How to ignore `nil` values using RxSwift without using❗️

ignoreNil.swift

// Create an `Observable` of Optional<Int>
let values: Observable<Int?> = [1, 2, .None, 3, .None, 4, 5].toObservable()


// Method 1: using a free function
// Requires passing the function to `flatMap`

func ignoreNil<A>(x: A?) -> Observable<A> {
  return x.map { Observable.just($0) } ?? Observable.empty()
}

values
  .flatMap(ignoreNil)
  .subscribeNext { print($0) }

/*
1
2
3
4
5
*/


// Method 2: extending Observable
// More convenient to use, but more painful to implement!

public protocol OptionalType {
  associatedtype Wrapped

  var optional: Wrapped? { get }
}

extension Optional: OptionalType {
  public var optional: Wrapped? { return self }
}

// Unfortunately the extra type annotations are required, otherwise the compiler gives an incomprehensible error.
extension Observable where Element: OptionalType {
  func ignoreNil() -> Observable<Element.Wrapped> {
    return flatMap { value in
      value.optional.map { Observable<Element.Wrapped>.just($0) } ?? Observable<Element.Wrapped>.empty()
    }
  }
}

values
  .ignoreNil()
  .subscribeNext { print($0) }

/*
1
2
3
4
5
*/

flatMap { Observable.from( optional: $0.optional ) }

fwiw, I like:

flatMap(Observable.from(optional:))