Best way to represent constraints on values in Scala? -

what best way express that, say, int field or parameter should never negative?

the first thing comes mind annotation on type, case class foo(x: int @notnegative). i'd have invent own annotation, , there wouldn't sort of compile-time checking or anything.

is there better way?

why not using separate data type?

class natural private (val value: int) {    require(value >= 0)     def +(that:natural) = new natural(this.value + that.value)    def *(that:natural) = new natural(this.value * that.value)    def %(that:natural) = new natural(this.value % that.value)    def |-|(that:natural) = natural.abs(this.value - that.value) //absolute difference     override def tostring = value.tostring }  object natural {   implicit def nat2int(n:natural) = n.value   def abs(n:int) = new natural(math.abs(n)) } 

usage:

val = natural.abs(4711) val b = natural.abs(-42) val c = + b val d = b -  // works due implicit conversion, d typed int println(a < b) //works due implicit conversion