Skip to content

hpique/SwiftSingleton

master
Switch branches/tags
Code

Latest commit

 

Git stats

Files

Permalink
Failed to load latest commit information.
Type
Name
Latest commit message
Commit time
 
 
 
 
 
 
 
 

SwiftSingleton

tl;dr: Use the class constant approach if you are using Swift 1.2 or above and the nested struct approach if you need to support earlier versions.

An exploration of the Singleton pattern in Swift. All approaches below support lazy initialization and thread safety.

Issues and pull requests welcome.

Approach A: Class constant

class SingletonA {
    
    static let sharedInstance = SingletonA()
    
    init() {
        println("AAA");
    }
    
}

This approach supports lazy initialization because Swift lazily initializes class constants (and variables), and is thread safe by the definition of let.

Class constants were introduced in Swift 1.2. If you need to support an earlier version of Swift, use the nested struct approach below or a global constant.

Approach B: Nested struct

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

Here we are using the static constant of a nested struct as a class constant. This is a workaround for the lack of static class constants in Swift 1.1 and earlier, and still works as a workaround for the lack of static constants and variables in functions.

Approach C: dispatch_once

The traditional Objective-C approach ported to Swift.

class SingletonC {
    
    class var sharedInstance: SingletonC {
        struct Static {
            static var onceToken: dispatch_once_t = 0
            static var instance: SingletonC? = nil
        }
        dispatch_once(&Static.onceToken) {
            Static.instance = SingletonC()
        }
        return Static.instance!
    }
}

I'm fairly certain there's no advantage over the nested struct approach but I'm including it anyway as I find the differences in syntax interesting.

About

An exploration of the Singleton pattern in Swift

Resources

License

Stars

Watchers

Forks

Releases

No releases published

Packages

No packages published