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June 29, 2017 09:13
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Finding out type of prepend.Out
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| case class Record[A](userId: UUID, createdAt: LocalDateTime, version: Long, data: A) | |
| type MetaData = UUID :: LocalDateTime :: Long :: HNil | |
| def length[R <: HList](record: Record[A]) | |
| (implicit gen: Generic.Aux[A, R], | |
| prepend: Prepend[R, MetaData]) = { | |
| val data = gen.to(record.data) | |
| val meta = record.userId :: record.createdAt :: record.version :: HNil | |
| val toWrite = data ::: meta | |
| // next line fails, missing Length[prepend.Out], but prepend.Out cannot be used in the implicit arg list. | |
| // What should be an alternate, but valid type signature of prepend.Out? | |
| val natLen = toWrite.length | |
| // Not gotten here, but probably yet another signature issue in waiting. | |
| Nat.toInt(natLen) | |
| } |
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