Serialize a Swift object to JSON or Dictionary, with selective properties.

Serializable.swift

/**
    Purpose:
        Convert (or Serialize) an object to a JSON String or Dictionary.
    Usage:
        Use 'Serialize.toJSON' on instances of classes that:
        - Inherit from NSObject
        - Implement 'Serializable' protocol
        - Implement the property 'jsonProperties' and return an array of strings with names of all the properties to be serialized
    Inspiration/Alternative:
        https://gist.github.com/anaimi/ad336b44d718430195f8
        https://gist.github.com/turowicz/e7746a9c035356f9483d
*/

import Foundation

@objc protocol Serializable {
    var jsonProperties:Array<String> { get }
    func valueForKey(key: String!) -> AnyObject!
}

struct Serialize {
    static func toDictionary(obj:Serializable) -> NSDictionary {
        // make dictionary
        var dict = Dictionary<String, AnyObject>()
        
        // add values
        for prop in obj.jsonProperties {
            let val:AnyObject! = obj.valueForKey(prop)
            
            if val is String{
                dict[prop] = val as! String
            }
            else if val is Int{
                dict[prop] = val as! Int
            }
            else if val is Double{
                dict[prop] = val as! Double
            }
            else if val is Array<String>{
                dict[prop] = val as! Array<String>
            }
            else if val is Serializable{
                dict[prop] = toJSON(val as! Serializable)
            }
            else if val is Array<Serializable>{
                var arr = Array<NSDictionary>()
                for item in (val as! Array<Serializable>) {
                    arr.append(toDictionary(item))
                }
                dict[prop] = arr
            }
        }
        // return dict
        return dict
    }
    
    static func toJSON(obj:Serializable) -> String? {
        // get dict
        let dict = toDictionary(obj)
        do {
            // make JSON
            let data = try NSJSONSerialization.dataWithJSONObject(dict, options:NSJSONWritingOptions(rawValue: 0))
            // return result as a String
            return NSString(data: data, encoding: NSUTF8StringEncoding) as? String
        }
        catch _ {
            return nil
        }
    }
}