RxSwift: Convert Observable to a Variable - rx-swift

Question

How do I convert an Observable of type Int to a Variable of type Int?
Here is what I have tried so far:
let obs: Observable<Int> = Observable.of(4)
let variable: Variable<Int> = obs
.flatMap { num in
return Variable<Int>(num)
}
Using flatMap feels like the most logical way of doing the conversion, however, I get a compiler error which essentially says that it does not like the flatMap returning anything that is not an observable. Any ideas?
EDIT:
Just to give some context as to why I need to convert the Observable into a Variable:
I need my viewModel to drive a UIPickerView inside a ViewController. Currently, I have two exposed properties in my ViewModel, items: Observable<[String]> (which is the datasource for the UIPickerView) and selectedIndex: Variable. The selectedIndex will drive the initial value of the UIPickerView but also keep track of any changes the user makes.
The reason I needed to convert from the Observable to Variable was that I needed to figure out which index of the UIPickerView should be selected initially:
items.map { days -> Int in
if let index = days.index(where: { str in
return str == selectedDay
}) {
return index
}
return 0
}
.flatMap { num in
return Variable<Int>(num)
}
I'm now wondering if I'm over complicating things, and if instead of the Variable in I should just have an Observable.

Answer 1

A few points here:
First, You should not use Variable as it's deprecated (gonna be entirely deprecated in Swift 5 probably). Look at BehaviorSubject and BehaviorRelay instead.
About your question, I'm not sure what is the use case for having a Variable equal to an Observable, so there are two different thoughts I have:
You can bind an Observable to a Variable/Subject/Relay (e.g. observable.bind(to: variable))
You can actually go the other way around an get an Observable from the Variable, which might make more sense. e.g. variable.asObservable()