code: /*
   * Copyright 2012-2018 Chronicle Map Contributors
   *
   * Licensed 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 net.openhft.chronicle.map;
  
  import net.openhft.chronicle.hash.Data;
  import org.jetbrains.annotations.NotNull;
  
  /**
   * Abstracts returning a value from a query to a {@link ChronicleMap}, used in {@link MapMethods}.
   * This interface is not supposed to be implemented in user code.
   *
   * @param <V> the type of values in the {@code ChronicleMap}
   */
  public interface ReturnValue<V> {
      /**
       * Calling this method on a {@code ReturnValue} object, provided as an argument in a method from
       * {@link MapMethods}, designates that the {@code ChronicleMap}'s method (backed by this
       * {@code MapMethods}'s method) should return the given {@code value}.
       * <p>
       * <p>It is not allowed to call {@code returnValue()} twice during a single {@code MapMethods}'s
       * method call.
       * <p>
       * <p>Not calling {@code returnValue()} during {@code MapMethods}'s method call will make the
       * backed {@code ChronicleMap}'s method to return {@code null}.
       *
       * @param value a {@code Data} object wrapping a value, which should be returned from a
       *              {@code ChronicleMap}'s method, backed by the {@code MapMethods}'s method, to
       *              which this {@code ReturnValue} instance was passed as an argument
       */
      void returnValue(@NotNull Data<V> value);
  }
  