Observe ReSwift subscriptions using RxSwift

RxReSwift.swift

import Foundation
import ReSwift
import RxSwift

private class StoreObserver<SelectedState>: StoreSubscriber {
    private let onNext: (SelectedState) -> Void
    init(onNext: @escaping (SelectedState) -> Void) {
        self.onNext = onNext
    }
    func newState(state: SelectedState) {
        onNext(state)
    }
}

extension Store {
    
    /**
     Observe a ReSwift subscription.
  
     ```
     store.observe { 
       $0.select { $0.shoeSize }.skipRepeats() 
     }.subscribe(onNext: { shoeSize in 
       print(shoeSize)
     })
     ```
     */
    func observe<SelectedState>(_ transform: @escaping (Subscription<State>) -> Subscription<SelectedState>) -> Observable<SelectedState> {
        return Observable.create { [weak self] observer in
            let storeObserver = StoreObserver(onNext: observer.onNext)
            self?.subscribe(storeObserver, transform: transform)
            return Disposables.create { [weak self] in
                self?.unsubscribe(storeObserver)
            }
        }
    }
    
    /**
     Observe a `KeyPath` in the store's state.
  
     ```
     store.observe(\.shoeSize).subscribe(onNext: { shoeSize in print(shoeSize) })
     ```
     */
    func observe<SelectedState>(_ keyPath: KeyPath<State, SelectedState>) -> Observable<SelectedState> {
        return observe{ $0.select{ $0[keyPath: keyPath] } }
    }

    /**
     Observe a `KeyPath` in the store's state.
  
     ```
     store.observe(\.shoeSize).subscribe(onNext: { shoeSize in print(shoeSize) })
     ```
     */  
    func observe<SelectedState: Equatable>(_ keyPath: KeyPath<State, SelectedState>) -> Observable<SelectedState> {
        return observe{ $0.select{ $0[keyPath: keyPath] }.skipRepeats() }
    }
    
}