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.operation;
023
024import cascading.flow.FlowProcess;
025import cascading.tuple.Fields;
026import cascading.tuple.Tuple;
027
028/**
029 * Class NoOp does nothing. It ignores all arguments and returns an empty {@link Tuple}, {@link Tuple#NULL}.
030 * <p>
031 * Use with {@link Fields#SWAP} to retain unknown fields, or use the {@link cascading.pipe.assembly.Discard}
032 * sub-assembly.
033 *
034 * @see Insert
035 * @see cascading.pipe.assembly.Discard
036 */
037public class NoOp extends BaseOperation implements Function
038  {
039  /** Constructor NoOp creates a new NoOp instance that will ignore the argument values and return no output. */
040  public NoOp()
041    {
042    super( ANY, Fields.NONE );
043    }
044
045  @Override
046  public void operate( FlowProcess flowProcess, FunctionCall functionCall )
047    {
048    functionCall.getOutputCollector().add( Tuple.NULL );
049    }
050  }