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Elegant, type-safe JSON parsing in Swift

If you're a clever programmer, then you probably use Codable types wherever you can do so. However, sometimes you need to parse some JSON data the structure of which you don't control. Previously, this was a painful operation:

let object = try (JSONSerialization.jsonObject(with: data) as! [String: Any])
guard let foo = object["foo"] as? Int, let bar = object["bar"] as? String, let array = object["array"] as? [Any] else {
guard let number = array[0] as? Double, let word = array[1] as? String, let dictionary = array[3] as? [String: Int] else {
guard let hello = dictionary["hello"] else {

With JSONParser, this process is elegant and effortless:

let parser = data.dictionaryParser // `data` is an instance of `Data` from `Foundation`
let foo = parser["foo", as: Int.self]
let bar = parser["bar", as: String.self]
let number = parser[arrayAt: "array"]?[0, as: Double.self]
let word = parser[arrayAt: "array"]?[1, as: String.self]
let hello = parser[arrayAt: "array"]?[dictionaryAt: 2]?["hello", as: Int.self]

You can also iterate over heterogenous JSON arrays and dictionaries:

try data.arrayParser.iterate { (proxy) in
	if let value = proxy.get(as: Int.self) {
		print(value * 2)
	} else if let value = proxy.get(as: Bool.self) {

JSONParser can work with other providers, not just Data from Foundation. Just have your custom class or struct conform to the JSONProvider protocol. It has only one mandatory interface member:

// This `Set` extension is already provided in the JSONParser package; use it as a guide for writing your own extensions for other types
extension Set: JSONProvider {

	public var parser: ArrayJSONParser? {
		get {
			return Array(self).parser


Convenient functions and subscript accessors are automatically provided for free, requiring no manual implementation:

let array = [
		"2": true
] as [AnyHashable]
let set = Set(array)
try set.iterate { (proxy) in
	print(proxy.get(as: Int.self) ?? proxy.get(as: [String: Bool].self)!)

JSONParser builds on top of Swift's robust generic-typing system to provide an easy, intuitive API for interacting with JSON data. It has no external dependencies and relies solely on Foundation APIs, so it works on Linux and Windows in addition to the various Apple platforms.