LumaJSON.swift

// Playground - noun: a place where people can play

import UIKit
class LumaJSONObject: Printable {
    
    var value: AnyObject?
    
    subscript(index: Int) -> LumaJSONObject? {
        return (value as? [AnyObject]).map { LumaJSONObject($0[index]) }
    }
    
    subscript(key: String) -> LumaJSONObject? {
        return (value as? NSDictionary).map { LumaJSONObject($0[key]) }
    }
    
    subscript(key: String) -> AnyObject? {
        return self[key]?.value
    }
    
    subscript(key: Int) -> AnyObject? {
        return self[key]?.value
    }
    
    init(_ value: AnyObject?) {
        self.value = value
    }
    
    var description: String {
        get {
            return "LumaJSONObject: \(self.value)"
        }
    }
}

class LumaJSON {
    
    func parse(json: String) -> LumaJSONObject? {
        if let jsonData = json.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false){
            var err: NSError?
            
            let parsed: AnyObject? = NSJSONSerialization.JSONObjectWithData(jsonData, options: .MutableLeaves, error: &err)
            
            if let parsedArray = parsed as? NSArray {
                return LumaJSONObject(parsedArray)
            }
            
            if let parsedDictionary = parsed as? NSDictionary {
                return LumaJSONObject(parsedDictionary)
            }
            
            return LumaJSONObject(parsed)
        }
        return nil
    }
}

let jsonStr = "{\"user\":{\"name\":\"jquave\",\"id\":542,\"url\":\"http://jamesonquave.com\"},\"friend_ids\":[299,341,492],\"alert_message\":\"Please verify e-mail address to continue\"}"

let luma = LumaJSON()
if let parsed = luma.parse(jsonStr) {
    
    // Simple Key/Value retreival
    if let alertMessage = parsed["alert_message"] as? String {
        println("Alert: \(alertMessage)")
    }
    
    // Nested JSON
    if let userName = parsed["user"]?["name"] as? String {
        println("Username is \(userName)")
    }
    
    // Nested object casting works using Swift's built-in mechanisms
    if let friendIDs = parsed["friend_ids"] as? [Int] {
        for friendID in friendIDs {
            println("Friend ID: \(friendID)")
        }
    }
}

Much simpler:

    subscript(key: String) -> String? {
        get {
            return self[key]?.value as? String
        }
    }