CODEWITHSUNDEEP
scala
SkyWalker
SkyWalker

Reputation: 14317

How to unwrap an Option with its correct type in pattern matching?

I have the following code that illustrates what I'd like to achieve but it doesn't compile ... I'd like to find out whether the configMap of type Map contains a key with value "runOnGrid" and if it does get its Boolean value.

val runOnGrid : Boolean = args.configMap.get("runOnGrid") match {
    case Some(value) : Option[Boolean] => value // <=== compiler error
    case None => false
}

but this doesn't work because I can't do Some(value) : Option[Boolean] namely I'm constrained to choose between matching by the value or by the type. To achieve this apparently I need better Scala kung fu ... can anyone advice?

UPDATE: meantime I figured this horrendous way to do it

val runOnGrid = args.configMap.get(("runOnGrid") match {
    case Some(value) => value.isInstanceOf[Boolean] && value.asInstanceOf[Boolean]
    case _ => false
}

UPDATE: ConfigMap is defined inside Scalatest as:

class ConfigMap(underlying: Map[String, Any]) extends Map[String, Any] ...

Upvotes: 0

Views: 8322

Answers (4)

iuriisusuk
iuriisusuk

Reputation: 434

In case configMap has a type Map[String, String] (when you read configs from file), you can do:

val runOnGrid : Boolean = args.configMap.get("runOnGrid") match {
    case Some("true") => true
    case Some("false") => false
    case _ => false
}

Upvotes: 0

Tzach Zohar
Tzach Zohar

Reputation: 37852

How about this workaround:

val runOnGrid : Boolean = args.configMap.get("runOnGrid") match {
  case Some(true) => true
  case _ => false
}

Upvotes: 3

aks
aks

Reputation: 1029

You are getting compile time error because you are mentioning type to case element, remove that and it will work,

So change to,

val runOnGrid : Boolean = args.configMap.get("runOnGrid") match {
    case Some(value) => value // <=== Changed
    case _ => false
}

Upvotes: 0

Nagarjuna Pamu
Nagarjuna Pamu

Reputation: 14825

You can do something like this Some(value: Boolean) value inside Some can be given a type annotation

val runOnGrid : Boolean = args.configMap.get("runOnGrid") match {
    case Some(value: Boolean) => value
    case _ => false
}

Upvotes: 5

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