class FieldItemBase

abstract class FieldItemBase extends Map implements FieldItemInterface {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultStorageSettings() {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function defaultFieldSettings() {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function mainPropertyName() {
        return 'value';
    }
    
    /**
     * {@inheritdoc}
     */
    public function __construct(DataDefinitionInterface $definition, $name = NULL, TypedDataInterface $parent = NULL) {
        parent::__construct($definition, $name, $parent);
        // Initialize computed properties by default, such that they get cloned
        // with the whole item.
        foreach ($this->definition
            ->getPropertyDefinitions() as $name => $definition) {
            if ($definition->isComputed()) {
                $this->properties[$name] = \Drupal::typedDataManager()->getPropertyInstance($this, $name);
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getEntity() {
        return $this->getParent()
            ->getEntity();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getLangcode() {
        return $this->getParent()
            ->getLangcode();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFieldDefinition() {
        return $this->definition
            ->getFieldDefinition();
    }
    
    /**
     * Returns the array of field settings.
     *
     * @return array
     *   The array of settings.
     */
    protected function getSettings() {
        return $this->getFieldDefinition()
            ->getSettings();
    }
    
    /**
     * Returns the value of a field setting.
     *
     * @param string $setting_name
     *   The setting name.
     *
     * @return mixed
     *   The setting value.
     */
    protected function getSetting($setting_name) {
        return $this->getFieldDefinition()
            ->getSetting($setting_name);
    }
    
    /**
     * {@inheritdoc}
     */
    public function setValue($values, $notify = TRUE) {
        // Treat the values as property value of the first property, if no array is
        // given.
        if (isset($values) && !is_array($values)) {
            $keys = array_keys($this->definition
                ->getPropertyDefinitions());
            $values = [
                $keys[0] => $values,
            ];
        }
        parent::setValue($values, $notify);
    }
    
    /**
     * {@inheritdoc}
     *
     * Different to the parent Map class, we avoid creating property objects as
     * far as possible in order to optimize performance. Thus we just update
     * $this->values if no property object has been created yet.
     */
    protected function writePropertyValue($property_name, $value) {
        // For defined properties there is either a property object or a plain
        // value that needs to be updated.
        if (isset($this->properties[$property_name])) {
            $this->properties[$property_name]
                ->setValue($value, FALSE);
        }
        else {
            $this->values[$property_name] = $value;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function __get($name) {
        // There is either a property object or a plain value - possibly for a
        // not-defined property. If we have a plain value, directly return it.
        if (isset($this->properties[$name])) {
            return $this->properties[$name]
                ->getValue();
        }
        elseif (isset($this->values[$name])) {
            return $this->values[$name];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function __set($name, $value) {
        // Support setting values via property objects, but take care in as the
        // value of the 'entity' property is typed data also.
        if ($value instanceof TypedDataInterface && !$value instanceof EntityInterface) {
            $value = $value->getValue();
        }
        $this->set($name, $value);
    }
    
    /**
     * {@inheritdoc}
     */
    public function __isset($name) {
        if (isset($this->properties[$name])) {
            return $this->properties[$name]
                ->getValue() !== NULL;
        }
        return isset($this->values[$name]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function __unset($name) {
        if ($this->definition
            ->getPropertyDefinition($name)) {
            $this->set($name, NULL);
        }
        else {
            // Explicitly unset the property in $this->values if a non-defined
            // property is unset, such that its key is removed from $this->values.
            unset($this->values[$name]);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function view($display_options = []) {
        $view_builder = \Drupal::entityTypeManager()->getViewBuilder($this->getEntity()
            ->getEntityTypeId());
        return $view_builder->viewFieldItem($this, $display_options);
    }
    
    /**
     * {@inheritdoc}
     */
    public function preSave() {
    }
    
    /**
     * {@inheritdoc}
     */
    public function postSave($update) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function delete() {
    }
    
    /**
     * {@inheritdoc}
     */
    public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteRevision() {
    }
    
    /**
     * {@inheritdoc}
     */
    public function storageSettingsForm(array &$form, FormStateInterface $form_state, $has_data) {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function storageSettingsToConfigData(array $settings) {
        return $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function storageSettingsFromConfigData(array $settings) {
        return $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function fieldSettingsToConfigData(array $settings) {
        return $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function fieldSettingsFromConfigData(array $settings) {
        return $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function calculateDependencies(FieldDefinitionInterface $field_definition) {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function calculateStorageDependencies(FieldStorageDefinitionInterface $field_definition) {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function onDependencyRemoval(FieldDefinitionInterface $field_definition, array $dependencies) {
        return FALSE;
    }

}