//Database 单例，第一种写法

class var instance: Database

{

struct Singleton

{

static let instance = Database()

}

return Singleton.instance

}

/*

//Database 单例，第二种写法

struct Static {

static var instance:Database? = nil

static var onceToken:dispatch_once_t = 0

}

class func sharedInstance() -> Database! {

/*

//普通闭包写法

dispatch_once(&Static.onceToken, { () -> Void in

Static.instance = Database()

})

*/

//尾随闭包写法

dispatch_once(&Static.onceToken) {

Static.instance = Database()

}

return Static.instance!

}

*/