單例的三種方式
1.Class constant
static let sharedInstance = Weatcher()
2.dispatch_once
class var sharedInstance : Weatcher {
struct Static {
static var onceToken : dispatch_once_t = 0
static var instance : Weatcher? = nil
}
dispatch_once(&Static.onceToken) {
Static.instance = Weatcher()
}
return Static.instance!
}
3.Nested struct
class var sharedInstance: Weatcher {
struct Static {
static let instance: Weatcher = Weatcher()
}
return Static.instance
}```