Example of rx extension

CurryRxSwift.swift

extension Observable {
    
    // MARK: For completionBlock(Element, Error) template methods
    
    public static func fromAsync(_ asyncRequest: @escaping (@escaping (Element?, Error?) -> Void) -> Void) -> Observable<Element> {
        return Observable.create { (o) -> Disposable in
            asyncRequest { res, error in
                if let err = error {
                    o.onError(err)
                    return
                }
                guard let element = res else {
                    o.onCompleted()
                    return
                }
                o.onNext(element)
                o.onCompleted()
            }
            return Disposables.create {}
        }
    }
    
    public static func fromAsync<T>(_ asyncRequest: @escaping (T, @escaping (Element?, Error?) -> Void) -> Void) -> (T) -> Observable<Element> {
        return { param1 in Observable.fromAsync(curry(function: asyncRequest)(param1)) }
    }
    
    public static func fromAsync<T, U>(_ asyncRequest: @escaping (T, U, @escaping(Element?, Error?) -> Void) -> Void) -> (T) -> (U) -> Observable<Element> {
        return { (param1: T) in
            return { (param2: U) in
                Observable.fromAsync(curry(function: asyncRequest)(param1)(param2))
            }
        }
    }
 }