Named Tuples as a library

Language Design
7

It turns out, you can use Dynamic for opaque types, for example:

opaque type NamedPair
    [LabelA <: LabelType, A, LabelB <: LabelType, B] <: Dynamic
    = (A, B) & Dynamic

Thanks to @Jasper-M who used it in Should extension methods works with Dynamic trait? - #2 by Jasper-M

Applying this change, the main method looks like this after each phase:
At the beginning:

val john = P(age = 42, name = "John")

println(john.age)

After erasure:

val john: Tuple2 =
  {
    val b$proxy1: Tuple2 = Tuple2.apply("name", "John")
    Tuple2.apply(Tuple2.apply("age", scala.Int.box(42))._2(),
      b$proxy1._2()):Tuple2
  }
println(
  {
    val $proxy1: Tuple.Pair$package =
      Tuple.Pair$package:Tuple.Pair$package
    val p$proxy1: Tuple2 = john:Tuple2
    p$proxy1._1()
  }
)

Adding back some syntactic sugar:

val john: Tuple2 = ( ("age", scala.Int.box(42))._2, ("name", "John")._2 )

println( john._1 )

It looks like the one thing missing is partial evaluation/constant folding of tuples

@Ichoran
I don’t know how to show the bytecode for it, but I guess it looks promising

I made a repo to host my experiments, you can see the updated example there