Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/1905#discussion_r60452526
--- Diff:
flink-libraries/flink-cep-scala/src/main/scala/org/apache/flink/cep/scala/pattern/package.scala
---
@@ -0,0 +1,42 @@
+/*
+ * 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.cep.scala
+
+import org.apache.flink.cep.pattern.{FollowedByPattern =>
JFollowedByPattern, Pattern => JPattern}
+
+import _root_.scala.reflect.ClassTag
+
+package object pattern {
+ /**
+ * Utility method to wrap { @link org.apache.flink.cep.pattern.Pattern}
and its subclasses
+ * for usage with the Scala API.
+ *
+ * @param javaPattern The underlying pattern from the Java API
+ * @tparam T Base type of the elements appearing in the pattern
+ * @tparam F Subtype of T to which the current pattern operator is
constrained
+ * @return A pattern from the Scala API which wraps the pattern from
the Java API
+ */
+ private[flink] def wrapPattern[
+ T: ClassTag, F <: T : ClassTag](javaPattern: JPattern[T, F])
+ : Pattern[T, F] = javaPattern match {
+ case f: JFollowedByPattern[T, F] => FollowedByPattern[T, F](f)
+ case p: JPattern[T, F] => Pattern[T, F](p)
+ case _ => null
--- End diff --
I am not sure if this case should trigger an exception, because the Java
API is actually allowed to return null here in case there is no previous
pattern. Our pattern will then wrap this as an undefined Option.
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