Add TypedEncoder for shapeless Record.

[tribbloid]

Add TypedEncoder for shapeless Record.

[pomadchin]

Hey there; indeed in RecordEncoder those are not required. However these implicits are necessary for the TypedEncoder.usingDerivation function.

I don't think that these are bad here, at least work as a sanity check for us. But any improvement PRs are very much welcome.

Didn't quite follow a part about the shapeless.Record and two stages; usually the idea is to hide shapeless inside and not let it leak into the user API. But shoot a PR I'd be happy to help you to get it merged 👍

[tribbloid]

it is only an experiment, will need some serious clean up (particularly the scalafmt part) and API revision before it becomes a feature.

Ideally, I would like to see schema-changing transformation like withColumnReplaced and withColumn yielding a:

TypedDataFrame = TypedDataSet[TypedRow[H]], which preserve both generics & labels of the source case class.

Instead of the old:

TypedDataSet[TupleX], which degrade all columns name into _1, _2, etc.

[tribbloid]

@pomadchin voila, adding an experimental PR that adopts 2-stage RecordEncoder derivation.

The 1st stage is now also used for TypedRow[T <: HList], which can be seen as a successor of the abandoned TypedDataFrame. See the new test for an example usage:

0baf604#diff-dd83f3b1d1a249804b5620473177ce6034efbc5f36b45a9b1ef01283cafd50f9R93