tkachuko tkachuko - 1 month ago 12
Scala Question

Case class without parameters alternative

During some simple scala coding exercise I ran into ideological problem of case classes without parameters and constructor parameters duplication.

It all started with the following two quite simple classes:

trait Namespace

case class Reply[T](namespace: Namespace, correlation: String, data: Try[T])

abstract class Request(val namespace: Namespace, val id: String = UUID.randomUUID().toString) {

def success[T](data: T) = Reply(namespace, id, Try(data))

def failure(msg: String) = Reply(namespace, id, Failure(new RuntimeException(msg)))
}


Now let's assume i have an entity
Post
and I want to add
All
class as a command to query all records of type
Post
. In my current set up it would be easier to actually write the following:

case class All extends Request(Posts)


However in this case I get compiler warning that case classes without parameters are deprecated. So one might suggest to rewrite it into the following:

case object All extends Request(Posts)


However in this case object All will be instantiated only once along with its
id
field which would like to avoid having unique id for each request.

Could you please suggest a better way of representing
All
command so that it would not be required to duplicate constructor arguments?

Thanks in advance?

Answer

The actual warning is that

case classes without a parameter list are not allowed; use either case objects or case classes with an explicit `()' as a parameter list.

So give this class an empty parameter list, just as suggested by the compiler:

case class All() extends Requests(Posts)
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