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[SPARK-4268][SQL] Use #::: to get benefit from Stream in SqlLexical.allCaseVersions #3132

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[SPARK-4268][SQL] Use #::: to get benefit from Stream in SqlLexical.allCaseVersions #3132

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4 changes: 2 additions & 2 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SparkSQLParser.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -97,10 +97,10 @@ class SqlLexical(val keywords: Seq[String]) extends StdLexical {

/** Generate all variations of upper and lower case of a given string */
def allCaseVersions(s: String, prefix: String = ""): Stream[String] = {
if (s == "") {
if (s.isEmpty) {
Stream(prefix)
} else {
allCaseVersions(s.tail, prefix + s.head.toLower) ++
allCaseVersions(s.tail, prefix + s.head.toLower) #:::
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@marmbrus marmbrus Nov 7, 2014

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Why is this better? Because its lazy? Given that these are all materialized eventually the possible benefit seems dubious given the drop in readability. (Please correct me if I'm wrong).

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@zsxwing zsxwing Nov 8, 2014

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Given that these are all materialized eventually

Didn't realize it. However, then why not use List? Since laziness is not necessary, using Stream is confusing.

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@marmbrus marmbrus Dec 2, 2014

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That is a good point, I don't know why it is a Stream but I guess this change is okay.

allCaseVersions(s.tail, prefix + s.head.toUpper)
}
}
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