class DataReferenceDefinition

class DataReferenceDefinition extends DataDefinition implements DataReferenceDefinitionInterface {
    
    /**
     * @var \Drupal\Core\TypedData\DataDefinitionInterface
     */
    protected $targetDefinition;
    
    /**
     * Creates a new data reference definition.
     *
     * @param string $target_data_type
     *   The data type of the referenced data.
     *
     * @return static
     */
    public static function create($target_data_type) {
        // This assumes implementations use a "TYPE_reference" naming pattern.
        $definition = parent::create($target_data_type . '_reference');
        return $definition->setTargetDefinition(\Drupal::typedDataManager()->createDataDefinition($target_data_type));
    }
    
    /**
     * {@inheritdoc}
     */
    public static function createFromDataType($data_type) {
        if (substr($data_type, -strlen('_reference')) != '_reference') {
            throw new \InvalidArgumentException('Data type must be of the form "{TARGET_TYPE}_reference"');
        }
        // Cut of the _reference suffix.
        return static::create(substr($data_type, 0, strlen($data_type) - strlen('_reference')));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTargetDefinition() {
        return $this->targetDefinition;
    }
    
    /**
     * Sets the definition of the referenced data.
     *
     * @param \Drupal\Core\TypedData\DataDefinitionInterface $definition
     *   The target definition to set.
     *
     * @return $this
     */
    public function setTargetDefinition(DataDefinitionInterface $definition) {
        $this->targetDefinition = $definition;
        return $this;
    }

}