thomasmueller commented on code in PR #2055: URL: https://github.com/apache/jackrabbit-oak/pull/2055#discussion_r1956167341
########## oak-commons/src/main/java/org/apache/jackrabbit/oak/commons/collections/IterableUtils.java: ########## @@ -0,0 +1,145 @@ +/* + * 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.jackrabbit.oak.commons.collections; + +import org.apache.commons.collections4.iterators.LazyIteratorChain; + +import java.util.Iterator; +import java.util.Objects; + +/** + * Utility methods for {@link Iterable} conversions. + */ +public class IterableUtils { + + private IterableUtils() { + // no instances for you + } + + /** + * Combines two iterables into a single iterable. + * <p> + * The returned iterable has an iterator that traverses the elements in {@code a}, + * followed by the elements in {@code b}. The source iterators are not polled until necessary. + * <p> + * The returned iterable's iterator supports {@code remove()} when the corresponding + * input iterator supports it. + * + * @param <E> the element type + * @param a the first iterable, may not be null + * @param b the second iterable, may not be null + * @return a new iterable, combining the provided iterables + * @throws NullPointerException if either of the provided iterables is null + */ + public static <E> Iterable<E> chainedIterable(final Iterable<? extends E> a, + final Iterable<? extends E> b) { + return org.apache.commons.collections4.IterableUtils.chainedIterable(a, b); + } + + /** + * Combines three iterables into a single iterable. + * <p> + * The returned iterable has an iterator that traverses the elements in {@code a}, + * followed by the elements in {@code b} and {@code c}. The source + * iterators are not polled until necessary. + * <p> + * The returned iterable's iterator supports {@code remove()} when the corresponding + * input iterator supports it. + * + * @param <E> the element type + * @param a the first iterable, may not be null + * @param b the second iterable, may not be null + * @param c the third iterable, may not be null + * @return a new iterable, combining the provided iterables + * @throws NullPointerException if either of the provided iterables is null + */ + public static <E> Iterable<E> chainedIterable(final Iterable<? extends E> a, + final Iterable<? extends E> b, + final Iterable<? extends E> c) { + return org.apache.commons.collections4.IterableUtils.chainedIterable(a, b, c); + } + + /** + * Combines four iterables into a single iterable. + * <p> + * The returned iterable has an iterator that traverses the elements in {@code a}, + * followed by the elements in {@code b}, {@code c} and {@code d}. The source + * iterators are not polled until necessary. + * <p> + * The returned iterable's iterator supports {@code remove()} when the corresponding + * input iterator supports it. + * + * @param <E> the element type + * @param a the first iterable, may not be null + * @param b the second iterable, may not be null + * @param c the third iterable, may not be null + * @param d the fourth iterable, may not be null + * @return a new iterable, combining the provided iterables + * @throws NullPointerException if either of the provided iterables is null + */ + public static <E> Iterable<E> chainedIterable(final Iterable<? extends E> a, + final Iterable<? extends E> b, + final Iterable<? extends E> c, + final Iterable<? extends E> d) { + return org.apache.commons.collections4.IterableUtils.chainedIterable(a, b, c, d); + } + + /** + * Combines the provided iterables into a single iterable. + * <p> + * The returned iterable has an iterator that traverses the elements in the order + * of the arguments, i.e. iterables[0], iterables[1], .... The source iterators + * are not polled until necessary. + * <p> + * The returned iterable's iterator supports {@code remove()} when the corresponding + * input iterator supports it. + * + * @param <E> the element type + * @param iterables the iterables to combine, may not be null + * @return a new iterable, combining the provided iterables + * @throws NullPointerException if either of the provided iterables is null + */ + @SafeVarargs + public static <E> Iterable<E> chainedIterable(final Iterable<? extends E>... iterables) { + Objects.requireNonNull(iterables); + return org.apache.commons.collections4.IterableUtils.chainedIterable(iterables); + } + + /** + * Creates an {@code Iterable} that chains multiple {@code Iterable} instances into a single {@code Iterable}. + * <p> + * The returned {@code Iterable} will iterate over all elements of the first {@code Iterable}, + * then all elements of the second, and so on. + * + * @param <E> the type of elements returned by the iterator + * @param iterables an {@code Iterable} of {@code Iterable} instances to be chained + * @return an {@code Iterable} that provides a single view of all elements in the input {@code Iterable} instances + * @throws NullPointerException if the input {@code Iterable} or any of its elements are null + */ + public static <E> Iterable<E> chainedIterable(final Iterable<? extends Iterable<? extends E>> iterables) { Review Comment: Is this actually used anywhere in the code? -- This is an automated message from the Apache Git Service. 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