DefaultValue

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"))))
}