[GitHub] [incubator-pekko-connectors] mdedetrich commented on pull request #160: Add Scala3 support for Geode

["mdedetrich (via GitHub)" <gi...@apache.org>]

mdedetrich commented on PR #160:
URL: https://github.com/apache/incubator-pekko-connectors/pull/160#issuecomment-1685880588

   So I managed to make some decent progress, I figured out the biggest issue I was having before is not having a type level data structure to represent the field's/types of a case class. With shapeless there is a `FieldType` however there didn't seem to be an equivalent for Scala 3's inbuild generics.
   
   Thankfully I came across https://scalac.io/blog/inline-your-boilerplate-harnessing-scala3-metaprogramming-without-macros/ which provided the exact data structure needed, i.e.
   
   ```scala
   import scala.compiletime.*
   import scala.deriving.*
   sealed trait Field[Label <: String, Type]
   
   object Field {
     type FromLabelsAndTypes[Labels <: Tuple, Types <: Tuple] <: Tuple =
       (Labels, Types) match {
         case (EmptyTuple, EmptyTuple) => EmptyTuple
         case (labelHead *: labelTail, typeHead *: typeTail) =>
           Field[labelHead, typeHead] *: FromLabelsAndTypes[labelTail, typeTail]
       }
   }
   ```
   
   You can then create this type level data structure using a mirror, i.e.
   
   ```scala
   case class Test(string: String, int: Int)
   
   val mirror = summon[Mirror.ProductOf[Test]]
   
   type Fields = FromLabelsAndTypes[mirror.MirroredElemLabels, mirror.MirroredElemTypes]
   // defined alias type Fields = (Field["string", String], Field["int", Int])
   ```
   
   Which is actually whats needed, i.e a type with each element being a `Field` that contains the case class fieldname on the left and the case class type on the right.
   
   The PR isn't completely done but this a big step. Pinging @jrudolph because you showed interest before.


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