A simpe JSONObject in swift to wrap around objective c return objects.

JSONObject.swift

import Foundation

/// Class for handling errors related to the parent class.
///
enum JSONValidationErrors: ErrorType, CustomDebugStringConvertible, CustomStringConvertible {
    
    case ExpectedDictionary
    case ExpectedArray
    case MissingKey(String)
    case MissingIndex(Int)
    case ConversionFailed(String)
    case DateConversionFailed(String)
    
    func localizedFailureReason() -> String {
        switch self {
        case .ExpectedDictionary:
            return NSLocalizedString("Expected to find Dictionary in JSON response.", comment: "Error message to show when reading from a JSON object and a expected dictionary is not found.")
        case .ExpectedArray:
            return NSLocalizedString("Expected to find Array in JSON response.", comment: "Error message to show when reading from a JSON object and a expected array is not found.")
        case MissingKey(let key):
                return NSString(format:NSLocalizedString("Missing \"%@\" element in JSON response.", comment: "Error message to show when parsing a JSON dictionary and a expected key is not found."),
                    "\(key)") as String
        case ConversionFailed(let key):
            return NSString(format:NSLocalizedString("Failed to convert object to %@ type.", comment: "Error message to show when converstion to a expected type failed."),
                "\(key)") as String
        case DateConversionFailed(let key):
                return NSString(format:NSLocalizedString("Failed to convert %@ to date.", comment: "Error message to show when parsing a JSON dictionary field where a date was expected but the parsing failed."),
                    "\(key)") as String
        case MissingIndex(let index):
            return NSString(format:NSLocalizedString("Missing \"%i\" element in response array.", comment:"Error message to show when parsing a JSON array and an expected index is not found."),
                index) as String
        }
    }
    
    
    func convertToNSError() -> NSError {
        let userInfo = [NSLocalizedFailureReasonErrorKey: self.localizedFailureReason()]
        return NSError(domain: "JSONValidationErrors", code: self._code, userInfo: userInfo)
    }
    
    var description:String{ get { return localizedFailureReason() }}
    
    var debugDescription:String{ get { return localizedFailureReason() }}
}

class JSONObject {

    let json: AnyObject?
    
    init(json: AnyObject?){
        self.json = json
    }
    
    func dictionary() throws -> [String: AnyObject] {
        guard let dictionary = json as? [String: AnyObject] else {
            throw JSONValidationErrors.ExpectedDictionary
        }
        return dictionary;
    }
    
    func array() throws -> [AnyObject] {
        guard let array = json as? [AnyObject] else {
            throw JSONValidationErrors.ExpectedArray
        }
        return array;
    }
    
    func string() throws -> String {
        guard let result = json as? String else {
            throw JSONValidationErrors.ConversionFailed("String")
        }
        return result;
    }

    func double() throws -> Double {
        guard let result = json as? Double else {
            throw JSONValidationErrors.ConversionFailed("Double")
        }
        return result;
    }

    func bool() throws -> Bool {
        guard let result = json as? Bool else {
            throw JSONValidationErrors.ConversionFailed("Bool")
        }
        return result;
    }
    
    func objectAtKey(key: String) throws -> JSONObject {
        guard let dictionary = json as? [String: AnyObject] else {
            throw JSONValidationErrors.ExpectedDictionary
        }
        guard let obj = dictionary[key] else {
            throw JSONValidationErrors.MissingKey(key)
        }
        
        return JSONObject(json: obj)
    }
    
    func objectAtIndex(index: Int) throws -> JSONObject {
        guard let array = json as? [AnyObject] else {
            throw JSONValidationErrors.ExpectedArray
        }
        
        guard (index >= 0) && (index < array.count) else {
                throw JSONValidationErrors.MissingIndex(index)
        }
        
        let obj = array[index]
        
        return JSONObject(json: obj)
    }
    
    func dateWithFormatter(dateFormatter:NSDateFormatter) throws -> NSDate {
        
        let dateString = try self.string() as String
        guard let date = dateFormatter.dateFromString(dateString) else {
            throw JSONValidationErrors.DateConversionFailed("")
        }
        
        return date
    }
    
}