Option in the Scala language is a container for zero or one element of a given type.
Option in scala is a container for zero or one element of a given type.
Questions tagged [scala-option]
232 questions
7
votes
1 answer
Nested Scala matchers why Some(Some(1),1) can't match?
It seems that nested matching doesn't work, which is a strange limitation.
An example of the behaviour follows:
Some(Some(1),2) match {
| case Some(Some(a),b) => a
| case e => e
| }
:9: error: wrong number of arguments for : (x:…
Bryan Hunt
- 3,685
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- 36
7
votes
1 answer
how to read json with an optional field serialized by a missing field, in upickle
I use upickle for serializing json in scalajs. I need to be able to parse optional fields, represented by a null value and by a missing field (standard json on the web).
With OptionPickler, I can accept nullable items.
However, how can I accept…
David Portabella
- 12,390
- 27
- 101
- 182
7
votes
5 answers
Using Option all over the place feels a bit awkward. Am I doing something wrong?
As a result of articles I read about the Option class which helps you avoid NullPointerException's, I started to use it all over the place. Imagine something like this:
var file:Option[File] = None
and later when I use it:
val actualFile =…
Geo
- 93,257
- 117
- 344
- 520
7
votes
1 answer
In what way is Scala's Option fold a catamorphism?
The answer to this question suggests that the fold method on Option in Scala is a catamoprhism. From the wikipedia a catamophism is "the unique homomorphism from an initial algebra into some other algebra. The concept has been applied to functional…
Patrick
- 201
- 1
- 6
7
votes
2 answers
Lazily coalesce Options in Scala
I have several ways of calculating a value, in decreasing preference.
firstWay()
second() + way()
orA(thirdWay())
Each of these returns an Option. I want to "coalesce" these and get an Option which the the value returned by the first Some of these,…
Paul Draper
- 78,542
- 46
- 206
- 285
6
votes
2 answers
Scala: selecting function returning Option versus PartialFunction
I'm a relative Scala beginner and would like some advice on how to proceed on an implementation that seems like it can be done either with a function returning Option or with PartialFunction. I've read all the related posts I could find (see bottom…
Gregor Scheidt
- 3,952
- 4
- 24
- 28
6
votes
2 answers
Best way to score current extremum in collection type
I’m currently a little tired so I might be missing the obvious.
I have a var _minVal: Option[Double], which shall hold the minimal value contained in a collection of Doubles (or None, if the collection is empty)
When adding a new item to the…
flying sheep
- 8,475
- 5
- 56
- 73
6
votes
3 answers
Call a method on the value of Scala Option if present
I am trying to figure out the best way to refactor the following code to eliminate the use of Option.get(). I know that using the get method is considered bad practice.
if (myConnection.isDefined) {
myConnection.get.close
}
where myConnection is…
JoeMjr2
- 3,804
- 4
- 34
- 62
6
votes
3 answers
Working with options in Scala (best practices)
I have a method that I wrote to enrich person data by performing an API call and adding the enriched data.
I have this case class:
case class Person(personData: PersonData, dataEnrichment: Option[DataEnrichment])
My method is supposed to return…
MNY
- 1,506
- 5
- 21
- 34
6
votes
1 answer
Scala most elegant way to handle option and throw exception from Scala Map
I have a map and want to:
retrieve value without handling Option
log a message when there is no such the key.
nice to return a default value ( in addition to log a message) when the key is not present. This is optional because when the code fails…
Raymond Chenon
- 11,482
- 15
- 77
- 110
6
votes
1 answer
How to convert/wrap a sequence in scala to an Option[Seq] so that if the list is empty, the Option is None
I could do this with an if an statement, but there is probably a "scala" way to do this.
def notScalaConv(in: Seq[String]): Option[Seq[String]] = {
if (in.isEmpty)
None
else
Option(in)
}
marathon
- 7,881
- 17
- 74
- 137
6
votes
3 answers
Calling Java API from Scala with null argument
I have some Scala code that needs to call a Java API
The Java API takes arguments that may be null. My Scala, of course, uses Option.
For example, let's say I have a Java object constructor Foo(Integer) where the Integer may be null. I want to…
opus111
- 2,744
- 4
- 25
- 41
6
votes
5 answers
How do you stop building an Option[Collection] upon reaching the first None?
When building up a collection inside an Option, each attempt to make the next member of the collection might fail, making the collection as a whole a failure, too. Upon the first failure to make a member, I'd like to give up immediately and return…
Ben Kovitz
- 4,920
- 1
- 22
- 50
6
votes
2 answers
Scala - Match Tuple of Options
I have:
val foo = Some(List(1, 2, 3)) -> Some("y")
I would like to cast match it:
foo match {
case (Some(x), Some(y)) => println(x + " " + y)
case _ => println("error")
This works fine for Some(List(1, 2, 3) -> Some("score")) but fails for…
Karsten
- 882
- 6
- 18
6
votes
5 answers
Chaining scala Try instances that contain Options
I am trying to find a cleaner way to express code that looks similar to this:
def method1: Try[Option[String]] = ???
def method2: Try[Option[String]] = ???
def method3: Try[Option[String]] = ???
method1 match
{
case f: Failure[Option[String]] =>…
Spencer Stejskal
- 498
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- 15