/*
 * This file is part of ELKI:
 * Environment for Developing KDD-Applications Supported by Index-Structures
 *
 * Copyright (C) 2022
 * ELKI Development Team
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package elki.database.ids;

import elki.database.datastore.DBIDDataStore;

/**
 * (Persistent) variable storing a DBID reference.
 * <p>
 * In contrast to the {@link DBIDRef} API, which are read-only references, this
 * variable can be updated to point to a different DBID, e.g., the current best
 * candidate.
 *
 * @author Erich Schubert
 * @since 0.5.5
 */
public interface DBIDVar extends DBIDRef, ArrayDBIDs, SetDBIDs {
  /**
   * Assign a new value for the reference.
   *
   * @param ref Reference
   * @return {@code this}, for inlining.
   */
  DBIDVar set(DBIDRef ref);

  /**
   * Update variable from a data store.
   *
   * @param store Data store
   * @param ref Reference
   * @return {@code this}, for inlining.
   */
  DBIDVar from(DBIDDataStore store, DBIDRef ref);

  /**
   * Clear the contents.
   */
  void unset();

  /**
   * Test if the variable is well-defined.
   *
   * @return {@code true} when assigned.
   */
  boolean isSet();
}
