Swift入坑--单例

class func sharedInstance() -> ClassName {
struct singleton{
static var once: dispatch_once_t = 0
static var instance: <span style="font-family: Arial, Helvetica, sans-serif;">ClassName</span><span style="font-family: Arial, Helvetica, sans-serif;">? = nil</span>
}
dispatch_once(&singleton.once,{
singleton.instance = <span style="font-family: Arial, Helvetica, sans-serif;">ClassName</span>()
}
)
return singleton.instance!
}