Anyone got any tips on abstracting over an `is` check and smart cast in a `when` statement? Problem ...

# getting-started

[Rob Elliot]

Anyone got any tips on abstracting over an is check and smart cast in a when statement? Problem in thread...

[Rob Elliot]

It doesn't take a coding genius to spot the duplication here, but I'm struggling to work out how to pull out a parameterised method to get rid of it...

Untitled.kt

[Adam S]

it looks like you just need need to make the function generic, so Json Object/Array/String is passed in as T.

inline fun <reified T> fetch(key: String): Outcome<FailedLookupResult, T> =
  ifContains(key) {
    when (val candidate = get(key)) {
      is T -> candidate.success()
      null -> NullValue(key).failure()
      else -> UnexpectedType(key, candidate).failure()
    }
  }

(Using reified might not be necessary - I can’t remember off the top of my head)

[Rob Elliot]

Oh, so you can... thanks! That's embarrassing, should have been able to work that out on my tod.

[Adam S]

I just had to mess around with generics & reified so it’s fresh in my mind :)

[Matteo Mirk]

Maybe if the Json.* classes have some common ancestor (ie JsonNode) I would add an upper bound for better type safety T:JsonNode
@Adam S reified is needed only if you need to access T inside the function, so I'd say yes in this case it's mandatory