001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.functor.core;
018
019 import org.apache.commons.functor.BinaryFunction;
020 import org.apache.commons.functor.BinaryPredicate;
021 import org.apache.commons.functor.adapter.BinaryFunctionBinaryPredicate;
022 import org.apache.commons.functor.adapter.IgnoreRightFunction;
023
024 /**
025 * Holder class for a left-identity <code>BinaryFunction</code> (evaluates to the left argument) and a left-identity
026 * <code>BinaryPredicate</code> (tests whether left <code>Boolean</code> argument equals <code>Boolean.TRUE</code>).
027 *
028 * @version $Revision: 1160411 $ $Date: 2011-08-22 22:09:01 +0200 (Mon, 22 Aug 2011) $
029 * @author Rodney Waldhoff
030 * @author Matt Benson
031 */
032 public final class LeftIdentity {
033
034 // static attributes
035 // ------------------------------------------------------------------------
036 /**
037 * Left-identity function.
038 */
039 public static final BinaryFunction<Object, Object, Object> FUNCTION = LeftIdentity.<Object, Object>function();
040
041 /**
042 * Left-identity predicate.
043 */
044 public static final BinaryPredicate<Boolean, Object> PREDICATE = LeftIdentity.<Object>predicate();
045
046 // constructor
047 // ------------------------------------------------------------------------
048 /**
049 * Create a new LeftIdentity (for clients that require an object).
050 */
051 public LeftIdentity() {
052 }
053
054 // static methods
055 // ------------------------------------------------------------------------
056
057 /**
058 * Get a Left-identity BinaryFunction.
059 * @param <L> the left argument type.
060 * @param <R> the right argument type.
061 * @return BinaryFunction<L, R, L>
062 */
063 public static <L, R> BinaryFunction<L, R, L> function() {
064 return IgnoreRightFunction.adapt(new Identity<L>());
065 }
066
067 /**
068 * Get a left-identity BinaryPredicate.
069 * @param <R> the right argument type.
070 * @return BinaryPredicate<Boolean, R>
071 */
072 public static <R> BinaryPredicate<Boolean, R> predicate() {
073 return BinaryFunctionBinaryPredicate.adapt(IgnoreRightFunction
074 .<Boolean, R, Boolean> adapt(new Identity<Boolean>()));
075 }
076 }