/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.ignite.internal.util.lang;
import org.apache.ignite.lang.IgniteOutClosure;
import org.jetbrains.annotations.Nullable;
/**
* Defines generic {@code for-all} or {@code reduce} type of closure. Unlike {@code for-each} type of closure
* that returns optional value on each execution of the closure - the reducer returns a single
* value for one or more collected values.
* <p>
* Closures are a first-class functions that are defined with
* (or closed over) their free variables that are bound to the closure scope at execution. Since
* Java 6 doesn't provide a language construct for first-class function the closures are implemented
* as abstract classes.
* <h2 class="header">Thread Safety</h2>
* Note that this interface does not impose or assume any specific thread-safety by its
* implementations. Each implementation can elect what type of thread-safety it provides,
* if any.
* @param <E1> Type of the first free variable, i.e. the element the closure is called on.
* @param <E2> Type of the second free variable, i.e. the element the closure is called on.
* @param <E3> Type of the third free variable, i.e. the element the closure is called on.
* @param <R> Type of the closure's return value.
*/
public interface IgniteReducer3<E1, E2, E3, R> extends IgniteOutClosure<R> {
/**
* Collects given values. All values will be reduced by {@link #apply()} method.
* <p>
* The {@code null}s could be passed if the data being collected is indeed {@code null}.
* If execution failed this method will not be called.
*
* @param e1 First bound free variable, i.e. the element the closure is called on.
* @param e2 Second bound free variable, i.e. the element the closure is called on.
* @param e3 Third bound free variable, i.e. the element the closure is called on.
* @return {@code true} to continue collecting, {@code false} to instruct caller to stop
* collecting and call {@link #apply()} method.
*/
public boolean collect(@Nullable E1 e1, @Nullable E2 e2, @Nullable E3 e3);
}