001/*
002 * Copyright (c) 2016-2017 Chris K Wensel <chris@wensel.net>. All Rights Reserved.
003 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
004 *
005 * Project and contact information: http://www.cascading.org/
006 *
007 * This file is part of the Cascading project.
008 *
009 * Licensed under the Apache License, Version 2.0 (the "License");
010 * you may not use this file except in compliance with the License.
011 * You may obtain a copy of the License at
012 *
013 *     http://www.apache.org/licenses/LICENSE-2.0
014 *
015 * Unless required by applicable law or agreed to in writing, software
016 * distributed under the License is distributed on an "AS IS" BASIS,
017 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
018 * See the License for the specific language governing permissions and
019 * limitations under the License.
020 */
021
022package cascading.pipe;
023
024import cascading.flow.planner.Scope;
025import cascading.tuple.Fields;
026
027/**
028 * The Boundary class is only used internally by the planner to mark the boundaries between partitions within
029 * the element graph.
030 * <p>
031 * In MapReduce, Taps are used. But in DAG models, Boundary would specify where a system dependent interface should
032 * be used.
033 */
034public class Boundary extends Pipe
035  {
036  /**
037   * Intentionally does not provide a chaining constructor, as Boundary should not be inserted into an assembly
038   * by a user.
039   */
040  public Boundary()
041    {
042    }
043
044  @Override
045  public String getName()
046    {
047    return Pipe.id( this );
048    }
049
050  @Override
051  public Fields resolveIncomingOperationPassThroughFields( Scope incomingScope )
052    {
053    return incomingScope.getIncomingFunctionPassThroughFields();
054    }
055  }