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// Copyright 2014 Google Inc. All rights reserved.
//
// 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.google.devtools.build.lib.collect;
import com.google.common.base.Joiner;
import com.google.common.collect.AbstractIterator;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
/**
* An immutable chain of immutable Iterables.
*
* <p>This class is defined for the sole purpose of being able to check for immutability
* (using instanceof). Otherwise, we could use a plain Iterable (as returned by
* {@code Iterables.concat()}).
*
* @see CollectionUtils#checkImmutable(Iterable)
*/
public final class IterablesChain<T> implements Iterable<T> {
private final Iterable<T> chain;
private IterablesChain(Iterable<T> chain) {
this.chain = chain;
}
@Override
public Iterator<T> iterator() {
return chain.iterator();
}
public static <T> Builder<T> builder() {
return new Builder<>();
}
@Override
public String toString() {
return "[" + Joiner.on(", ").join(this) + "]";
}
/**
* Builder for IterablesChain.
*
*
*/
public static class Builder<T> {
private List<Iterable<T>> iterables = new ArrayList<>();
private boolean deduplicate;
private Builder() {
}
/**
* Adds an immutable iterable to the end of the chain.
*
* <p>If the iterable can not be confirmed to be immutable, a runtime error is thrown.
*/
public Builder<T> add(Iterable<T> iterable) {
CollectionUtils.checkImmutable(iterable);
if (!Iterables.isEmpty(iterable)) {
iterables.add(iterable);
}
return this;
}
/**
* Adds a single element to the chain.
*/
public Builder<T> addElement(T element) {
iterables.add(ImmutableList.of(element));
return this;
}
/**
* Returns true if the chain is empty.
*/
public boolean isEmpty() {
return iterables.isEmpty();
}
/**
* If this is called, the the resulting {@link IterablesChain} object uses a hash set to remove
* duplicate elements.
*/
public Builder<T> deduplicate() {
this.deduplicate = true;
return this;
}
/**
* Builds an iterable that iterates through all elements in this chain.
*/
public IterablesChain<T> build() {
if (isEmpty()) {
return new IterablesChain<>(ImmutableList.<T>of());
}
Iterable<T> concat = Iterables.concat(ImmutableList.copyOf(iterables));
return new IterablesChain<>(deduplicate ? new Deduper<>(concat) : concat);
}
}
/**
* An iterable implementation that removes duplicate elements (as determined by equals), using a
* hash set.
*/
private static final class Deduper<T> implements Iterable<T> {
private final Iterable<T> iterable;
public Deduper(Iterable<T> iterable) {
this.iterable = iterable;
}
@Override
public Iterator<T> iterator() {
return new DedupingIterator<T>(iterable.iterator());
}
}
/**
* An iterator implementation that removes duplicate elements (as determined by equals), using a
* hash set.
*/
private static final class DedupingIterator<T> extends AbstractIterator<T> {
private final HashSet<T> set = new HashSet<>();
private final Iterator<T> it;
public DedupingIterator(Iterator<T> it) {
this.it = it;
}
@Override
protected T computeNext() {
while (it.hasNext()) {
T next = it.next();
if (set.add(next)) {
return next;
}
}
return endOfData();
}
}
}
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