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Either.java
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Either.java
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/*
* Copyright (C) 2018-2020 Toshiaki Maki <makingx@gmail.com>
*
* 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 am.ik.yavi.fn;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;
import am.ik.yavi.jsr305.Nullable;
public final class Either<L, R> {
final L left;
final R right;
Either(@Nullable L left, @Nullable R right) {
if (left == null && right == null) {
throw new IllegalArgumentException("Both left and right are null!");
}
this.left = left;
this.right = right;
}
public static <L, R> Either<L, R> left(L left) {
return new Either<>(left, null);
}
public static <L, R> Either<L, R> right(R right) {
return new Either<>(null, right);
}
public <X, Y> Either<X, Y> bimap(Function<L, X> leftMapper,
Function<R, Y> rightMapper) {
if (isLeft()) {
return new Either<>(leftMapper.apply(this.left), null);
}
return new Either<>(null, rightMapper.apply(this.right));
}
@Override
public boolean equals(@Nullable Object o) {
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
Either<?, ?> either = (Either<?, ?>) o;
return Objects.equals(left, either.left) && Objects.equals(right, either.right);
}
public <U> U fold(Function<L, U> leftMapper, Function<R, U> rightMapper) {
if (isLeft()) {
return leftMapper.apply(this.left);
}
return rightMapper.apply(this.right);
}
@Override
public int hashCode() {
return Objects.hash(left, right);
}
public boolean isLeft() {
return this.left != null;
}
public boolean isRight() {
return this.right != null;
}
public Optional<L> left() {
return Optional.ofNullable(this.left);
}
public <X> Either<X, R> leftMap(Function<L, X> leftMapper) {
if (isLeft()) {
return new Either<>(leftMapper.apply(this.left), null);
}
return new Either<>(null, this.right);
}
public L leftOrElseGet(Function<R, L> rightToLeft) {
return this.left().orElseGet(() -> rightToLeft.apply(this.right));
}
/**
* @since 0.3.0
*/
public <X extends Throwable> L leftOrElseThrow(
Function<R, ? extends X> exceptionSupplier) throws X {
return this.left().orElseThrow(() -> exceptionSupplier.apply(this.right));
}
/**
* Use {@link #peekLeft(Consumer)} instead.
*/
@Deprecated
public Either<L, R> doOnLeft(Consumer<L> action) {
return this.peekLeft(action);
}
public Either<L, R> peekLeft(Consumer<L> action) {
if (this.isLeft()) {
action.accept(this.left);
}
return this;
}
public Optional<R> right() {
return Optional.ofNullable(this.right);
}
public <Y> Either<L, Y> rightMap(Function<R, Y> rightMapper) {
if (isRight()) {
return new Either<>(null, rightMapper.apply(this.right));
}
return new Either<>(this.left, null);
}
public R rightOrElseGet(Function<L, R> leftToRight) {
return this.right().orElseGet(() -> leftToRight.apply(this.left));
}
/**
* @since 0.3.0
*/
public <X extends Throwable> R rightOrElseThrow(
Function<L, ? extends X> exceptionSupplier) throws X {
return this.right().orElseThrow(() -> exceptionSupplier.apply(this.left));
}
/**
* Use {@link #peekRight(Consumer)} instead.
*/
@Deprecated
public Either<L, R> doOnRight(Consumer<R> action) {
return this.peekRight(action);
}
public Either<L, R> peekRight(Consumer<R> action) {
if (this.isRight()) {
action.accept(this.right);
}
return this;
}
public Either<R, L> swap() {
return new Either<>(this.right, this.left);
}
}