Reflector.swift

protocol Mirrorible {
    var mirror: Mirror { get }
}

extension Mirrorible {
    subscript (descendant key: String) -> Any {
        return self.mirror.descendant(key) as Any
    }
}

final class Reflector<T> where T: Mirrorible {
    private var propertyNameCache: [PartialKeyPath<T>: String]
    private var keyPathCache: [String: PartialKeyPath<T>]
    private var mirror: Mirror

    var value: T

    var keyPaths: [String: PartialKeyPath<T>] {
        return self.keyPathCache
    }

    var propertyNames: [PartialKeyPath<T>: String] {
        return self.propertyNameCache
    }

    init(_ value: T) {
        self.value = value
        self.mirror = Mirror(reflecting: value)
        self.propertyNameCache = [:]
        self.keyPathCache = [:]

        self.loadCache()
    }

    private func loadCache() {
        self.mirror.children.forEach { child in
            if let name = child.label {
                let keyPath = \T.[descendant: name] as PartialKeyPath
                self.propertyNameCache[keyPath] = name
                self.keyPathCache[name] = keyPath
            }
        }
    }
}