CODEWITHSUNDEEP
scalaimplicit-conversionhigher-kinded-typescompanion-object
jens
jens

Reputation: 453

Extend user defined higher kinded type

I have a user defined alias for a higher kinded type in scala:

type FutureOfLastError = Future[LastError]

I also have a value of that type:

val myFuture: FutureOfLastError = ...

To write readable Code I would like to define (for example) a method like

def mapToString = { ... }

which maps an instance of FutureOfLastError to a Future[String] and call it like

myFuture mapToString

How can I do this? Is it even possible? I already tried encapsulation in a case class, all kinds of implicit conversions that came to my mind.

My favourite choice would be a companion object on the type-alias, but I couldn't get it to work because I cannot call the methods of trait Future (like map, etc.) from the companion object.

Upvotes: 1

Views: 129

Answers (1)

Régis Jean-Gilles
Régis Jean-Gilles

Reputation: 32739

You don't need to actually extend the class, you can just use an implicit class (which is just syntactic sugar for the "enrich my library" pattern). Something as simple as this should do it:

implicit class MyFutureOps( future: FutureOfLastError ) {
  def mapToString = future.map(_.toString)
}

Upvotes: 1

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