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 storm.trident.operation;
  
  import storm.trident.tuple.TridentTuple;
  
  import java.util.Map;
  
  /**
   * A function takes in a set of input fields and emits zero or more tuples as output. The fields of the output tuple
   * are appended to the original input tuple in the stream. If a function emits no tuples, the original input tuple is
   * filtered out. Otherwise, the input tuple is duplicated for each output tuple.
   *
   * For example, if you have the following function:
   *
   * ```java
   * public class MyFunction extends BaseFunction {
   *      public void execute(TridentTuple tuple, TridentCollector collector) {
   *      for(int i=0; i < tuple.getInteger(0); i++) {
   *          collector.emit(new Values(i));
   *      }
   *    }
   * }
   *
   * ```
   *
   * Now suppose you have a stream in the variable `mystream` with the fields `["a", "b", "c"]` with the following tuples:
   *
   * ```
   * [1, 2, 3]
   * [4, 1, 6]
   * [3, 0, 8]
   * ```
   * If you had the following code in your topology definition:
   *
   * ```java
   * mystream.each(new Fields("b"), new MyFunction(), new Fields("d")))
   * ```
   *
   * The resulting tuples would have the fields `["a", "b", "c", "d"]` and look like this:
   *
   * ```
   * [1, 2, 3, 0]
   * [1, 2, 3, 1]
   * [4, 1, 6, 0]
   * ```
   *
   * In this case, the parameter `new Fields("b")` tells Trident that you would like to select the field "b" as input
   * to the function, and that will be the only field in the Tuple passed to the `execute()` method. The value of "b" in
   * the first tuple (2) causes the for loop to execute twice, so 2 tuples are emitted. similarly the second tuple causes
   * one tuple to be emitted. For the third tuple, the value of 0 causes the `for` loop to be skipped, so nothing is
   * emitted and the incoming tuple is filtered out of the stream.
   *
   * ### Configuration
   * If your `Function` implementation has configuration requirements, you will typically want to extend
   * {@link org.apache.storm.trident.operation.BaseFunction} and override the
   * {@link org.apache.storm.trident.operation.Operation#prepare(Map, TridentOperationContext)} method to perform your custom
   * initialization.
   *
   * ### Performance Considerations
   * Because Trident Functions perform logic on individual tuples -- as opposed to batches -- it is advisable
   * to avoid expensive operations such as database operations in a Function, if possible. For data store interactions
   * it is better to use a {@link org.apache.storm.trident.state.State} or
   * {@link org.apache.storm.trident.state.QueryFunction} implementation since Trident states operate on batch partitions
   * and can perform bulk updates to a database.
   *
   *
   */
  public interface Function extends EachOperation {
      /**
       * Performs the function logic on an individual tuple and emits 0 or more tuples.
       *
       * @param tuple The incoming tuple
       * @param collector A collector instance that can be used to emit tuples
       */
      void execute(TridentTuple tuple, TridentCollector collector);
  }
  