Typed-NSNotificationCenter.swift

class NotificationToken {

    let token: NSObjectProtocol
    let center: NSNotificationCenter

    init(token: NSObjectProtocol, center: NSNotificationCenter) {
        self.token = token
        self.center = center
    }

    deinit {
        center.removeObserver(token)
    }

}

protocol CustomNotification: RawRepresentable {
    func notify(center: NSNotificationCenter)
    func notify<A>(center: NSNotificationCenter, with object: A)
    func addObserver<A>(center: NSNotificationCenter, using block: (A) -> Void) -> NotificationToken
}

final class NotificationBox<T> {
    let value: T
    init(_ value: T) {
        self.value = value
    }
}

extension CustomNotification where Self.RawValue == String {

    func notify(center: NSNotificationCenter = .defaultCenter()) {
        let notification = NSNotification(name: self.rawValue, object: nil)
        dispatch_async(dispatch_get_main_queue()) {
            center.postNotification(notification)
        }
    }

    func notify<A>(center: NSNotificationCenter = .defaultCenter(), with object: A) {
        let notification = NSNotification(name: self.rawValue, object: NotificationBox(object))
        dispatch_async(dispatch_get_main_queue()) {
            center.postNotification(notification)
        }
    }

    func addObserver<A>(center: NSNotificationCenter = .defaultCenter(), using block: (A) -> Void) -> NotificationToken {
        let token = center.addObserverForName(self.rawValue, object: nil, queue: nil, usingBlock: { notification in
            if let boxedObject = notification.object as? NotificationBox<A> {
                block(boxedObject.value)
            }
        })
        return NotificationToken(token: token, center: center)
    }

}

enum AccountNotification: String, CustomNotification {

    case Cards
    case TaxEstimate
    
}

Usage:

// Refresh automatically
cardNotificationToken = AccountNotification.Cards.addObserver { [weak self] (cards: [Card]) in
    // Assuming the default card is the first one
    self?.configure(with: cards.first)
}
AccountNotification.Cards.requestUpdate()