Dispatch_once Singleton mode in Swift

Here are three ways to implement a singleton pattern, which supports lazy initialization and thread safety

• Global variables
• Structure
• Dispatch_once

Global variables:

Global variables, not class variables, are used here because class variables are not supported

Private Let _singletonsharedinstance = Singleton () class Singleton  {    class var Sharedinstance:singleton {        Return _singletonsharedinstance    }}

Structure:

Unlike classes, structs can define static variables and, by using this method, promote static variables to class variables (this method is recommended before supporting class variables)

Class Singleton {    class var Sharedinstance:singleton {        struct static {            static let Instance:singleton = Sin Gleton ()        }        return static.instance    }}

Dispatch_once:

The traditional OC approach to Swift's interface

Class Singleton {    class var Sharedinstance:singleton {        struct Static {            static var oncetoken:dispatch_once_ t = 0            static var Instance:singleton? = Nil        }        dispatch_once (&static.oncetoken) {            static.instance = S Ingleton ()        }        return static.instance!    }}

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Dispatch_once Singleton mode in Swift