CODEWITHSUNDEEP
scalapattern-matching
Ra Ka
Ra Ka

Reputation: 3055

Understanding Scala's Extractor - Pattern with Zero variable and Boolean Result

Currently I am learning Scala Extractor and stuck in following confusion. I am unable to understand the following code. In the below pattern match, How UpperCase() return a String while the unapply method is designed to return Boolean?

  object UpperCase {
    def unapply(s: String): Boolean = s.toUpperCase == s
  }

  println(UpperCase.unapply("RAK")) //print boolean true or false.

  "RAK" match{
    case status @ UpperCase() => println("yes - "+ status) //How status holds RAK not boolean value?
    case _ => println("No")
  }

Upvotes: 3

Views: 149

Answers (1)

obourgain
obourgain

Reputation: 9336

You are using a boolean extractor, that matches all values v for which x.unapply(v) yields true. The @ is a pattern binder, which binds the variable status to the value matched by the pattern.

In your example, the pattern match the String "RAK", which is bound to the variable status.

Upvotes: 4

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