CODEWITHSUNDEEP
iosswiftsingleton
user4790024
user4790024

Reputation:

How to Create Singleton Object in swift

I am learning about Singleton pattern in swift and efficient way to create a Singleton class and found out the best way to create as below.

class SingletonClass{
    static let sharedInstance = SingletonClass()
}

Since i have use the let statement it is read only property and has to be thread safe so there is no need of dispatch_once() as of Objective C.And static is used to make the sharedInstance variable as a class variable i guess.

But how does this guarantee there is only one instance created throughout the application?is there a small thing i am missing?

Upvotes: 19

Views: 20601

Answers (4)

Vatsal
Vatsal

Reputation: 18181

If you want to prevent instantiation of your class (effectively restricting usage to only the singleton), then you mark your initializer as private:

class SingletonClass {

    static let shared = SingletonClass()

    private init() {
        // initializer code here
    }
}

Upvotes: 25

YanSte
YanSte

Reputation: 10839

Make private init, for example :

final class Singleton {

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

    //MARK: Shared Instance

    static let sharedInstance: Singleton = Singleton()

    //MARK: Local Variable

    var emptyStringArray : [String] = []

}

Upvotes: 5

onmyway133
onmyway133

Reputation: 48085

You're right. And you may want to read Files and Initialization about how global and static variable are handle in Swift

Swift use this approach

Initialize lazily, run the initializer for a global the first time it is referenced, similar to Java.

It says

it allows custom initializers, startup time in Swift scales cleanly with no global initializers to slow it down, and the order of execution is completely predictable.

The lazy initializer for a global variable (also for static members of structs and enums) is run the first time that global is accessed, and is launched as dispatch_once to make sure that the initialization is atomic. This enables a cool way to use dispatch_once in your code: just declare a global variable with an initializer and mark it private.

Upvotes: 1

wilforeal
wilforeal

Reputation: 369

What guarantees it is only created once is the keyword static. you can reference this article: https://thatthinginswift.com/singletons/

Hope that helps.

The static keyword denotes that a member variable, or method, can be accessed without requiring an instantiation of the class to which it belongs. In simple terms, it means that you can call a method, even if you've never created the object to which it belongs

Upvotes: 10

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