001    /*
002     * Copyright (c) 2007-2015 Concurrent, 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    
021    package cascading.operation;
022    
023    import cascading.flow.FlowProcess;
024    import cascading.tuple.Fields;
025    import 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     */
036    public 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      }