Memory efficient version of SwiftyJSON

3 years after


This repo is a cheeky rewrite of lingoer's excellent SwiftyJSON repo for processing JSON data in Swift altered to use the objects returned by the JSON parser rather than converting all data into Swift representation using an enum. It requires less memory and should be a little faster for large messages. It's backward compatible but contains the additional feature of the JSON being writable so you can use it to construct messages (intermediate nodes are "auto-vivified"):

var JSON = JSONValue(NSMutableDictionary())
JSON["milestone"]["creator"]["login"] = JSONValue( "lingoer")
var msg = JSON.rawJSONString
XCTAssertEqual(msg,"{\"milestone\":{\"creator\":{\"login\":\"lingoer\"}}}", "wrong build")

For more details see the unit tests. The original README follows:


SwiftyJSON makes it easy to deal with JSON data in Swift.

Why is the typical JSON handling in Swift NOT good?

Swift is very strict about types, it's good while explicit typing left us little chance to make mistakes. But while dealing with things that naturally implicit about types such as JSON, it's painful.

Take the Twitter API for example: say we want to retrieve a user's "name" value of some tweet in Swift (according to Twitter's API https://dev.twitter.com/docs/api/1.1/get/statuses/home_timeline)

    "text": "just another test",
    "user": {
      "name": "OAuth Dancer",
      "favourites_count": 7,
      "entities": {
        "url": {
          "urls": [
              "expanded_url": null,
              "url": "http://bit.ly/oauth-dancer",
              "indices": [
              "display_url": null
    "in_reply_to_screen_name": null,

The code would look like this:

let jsonObject : AnyObject! = NSJSONSerialization.JSONObjectWithData(dataFromTwitter, options: NSJSONReadingOptions.MutableContainers, error: nil)
if let statusesArray = jsonObject as? NSArray{
    if let aStatus = statusesArray[0] as? NSDictionary{
        if let user = aStatus["user"] as? NSDictionary{
            if let userName = user["name"] as? NSDictionary{
                //Finally We Got The Name


It's not good.

Even if we use optional chaining, it would also cause a mess:

let jsonObject : AnyObject! = NSJSONSerialization.JSONObjectWithData(dataFromTwitter, options: NSJSONReadingOptions.MutableContainers, error: nil)
if let userName = (((jsonObject as? NSArray)?[0] as? NSDictionary)?["user"] as? NSDictionary)?["name"]{
  //What A disaster above

An unreadable mess for something like this should really be simple!


With SwiftyJSON all you have to do is:

let json = JSONValue(dataFromNetworking)
if let userName = json[0]["user"]["name"].string{
  //Now you got your value

And don't worry about the Optional Wrapping thing, it's done for you automatically

let json = JSONValue(dataFromNetworking)
if let userName = json[999999]["wrong_key"]["wrong_name"].string{
  //Calm down, take it easy, the ".string" property still produces the correct Optional String type with safety
let json = JSONValue(jsonObject)
switch json["user_id"]{
case .JString(let stringValue):
    let id = stringValue.toInt()
case .JNumber(let numberValue):
    let id = numberValue.integerValue
    println("ooops!!! JSON Data is Unexpected or Broken")

Error Handling

let json = JSONValue(dataFromNetworking)["some_key"]["some_wrong_key"]["wrong_name"]
if json{
  //JSONValue it self confirm to Protocol "LogicValue", with JSONValue.JInvalid produce false and others produce true
  //> JSON Keypath Error: Incorrect Keypath "some_wrong_key/wrong_name"
  //It always tells you where your key starts went wrong
  switch json{
  case .JInvalid(let error):
    //An NSError containing detailed error information 


CocoaPods is not fully supported for Swift yet, to use this library in your project you should:

  1. for Projects just drag SwiftyJSON.swift to the project tree
  2. for Workspaces you may include the whole SwiftyJSON.xcodeproj as suggested by @garnett

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