Experiment with newtypes and scala-newtype

[fthomas]

RefineJavapSpec.scala shows the boxing behavior and runtime overhead of the different refinement carrier that refined supports which are currently Refined, shapeless.tag.@@, and scalaz.@@ (via the refined-scalaz module).

For reference types, all three carrier types do not box but using Refined causes an additional function call. For value types only shapeless.@@ does not seem to box but causes two additional function calls. While the runtime overhead of shapeless.tag.@@ and scalaz.@@ is lower than for Refined, the latter is less susceptible to compiler bugs and quirks like:

• refining with type aliases does not work #21 (aka Type aliases with return type inference works bad scala/bug#8740) (shapeless.tag.@@ does not work with aliases)
• Cannot derive Encoder/Decoder for a case class containing members with shapeless-tagged refinements. circe/circe#220, problem encoding tagged types alexarchambault/argonaut-shapeless#31, Generic extras encoders with Scalaz tags circe/circe#784 (generic derivation with shapeless.tag.@@ and scalaz.@@ does not work reliably)

We should experiment if @alexknvl's https://github.com/alexknvl/newtypes or @carymrobbins https://github.com/estatico/scala-newtype could provide a viable replacement for Refined with lower (or zero) runtime overhead.

[carymrobbins]

@fthomas FWIW, I recently added @newsubtype macro support, which gets us unboxed primitives -

estatico/scala-newtype#14

I plan on cutting a release including this feature in the near future. If folks are wanting this sooner rather than later I can prioritize as need be.

[fthomas]

@carymrobbins Unboxed primitives sounds great and the subtyping relation fits well for refinement types. I'll will definitely try that for refined. There is no hurry to cut a release from my side, It'll take a me little while before I can do these experiments.