Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/10205#discussion_r53542099
--- Diff: core/src/main/scala/org/apache/spark/config/ConfigEntry.scala ---
@@ -0,0 +1,247 @@
+/*
+ * 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.config
+
+import java.util.concurrent.TimeUnit
+
+import org.apache.spark.SparkConf
+import org.apache.spark.network.util.{ByteUnit, JavaUtils}
+
+/**
+ * An entry contains all meta information for a configuration.
+ *
+ * @param key the key for the configuration
+ * @param defaultValue the default value for the configuration
+ * @param valueConverter how to convert a string to the value. It should
throw an exception if the
+ * string does not have the required format.
+ * @param stringConverter how to convert a value to a string that the user
can use it as a valid
+ * string value. It's usually `toString`. But
sometimes, a custom converter
+ * is necessary. E.g., if T is List[String], `a, b,
c` is better than
+ * `List(a, b, c)`.
+ * @param doc the document for the configuration
+ * @param isPublic if this configuration is public to the user. If it's
`false`, this
+ * configuration is only used internally and we should not
expose it to the user.
+ * @tparam T the value type
+ */
+private[spark] class ConfigEntry[T] (
+ val key: String,
+ val defaultValue: Option[T],
+ val valueConverter: String => T,
+ val stringConverter: T => String,
+ val doc: String,
+ val isPublic: Boolean) {
+
+ def defaultValueString: String =
defaultValue.map(stringConverter).getOrElse("<undefined>")
+
+ /**
+ * Returns a new ConfigEntry that wraps the value in an Option, for
config entries that do
+ * not require a value.
+ */
+ def optional: OptionalConfigEntry[T] = {
+ require(!defaultValue.isDefined, s"$this has a default value, cannot
be optional.")
+ new OptionalConfigEntry(key, valueConverter, stringConverter, doc,
isPublic)
--- End diff --
I thought about this one quite a bit. My understanding is that this exists
because we have configs without default values and we just want to get the
value as an option. However, in my mind all configs are optional to begin with
(maybe except for `spark.master` etc.) but an "optional config" here means
something different.
I think a more intuitive way might be just to add a
`conf.getOption(configEntry: ConfigEntry[T])` that doesn't try to get the
default value. If it's set, we get `Some(x)`, else if there's a default value
we get `Some(y)`, otherwise `None`. This has three main benefits that I can
think of:
- you don't need to add `.optional` after most configs
- it's clear that the return type is an option. Today `conf.get` sometimes
returns an `Option`, which is weird to me.
- you don't really need the `readFrom` abstraction anymore (assuming we
find another way to express fallback)
What do you think?
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