Alexander 4.0.0

Alexander 4.0.0

LangLanguage SwiftSwift
License MIT
ReleasedLast Release Jan 2017
SwiftSwift Version 3.0
SPMSupports SPM

Maintained by Caleb Davenport, Jonathan Baker.

Alexander 4.0.0

  • By
  • Caleb Davenport and Jonathan Baker


Alexander is an extremely simple JSON helper written in Swift. It brings type safety and Foundation helpers to the cumbersome task of JSON unpacking.


Xcode Swift iOS tvOS OS X
8.0 3.0 8.0 9.0 10.9



Make a new DecoderType that can unpack your object.

struct User {
    var ID: String
    var name: String
    var email: String

struct UserDecoder: DecoderType {
    typealias Value = User
    static func decode(JSON: Alexander.JSON) -> Value? {
            let ID = JSON["id"]?.stringValue,
            let name = JSON["name"]?.stringValue,
            let email = JSON["email"]?.stringValue
        else {
            return nil
        return User(ID: ID, name: name, email: email)

Now you can do let author = JSON["user"]?.decode(UserDecoder) to get a single user, or let users = JSON["users"]?.decodeArray(UserDecoder) to get an array of users.

You can make DecodableTypes for all kinds of things.

struct SizeDecoder {
    typealias Value = CGSize
    static func decode(JSON: Alexander.JSON) -> Value? {
            let width = JSON["width"]?.doubleValue,
            let height = JSON["height"]?.doubleValue
        else {
            return nil
        return CGSize(width: width, height: height)

Alexander ships with a handful of decoders for common types:

  • DateTimeIntervalSince1970Decoder
  • DateTimeIntervalSinceReferenceDateDecoder
  • URLDecoder
  • RawRepresentableDecoder

Nested Objects

Most of Alexander’s power comes from its two subscript operators: subscript[key: String] -> JSON? and subscript[index: Int] -> JSON?. These operators allow you to unpack nested objects without having to refer to each intermediate step by hand. Something like let nextCursor = JSON["meta"]?["pagination"]?["next_cursor"]?.stringValue is a single line of code.

Enums & RawRepresentable

You can also decode anything that conforms to the RawRepresentable type. For example, assume the following enum:

enum Planet: String {
    case Mercury = "mercury"
    case Venus = "venus"
    case Earth = "earth"
    case Mars = "mars"
    case Jupiter = "jupiter"
    case Saturn = "saturn"
    case Uranus = "uranus"
    case Neptune = "neptune"
    // case Pluto = "pluto" =(

Because Planet is backed by a String raw value type, it is inheriently RawRepresentable. This means you can do let planet = JSON["planet"]?.decode(RawRepresentableDecoder<Planet>) or let planets = JSON["planets"]?.decodeArray(RawRepresentableDecoder<Planet>).