Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/14332#discussion_r72016327
--- Diff:
examples/src/main/scala/org/apache/spark/examples/ml/DataFrameExample.scala ---
@@ -54,14 +54,13 @@ object DataFrameExample {
}
}
- parser.parse(args, defaultParams).map { params =>
- run(params)
- }.getOrElse {
- sys.exit(1)
+ parser.parse(args, defaultParams) match {
+ case Some(params) => run(params)
+ case _ => sys.exit(1)
}
--- End diff --
I'm reading http://www.scala-lang.org/api/2.11.8/#scala.Option
The only operations where a function operates on an `Option` have no side
effect:
`val upper = name map { _.trim } filter { _.length != 0 } map {
_.toUpperCase }`
Side effects are applied to the result of `getOrElse` only. What are you
reading?
I wonder if the example conflates two things. It's definitely less
idiomatic to accomplish the _transformation_ with `match`. `println(option
match ...)` would be odd. It pushes the `println` inside though which makes it
less clear what about this is unidiomatic. The code snippets don't actually do
the same thing, even.
I think you're suggesting that this implies the former is more idiomatic.
Yes, but it's also not what you're arguing for. It's crucially different in
that we're talking about `Option.map` or `fold` to achieve side effects. The
example specifically doesn't do that. Calling them "essentially equivalent"
hand-waves past the very point.
I understand FP fine; none of this is beyond any of us. I just don't think
your argument holds together. I am not going to change this code based on this.
I'd welcome other opinions though.
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