swift 单例定义

方法一：

import Foundation

class SingleOne {

//单例

static let shareSingleOne = SingleOne()

}

方法二：

import Foundation

class SingleTwo {

//单例

class func shareSingleTwo()->SingleTwo{

struct Singleton{

static var onceToken : dispatch_once_t = 0

static var single:SingleTwo?

}

dispatch_once(&Singleton.onceToken,{

Singleton.single=shareSingleTwo()

}

)

return Singleton.single!

}

}

方法三：

import Foundation

//全局的常量

let single = SingleThree()

class SingleThree {

class var sharedInstance : SingleThree {

return single

}

}

方法四：

import Foundation

class SingleFour {

static var sharedInstance : SingleFour {

struct Static {

static let instance : SingleFour = SingleFour()

}

return Static.instance

}

}