Observable.swift

public class Observable<Element>: ObservableType {
    public typealias E = Element
    private let _subscribeHandler: (Observer<Element>) -> Disposable
    
    public init(_ subscribtionClosure: @escaping (Observer<Element>) -> Disposable) {
        _subscribeHandler = subscribtionClosure
    }
    
    public func subscribe<O : ObserverType>(observer: O) -> Disposable where O.E == E {
        let sink = Sink(forvard: observer, subscribtionHandler: _subscribeHandler)
        sink.run()
        return sink
    }
}