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/turowicz/e7746a9c035356f9483d

*/

import Foundation

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

struct Serialize {
    static func toDictionary(obj:Serializable) throws -> NSDictionary {
        // make dictionary
        var dict = [String: AnyObject]()
        
        // add values
        for prop in obj.jsonProperties {
            let val: AnyObject? = obj.valueForKey(prop)
            
            if let val = val as? String {
                dict[prop] = val
            }
                
            if let val = val as? Int {
                dict[prop] = val
            }
                
            if let val = val as? Double {
                dict[prop] = val
            }
            
            if let val = val as? [String] {
                dict[prop] = val
            }
            
            if let val = val as? Serializable {
                dict[prop] = try toJSON(val)
            }
            
            if let val = val as? [Serializable] {
                var arr = Array<NSDictionary>()
                
                for item in val {
                    arr.append(try toDictionary(item))
                }
                
                dict[prop] = arr
            }
            
        }
        
        // return dict
        return dict
    }
    
    static func toJSON(obj:Serializable) throws -> String? {
        // get dict
        let dict = try toDictionary(obj)

        let data = try NSJSONSerialization.dataWithJSONObject(dict, options:NSJSONWritingOptions(rawValue: 0))
        return String(data: data, encoding: NSUTF8StringEncoding)
        
        // return result

    }
}