Is there a way to wrap an iterator inside a custom iterator? I want to do some logic before returnin...

# android

[Ben Butterworth]

Is there a way to wrap an iterator inside a custom iterator? I want to do some logic before returning the values from an iterator, but encapsulate it. A naive approach I tried,

myMapObject.asSequence().map {
  yield Pair(it.key, processValue(it.value))
}

but the iterator method override fun next(): Pair<String, OutputType> {} doesn't return sequences, but the actual value. My understanding of yield is that it needs to be inside a coroutine, so yield isn't really what im looking for? (im taking cues from the python yield keyword, which is very different)

[Vampire]

Nowhere in your approach is any iterator involved.
And yield is not necessary here, it would allow you to produce values for an arbitrary sequence.
It is a suspending function, so it has to be called from a suspending function: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.sequences/-sequence-scope/yield.html
If you for example use the sequence function, the lambda you give it is a suspending function, so you can call yield in it: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.sequences/sequence.html

But as you just want to map the elements of an existing sequence, yield is not what you are after, just omit it and you have what you want.

[Ben Butterworth]

Sorry, i omitted the Iterator code, but this currently sits inside override fun next(): Pair<String, ObjectType> {}

it cant return a sequence, which is why it wont work. I want it to be an iterator so clients can call each item independently. Unless this is also possible with sequences?

[Vampire]

Sequences are the lazy Kotlin variant of iterators.
Much like `Stream`s in Java.
https://kotlinlang.org/docs/reference/sequences.html

[Ben Butterworth]

Yes i know, i think asking about sequences was a redherring in my question. thats not my problem/ solution. It was just my first attempt which i discarded

My main objective is to wrap an iterator with more logic, and the clients can use this iterator.

[Ben Butterworth]

Having said that, i might as well change the clients to use a sequence, because i dont know how to encapsulate an iterator with extra logic.

[Vampire]

There are many ways, at least one indeed involves sequences, like for example

myMapObject.asSequence().map { Pair(it.key, processValue(it.value)) }.iterator()

[Vampire]

But if your client is using Kotlin, maybe using sequences is actually the better idea.

[Ben Butterworth]

Ohh, thats a nice solution 😃, i was creating a nested Iterator subclass (boiler plate code)… and even that was not working. Thanks