Reactive proxy

Reactive.swift

//
//  Reactive.swift
//  RxSwift
//
//  Created by Yury Korolev on 5/2/16.
//  Copyright © 2016 Krunoslav Zaher. All rights reserved.
//

/**
 Use `Reactive` proxy as customization point for constrained protocol extensions.

 General pattern would be:

 // 1. Extend Reactive protocol with constrain on Base
 // Read as: Reactive Extension where Base is a SomeType
 extension Reactive where Base: SomeType {
 // 2. Put any specific reactive extension for SomeType here
 }

 With this approach we can have more specialized methods and properties using
 `Base` and not just specialized on common base type.

 */

public struct Reactive<Base> {
    /// Base object to extend.
    public let base: Base

    /// Creates extensions with base object.
    ///
    /// - parameter base: Base object.
    public init(_ base: Base) {
        self.base = base
    }
}

/// A type that has reactive extensions.
public protocol ReactiveCompatible {
    /// Extended type
    associatedtype CompatibleType

    /// Reactive extensions.
    static var rx: Reactive<CompatibleType>.Type { get set }

    /// Reactive extensions.
    var rx: Reactive<CompatibleType> { get set }
}

extension ReactiveCompatible {
    /// Reactive extensions.
    public static var rx: Reactive<Self>.Type {
        get {
            return Reactive<Self>.self
        }
        set {
            // this enables using Reactive to "mutate" base type
        }
    }

    /// Reactive extensions.
    public var rx: Reactive<Self> {
        get {
            return Reactive(self)
        }
        set {
            // this enables using Reactive to "mutate" base object
        }
    }
}

import class Foundation.NSObject

/// Extend NSObject with `rx` proxy.
extension NSObject: ReactiveCompatible { }

Sample.swift

extension ObservableType {
    public func retryPromptOn(_ vc: UIViewController) -> Observable<E> {
        return self.retryWhen { (error: Observable<Error>) -> Observable<Void> in
            return vc.rx.retryPrompt(error: error)
        }
    }
}

extension Reactive where Base: UIViewController {
    func retryPrompt(error: Observable<Error>) -> Observable<Void> {
        let retry =  PublishSubject<Void>()
        error.subscribe { (error: Event<Error>) in
            let alert = UIAlertController(title: error.element?.localizedDescription, message: "Retry?", preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "No", style: .cancel) { _ in
                retry.onError(error.element!)
            })
            alert.addAction(UIAlertAction(title: "Retry", style: .default) { _ in
                retry.onNext()
            })
            self.base.present(alert, animated: true)
        }
        return retry
    }
}