Example of the singleton pattern in Swift

singleton-pattern.swift

//XCode Playground Friendly

/**
 Singleton Pattern - Ensures that only one instance of a object exists in the application context
 usefull for things that will have a global context across the app.
 Ex: An internet connection, Credentials, etc.
 
 * Can only be used for reference types.
 */

/*
 Implementation using private initializer - This is threadsafe and the simplest implementation
 */
class Singleton {
    static let sharedInstance = Singleton() //<- Singleton Instance
    var instanceNum: Int = 0
    
    private init() { /* Additional instances cannot be created */ }
}

/* Test Code */
let instance1 = Singleton.sharedInstance
let instance2 = Singleton.sharedInstance

instance1.instanceNum = 1
instance2.instanceNum = 2
assert(instance1.instanceNum == 2)

How if instantiation needs a parameter?

How if instantiation needs a parameter?

@jhoanrivers

Hi, there is no parameter in the initialization. The initializer is actually private.