Kotlin lambda syntax confusion

Question

I'm confused by Kotlin lambda syntax.

At first, I have

.subscribe(
          { println(it) }
          , { println(it.message) }
          , { println("completed") }
      )

which works fine.

Then I moved the onNext to another class called GroupRecyclerViewAdapter which implements Action1<ArrayList<Group>>.

.subscribe(
          view.adapter as GroupRecyclerViewAdapter
          , { println(it.message) }
          , { println("completed") }
      )

However, I got the error:

Error:(42, 17) Type mismatch: inferred type is () -> ??? but rx.functions.Action1<kotlin.Throwable!>! was expected
Error:(42, 27) Unresolved reference: it
Error:(43, 17) Type mismatch: inferred type is () -> kotlin.Unit but rx.functions.Action0! was expected

I can fix the error by changing to:

.subscribe(
          view.adapter as GroupRecyclerViewAdapter
          , Action1<kotlin.Throwable> { println(it.message) }
          , Action0 { println("completed") }
      )

Is there a way to write the lambda without specifying a type? (Action1<kotlin.Throwable>, Action0)

Note: subscribe is RxJava method

Edit 1

class GroupRecyclerViewAdapter(private val groups: MutableList<Group>,
                           private val listener: OnListFragmentInteractionListener?) :
RecyclerView.Adapter<GroupRecyclerViewAdapter.ViewHolder>(), Action1<ArrayList<Group>> {

its nice if you can include the error message as text, will help others find this post. You can compile, to get the same error you saw in the editor. Then cut-n-paste — Jayson Minard
– Jayson Minard, Commented Jan 24, 2016 at 22:23

Jayson Minard · Accepted Answer · 2016-01-25 10:32:34Z

12

view.adapter as GroupRecyclerViewAdapter part should be lambda func, not Action, since onError and onComplete also lambdas

so, to fix this try:

.subscribe(
          { (view.adapter as GroupRecyclerViewAdapter).call(it) }
          , { println(it.message) }
          , { println("completed") }
      )

with your names (replace Unit with your type)

class GroupRecyclerViewAdapter : Action1<Unit> {
    override fun call(t: Unit?) {
        print ("onNext")
    }
}

with lambdas

val ga = GroupRecyclerViewAdapter()
...subscribe(
    { result -> ga.call(result) },
    { error -> print ("error $error") },
    { print ("completed") })

with actions

...subscribe(
    ga,
    Action1{ error -> print ("error $error") },
    Action0{ print ("completed") })

pick one

edited Jan 25, 2016 at 10:32

Jayson Minard

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answered Jan 24, 2016 at 2:06

vigilancer

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22 Comments

pt2121 Over a year ago

Nope, doesn't work. if it's the case, why my last snippet works then?

vigilancer Over a year ago

because in last example they all Actions. give me a sec i'll try

vigilancer Over a year ago

please provide view.adapter signature at least. is it really Action1? if it is in my example it should be (view.adapter as GroupRecyclerViewAdapter).call(it), sorry

pt2121 Over a year ago

Sure. added it. it's Action1

voddan Over a year ago

Hey guys, did it work or didn't? And where the rule of not using SAM with lambdas has come from? Never heard of that.

|

Kirill Rakhman · Accepted Answer · 2016-01-25 14:19:58Z

2

You have two versions of the subscribe method to choose from:

The first (the real one) has the signature subscribe(Action1<ArrayList<Group>>, Action1<Throwable>, Action0).
The second version is generated by the Kotlin compiler and has the signature subscribe((ArrayList<Group>>) -> Unit, (Throwable) -> Unit, () -> Unit)

In your code, however, you pass the following parameter types:

subscribe(
    view.adapter as GroupRecyclerViewAdapter, // Action1<Throwable>
    { println(it.message) },  // (Throwable) -> Unit
    { println("completed") } // () -> Unit
)

As you can see, these parameter types satisfy none of the available signatures. The other answer gives you some solutions to your problem. In addition, you can make GroupRecyclerViewAdapter implement the functional type Function1<ArrayList<Group>, Unit> (they're interfaces, too) instead of Action1<ArrayList<Group>>.

edited Jan 25, 2016 at 14:19

answered Jan 25, 2016 at 12:34

Kirill Rakhman

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1 Comment

Marcin Koziński Over a year ago

Would be nice to mix and match though!

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