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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.nestedset;
import com.google.common.collect.ImmutableCollection;
/**
* A nested set expander that implements naive left-to-right preordering.
*
* <p>For example, for the nested set {B, D, {A, C}}, the iteration order is "B D A C".
*
* <p>This implementation is intended for backwards-compatible nested set replacements of code that
* uses naive preordering.
*
* <p>The implementation is called naive because it does no special treatment of dependency graphs
* that are not trees. For such graphs the property of parent-before-dependencies in the iteration
* order will not be upheld. For example, the diamond-shape graph A->{B, C}, B->{D}, C->{D} will be
* enumerated as "A B D C" rather than "A B C D" or "A C B D".
*
* <p>The difference from {@link LinkOrderNestedSet} is that this implementation gives priority to
* left-to-right order over dependencies-after-parent ordering. Note that the latter is usually more
* important, so please use {@link LinkOrderNestedSet} whenever possible.
*/
final class NaiveLinkOrderExpander<E> implements NestedSetExpander<E> {
@SuppressWarnings("unchecked")
@Override
public void expandInto(NestedSet<E> set, Uniqueifier uniqueifier,
ImmutableCollection.Builder<E> builder) {
for (Object e : set.directMembers()) {
if (uniqueifier.isUnique(e)) {
builder.add((E) e);
}
}
for (NestedSet<E> subset : set.transitiveSets()) {
if (!subset.isEmpty() && uniqueifier.isUnique(subset)) {
expandInto(subset, uniqueifier, builder);
}
}
}
}
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