Debugging Compile Errors

When writing elegant RxSwift/RxCocoa code, you are probably relying heavily on compiler to deduce types of Observables. This is one of the reasons why Swift is awesome, but it can also be frustrating sometimes.

images = word
    .filter { $0.containsString("important") }
    .flatMap { word in
        return self.api.loadFlickrFeed("karate")
            .catchError { error in
                return just(JSON(1))
            }
      }

If compiler reports that there is an error somewhere in this expression, I would suggest first annotating return types.

images = word
    .filter { s -> Bool in s.containsString("important") }
    .flatMap { word -> Observable<JSON> in
        return self.api.loadFlickrFeed("karate")
            .catchError { error -> Observable<JSON> in
                return just(JSON(1))
            }
      }

If that doesn't work, you can continue adding more type annotations until you've localized the error.

images = word
    .filter { (s: String) -> Bool in s.containsString("important") }
    .flatMap { (word: String) -> Observable<JSON> in
        return self.api.loadFlickrFeed("karate")
            .catchError { (error: Error) -> Observable<JSON> in
                return just(JSON(1))
            }
      }

I would suggest first annotating return types and arguments of closures.

Usually after you have fixed the error, you can remove the type annotations to clean up your code again.