[DEPRECATED] The easy to use Swift JSON encoder

What's New

Wrap 3.0.1


Wrap now uses the Swift 4 version of the Swift Package Description API.

View build details and download artifacts on buddybuild:
Wrap (iOS, Wrap-iOS)


Unbox | Wrap

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Wrap is an easy to use Swift JSON encoder. Don't spend hours writing JSON encoding code - just wrap it instead!

Using Wrap is as easy as calling wrap() on any instance of a class or struct that you wish to encode. It automatically encodes all of your type’s properties, including nested objects, collections, enums and more!

It also provides a suite of simple but powerful customization APIs that enables you to use it on any model setup with ease.

Basic example

Say you have your usual-suspect User model:

struct User {
    let name: String
    let age: Int

let user = User(name: "John", age: 28)

Using wrap() you can now encode a User instance with one command:

let dictionary: [String : Any] = try wrap(user)

Which will produce the following Dictionary:

    "name": "John",
    "age": 28

Advanced example

The first was a pretty simple example, but Wrap can encode even the most complicated structures for you, with both optional, non-optional and custom type values, all without any extra code on your part. Let’s say we have the following model setup:

struct SpaceShip {
    let type: SpaceShipType
    let weight: Double
    let engine: Engine
    let passengers: [Astronaut]
    let launchLiveStreamURL: URL?
    let lastPilot: Astronaut?

enum SpaceShipType: Int, WrappableEnum {
    case apollo
    case sputnik

struct Engine {
    let manufacturer: String
    let fuelConsumption: Float

struct Astronaut {
    let name: String

Let’s create an instance of SpaceShip:

let ship = SpaceShip(
    type: .apollo,
    weight: 3999.72,
    engine: Engine(
        manufacturer: "The Space Company",
        fuelConsumption: 17.2321
    passengers: [
        Astronaut(name: "Mike"),
        Astronaut(name: "Amanda")
    launchLiveStreamURL: URL(string: "http://livestream.com"),
    lastPilot: nil

And now let’s encode it with one call to wrap():

let dictionary: WrappedDictionary = try wrap(ship)

Which will produce the following dictionary:

    "type": 0,
    "weight": 3999.72,
    "engine": {
        "manufacturer": "The Space Company",
        "fuelConsumption": 17.2321
    "passengers": [
        {"name": "Mike"},
        {"name": "Amanda"}
    "launchLiveStreamURL": "http://livestream.com"

As you can see, Wrap automatically encoded the URL property to its absoluteString, and ignored any properties that were nil (reducing the size of the produced JSON).


While automation is awesome, customization is just as important. Thankfully, Wrap provides several override points that enables you to easily tweak its default behavior.

Customizing keys

Per default Wrap uses the property names of a type as its encoding keys, but sometimes this is not what you’re looking for. You can choose to override any or all of a type’s encoding keys by making it conform to WrapCustomizable and implementing keyForWrapping(propertyNamed:), like this:

struct Book: WrapCustomizable {
    let title: String
    let authorName: String

    func keyForWrapping(propertyNamed propertyName: String) -> String? {
        if propertyName == "authorName" {
            return "author_name"

        return propertyName

You can also use the keyForWrapping(propertyNamed:) API to skip a property entirely, by returning nil from this method for it.

Custom key types

You might have nested dictionaries that are not keyed on Strings, and for those Wrap provides the WrappableKey protocol. This enables you to easily convert any type into a string that can be used as a JSON key.

Encoding keys as snake_case

If you want the dictionary that Wrap produces to have snake_cased keys rather than the default (which is matching the names of the properties that were encoded), you can easily do so by conforming to WrapCustomizable and returning .convertToSnakeCase from the wrapKeyStyle property. Doing that will, for example, convert the property name myProperty into the key my_property.

Customized wrapping

For some nested types, you might want to handle the wrapping yourself. This may be especially true for any custom collections, or types that have a completely different representation when encoded. To do that, make a type conform to WrapCustomizable and implement wrap(context:dateFormatter:), like this:

struct Library: WrapCustomizable {
    private let booksByID: [String : Book]

    func wrap(context: Any?, dateFormatter: DateFormatter?) -> Any? {
        return Wrapper(context: context, dateFormatter: dateFormatter).wrap(self.booksByID)

Enum support

Wrap also makes it super easy to encode any enum values that your types are using. If an enum is based on a raw type (such as String or Int), all you have to do is to declare conformance to WrappableEnum, and the rest is taken care of for you.

Non-raw type enum values are also automatically encoded. The default behavior encodes any values that don’t have associated values as their string representation, and those that do have associated values as a dictionary (with the string representation as the key), like this:

enum Profession {
    case developer(favoriteLanguageName: String)
    case lawyer

struct Person {
    let profession = Profession.developer(favoriteLanguageName: "Swift")
    let hobbyProfession = Profession.lawyer

Encodes into:

    "profession": {
        "developer": "Swift"
    "hobbyProfession": "lawyer"

Contextual objects

To be able to easily encode any dependencies that you might want to use during the encoding process, Wrap provides the ability to supply a contextual object when initiating the wrapping process (by calling wrap(object, context: myContext).

A context can be of Any type and is accessible in all WrapCustomizable wrapping methods. Here is an example, where we send in a prefix to add to a Book’s title:

struct Book: WrapCustomizable {
    let title: String

    func wrap(context: Any?, dateFormatter: DateFormatter?) -> Any? {
        guard let prefix = context as? String else {
            return nil

        return [
            "title" : prefix + self.title

String serialization

let data = try wrap(object) as Data
let string = String(data: data, encoding: .utf8)


Wrap supports the following platforms:

  • 📱 iOS 8+
  • 🖥 macOS 10.9+
  • ⌚️ watchOS 2+
  • 📺 tvOS 9+
  • 🐧 Linux


Wrap can be easily used in either a Swift script, command line tool or in an app for iOS, macOS, watchOS, tvOS or Linux.

In an application


  • Drag the file Wrap.swift into your application's Xcode project.


In a script

  • Install Marathon.
  • Add Wrap using $ marathon add https://github.com/JohnSundell/Wrap.git.
  • Run your script using $ marathon run <path-to-your-script>.

In a command line tool

  • Drag the file Wrap.swift into your command line tool's Xcode project.

Hope you enjoy wrapping your objects!

For more updates on Wrap, and my other open source projects, follow me on Twitter: @johnsundell

Also make sure to check out Unbox that let’s you easily decode JSON.


  • Swift Tools 4.0.0
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Last updated: Sun Jan 07 2024 18:18:30 GMT-1000 (Hawaii-Aleutian Standard Time)