KeyValueObservable.swift

final class ObservationStore<T> {
    fileprivate var observationInfos = [Observation: (PartialKeyPath<T>) -> Bool]()
    
    var observations: [Observation] {
        return observationInfos.map({ $0.key })
    }
    
    func removeAll() {
        observationInfos.removeAll()
    }
}

struct Observation: Hashable {
    fileprivate let identifier = UUID()
    
    struct Options: OptionSet {
        let rawValue: Int
        static let initial = Options(rawValue: 1 << 0)
    }
}