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
4
votes
7 answers
Scala - Option.getOrElse() "type erasure"?
I am trying to use the Option.getOrElse() method but it returns etiher Any or ScalaObject instead of an instance of the correct class that the Option was parametrized with. I can't find any mention about this problem and it does not seem like it…
noncom
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4
votes
2 answers
Filtering on Scala Option[Set]
I have a Scala value of type Option[Set[String]] that I am trying to use in a collection filter method:
val opt: Option[Set[String]] = ...
collection.filter {
value =>
opt match {
case Some(set) => set.contains(value)
case None => true
…
Ralph
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3
votes
4 answers
Confused by "Scala in Depth" Option example
Chapter 2 of the new Manning book, "Scala in Depth" by Josh Sueresh is posted here. In reading the article, I came across this bit of code:
def getTemporaryDirectory(tmpArg : Option[String]) : java.io.File = {
tmpArg.map(name => new…
chaotic3quilibrium
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3
votes
3 answers
Producing a partially applied function from method of type in an Option
Suppose I'm writing a GUI
class Kitteh (val age: Int) {
require (age < 5)
def saveMeow(file: File) = { /* implementation */ }
def savePurr(file: File) = { /* implementation */ }
}
The frame has a field for the current Kitteh, which is an…
Luigi Plinge
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3
votes
0 answers
Scala: Updating a field of an object in an Option
What is idiomatic way of updating a field in an object inside a scala option?
flag is a boolean field in item,and I just want to reverse its value:
val newOption = itemOption.map(item => item.copy(flag = !item.flag))
Is this correct way?
Mandroid
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3
votes
3 answers
Options in Scala with Boolean default value with getOrElse
I have a map with some pairs and I want to assign a default value(Boolean) for a key, the default value for a key is a string when I used getOrElse and I'm looking for a way to do it for a int or boolean.
for Eg:
val someMap= Map("key1"->"value1",…
knowledge_seeker
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3
votes
2 answers
Trouble serializing optional value class instances with json4s
I'm trying to serialize a case class with optional value-class field to JSON using json4s. So far, I'm not able to get the optional value-class field rendered correctly (see the snippet below with examples).
I tried json-native and json-jackson…
Roman
- 64,384
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3
votes
2 answers
How to yield multiple values?
I have a for comprehension like:
val ao = Option(1)
val bo = Option(2)
val (x,y) = for (a <- ao; b <- bo) yield (a+b, b+a*2)
However this does not work. For comprehension returns Option[(Int,Int)] but cannot be assigned to individual x and y.
If I…
SwiftMango
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3
votes
2 answers
Where is the method that boxes an AnyRef into an Option?
In this blogpost by James Iry, he writes:
Plus, Scala has an "option" method that promotes a value to either Some(value) or None depending on whether it's null or not ...
I can't seem to find this option method anywhere in the scaladoc.
Iulian…
Frankie Ribery
- 11,933
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3
votes
4 answers
Behaviour of Options inside for comprehension is Scala
Two newbie questions.
It seems that for comprehension knows about Options and can skip automatically None and unwrap Some, e.g.
val x = Map("a" -> List(1,2,3), "b" -> List(4,5,6), "c" -> List(7,8,9))
val r = for {map_key <- List("WRONG_KEY", "a",…
Alexey Kalmykov
- 1,958
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3
votes
1 answer
Get Future objects from Future Options in Scala
I am new to Scala from Java so the functional programming thing is still a bit difficult for me to understand. I have a project in Play framework. I need to query the database to get rows with ids and display them in a html template.
Here is my…
Ken
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- 10
3
votes
1 answer
Asymmetry of (Some (x), None).min and max
Accidentally, I observed an asymmetry.
Let's have a list:
val li = List (Some (3), Some (2), None, Some (9))
li: List[Option[Int]] = List(Some(3), Some(2), None, Some(9))
scala> li.max
res54: Option[Int] = Some(9)
Ok - Some(9) is bigger than…
user unknown
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3
votes
2 answers
When to use Option#orNull
As I understand we should avoid using null in Scala. And if some field is not logically valid to have "no-value" then we should not use Option to avoid overusing of Options.
So lets look to code.
I have class
case class User (name: String)
and I…
WelcomeTo
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3
votes
2 answers
Best Practices for nested Scala Option fields?
I've got a number of nested objects, all wrapped in a Scala Option type. Elsewhere in my project I'm having to call an attribute that is embedded some 5 levels deep (some of which are Lists), each time making a call to .get. This way I end up with…
GroomedGorilla
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3
votes
1 answer
Dealing Options from a Map.get in Scala
I've a Scala Map that contains a bunch of parameters that I get in a HTTP request.
val queryParams = Map( ("keyword" -> "k"), ("from" -> "f"), ("to" -> "t"), ("limit" -> "l") )
I've a method that takes all these parameters.
def someMethod(…
Soumya Simanta
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