Swift: extensions


Swift is a programming language that has quickly become the go-to for developing mobile apps. It’s designed to be fast and efficient, making it perfect for iOS and Android apps. But what you may not know is that Swift also has extensions. Extensions are built-in features that let you do more with Swift, from adding new functionality to speeding up your workflow. In this blog post, we will explore what extensions are and how they can help you work faster and more efficiently. We will also provide a few tips on how to get started using them.

What is an Extension?

An extension is a piece of code that can be added to a project to extend its functionality. Extensions are written in the Swift programming language and can be used to add new features, modify existing functions, or add support for different platforms or devices.

There are a few different types of extensions available in Swift. The most common type is an Objective-C extension, which allows projects written in Swift to access the functionality of Objective-C code. There are also third-party extensions available that allow developers to add new features or customize existing ones.

To install an extension, first you need to download it from the Extensions gallery on Apple’s developer website. Once you have downloaded the extension, open your project in Xcode and select the ‘Extensions’ tab. Then drag and drop the extension onto the ‘Projects’ section of the tab.

To use an extension in your project, you first need to import it into your codebase. To do this, open your project in Xcode and select the appropriate module (for example, ‘Classes’). Next, click on the ‘Utilities’ tab and then click on ‘Import Extension’. Select the file that you downloaded from Apple’s developer website and let Xcode automatically add it to your project.

If you want to disable an extension permanently, you can do so by selecting it in the ‘Projects’ section of the ‘Extensions’ tab and clicking on the ‘Disable’ button next to it.

What are the Types of Extensions?

There are a few types of extensions you can use in Swift.

The first type is called a static extension. Static extensions are implemented in the same file as the function they’re extending and don’t require any additional files. They’re useful when you want to add functionality to a function without having to write any new code.

The second type of extension is an instance extension. Instance extensions are implemented in separate files and are added to functions after they’ve been defined. This allows you to modularize your code and keep related code together. They’re also useful when you want to extend a function with different behavior for different instances.

The final type of extension is an optional extension. Optional extensions allow you to specify whether or not the extension should be included when the function is compiled. This is useful if you want to disable an extension or include it only if certain conditions are met.

How to get an Extension?

If you want an extension for your Swift code, you first need to sign up for a Codea account. After you’ve registered, you can find the Extensions Page under the My Account heading on the homepage. There, you’ll see a list of extensions available for download.

Once you have downloaded and installed the extension, open a new file in Swift and type the following:

extension Coding { }

This will create an empty extension module at the top of your file. Now you’ll need to write some code inside the module. For example, if you want to add support forildeclarations, you could do something like this:

extension Coding { func deinline(name: String) -> Void { } }

What are the Requirements for an Extension?

The Swift language provides a foundation for creating powerful extensions. Extensions are written in the same language as your app, and they provide additional functionality to your app. To make an extension available to your users, you need to:

Create a Package. For extensions that you distribute through CocoaPods or Carthage, you need to create a package containing your extension. This package needs a unique identifier (UUID) and should be added to your project’s Xcode project file (.xcworkspace). You can find more information on creating packages in the Swift documentation.

Configure an App Store. Your extension must be configured for the App Store before it can be installed on an iOS device or Mac. For more information, see Configuring an Extension for the App Store.

Add Extension Sources. After you have created your package and configured the App Store, you need to add sources of third-party code that your extension uses. You can find detailed instructions for adding sources in the Swift documentation.

How to Know If You Are Eligible for an Extension?

If you have been trying to get an extension from your credit card issuer, and your request has been denied, there are some things you can do to try and increase your chances of being approved. First, make sure that you are eligible for an extension. Here are a few guidelines to keep in mind:

– Your credit card should be in good standing. If it is past its due date or has had Problems with payments in the past, your issuer may not be willing to give you an extension.

– You should have tried to get an extension before filing for bankruptcy. An essential criterion that could influence the approval of your extension is your effort to amicably settle the dispute with your credit card issuer prior to resorting to bankruptcy. Demonstrating good faith in resolving the matter can play a significant role in the decision-making process.

– You should not have missed any payments on your credit card account during the six months leading up to when you filed for bankruptcy.

If you meet all of these criteria, there is a greater chance that you will be approved for an extension.

What to do if You Get an Extension and Don’t Use It?

If you have an extension that you haven’t used in a while, it’s best to remove it before getting an extension. Otherwise, your account may be penalized. If you don’t use your extension within a certain timeframe, Apple may remove it from your account.


If you’re looking to add a little extra length to your hair, extensions are the perfect solution. Before getting extensions, there are several important factors to consider. Understand that extensions vary greatly in quality, so it’s crucial to choose a skilled provider who can tailor the extensions to suit your unique requirements, ensuring a seamless match in style and color.

Additionally, be aware that extensions can be costly, accounting for the price of the hair itself, as well as other necessary materials like glue and needles. Moreover, the process can be time-consuming, requiring a significant salon appointment. Extensions can last anywhere from six months to two years or longer with proper care and maintenance.


1. What are extensions in Swift?

Answer: Extensions in Swift provide a way to add new functionality to existing types (such as classes, structures, enumerations, or protocols) without modifying the original source code. They can add computed properties, methods, initializers, subscripts, and nested types.

2. How do you define an extension in Swift?

Answer: To define an extension in Swift, you use the extension keyword followed by the name of the type you want to extend. Here’s an example of an extension adding a method to the String type:

extension String {

func reversedString() -> String {

return String(self.reversed())



You can now call reversedString() on any String instance:

let original = “Hello”

let reversed = original.reversedString()

print(reversed) // Outputs: “olleH”

3. Can extensions add stored properties to types in Swift?

Answer: No, extensions in Swift cannot add stored properties to types. They can only add computed properties, methods, initializers, subscripts, and nested types. Stored properties can only be added to a type’s original declaration or via subclasses.

4. How do you add a computed property to a type using an extension?

Answer: You can add a computed property to a type using an extension by defining a property with a getter (and optionally a setter). Here’s an example adding a computed property to Double:

extension Double {

var squared: Double {

return self * self



You can now access the squared property on any Double value:

let number: Double = 3.0

print(number.squared) // Outputs: 9.0

5. Can extensions in Swift conform a type to a protocol?

Answer: Yes, extensions can be used to conform a type to a protocol, adding the necessary properties and methods to fulfill the protocol requirements. Here’s an example:

protocol Describable {

func describe() -> String



extension Int: Describable {

func describe() -> String {

return “This is the number \(self)”




let number = 42

print(number.describe()) // Outputs: “This is the number 42”

6. How do you add an initializer to a type using an extension?

Answer: You can add an initializer to a type using an extension by defining it within the extension. Here’s an example adding a new initializer to UIColor:

import UIKit


extension UIColor {

convenience init(red: Int, green: Int, blue: Int) {

self.init(red: CGFloat(red) / 255.0,

green: CGFloat(green) / 255.0,

blue: CGFloat(blue) / 255.0,

alpha: 1.0)



You can now use the new initializer to create a UIColor instance:

let customColor = UIColor(red: 255, green: 0, blue: 0)

7. What are some best practices when using extensions in Swift?


  • Organize by functionality: Group related methods, properties, and initializers within the same extension to keep the code organized and readable.
  • Use extensions to conform to protocols: Implement protocol conformance in extensions to clearly separate protocol-related functionality from the main type declaration.
  • Avoid overuse: While extensions are powerful, overusing them can lead to fragmented and hard-to-maintain code. Use them judiciously to add meaningful and related functionality.
  • Add comments: Document the purpose of extensions and the added functionality to make the code more understandable for other developers.


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