001    // Copyright 2010 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    // http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.func;
016    
017    /**
018     * A reducer takes an accumulator value and a single value from a collection and computes a new
019     * accumulator value.
020     * <A> type of accumulator
021     * <T> type of collection value
022     * 
023     * @since 5.2.0
024     */
025    public interface Reducer<A, T>
026    {
027        /**
028         * Run a computation using the current value of the accumulator and an element (from a Flow),
029         * and return the new accumulator.
030         */
031        A reduce(A accumulator, T element);
032    }