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Does Scala have Java's ternary operator?

Posted on October 13, 2008, in Programming

I hear this question a lot. Yes it does. Instead of c ? p : q, it is written if(c) p else q.

This may not be preferable. Perhaps you’d like to write it using the same syntax as Java. Sadly, you can’t. This is because : is not a valid identifier. Fear not, | is! Would you settle for this?

c ? p | q

Then you’ll need the following code. Notice the call-by-name (=>) annotations on the arguments. This evaluation strategy is required to correctly rewrite Java’s ternary operator. This cannot be done in Java itself.

case class Bool(b: Boolean) {
  def ?[X](t: => X) = new {
    def |(f: => X) = if(b) t else f
  }
}

object Bool {
  implicit def BooleanBool(b: Boolean) = Bool(b)
}

Here is an example using the new operator that we just defined:

object T {
  val condition = true

  import Bool._

  // yay!
  val x = condition ? "yes" | "no"
}

Have fun ;)