Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/10205#discussion_r53876472
--- 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"$this has a default value, cannot
be optional.")
+ new OptionalConfigEntry(key, valueConverter, stringConverter, doc,
isPublic)
+ }
+
+ def readFrom(conf: SparkConf): T = {
+ conf.getOption(key).map(valueConverter).orElse(defaultValue).getOrElse(
+ throw new NoSuchElementException(s"$key is not set."))
+ }
+
+ override def toString: String = {
+ s"ConfigEntry(key=$key, defaultValue=$defaultValueString, doc=$doc,
public=$isPublic)"
+ }
+}
+
+private[spark] class OptionalConfigEntry[T](
+ override val key: String,
+ val _valueConverter: String => T,
+ val _stringConverter: T => String,
+ override val doc: String,
+ override val isPublic: Boolean)
+ extends ConfigEntry[Option[T]](key, None, s =>
Some(_valueConverter(s)),
+ null, doc, isPublic) {
--- End diff --
Laziness, mostly, since this isn't really used outside of SQLConf and
SQLConf doesn't have optional configs. But I'll add something.
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