Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/2768#discussion_r89128914
--- Diff:
flink-core/src/main/java/org/apache/flink/api/common/state/SimpleStateDescriptor.java
---
@@ -0,0 +1,226 @@
+/*
+ * 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.common.state;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.api.common.ExecutionConfig;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.java.typeutils.TypeExtractor;
+import org.apache.flink.core.memory.DataInputViewStreamWrapper;
+import org.apache.flink.core.memory.DataOutputViewStreamWrapper;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+
+import static java.util.Objects.requireNonNull;
+
+/**
+ * Base class for the descriptors of simple states. A {@code
SimpleStateDescriptor} is used
+ * for creating partitioned simple states whose values are not composited.
+ *
+ * <p>Subclasses must correctly implement {@link #equals(Object)} and
{@link #hashCode()}.
+ *
+ * @param <T> The type of the value in the state.
+ * @param <S> The type of the created state.
+ */
+@PublicEvolving
+public abstract class SimpleStateDescriptor<T, S extends State<T>> extends
StateDescriptor<S> {
+ private static final long serialVersionUID = 1L;
+
+ /** The serializer for the type. May be eagerly initialized in the
constructor,
+ * or lazily once the type is serialized or an ExecutionConfig is
provided. */
+ protected TypeSerializer<T> typeSerializer;
+
+ /** The type information describing the value type. Only used to lazily
create the serializer
+ * and dropped during serialization */
+ private transient TypeInformation<T> typeInfo;
+
+ /** The default value returned by the state when no other value is
bound to a key */
+ protected transient T defaultValue;
--- End diff --
We might think about renaming this because for `FoldingState` it's not a
default value but the initial accumulation value. (Just a suggestion, not
strictly necessary)
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