typeLevelArithmeticProto.scala

sealed trait NaturalNumber
sealed trait _0 extends NaturalNumber
sealed trait _1 extends _0
sealed trait _2 extends _1
sealed trait _3 extends _2
sealed trait _4 extends _3
sealed trait _5 extends _4
sealed trait _6 extends _5
sealed trait _7 extends _6
sealed trait _8 extends _7
sealed trait _9 extends _8
sealed trait _10 extends _9

//////////////////////////////////////////////////

type IsEqual[N <: NaturalNumber, M <: NaturalNumber] = N =:= M
type IsLessOrEqual[N <: NaturalNumber, M <: NaturalNumber] = N <:< M

//////////////////////////////////////////////////

sealed trait VersionNumber{
  type Nat <:NaturalNumber
}

object V0 extends VersionNumber{ override type Nat = _0 }
object V1 extends VersionNumber{ override type Nat = _1 }
object V2 extends VersionNumber{ override type Nat = _2 }
object V3 extends VersionNumber{ override type Nat = _3 }
object V4 extends VersionNumber{ override type Nat = _4 }
object V5 extends VersionNumber{ override type Nat = _5 }
object V6 extends VersionNumber{ override type Nat = _6 }
object V7 extends VersionNumber{ override type Nat = _7 }
object V8 extends VersionNumber{ override type Nat = _8 }
object V9 extends VersionNumber{ override type Nat = _9 }
object V10 extends VersionNumber{ override type Nat = _10 }

//////////////////////////////////////////////////

trait ResourceManifest {
  def getResource: Int
  type Major <: NaturalNumber
  type Minor <: NaturalNumber
}


object Resource42 extends ResourceManifest {
  def getResource: Int = 42
  type Major = _2
  type Minor = _3
}


//it takes VersionNumbers as parameters and implicitly checks if the version Numbers "match" that of the manifest. Fails to compile if they don't@implicitNotFound(msg = "The required version is not compatible with the specified version information inside the resource manifest")
def getResource(manifest: ResourceManifest)(maj: VersionNumber, min: VersionNumber)
               (implicit
                maj_check: manifest.Major IsEqual maj.Nat,
                min_check: manifest.Minor IsLessOrEqual min.Nat
               ) = manifest.getResource


//getResource(Resource42)(V1,V0)// want version 1.0 => fails to compile due to incompatible Major version

getResource(Resource42)(V2, V2) // want version 2.2 => compiles
getResource(Resource42)(V2, V3) // want version 2.3 => compiles


//getResource(Resource42)(V2,V4) // want version 2.4 => fails to compile as that version is not available yet.
//getResource(Resource42)(V3,V0)// want version 3.0 => fails to compile due to incompatible Major version

This is a mechanism for versioning mono-repo services. instead of relying on a versioned client or embeding the version information in a header and then realising the server has rejected/deprecated your request.
we can instead make services provide a series of "manifest" objects which contain the type and version information and the client code can fail compilation if the version information is not right.