Github user dyanarose commented on a diff in the pull request:
https://github.com/apache/flink/pull/5295#discussion_r161807828
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/windowing/assigners/DynamicEventTimeSessionWindows.java
---
@@ -0,0 +1,101 @@
+/*
+ * 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.windowing.assigners;
+
+import org.apache.flink.api.common.ExecutionConfig;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import
org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.streaming.api.windowing.triggers.Trigger;
+import
org.apache.flink.streaming.api.windowing.triggers.TypedEventTimeTrigger;
+import org.apache.flink.streaming.api.windowing.windows.TimeWindow;
+
+import java.util.Collection;
+import java.util.Collections;
+
+/**
+ * A {@link WindowAssigner} that windows elements into sessions based on
the timestamp of the
+ * elements. Windows cannot overlap.
+ *
+ * <p>For example, in order to window into windows with a dynamic time gap:
+ * <pre> {@code
+ * DataStream<Tuple2<String, Integer>> in = ...;
+ * KeyedStream<String, Tuple2<String, Integer>> keyed = in.keyBy(...);
+ * WindowedStream<Tuple2<String, Integer>, String, TimeWindows> windowed =
+ * keyed.window(DynamicEventTimeSessionWindows.withDynamicGap({@link
SessionWindowTimeGapExtractor }));
+ * } </pre>
+ *
+ * @param <T> The type of the input elements
+ */
+public class DynamicEventTimeSessionWindows<T> extends
MergingWindowAssigner<T, TimeWindow> {
+ private static final long serialVersionUID = 1L;
--- End diff --
The Typed requirement comes from the desire to allow the
SessionWindowTimeGapExtractor to accept a correctly typed element.
To do that the Assigner itself needs to be typed, which means that the
trigger needs to be typed and so on.
If the SessionWindowTimeGapExtractor extract method instead took `object`,
requiring that the implementer cast it, then the new Typed classes wouldn't be
necessary.
I don't find that to be the most user friendly interface though, when the
type information is available. But, yeah, I'm not happy with having to
implement these exact copy classes either...
---
