Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/1097#discussion_r39492448
--- Diff:
flink-java/src/main/java/org/apache/flink/api/java/utils/Option.java ---
@@ -0,0 +1,129 @@
+/*
+ * 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.utils;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Internal representation of a parameter passed to a user defined
function.
+ */
+public class Option<T> {
+
+ private String longName;
+ private String shortName;
+
+ private T defaultValue;
+ private Set<T> choices;
+
+ private String helpText;
+
+ public Option(String name) {
+ this.longName = name;
+ this.choices = new HashSet<>();
+ }
+
+ /**
+ * Define a alternative / short name of the Parameter.
+ *
+ * @param shortName - short version of the parameter name
+ * @return the updated Option
+ */
+ public Option<T> alt(String shortName) {
+ this.shortName = shortName;
+ return this;
+ }
+
+ /**
+ * Define a default value for the option.
+ *
+ * Throws an exception if the list of possible values for the parameter
is not empty and the default value passed
+ * is not in the list.
+ *
+ * @param defaultValue - the default value
+ * @return the updated Option
+ */
+ public Option<T> defaultValue(T defaultValue) {
+ if (this.choices.isEmpty()) {
+ return this.setDefaultValue(defaultValue);
+ } else {
+ if (this.choices.contains(defaultValue)) {
+ return this.setDefaultValue(defaultValue);
+ } else {
+ throw new
IllegalArgumentException("defaultValue passed is not in the list of expected
values.");
+ }
+ }
+ }
+
+ /**
+ * Restrict the list of possible values of the parameter.
+ *
+ * @param choices - the allowed values of the parameter.
+ * @return the updated Option
+ */
+ public Option<T> choices(T... choices) {
+ Collections.addAll(this.choices, choices);
--- End diff --
Add check that `defaultValue` (if already set) is in choices.
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