..6b2eeac 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'options_select' widget.
@@ -30,7 +31,7 @@ class SelectWidget extends OptionsWidgetBase {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element = parent::formElement($items, $delta, $element, $langcode, $form, $form_state);
 
     $element += array(
diff --git a/core/modules/picture/lib/Drupal/picture/Plugin/field/formatter/PictureFormatter.php b/core/modules/picture/lib/Drupal/picture/Plugin/field/formatter/PictureFormatter.php
index 0647a39..bee6d28 100644
--- a/core/modules/picture/lib/Drupal/picture/Plugin/field/formatter/PictureFormatter.php
+++ b/core/modules/picture/lib/Drupal/picture/Plugin/field/formatter/PictureFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin for picture formatter.
@@ -115,7 +116,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
     // Check if the formatter involves a link.
     if ($this->getSetting('image_link') == 'content') {
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/EntityReferenceTaxonomyTermRssFormatter.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/EntityReferenceTaxonomyTermRssFormatter.php
index eeb7437..968b95c 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/EntityReferenceTaxonomyTermRssFormatter.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/EntityReferenceTaxonomyTermRssFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\entity_reference\Plugin\field\formatter\EntityReferenceFormatterBase;
 
 /**
@@ -32,7 +33,7 @@ class EntityReferenceTaxonomyTermRssFormatter extends EntityReferenceFormatterBa
   /**
    * Overrides Drupal\entity_reference\Plugin\field\formatter\EntityReferenceFormatterBase::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/LinkFormatter.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/LinkFormatter.php
index 63dbc0f..5a40796 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/LinkFormatter.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/LinkFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\taxonomy\Plugin\field\formatter\TaxonomyFormatterBase;
 
@@ -30,7 +31,7 @@ class LinkFormatter extends TaxonomyFormatterBase {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     // Terms without tid do not exist yet, theme such terms as just their name.
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/PlainFormatter.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/PlainFormatter.php
index 0294cb4..664590c 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/PlainFormatter.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/PlainFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\taxonomy\Plugin\field\formatter\TaxonomyFormatterBase;
 
@@ -30,7 +31,7 @@ class PlainFormatter extends TaxonomyFormatterBase {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/RSSCategoryFormatter.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/RSSCategoryFormatter.php
index e1cd48d..f11dbd8 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/RSSCategoryFormatter.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/RSSCategoryFormatter.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\taxonomy\Plugin\field\formatter\TaxonomyFormatterBase;
 
@@ -30,7 +31,7 @@ class RSSCategoryFormatter extends TaxonomyFormatterBase {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     // Terms whose tid is 'autocreate' do not exist yet and $item['entity'] is
     // not set. Theme such terms as just their name.
     foreach ($items as $item) {
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/TaxonomyFormatterBase.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/TaxonomyFormatterBase.php
index 6f688da..a20ecc0 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/TaxonomyFormatterBase.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/TaxonomyFormatterBase.php
@@ -10,6 +10,7 @@
 use Drupal\field\Annotation\FieldFormatter;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 
 /**
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/widget/TaxonomyAutocompleteWidget.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/widget/TaxonomyAutocompleteWidget.php
index c0ef1f6..fbf0c83 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/widget/TaxonomyAutocompleteWidget.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/widget/TaxonomyAutocompleteWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -47,7 +48,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $tags = array();
     foreach ($items as $item) {
       $tags[$item['tid']] = isset($item['taxonomy_term']) ? $item['taxonomy_term'] : taxonomy_term_load($item['tid']);
diff --git a/core/modules/telephone/lib/Drupal/telephone/Plugin/field/formatter/TelephoneLinkFormatter.php b/core/modules/telephone/lib/Drupal/telephone/Plugin/field/formatter/TelephoneLinkFormatter.php
index 208d6bd..7406074 100644
--- a/core/modules/telephone/lib/Drupal/telephone/Plugin/field/formatter/TelephoneLinkFormatter.php
+++ b/core/modules/telephone/lib/Drupal/telephone/Plugin/field/formatter/TelephoneLinkFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'telephone_link' formatter.
@@ -62,18 +63,18 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function prepareView(array $entities, $langcode, array &$items) {
+  public function prepareView(array $entities, $langcode, FieldInterface $items) {
     $settings = $this->getSettings();
 
     foreach ($entities as $id => $entity) {
-      foreach ($items[$id] as &$item) {
+      foreach ($items[$id] as $item) {
         // If available, set custom link text.
         if (!empty($settings['title'])) {
-          $item['title'] = $settings['title'];
+          $item->title = $settings['title'];
         }
         // Otherwise, use telephone number itself as title.
         else {
-          $item['title'] = $item['value'];
+          $item->title = $item->value;
         }
       }
     }
@@ -82,7 +83,7 @@ public function prepareView(array $entities, $langcode, array &$items) {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $element = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/telephone/lib/Drupal/telephone/Plugin/field/widget/TelephoneDefaultWidget.php b/core/modules/telephone/lib/Drupal/telephone/Plugin/field/widget/TelephoneDefaultWidget.php
index 66884fe..e89b79f 100644
--- a/core/modules/telephone/lib/Drupal/telephone/Plugin/field/widget/TelephoneDefaultWidget.php
+++ b/core/modules/telephone/lib/Drupal/telephone/Plugin/field/widget/TelephoneDefaultWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -44,7 +45,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * Implements \Drupal\field\Plugin\Type\Widget\WidgetInterface::formElement().
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element['value'] = $element + array(
       '#type' => 'tel',
       '#default_value' => isset($items[$delta]['value']) ? $items[$delta]['value'] : NULL,
diff --git a/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextDefaultFormatter.php b/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextDefaultFormatter.php
index 52b2388..429b468 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextDefaultFormatter.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextDefaultFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'text_default' formatter.
@@ -32,13 +33,16 @@
 class TextDefaultFormatter extends FormatterBase {
 
   /**
-   * Implements Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
+   * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
-      $output = text_sanitize($this->getFieldSetting('text_processing'), $langcode, $item, 'value');
+      // @todo Convert text_sanitize() to work on an NG $item (this requires
+      //   http://drupal.org/node/1969728.)
+      $itemBC = $item->getValue(TRUE);
+      $output = text_sanitize($this->getFieldSetting('text_processing'), $langcode, $itemBC, 'value');
       $elements[$delta] = array('#markup' => $output);
     }
 
diff --git a/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextPlainFormatter.php b/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextPlainFormatter.php
index 813bb92..fd0f4ab 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextPlainFormatter.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextPlainFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'text_plain' formatter.
@@ -34,7 +35,7 @@ class TextPlainFormatter extends FormatterBase {
   /**
    * Implements Drupal\field\Plugin\Type\Formatter\FormatterInterface::viewElements().
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     foreach ($items as $delta => $item) {
diff --git a/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextTrimmedFormatter.php b/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextTrimmedFormatter.php
index 88ef0c5..585f5f0 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextTrimmedFormatter.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/field/formatter/TextTrimmedFormatter.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\field\Plugin\Type\Formatter\FormatterBase;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'text_trimmed'' formatter.
@@ -65,7 +66,7 @@ public function settingsSummary() {
   /**
    * {@inheritdoc}
    */
-  public function viewElements(EntityInterface $entity, $langcode, array $items) {
+  public function viewElements(EntityInterface $entity, $langcode, FieldInterface $items) {
     $elements = array();
 
     $text_processing = $this->getFieldSetting('text_processing');
diff --git a/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWidget.php b/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWidget.php
index 2fe37a0..90e68d3 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWidget.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -52,7 +53,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $main_widget = $element + array(
       '#type' => 'textarea',
       '#default_value' => isset($items[$delta]['value']) ? $items[$delta]['value'] : NULL,
diff --git a/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWithSummaryWidget.php b/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWithSummaryWidget.php
index b98ce32..9141311 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWithSummaryWidget.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextareaWithSummaryWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 
 /**
  * Plugin implementation of the 'text_textarea_with_summary' widget.
@@ -32,7 +33,7 @@ class TextareaWithSummaryWidget extends TextareaWidget {
   /**
    * {@inheritdoc}
    */
-  function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $element = parent::formElement($items, $delta, $element, $langcode, $form, $form_state);
 
     $display_summary = !empty($items[$delta]['summary']) || $this->getFieldSetting('display_summary');
diff --git a/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextfieldWidget.php b/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextfieldWidget.php
index 7012c75..b56b38b 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextfieldWidget.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/field/widget/TextfieldWidget.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
+use Drupal\Core\Entity\Field\FieldInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 
 /**
@@ -52,7 +53,7 @@ public function settingsForm(array $form, array &$form_state) {
   /**
    * {@inheritdoc}
    */
-  public function formElement(array $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
+  public function formElement(FieldInterface $items, $delta, array $element, $langcode, array &$form, array &$form_state) {
     $main_widget = $element + array(
       '#type' => 'textfield',
       '#default_value' => isset($items[$delta]['value']) ? $items[$delta]['value'] : NULL,