Question: How to use this in context of an http4s app wish FS2 about mongo4cats

[Kirill5k]

Hello. There is no such thing as dumb questions!

F[_] in this case is just an abstract type, which potentially can be anything (as long as its implementation has characteristics of Async). So your impl method can look like this:

  def impl[F[_] : Async](M: MongoClient[F]): VersionRegistry[F] = new VersionRegistry[F] :
    def get(beta: String): F[Option[VersionRegistry.Versions]] =
      for 
        db <- M.getDatabase("sdkman")
        coll <- db.getCollectionWithCodec[T]("versions")
        version <- coll.find(Filter.eq("name", beta)).first
      yield version

Furthermore, you don't need to create new database instance on every request; rather than passing a MongoClient, you could pass a MongoCollection instead and this will let you achieve exactly what you need:

  def stream[F[_] : Async]: Stream[F, Unit] =
    for {
      client <- Stream.resource(MongoClient.fromConnectionString("mongodb://localhost:27017"))
      database <- Stream.eval(client.getDatabase("sdkman"))
      collection <- Stream.eval(database.getCollection("versions"))
      versionsAlg = VersionRegistry.impl[F](collection)
      ...
    } yield ()

[marc0der]

Hi @Kirill5k, thanks so much for getting back to me and pointing me in the right direction. I managed to get the whole thing working as you suggested (I've pushed my changes to the same repo in case you were curious). One thing I couldn't get working was initialisation of the codec using the mongodriver marcros, but I've just gone for doing a manual transformation from bson to case classes which works fine.

Thanks again!