Get type of a "singleton type"

Question

We can create a literal types via shapeless:

import shapeless.syntax.singleton._
var x = 42.narrow
// x: Int(42) = 42

But how can I operate with Int(42) as a type if it's even impossible to create type alias

type Answ = Int(42) // won't compile
// or
def doSmth(value: Int(42)) = ... // won't compile

Answer 1

1. In Typelevel Scala you can write just

   val x: 42 = 42
   
   type Answ = 42
   
   def doSmth(value: 42) = ???
   

2. In Dotty Scala you can write the same.

3. In Lightbend Scala (i.e. standard Scala) + Shapeless you can write

   import shapeless.Witness
   import shapeless.syntax.singleton._
   
   val x: Witness.`42`.T = 42.narrow
   
   type Answ = Witness.`42`.T
   
   def doSmth(value: Witness.`42`.T) = ???
   

In case 1) build.sbt should be

scalaOrganization := "org.typelevel"
scalaVersion := "2.12.3-bin-typelevel-4"
scalacOptions += "-Yliteral-types"

In case 2) build.sbt should be

scalaOrganization := "ch.epfl.lamp"
scalaVersion := "0.3.0-RC2"

and plugins.sbt

addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.1.5")

In case 3) build.sbt should be

scalaOrganization := "org.scala-lang"
scalaVersion := "2.12.3"
libraryDependencies += "com.chuusai" %% "shapeless" % "2.3.2"

4. or you can use Typelevel Scala and Shapeless at the same time.

---

Update. Since version 2.13.0 there are literal types in standard Scala

val x: 42 = 42
val x1: 42 = valueOf[42]

type Answ = 42

def doSmth(value: 42) = ???

https://github.com/scala/scala/releases/v2.13.0 (Language changes / Literal types)