class FieldItemDataDefinition

class FieldItemDataDefinition extends DataDefinition implements FieldItemDataDefinitionInterface {
    
    /**
     * The field definition the item definition belongs to.
     *
     * @var \Drupal\Core\Field\FieldDefinitionInterface
     */
    protected $fieldDefinition;
    
    /**
     * {@inheritdoc}
     */
    public static function createFromDataType($data_type) {
        // The data type of a field item is in the form of "field_item:$field_type".
        $parts = explode(':', $data_type, 2);
        if ($parts[0] != 'field_item') {
            throw new \InvalidArgumentException('Data type must be in the form of "field_item:FIELD_TYPE".');
        }
        $field_definition = BaseFieldDefinition::create($parts[1]);
        return $field_definition->getItemDefinition();
    }
    
    /**
     * Creates a new field item definition.
     *
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The field definition the item definition belongs to.
     *
     * @return static
     */
    public static function create($field_definition) {
        $definition['type'] = 'field_item:' . $field_definition->getType();
        $item_definition = new static($definition);
        $item_definition->fieldDefinition = $field_definition;
        return $item_definition;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPropertyDefinition($name) {
        return $this->fieldDefinition
            ->getFieldStorageDefinition()
            ->getPropertyDefinition($name);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPropertyDefinitions() {
        return $this->fieldDefinition
            ->getFieldStorageDefinition()
            ->getPropertyDefinitions();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMainPropertyName() {
        return $this->fieldDefinition
            ->getFieldStorageDefinition()
            ->getMainPropertyName();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFieldDefinition() {
        return $this->fieldDefinition;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setFieldDefinition($field_definition) {
        $this->fieldDefinition = $field_definition;
        return $this;
    }
    
    /**
     * Gets the label of the field type.
     *
     * If the label hasn't been set, then fall back to the label of the
     * typed data definition.
     *
     * @return string
     *   The label of the field type.
     *
     * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
     */
    public function getLabel() {
        return parent::getLabel() ?: $this->getTypedDataManager()
            ->getDefinition($this->getDataType())['label'];
    }

}