Generically create an RxSwift Single observable from any Alamofire's Result type based asynchronous callback function.

Single+Result.swift

import RxSwift
import Alamofire

extension Single {
    static func make<T>(from resultFn: @escaping (@escaping (Result<T>) -> Void) -> Void) -> Single<T> {
        return Single<T>.create { sub in
            resultFn { result in
                switch result {
                case .success(let value):
                    sub(SingleEvent.success(value))
                case .failure(let error):
                    sub(SingleEvent.error(error))
                }
            }
            return Disposables.create()
        }
    }
}