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https://issues.apache.org/jira/browse/FLINK-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14642514#comment-14642514
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ASF GitHub Bot commented on FLINK-2405:
---------------------------------------
Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/936#discussion_r35520346
--- Diff:
flink-staging/flink-streaming/flink-streaming-scala/src/main/scala/org/apache/flink/streaming/api/scala/function/StatefulFunction.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.streaming.api.scala.function
+
+import org.apache.flink.api.common.functions.RichFunction
+import org.apache.flink.configuration.Configuration
+import org.apache.flink.api.common.state.OperatorState
+
+trait StatefulFunction[I, O, S] extends RichFunction {
--- End diff --
Scala docs are missing here.
> Add stateful transformations using lambdas to the Streaming Scala API
> ---------------------------------------------------------------------
>
> Key: FLINK-2405
> URL: https://issues.apache.org/jira/browse/FLINK-2405
> Project: Flink
> Issue Type: New Feature
> Components: Scala API, Streaming
> Reporter: Gyula Fora
> Assignee: Gyula Fora
> Priority: Minor
>
> I propose to extend the Streaming Scala API methods (map, flatmap, filter
> etc) with versions that take stateful functions as lambdas. This would allow
> for a nice functional way of defining stateful transformations:
> Example:
> def mapWithState( fun: (I, Option[S]) => (O, Option[S]), stateByKey: Boolean
> = false)
> The stateByKey optional flag allows the user to partition the state by key
> when applied on a KeyedDataStream.
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