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singletonswift3
RobertJoseph
RobertJoseph

Reputation: 8158

Singleton with properties in Swift 3

In Apple's Using Swift with Cocoa and Objective-C document (updated for Swift 3) they give the following example of the Singleton pattern:

class Singleton {
    static let sharedInstance: Singleton = {
        let instance = Singleton()

        // setup code

        return instance
    }()
}

Let's imagine that this singleton needs to manage a variable array of Strings. How/where would I declare that property and ensure it gets initialized properly to an empty [String] array?

Upvotes: 89

Views: 84102

Answers (4)

YanSte
YanSte

Reputation: 10839

For me this is the best way, make init private. Swift 3 \ 4 \ 5 syntax

// MARK: - Singleton

final class Singleton {

    // Can't init is singleton
    private init() { }

    // MARK: Shared Instance

    static let shared = Singleton()

    // MARK: Local Variable

    var emptyStringArray = [String]()

}

Upvotes: 237

Mehul Sojitra
Mehul Sojitra

Reputation: 1181

As per the apple's documentation: In Swift, you can simply use a static type property, which is guaranteed to be lazily initialized only once, even when accessed across multiple threads simultaneously.

class Singleton {

    // MARK: - Shared

    static let shared = Singleton()
}

With initialization method:

class Singleton {

    // MARK: - Shared

    static let shared = Singleton()

    // MARK: - Initializer

    private init() {
    }

}

Upvotes: 30

user6375148
user6375148

Reputation:

You can initialize an empty array like this.

class Singleton {

    //MARK: Shared Instance

    static let sharedInstance : Singleton = {
        let instance = Singleton(array: [])
        return instance
    }()

    //MARK: Local Variable

    var emptyStringArray : [String]

    //MARK: Init

    init( array : [String]) {
        emptyStringArray = array
    }
}

Or if you prefer a different approach, this one will do fine.

class Singleton {

    //MARK: Shared Instance

    static let sharedInstance : Singleton = {
        let instance = Singleton()
        return instance
    }()

    //MARK: Local Variable

    var emptyStringArray : [String]? = nil

    //MARK: Init

    convenience init() {
        self.init(array : [])
    }

    //MARK: Init Array

    init( array : [String]) {
        emptyStringArray = array
    }
}

Upvotes: 59

gnasher729
gnasher729

Reputation: 52538

Any initialisation would be done in an init method. No difference here between a singleton and a non-singleton.

Upvotes: 0

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