interface FieldItemListInterface

interface FieldItemListInterface extends ListInterface, AccessibleInterface {
    
    /**
     * Gets the entity that field belongs to.
     *
     * @return \Drupal\Core\Entity\FieldableEntityInterface
     *   The entity object. If the entity is translatable and a specific
     *   translation is required, always request it by calling ::getTranslation()
     *   or ::getUntranslated() as the language of the returned object is not
     *   defined.
     */
    public function getEntity();
    
    /**
     * Sets the langcode of the field values held in the object.
     *
     * @param string $langcode
     *   The langcode.
     */
    public function setLangcode($langcode);
    
    /**
     * Gets the langcode of the field values held in the object.
     *
     * @return string
     *   The langcode.
     */
    public function getLangcode();
    
    /**
     * Gets the field definition.
     *
     * @return \Drupal\Core\Field\FieldDefinitionInterface
     *   The field definition.
     */
    public function getFieldDefinition();
    
    /**
     * Returns the array of field settings.
     *
     * @return array
     *   An array of key/value pairs.
     */
    public function getSettings();
    
    /**
     * Returns the value of a given field setting.
     *
     * @param string $setting_name
     *   The setting name.
     *
     * @return mixed
     *   The setting value.
     */
    public function getSetting($setting_name);
    
    /**
     * Contains the default access logic of this field.
     *
     * See \Drupal\Core\Entity\EntityAccessControlHandlerInterface::fieldAccess() for
     * the parameter documentation.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The access result.
     */
    public function defaultAccess($operation = 'view', ?AccountInterface $account = NULL);
    
    /**
     * Filters out empty field items and re-numbers the item deltas.
     *
     * @return $this
     */
    public function filterEmptyItems();
    
    /**
     * Magic method: Gets a property value of to the first field item.
     *
     * @see \Drupal\Core\Field\FieldItemInterface::__set()
     */
    public function __get($property_name);
    
    /**
     * Magic method: Sets a property value of the first field item.
     *
     * @see \Drupal\Core\Field\FieldItemInterface::__get()
     */
    public function __set($property_name, $value);
    
    /**
     * Magic method: Determines whether a property of the first field item is set.
     *
     * @see \Drupal\Core\Field\FieldItemInterface::__unset()
     */
    public function __isset($property_name);
    
    /**
     * Magic method: Unsets a property of the first field item.
     *
     * @see \Drupal\Core\Field\FieldItemInterface::__isset()
     */
    public function __unset($property_name);
    
    /**
     * Defines custom presave behavior for field values.
     *
     * This method is called during the process of saving an entity, just before
     * item values are written into storage.
     *
     * @see \Drupal\Core\Field\FieldItemInterface::preSave()
     */
    public function preSave();
    
    /**
     * Defines custom post-save behavior for field values.
     *
     * This method is called during the process of saving an entity, just after
     * item values are written into storage.
     *
     * @param bool $update
     *   Specifies whether the entity is being updated or created.
     *
     * @return bool
     *   Whether field items should be rewritten to the storage as a consequence
     *   of the logic implemented by the custom behavior.
     *
     * @see \Drupal\Core\Field\FieldItemInterface::postSave()
     */
    public function postSave($update);
    
    /**
     * Defines custom delete behavior for field values.
     *
     * This method is called during the process of deleting an entity, just before
     * values are deleted from storage.
     */
    public function delete();
    
    /**
     * Defines custom revision delete behavior for field values.
     *
     * This method is called from during the process of deleting an entity
     * revision, just before the field values are deleted from storage. It is only
     * called for entity types that support revisioning.
     */
    public function deleteRevision();
    
    /**
     * Returns a renderable array for the field items.
     *
     * @param string|array $display_options
     *   Can be either the name of a view mode, or an array of display settings.
     *   See EntityViewBuilderInterface::viewField() for more information.
     *
     * @return array
     *   A renderable array for the field values.
     *
     * @see \Drupal\Core\Entity\EntityViewBuilderInterface::viewField()
     * @see \Drupal\Core\Field\FieldItemInterface::view()
     */
    public function view($display_options = []);
    
    /**
     * Populates a specified number of field items with valid sample data.
     *
     * @param int $count
     *   The number of items to create.
     */
    public function generateSampleItems($count = 1);
    
    /**
     * Returns a form for the default value input.
     *
     * Invoked from \Drupal\field_ui\Form\FieldConfigEditForm to allow
     * administrators to configure instance-level default value.
     *
     * @param array $form
     *   The form where the settings form is being included in.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state of the (entire) configuration form.
     *
     * @return array
     *   The form definition for the field default value.
     */
    public function defaultValuesForm(array &$form, FormStateInterface $form_state);
    
    /**
     * Validates the submitted default value.
     *
     * Invoked from \Drupal\field_ui\Form\FieldConfigEditForm to allow
     * administrators to configure instance-level default value.
     *
     * @param array $element
     *   The default value form element.
     * @param array $form
     *   The form where the settings form is being included in.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state of the (entire) configuration form.
     */
    public function defaultValuesFormValidate(array $element, array &$form, FormStateInterface $form_state);
    
    /**
     * Processes the submitted default value.
     *
     * Invoked from \Drupal\field_ui\Form\FieldConfigEditForm to allow
     * administrators to configure instance-level default value.
     *
     * @param array $element
     *   The default value form element.
     * @param array $form
     *   The form where the settings form is being included in.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state of the (entire) configuration form.
     *
     * @return array
     *   The field default value.
     */
    public function defaultValuesFormSubmit(array $element, array &$form, FormStateInterface $form_state);
    
    /**
     * Processes the default value before being applied.
     *
     * Defined or configured default values of a field might need some processing
     * in order to be a valid runtime value for the field type; e.g., a date field
     * could process the defined value of 'NOW' to a valid date.
     *
     * @param array $default_value
     *   The unprocessed default value defined for the field, as a numerically
     *   indexed array of items, each item being an array of property/value pairs.
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The entity for which the default value is generated.
     * @param \Drupal\Core\Field\FieldDefinitionInterface $definition
     *   The definition of the field.
     *
     * @return array
     *   The return default value for the field.
     */
    public static function processDefaultValue($default_value, FieldableEntityInterface $entity, FieldDefinitionInterface $definition);
    
    /**
     * Determines equality to another object implementing FieldItemListInterface.
     *
     * This method is usually used by the storage to check for not computed
     * value changes, which will be saved into the storage.
     *
     * @param \Drupal\Core\Field\FieldItemListInterface $list_to_compare
     *   The field item list to compare to.
     *
     * @return bool
     *   TRUE if the field item lists are equal, FALSE if not.
     */
    public function equals(FieldItemListInterface $list_to_compare);
    
    /**
     * Determines whether the field has relevant changes.
     *
     * This is for example used to determine if a revision of an entity has
     * changes in a given translation. Unlike
     * \Drupal\Core\Field\FieldItemListInterface::equals(), this can report
     * that for example an untranslatable field, despite being changed and
     * therefore technically affecting all translations, is only internal metadata
     * or only affects a single translation.
     *
     * @param \Drupal\Core\Field\FieldItemListInterface $original_items
     *   The original field items to compare against.
     * @param string $langcode
     *   The language that should be checked.
     *
     * @return bool
     *   TRUE if the field has relevant changes, FALSE if not.
     */
    public function hasAffectingChanges(FieldItemListInterface $original_items, $langcode);

}