optional-operator.swift

import Foundation
import RxSwift

// HACK: Since the built-in Optional<T> is a generic type, not a protocol we cannot apply
//   constraints on it. This protocol allows us to constraint our Rx operators onto
//   optional types
protocol OptionalType {
    associatedtype WrappedType
}

extension Optional: OptionalType {
    typealias WrappedType = Wrapped
}

extension ObservableType where E: OptionalType {
    func filterNonNil() -> Observable<E.WrappedType> {
        return self.filter({ $0 != nil })
            .map({ $0 as! E.WrappedType })
    }
}

let disposables = DisposeBag()

func test() {
    Observable<String?>.of("hello", nil, "world", nil, "end")
        .filterNonNil()
        .subscribeNext({ print($0) })
        .addDisposableTo(disposables)
}