Naive KeyPath code for dictionaries and arrays

KeyPathAccessible.swift

public protocol KeyPathComponent { }

extension String: KeyPathComponent { }
extension Int: KeyPathComponent { }

public protocol KeyPathAccessible {
    func value<T>(at component: KeyPathComponent) -> T?
}

extension KeyPathAccessible {
    private func component(at component: KeyPathComponent) -> KeyPathAccessible? {
        return value(at: component)
    }
    public func value<T>(at start: KeyPathComponent, _ rest: KeyPathComponent...) -> T? {
        guard !rest.isEmpty else { return self.value(at: start) }

        return rest
            .dropLast()
            .reduce(component(at: start)) { acc, next in acc.flatMap { $0.component(at: next) } }?
            .value(at: rest.last!)
    }
}

extension Dictionary: KeyPathAccessible {
    public func value<T>(at component: KeyPathComponent) -> T? {
        return (component as? Key).flatMap { self[$0] as? T }
    }
}
extension Array: KeyPathAccessible {
    public func value<T>(at component: KeyPathComponent) -> T? {
        return (component as? Int).flatMap { self[$0] as? T }
    }
}

import Foundation
extension NSArray: KeyPathAccessible {
    public func value<T>(at component: KeyPathComponent) -> T? { return (self as Array).value(at: component) }
}
extension NSDictionary: KeyPathAccessible {
    public func value<T>(at component: KeyPathComponent) -> T? { return (self as Dictionary).value(at: component) }
}