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Last active Aug 20, 2019
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/** Always positive integer, nobody can do `new PositiveInt(-3)` */
class PositiveInt private(value: Int) extends AnyVal
/** Set of constructors for PositiveInt */
object PositiveInt {
/** The only proper constructor. Everything else is workaround */
def fromInt(int: Int): Option[PositiveInt] = if (int > 0) Some(new PositiveInt(int)) else None
* This is a workaround and must be called ONLY when caller is sure the `int` is positive
* *Every function calling `unsafeFromInt` is unsafe by definition*
def unsafeFromInt(int: Int): PositiveInt = new PositiveInt(int)
object DownstreamModule {
/** Totally safe function, by contract. Cannot throw an exception */
def repeat[A](element: A, index: PositiveInt): List[A] = ???
// Let's imagine we want to get a sum of N integers (for some reasons by filling a list with it)
/** Ths is what we have now. It's still unsafe function */
def invalid(value: Int, n: Int) =
repeat(value, PositiveInt.unsafeFromInt(n)).sum
/** This is what we should have. It is safe function - we don't care where we got PositiveInt from, we just assume its valid */
def valid(value: Int, n: PositiveInt) =
repeat(value, n).sum
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