Github user koeninger commented on a diff in the pull request:
https://github.com/apache/spark/pull/3798#discussion_r23729727
--- Diff:
external/kafka/src/main/scala/org/apache/spark/rdd/kafka/OffsetRange.scala ---
@@ -0,0 +1,70 @@
+/*
+ * 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.spark.rdd.kafka
+
+/** Represents a range of offsets from a single Kafka TopicAndPartition */
+trait OffsetRange {
--- End diff --
It's a trait with no implemented methods, so it will get compiled to a
single class file with the same bytecode as a java interface (plus a scala
signature annotation). It won't make a separate OffsetRange$class.class file
as you may have seen for scala traits with default method implementations.
The point of the trait/interface is that, as far as I understood, you were
concerned about publicly exposing KafkaRDDPartition (which already is just a
simple class, not a case class). If you want one common supertype for both
KafkaRDDPartition and whatever people pass into public methods to construct a
KafkaRDD, your choices are an interface or a (possibly abstract) class. I
think an interface is cleaner.
TLDR
- if you're fine with exposing KafkaRDDPartition, let's just do that.
- if you're super concerned that a trait with no implementation can't be
used from java, i'll move it to java code and change "trait" for "interface"
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