Newts
Better newtypes for Scala based on the following two articles:
Quick Start
addCompilerPlugin("org.scalameta" % "paradise" % "3.0.0-M10" cross CrossVersion.full)
resolvers += Resolver.bintrayRepo("alexknvl", "maven")
libraryDependencies += "com.alexknvl" %% "newtypes" % "0.3.0"Use this fork
of scalameta/paradise until https://github.com/scalameta/paradise/pull/207 is merged in if you need
companion object support and can't use paradise-3.0.0-M10 (it supports only 2.12.3+).
Clone it and publishM2 in sbt, then change the paradise plugin to:
addCompilerPlugin("org.scalameta" % "paradise" % "3.0.0-alex" cross CrossVersion.full)Why newts?
| Features | AnyVal |
@newtypes.opaque |
@newtypes.translucent |
|---|---|---|---|
isInstanceOf |
Yes | No | No |
Generics box AnyRef subtypes |
Yes | No | No |
| Generics box primitives | Yes | Yes | Yes |
| Primitives box | No | Yes | No |
| Up-cast works | No | No | Yes |
| Down-cast works | No | No | No |
| Any methods | Yes | Yes | Yes |
| Overrides | Yes | No | No |
| Virtual dispatch | Yes | No | No |
| Typeclass-based dispatch | Yes | Yes | Yes |
Wrap List elements |
O(N) | O(1) (using subst) |
O(1) (using subst) |
Unwrap List elements |
O(N) | O(1) (using subst and Is) |
O(1) (automatic widening) |
| Supports HK parameters | Yes | Yes | Yes |
| Supports existential parameters | Yes | Yes | Yes |
What does it do?
@opaque type ArrayWrapper[A] = Array[A]
@translucent type Flags = Intbecomes
type ArrayWrapper[A] = ArrayWrapper.Type[A]
object ArrayWrapper {
type Base$$1
trait Tag$$1 extends Any
type Type[A] <: Base$$1 with Tag$$1
object Impl {
def apply[A](value: Array[A]): Type[A] = value.asInstanceOf[Type[A]]
def unwrap[A](value: Type[A]): Array[A] = value.asInstanceOf[Array[A]]
def subst[F[_], A](value: F[Array[A]]): F[Type[A]] = value.asInstanceOf[F[Type[A]]]
}
}
type Flags = Flags.Type
object Flags {
trait Tag$$1 extends Any
type Type <: Int with Tag$$1
object Impl {
def apply(value: Int): Type = value.asInstanceOf[Type]
def unwrap(value: Type): Int = value.asInstanceOf[Int]
def subst[F[_]](value: F[Int]): F[Type] = value.asInstanceOf[F[Type]]
}
}License
Code is provided under the MIT license available at https://opensource.org/licenses/MIT, as well as in the LICENSE file.