xyz.cofe.json4s3.derv

case class Append(value:String)
object Append:
given DefaultValue[Append] with
  override def defaultValue: Option[Append] = Some(Append("def_value"))

 case class DefVal( a:String )
object DefVal:
  given defval:DefaultValue[DefVal] = new DefaultValue[DefVal] {
    override def defaultValue: Option[DefVal] = Some(DefVal("sample"))
  }
case class ItemWithDef( a:Int, b:DefVal )

test("default") {
  assert("""{ "a": 1 }"""
    .jsonAs[ItemWithDef] == Right(ItemWithDef(1,DefVal("sample"))))
}

sealed trait BaseSample
case class ChildOne( a:Int ) extends BaseSample
case class ChildTwo( a:String ) extends BaseSample

import xyz.cofe.json4s3.derv.FromJsonBuilder._
implicit val baseSampleFromJson : FromJson[BaseSample] =
 FromJson.builder
   .select[ChildOne]( q => q("type").string === "1" )
   .select[ChildTwo]( q => q("type").string === "2" )
   .build