ambiguous use of overload

playground.swift

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

import UIKit

enum ParseError: ErrorType
{
    case MissingKey(key: String)
    case TypeMismatch(expected: String, actual: String)
}

class AppleSauce
{
    let sessionToken: String
    let sessionKey: String
    let sessionPoop: String?
    
    init(sessionKey: String, sessionToken: String, sessionPoop: String?)
    {
        self.sessionKey = sessionKey
        self.sessionToken = sessionToken
        self.sessionPoop = sessionPoop
    }
    
    convenience init(JSON: [String : AnyObject?]) throws
    {
        do
        {
            let _sessionPoop: String? = try AppleSauce.extract(JSON, key:"session_poop")
            let _sessionToken : String = try AppleSauce.extract(JSON, key:"session_token")
            let _sessionKey : String = try AppleSauce.extract(JSON, key:"session_key")
            self.init(sessionKey: _sessionKey, sessionToken: _sessionToken, sessionPoop: _sessionPoop)
        }
        catch let e
        {
            self.init(sessionKey: "", sessionToken: "", sessionPoop:"")
            print("Error: \(e)")
            throw e
        }
    }
    
    class func extract<T>(JSON: [String : AnyObject?], key: String) throws -> T
    {
        do
        {
            if let value = JSON[key]
            {
                if let casted = value as? T
                {
                    return casted
                }
                else
                {
                    throw ParseError.TypeMismatch(expected: "\(T.self)", actual: "\(value.dynamicType)")
                }
            }
            else
            {
                throw ParseError.MissingKey(key: key)
            }
        }
        catch let e
        {
            throw e
        }
    }
    class func extract<T>(JSON: [String : AnyObject?], key: String) throws -> T?
    {
        do
        {
            let value: T = try extract(JSON, key: key)
            return value
        }
        catch ParseError.MissingKey
        {
            return nil 
        }
    }
}