Singleton Swiftly

less than 1 minute read

The Singleton pattern makes sure only one instance of a given class exists. Usually, that single instance is lazily loaded when it is needed. There are a bunch of examples of this built into iOS such as:

NSUserDefaults.standardUserDefaults()
UIApplication.sharedApplication()

I’m not going to tell you when you might need this pattern, there is a bunch of information out there on this. But I want to show you how to do it in Swift and avoid the ugly Obj-C dispatch_once version you see everywhere.

Singleton for Swift v1.2+

This is an example for Swift greater than v1.2

class MyClass {
  static let sharedInstance = MyClass()
  init() {
    println("We did it!")
  }
}

Singleton for Swift < v1.2

This is an example for Swift less than v1.2. I have to be honest, if you are not using at least Swift v1.2 by the time this comes around, you need to switch over. You are missing out on a lot of good stuff.

class MyClass {
  
  class var sharedInstance: MyClass {
    struct Static {
      static let instance: MyClass = MyClass()
    }
    return Static.instance
  }
  
}