struct Repository {
    let name: String
    let description: String
    let stargazersCount: Int
    let language: String?
    let sometimesMissingKey: String?
    
    let owner: User // Struct conforming to Decodable
    let defaultBranch: Branch // Struct NOT conforming to Decodable
    
    var fullName: String { return "\(owner.login)/\(name)" }
}

extension Repository: Decodable {
    static func decode(j: Any) throws -> Repository {
        return try Repository(
                    name: j => "nested" => "name", 
                    description: j => "description", 
                    stargazersCount: j => "stargazers_count", 
                    language: j => "language", 
                    sometimesMissingKey: j =>? "sometimesMissingKey",
                    owner: j => "owner", 
                    defaultBranch: Branch(name: j => "default_branch")
                )
    }
}

do {
    let json = try NSJSONSerialization.JSONObjectWithData(data, options: [])
    let repo = try [Repository].decode(json)
} catch {
    print(error)
}

public protocol Decodable {
    static func decode(json: Any) throws -> Self
}

public func parse<T>(json: Any, path: [String], decode: (Any throws -> T)) throws -> T

public func => <T: Decodable>(json: Any, keyPath: KeyPath) throws -> T

let a: KeyPath = "a"
let b: KeyPath = ["a", "b"]
let c: KeyPath = "a" => "b" => "c"
let string: String? = json =>? "key1" => "key2" => "key3"`
                                ^^^^ allowed to be missing

public enum DecodingError: ErrorProtocol, Equatable {
    /// Thrown when optional casting from `Any` fails.
    ///
    /// This can happen both when trying to access a key on a object
    /// that isn't a `NSDictionary`, and failing to cast a `Castable`
    /// primitive.
    case typeMismatch(expected: Any.Type, actual: Any.Type, Metadata)
    
    /// Thrown when a given, required, key was not found in a dictionary.
    case missingKey(String, Metadata)
    
    /// Thrown from the `RawRepresentable` extension when
    /// `init(rawValue:)` returned `nil`.
    case rawRepresentableInitializationError(rawValue: Any, Metadata)
    
    /// When an error is thrown that isn't `DecodingError`, it 
    /// will be wrapped in `DecodingError.other` in order to also provide
    /// metadata about where the error was thrown.
    case other(ErrorProtocol, Metadata)
}

let dict: NSDictionary = ["object": ["repo": ["owner": ["id" : 1, "login": "anviking"]]]]

do {
    let username: String = try dict => "object" => "repo" => "owner" => "name"
} catch let error {
    print(error)
}
//
// MissingKeyError at object.repo.owner: name in {
//    id = 1;
//    login = anviking;
// }

public protocol DynamicDecodable {
    associatedtype DecodedType
    static var decoder: (Any) throws -> DecodedType {get set}
}

// Lets extend Bool.decoder so that it accepts certain strings:
Bool.decoder = { json in
    switch json {
    case let str as String where str == "true":
        return true
    case let str as String where str == "false":
        return false
    default:
        return try cast(json)
    }
}

Date.decoder = Date.decoder(using: formatter)