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.calcite.linq4j;
  
  import org.apache.calcite.linq4j.function.Function2;
  
  import java.util.Map;
  
  /**
   * Represents a collection of keys each mapped to one or more values.
   *
   * @param <K> Key type
   * @param <V> Value type
   */
  public interface Lookup<K, V>
      extends Map<K, Enumerable<V>>, Enumerable<Grouping<K, V>> {
    /**
     * Applies a transform function to each key and its associated values and
     * returns the results.
     *
     * @param resultSelector Result selector
     * @param <TResult> Result type
     *
     * @return Enumerable over results
     */
    <TResult> Enumerable<TResult> applyResultSelector(
        Function2<K, Enumerable<V>, TResult> resultSelector);
  }
  