Github user StephanEwen commented on a diff in the pull request:
https://github.com/apache/flink/pull/1371#discussion_r45198942
--- Diff:
flink-java/src/main/java/org/apache/flink/api/java/typeutils/Either.java ---
@@ -0,0 +1,147 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.flink.api.java.typeutils;
+
+/**
+ * This type represents a value of one two possible types, Left or Right
+ * (a disjoint union), inspired by Scala's Either type.
+ *
+ * @param <L> the type of Left
+ * @param <R> the type of Right
+ */
+public abstract class Either<L, R> {
+
+ /**
+ * Create a Left value of Either
+ */
+ public static <L, R> Either<L, R> left(L value) {
+ return new Left<L, R>(value);
+ }
+
+ /**
+ * Create a Right value of Either
+ */
+ public static <L, R> Either<L, R> right(R value) {
+ return new Right<L, R>(value);
+ }
+
+ /**
+ * Retrieve the Left value of Either.
+ * @return the Left value
+ * @throws IllegalStateException if called on a Right
+ */
+ public abstract L left() throws IllegalStateException;
+
+ /**
+ * Retrieve the Right value of Either.
+ * @return the Right value
+ * @throws IllegalStateException if called on a Left
+ */
+ public abstract R right() throws IllegalStateException;
+
+ /**
+ *
+ * @return true if this is a Left value, false if this is a Right value
+ */
+ public abstract boolean isLeft();
+
+ private static class Left<L, R> extends Either<L, R> {
+ final L value;
+
+ public Left(L value) {
+ this.value = value;
+ }
+
+ @Override
+ public L left() {
+ return value;
+ }
+
+ @Override
+ public R right() {
+ throw new IllegalStateException("Cannot retrieve Right
value on a Left");
+ }
+
+ @Override
+ public boolean equals(Object object) {
+ if (object instanceof Left<?, ?>) {
+ final Left<?, ?> other = (Left<?, ?>) object;
+ return value.equals(other.value);
+ }
+ return false;
+ }
+
+ @Override
+ public int hashCode() {
+ return value.hashCode();
+ }
+
+ @Override
+ public String toString() {
+ return "Either.left(" + value.toString() + ")";
--- End diff --
I think the Scala Either just prints "Left()", which is a little nicer,
IMHO, but totally up to you...
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