com.facebook.buck.util.MoreIterables.java Source code

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Here is the source code for com.facebook.buck.util.MoreIterables.java

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/*
 * Copyright 2014-present Facebook, Inc.
 *
 * 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.facebook.buck.util;

import com.facebook.buck.model.Pair;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;

import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

public class MoreIterables {

    private MoreIterables() {
    }

    private static <T> ImmutableList<Iterator<T>> iterators(Iterable<T> inputs[]) {
        ImmutableList.Builder<Iterator<T>> iterators = ImmutableList.builder();
        for (Iterable<T> input : inputs) {
            iterators.add(input.iterator());
        }
        return iterators.build();
    }

    /**
     * Combine the given iterables by peeling off items one at a time from each of the input
     * iterables until any one of the iterables are exhausted.
     */
    @SafeVarargs
    public static <T> Iterable<T> zipAndConcat(Iterable<T>... inputs) {

        // If no inputs were seen, just return an empty list.
        if (inputs.length == 0) {
            return ImmutableList.of();
        }

        ImmutableList.Builder<T> result = ImmutableList.builder();
        ImmutableList<Iterator<T>> iterators = iterators(inputs);

        // Keep grabbing rounds from the input iterators until we've exhausted one
        // of them, then return.
        List<T> round = Lists.newArrayListWithCapacity(inputs.length);
        while (true) {
            for (Iterator<T> iterator : iterators) {
                if (!iterator.hasNext()) {
                    return result.build();
                }
                round.add(iterator.next());
            }
            result.addAll(round);
            round.clear();
        }
    }

    /**
     * Returns a deduped version of toDedup and keeps the order of elements
     * If a key is contained more than once
     * (that is, there are multiple elements e1, e2... en, such that ei.equals(ej))
     * then the last one will be kept in the ordering
     */
    public static <T> Set<T> dedupKeepLast(Iterable<T> toDedup) {
        Set<T> dedupedSet = new LinkedHashSet<>();
        for (T t : toDedup) {
            if (dedupedSet.contains(t)) {
                dedupedSet.remove(t);
            }
            dedupedSet.add(t);
        }

        return dedupedSet;
    }

    /**
     * @return a new {@link Iterable} containing pairs of the original items along with the index of
     *         the current item.
     */
    public static <T> Iterable<Pair<Integer, T>> enumerate(Iterable<T> items) {
        return () -> new Iterator<Pair<Integer, T>>() {

            private int index = 0;
            private final Iterator<T> delegate = items.iterator();

            @Override
            public boolean hasNext() {
                return delegate.hasNext();
            }

            @Override
            public Pair<Integer, T> next() {
                return new Pair<>(index++, delegate.next());
            }

        };
    }

}