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GS Collections is a collections framework for Java. It has JDK-compatible List, Set and Map implementations with a rich API and set of utility classes that work with any JDK compatible Collections, Arrays, Maps or Strings. The iteration protocol was inspired by the Smalltalk collection framework.

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/*
 * Copyright 2012 Goldman Sachs.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.gs.collections.impl.block.procedure;

import com.gs.collections.api.block.function.Function;
import com.gs.collections.api.block.function.Function0;
import com.gs.collections.api.block.procedure.Procedure;
import com.gs.collections.api.block.procedure.Procedure2;
import com.gs.collections.api.map.MutableMap;

/**
 * This procedure is used to apply an aggregate function like sum on a grouped set of data.  The values in the
 * grouping must be mutable using this procedure.  An example would be using an AtomicInteger which can be mutated
 * vs. an Integer which cannot.
 */
public final class MutatingAggregationProcedure implements Procedure
{
    private static final long serialVersionUID = 1L;
    private final MutableMap map;
    private final Function groupBy;
    private final Function0 zeroValueFactory;
    private final Procedure2 mutatingAggregator;

    public MutatingAggregationProcedure(MutableMap map, Function groupBy, Function0 zeroValueFactory, Procedure2 mutatingAggregator)
    {
        this.map = map;
        this.groupBy = groupBy;
        this.zeroValueFactory = zeroValueFactory;
        this.mutatingAggregator = mutatingAggregator;
    }

    public void value(T each)
    {
        K key = this.groupBy.valueOf(each);
        V value = this.map.getIfAbsentPut(key, this.zeroValueFactory);
        this.mutatingAggregator.value(value, each);
    }
}