builder.scala

// httpApp and dispatcher are required
// asyncTimeout and chunkSize have defaults

// Builder[F[_]] with constructor args
AsyncHttp4sServlet
  .builder[IO](httpApp, dispatcher)
  .withAsyncTimeout(5.seconds)
  .withChunkSize(4096)
  .build
  
// Builder[F[_], State]
// No special syntax for required params
// State is a "phantom type"
// Implicit =:= on build to check required args were set
AsyncHttp4sServlet
  .builder[IO]
  .withHttpApp(httpApp)
  .withDispatcher(dispatcher)
  .withAsyncTimeout(5.seconds)
  .withChunkSize(4096)
  .build