content: /*
   *  Licensed to the Apache Software Foundation (ASF) under one
   *  or more contributor license agreements.  See the NOTICE file
   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you under the Apache License, Version 2.0 (the
   *  "License"); you may not use this file except in compliance
   *  with the License.  You may obtain a copy of the License at
   *
   *        http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing,
   *  software distributed under the License is distributed on an
   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   *  KIND, either express or implied.  See the License for the
   *  specific language governing permissions and limitations
   *  under the License.
   */
  package org.apache.causeway.applib.services.hint;
  
  /**
   * Provides a SPI for view models to implement to represent
   * their "logical" identity (stable even if the view model's state changes).
   *
   * <p>
   *     Hints are stored against the `Bookmark` of a domain object, essentially
   *     the identifier of the domain object. For a domain entity this identifier
   *     is fixed and unchanging but for view models the identifier changes each
   *     time the view model's state changes (the identifier is basically a
   *     digest of the object's state).
   *     This means that any hints stored against the view model's bookmark are
   *     in effect lost as soon as the view model is modified.
   * </p>
   *
   * <p>
   *     This SPI therefore allows a view model to take advantage of the hinting
   *     mechanism of the viewer by providing a "logical" identity stored which
   *     hints for the view model can be stored.
   * </p>
   *
   * @since 1.x {@index}
   */
  public interface HintIdProvider {
      String hintId();
  }
  