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69 lines
2.4 KiB
69 lines
2.4 KiB
/*
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* Copyright (C) 2016 The Dagger Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package dagger.internal.codegen.extension;
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import static com.google.common.base.Preconditions.checkNotNull;
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import static com.google.common.collect.Lists.asList;
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import java.util.Comparator;
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import java.util.Optional;
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import java.util.function.Function;
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/** Utilities for {@link Optional}s. */
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public final class Optionals {
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/**
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* A {@link Comparator} that puts empty {@link Optional}s before present ones, and compares
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* present {@link Optional}s by their values.
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*/
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public static <C extends Comparable<C>> Comparator<Optional<C>> optionalComparator() {
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return Comparator.comparing((Optional<C> optional) -> optional.isPresent())
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.thenComparing(Optional::get);
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}
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public static <T> Comparator<Optional<T>> emptiesLast(Comparator<? super T> valueComparator) {
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checkNotNull(valueComparator);
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return Comparator.comparing(o -> o.orElse(null), Comparator.nullsLast(valueComparator));
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}
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/** Returns the first argument that is present, or empty if none are. */
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@SafeVarargs
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public static <T> Optional<T> firstPresent(
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Optional<T> first, Optional<T> second, Optional<T>... rest) {
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return asList(first, second, rest).stream()
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.filter(Optional::isPresent)
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.findFirst()
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.orElse(Optional.empty());
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}
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/**
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* Walks a chain of present optionals as defined by successive calls to {@code nextFunction},
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* returning the value of the final optional that is present. The first optional in the chain is
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* the result of {@code nextFunction(start)}.
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*/
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public static <T> T rootmostValue(T start, Function<T, Optional<T>> nextFunction) {
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T current = start;
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for (Optional<T> next = nextFunction.apply(start);
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next.isPresent();
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next = nextFunction.apply(current)) {
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current = next.get();
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}
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return current;
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}
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private Optionals() {}
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}
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