Subscription.swift

import Foundation

public struct Subscription<State: Any> {
    
    let subscriber: AnyStoreSubscriber
    let selector: (State -> Any)
    
    init(aSubscriber: AnyStoreSubscriber) {
        
        self.subscriber = aSubscriber
        self.selector = { (state: Any) in state }
    }
    
    init(subscriber: AnyStoreSubscriber, filteringState selector: (State -> Any)) {
        
        self.subscriber = subscriber
        self.selector = selector
    }
    
    init<S: StoreSubscriber where S.StoreSubscriberStateType == State>(subscriber: S) {
        
        self.subscriber = subscriber
        self.selector = { $0 }
    }
    
    init<S: StoreSubscriber where S.StoreSubscriberStateType == State>(subscriber: S, filteringState selector: (State -> Any)) {
        
        self.subscriber = subscriber
        self.selector = selector
    }

}

class Foo: AnyStoreSubscriber {
    func _newState(state: Any) {
    }
}

extension String: StateType {}
class StringSubscriber: StoreSubscriber {

    typealias StoreSubscriberStateType = String

    
    func newState(state: StoreSubscriberStateType) { }
}

func bar() {
    //Subscription(aSubscriber: Foo()) // doesnt compile, cannot infer State
    _ = Subscription(subscriber: StringSubscriber())
    _ = Subscription(subscriber: StringSubscriber()) { state in
        
        return state.lowercaseString
    }
}