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// Copyright 2014 The Bazel Authors. 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.util;
import com.google.common.base.Function;
import java.util.Comparator;
import java.util.Objects;
import javax.annotation.Nullable;
/**
* An immutable, semantic-free ordered pair of nullable values. Avoid using it in public APIs.
*/
public final class Pair<A, B> {
/**
* Creates a new pair containing the given elements in order.
*/
public static <A, B> Pair<A, B> of(@Nullable A first, @Nullable B second) {
return new Pair<>(first, second);
}
/**
* The first element of the pair.
*/
@Nullable
public final A first;
/**
* The second element of the pair.
*/
@Nullable
public final B second;
/**
* Constructor. It is usually easier to call {@link #of}.
*/
public Pair(@Nullable A first, @Nullable B second) {
this.first = first;
this.second = second;
}
@Nullable
public A getFirst() {
return first;
}
@Nullable
public B getSecond() {
return second;
}
@Override
public String toString() {
return "(" + first + ", " + second + ")";
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (!(o instanceof Pair)) {
return false;
}
Pair<?, ?> p = (Pair<?, ?>) o;
return Objects.equals(first, p.first) && Objects.equals(second, p.second);
}
@Override
public int hashCode() {
return Objects.hash(first, second);
}
/**
* A function that maps to the first element in a pair.
*/
public static <A, B> Function<Pair<A, B>, A> firstFunction() {
return new Function<Pair<A, B>, A>() {
@Override
public A apply(Pair<A, B> pair) {
return pair.first;
}
};
}
/**
* A function that maps to the second element in a pair.
*/
public static <A, B> Function<Pair<A, B>, B> secondFunction() {
return new Function<Pair<A, B>, B>() {
@Override
public B apply(Pair<A, B> pair) {
return pair.second;
}
};
}
/**
* A comparator that compares pairs by comparing the first element.
*/
public static <T extends Comparable<T>, B> Comparator<Pair<T, B>> compareByFirst() {
return new Comparator<Pair<T, B>>() {
@Override
public int compare(Pair<T, B> o1, Pair<T, B> o2) {
return o1.first.compareTo(o2.first);
}
};
}
}
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