extension Keys {
    static let string      = Key<String>("string")
    static let url         = Key<NSURL>("url")
    static let number      = Key<NSNumber>("number")
    static let int         = Key<Int>("int")
    static let float       = Key<Float>("float")
    static let double      = Key<Double>("double")
    static let date        = Key<NSDate>("date")
    static let bool        = Key<Bool>("bool")
    static let array       = Key<Array<AnyObject>>("array")
    static let dictionary  = Key<[String : String]>("dictionary")
    
    // Support nested value.
    static let innerInt    = Key<Int>("array.0")
    static let innerArray  = Key<String>("array.1.0")
    static let innerString = Key<String>("dictionary.innerString")
}

let plistPath = NSBundle.mainBundle().pathForResource("Configuration", ofType: "plist")!
let config = Configuration(plistPath: plistPath)!

// You can get a plist value to type-safe.
let stringValue      = config.get(.string)!
let urlValue         = config.get(.url)!
let numberValue      = config.get(.number)!
let intValue         = config.get(.int)!
let floatValue       = config.get(.float)!
let doubleValue      = config.get(.double)!
let dateValue        = config.get(.date)!
let boolValue        = config.get(.bool)!
let arrayValue       = config.get(.array)!
let dictionaryValue  = config.get(.dictionary)!
let innerIntValue    = config.get(.innerInt)!
let innerArrayValue  = config.get(.innerArray)!
let innerStringValue = config.get(.innerString)!