Table of contents

Introduction

Patterns and their Types

2.1.

Wildcard Pattern

2.2.

Identifier Pattern

2.3.

Value-Binding Pattern

2.4.

Tupple Pattern

2.5.

Enumeration Case Pattern

2.6.

Optional Pattern

2.7.

Type-Casting Pattern

Singleton Class in Swift

3.1.

Global Acess

3.2.

Create a Singleton Class

3.2.1.

Create Global Variables

3.2.2.

Static Property and Private Initializer

Frequently Asked Questions

4.1.

Can a static variable be deinitialized in singleton?

4.2.

Mention some of the disadvantages of the singleton.

4.3.

What do you understand by enumerations in swift?

4.4.

What do you mean by optional in Swift?

Conclusion

Last Updated: Mar 27, 2024

Singleton Class in Swift

Author Naman Kukreja

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Introduction

As a developer, you always try to make your code more and more compact and with the same functionality, and sometimes you want to combine many features and add your features multiple times, but how do you achieve that in swift?

The answer is with the use of classes and structures. They both have the same functionalities, the only difference being classes are reference types and whereas structures are value types. One of the classes is that singleton is mainly used today. And for composite values, we can use patterns, and we will learn all about patterns and singleton class while moving further in this blog so let's move on without wasting anytime further.

Patterns and their Types

The pattern represents the structure of a composite value or a single value. In swift, there usually are two kinds of patterns, one which does not match any type of value and the other that matches any kind of value.

The first type of pattern is used for full pattern matching, and it is also useful when the values you are trying to find are not present in the runtime. These include type-casting, expression, optional, and enumeration case patterns. You can use these patterns in the do statement, switch statement, or in the case of if statement.

The second type of pattern is used for destructing values in a constant, simple variable, and optional bindings. These include any kind of tuple, identifier, and wildcard patterns.

Wildcard Pattern

A Wildcard pattern ignores and matches any value and consists of an underscore(_). Use a wildcard pattern when you don't care about the values being matched against. The following code, for example, iterates through the closed range 1...3, ignoring the current value of the range on each loop iteration:

for _ in 1...3 {
 
   // Do something three times.
 
}

Identifier Pattern

It matches any value, and if the value matches, it binds the matched value to a constant name or a variable.

As in the example below, Someval is an identifier pattern that matches the value 22. IF the matching succeeds, 22 is assigned or bound to the constant name Someval:

let Someval = 22

Value-Binding Pattern

Value-binding patterns associate matching values with variable or constant names. The let keyword binds a matched value to a constant name, while the var keyword is used to bind to the name of a variable. Identifier patterns used within the value-binding pattern:

let point = (3, 2)

switch point {
 
   // Bind x and y to the elements of point.
 
case let (x, y):
 
   print("The given point is at (\(x), \(y)).")

 
}

Tupple Pattern

A tupple pattern is a list of zero or more patterns enclosed in parenthesis separated by a comma(,). When a tuple pattern is used in the constant declaration or variable declaration, it can contain only identifier patterns, wildcard patterns, optional patterns, or any other tuple patterns that have those patterns. For example, the below code is not valid as (x,0) is an expression pattern.

let points = [(3, 0), (4, 0), (5, 1), (6, 0), (6, 1)]
 
for (x, 0) in points {
 
   /* ... */
 
}

Enumeration Case Pattern

In the Enumeration case pattern, we match the case of the existing enumeration type. They appear in switch statements, if, guard, while, and for in statements. It also matches the value that is wrapped in an optional. YOu must specify a tuple that contains a value that has an element for each associated value.

enum SomeEnum { case left, right }

 
let x: SomeEnum? = .left

 
switch x {
case .right:

 
   print("Turn right")
case .left:

 
   print("Turn left")
case nil:

 
   print("Keep going straight")

 
}

Optional Pattern

The optional pattern matches the values of the optional enumeration. They use an identifier pattern followed by a question mark(?) and appear similar to the enumeration pattern.

let someOptional: Int? = 42

 
// Match using an enumeration case pattern.

 
if case .some(let x) = someOptional {

 
   print(x)

 
}

Type-Casting Pattern

There are two types of type casting patterns one is a pattern, and the other is a pattern. The pattern type matches the same value as that of the specified value on the right side of the pattern at run time similarly, as the pattern matches the value with the right side specified value of as pattern at run time.

Singleton Class in Swift

In IOS, the singleton is the most widely used pattern in software development. Sometimes it is also considered an anti-pattern. Singletons are objects created only once and can be shared anywhere where they are required. Some of the examples are UserDefaults, FileManager, UIAccelerometer, and UIApplication.

It guarantees that only one instance is initialized in class. Sometimes you want your application to use only one instance. In these types of cases, the singleton pattern is essential and useful.

Global Acess

Earlier, the singleton pattern had a side efficiency that didn't provide global access, but this side effect has been removed in the latest versions of swift. Many developers use singleton patterns to use their singleton objects anywhere in their projects. We can use the default() method to access the default queue. This implies that any object of the class can access the default queue.

Create a Singleton Class

We need to follow some rules to create a singleton class.

Create Global Variables

We can create a singleton by defining a global variable. By defining them globally, then any object within a module can access the singleton object.

let sharedNetworkManager = NetworkManager(baseURL: API.baseURL)

 
class NetworkManager {

 
    // MARK: - Properties

 
    let baseURL: URL

 
    // Initialization

 
    init(baseURL: URL) {
        self.baseURL = baseURL
    }

 
}

This refers to that first, and the initializer runs the first time when the global variable is referred. The initialization is performed using dispatch_one() function. There are some disadvantages of using global variables. Also, like the network manager, the initializer can be declared in private, cluttering the global namespace.

Static Property and Private Initializer

Initializer allows instantiating the object of the class. And as the name suggests, it is a private initializer, which restricts the object creation outside the class.

class Example {
 
  ... 
  // create a private initializer
  private init() {
  }
}

 
// Error Code
let obj = Example()

Here we have created the example in private. SO we cannot create an object of Example outside the class as it will give an error.

While talking about the static property, we will create the object statically, and making the object static will allow the developer to access the object using the class name.

class Example{
  
  // static property to create singleton
  static let fileObj = Example()
  ... 
}

 
// access the singleton 
let data = Example.fileObj

Must Read: Singleton Design Pattern C#

Frequently Asked Questions

Can a static variable be deinitialized in singleton?

Yes, it will be deinitalize when the app stop working or running.

Mention some of the disadvantages of the singleton.

The singleton uses static memory, so the memory will not be free until the app stops working. They also create hidden dependencies.

What do you understand by enumerations in swift?

Enumerations refer to a group of related values.

What do you mean by optional in Swift?

Optional is a type of pattern that can store either a value or a nil.

Conclusion

In this article, we have extensively discussed the Singleton class in Swift, how to create it using different methods, align with patterns and their types with their explanation and examples.

If you are not much comfortable with Swift yet and looking for a tutorial, don't worry; Coding Ninjas has you covered. To learn, see Swift Tutorial for Beginners. And if you find swift difficult for some files like JSON, then visit SwiftyJSON. It is an extension of swift but quite easy.

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