Singleton.swift

final class Singleton {

    // MARK: - Singleton
    
    private struct Instance {
        static var dispatchToken: dispatch_once_t = 0
        static var instance: Singleton?
    }
    
    static var instance: Singleton {
        get {
            dispatch_once(&Instance.dispatchToken) {
                Instance.instance = Singleton()
            }
            return Instance.instance!
        }
    }
    
    // MARK: - Initializers
    
    private init() { }
}