001/*
002 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.operation;
022
023import cascading.flow.FlowProcess;
024import cascading.tuple.Fields;
025import cascading.tuple.Tuple;
026
027/**
028 * Class NoOp does nothing. It ignores all arguments and returns an empty {@link Tuple}, {@link Tuple#NULL}.
029 * <p/>
030 * Use with {@link Fields#SWAP} to retain unknown fields, or use the {@link cascading.pipe.assembly.Discard}
031 * sub-assembly.
032 *
033 * @see Insert
034 * @see cascading.pipe.assembly.Discard
035 */
036public class NoOp extends BaseOperation implements Function
037  {
038  /** Constructor NoOp creates a new NoOp instance that will ignore the argument values and return no output. */
039  public NoOp()
040    {
041    super( ANY, Fields.NONE );
042    }
043
044  @Override
045  public void operate( FlowProcess flowProcess, FunctionCall functionCall )
046    {
047    functionCall.getOutputCollector().add( Tuple.NULL );
048    }
049  }