CODEWITHSUNDEEP
scalaplayframework-2.0read-eval-print-loopfoldloops
Soumya Simanta
Soumya Simanta

Reputation: 11741

Creating a simple Iteratee gives type error ?

I'm trying to create a simple Iteratee using Play2 on the REPL based on this. But I get a missing parameters error. But if I provide a type parameter for ele it works. Can someone explain this ? 

scala> import play.api.libs.iteratee._
import play.api.libs.iteratee._

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> val i = Iteratee.fold(0){ ( acc, ele ) => acc + ele }
<console>:15: error: missing parameter type
       val i = Iteratee.fold(0){ ( acc, ele ) => acc + ele }
                                         ^
scala> val i = Iteratee.fold(0){ ( acc, ele:Int ) => acc + ele }
i: play.api.libs.iteratee.Iteratee[Int,Int] = play.api.libs.iteratee.ContIteratee@3feaaa9b

Upvotes: 1

Views: 56

Answers (1)

Travis Brown
Travis Brown

Reputation: 139038

Scala's type inference isn't smart enough to say "oh, you wrote acc + ele and I know that acc is an integer, so ele must also be an integer".

In context you often won't need the extra type annotation. For example, this compiles just fine:

Enumerator(1, 2, 3).run(Iteratee.fold(0) { (acc, ele) => acc + ele })

Or this:

val i: Iteratee[Int, Int] = Iteratee.fold(0) { (acc, ele) => acc + ele }

But without some extra context you're just going to have to provide that : Int.

Upvotes: 2

Related Questions