Scala Datatype for numeric real range

Question

Is there some idiomatic scala type to limit a floating point value to a given float range that is defined by a upper an lower bound?

Concrete i want to have a float type that is only allowed to have values between 0.0 and 1.0.

More concrete i am about to write a function that takes a Int and another function that maps this Int to the range between 0.0 and 1.0, in pseudo-scala:

def foo(x : Int, f : (Int => {0.0,...,1.0})) {
    // ....
}

Already searched the boards, but found nothing appropriate. some implicit-magic or custom typedef would be also ok for me.

Answer 1

You can use value classes as pointed by mhs:

case class Prob private( val x: Double ) extends AnyVal {
  def *( that: Prob ) = Prob( this.x * that.x )
  def opposite = Prob( 1-x )
}

object Prob {
  def make( x: Double ) = 
    if( x >=0 && x <= 1 ) 
      Prob(x) 
    else 
      throw new RuntimeException( "X must be between 0 and 1" )
}

They must be created using the factory method in the companion object, which will check that the range is correct:

scala> val x = Prob.make(0.5)
x: Prob = Prob(0.5)

scala> val y = Prob.make(1.1)
java.lang.RuntimeException: X must be between 0 and 1

However using operations that will never produce a number outside the range will not require validity check. For instance * or opposite.