validations in value classes

Question

SIP-15 implies one can use value classes to define for example new numeric classes, such as positive numbers. Is it possible to code such a constraint that the underlying >

Answer 1

You could use refined to lift the validation step to compile time by refining your Double with refined's Positive predicate:

import eu.timepit.refined.auto._
import eu.timepit.refined.numeric._
import shapeless.tag.@@

scala> implicit class Volatility(val underlying: Double @@ Positive) extends AnyVal
defined class Volatility

scala> Volatility(1.5)
res1: Volatility = Volatility@3ff80000

scala> Volatility(-1.5)
:52: error: Predicate failed: (-1.5 > 0).
       Volatility(-1.5)
                   ^

Note that the last error is a compile error and not a runtime error.