[FLINK-3049] [api breaking] Move 'Either' type to 'flink-core / org.apache.flink.types'

flink-core/src/main/java/org/apache/flink/types/Either.java

+/*
+ * 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.types;
+
+/**
+ * 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 final boolean isLeft() {
+		return getClass() == Left.class;
+	}
+
+	/**
+	 * 
+	 * @return true if this is a Right value, false if this is a Left value
+	 */
+	public final boolean isRight() {
+		return getClass() == Right.class;
+	}
+
+	/**
+	 * A left value of {@link Either}
+	 *
+	 * @param <L>
+	 *            the type of Left
+	 * @param <R>
+	 *            the type of Right
+	 */
+	public static class Left<L, R> extends Either<L, R> {
+		private final L value;
+
+		public Left(L value) {
+			this.value = java.util.Objects.requireNonNull(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 "Left(" + value.toString() + ")";
+		}
+
+		/**
+		 * Creates a left value of {@link Either}
+		 * 
+		 */
+		public static <L, R> Left<L, R> of(L left) {
+			return new Left<L, R>(left);
+		}
+	}
+
+	/**
+	 * A right value of {@link Either}
+	 *
+	 * @param <L>
+	 *            the type of Left
+	 * @param <R>
+	 *            the type of Right
+	 */
+	public static class Right<L, R> extends Either<L, R> {
+		private final R value;
+
+		public Right(R value) {
+			this.value = java.util.Objects.requireNonNull(value);
+		}
+
+		@Override
+		public L left() {
+			throw new IllegalStateException("Cannot retrieve Left value on a Right");
+		}
+
+		@Override
+		public R right() {
+			return value;
+		}
+
+		@Override
+		public boolean equals(Object object) {
+			if (object instanceof Right<?, ?>) {
+				final Right<?, ?> other = (Right<?, ?>) object;
+				return value.equals(other.value);
+			}
+			return false;
+		}
+
+		@Override
+		public int hashCode() {
+			return value.hashCode();
+		}
+
+		@Override
+		public String toString() {
+			return "Right(" + value.toString() + ")";
+		}
+
+		/**
+		 * Creates a right value of {@link Either}
+		 * 
+		 */
+		public static <L, R> Right<L, R> of(R right) {
+			return new Right<L, R>(right);
+		}
+	}
+}