What is Extension in Swift

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In Swift, an extension is a powerful feature that allows you to add new functionality to an existing class, structure, enumeration, or protocol type without modifying the original source code. Extensions can add computed properties, methods, initializers, subscripts, and nested types to the existing type.

This is example of extension.

extension TimeModel {
    var timeFormatted: String {
        let minutes = timeRemaining / 60
        let seconds = timeRemaining % 60
        return String(format: "%02d:%02d", minutes, seconds)
    }
}

Breakdown

Extension Declaration

extension TimeModel declares an extension to the TimeModel type. This means you are adding new functionality to the TimeModel type.

Computed Property:

var timeFormatted: String is a computed property. It does not store a value directly but computes it on the fly whenever it is accessed.

Inside the computed property:

• let minutes = timeRemaining / 60 calculates the minutes by dividing timeRemaining by 60.
• let seconds = timeRemaining % 60 calculates the remaining seconds by taking the remainder of timeRemaining divided by 60.
• return String(format: "%02d:%02d", minutes, seconds) formats the minutes and seconds into a string in the "MM:SS" format, ensuring two digits for both minutes and seconds, padding with zeros if necessary.

Purpose

In Swift, an `extension` is a feature that allows you to add new functionality to an existing class, structure, enumeration, or protocol type. This includes adding computed properties, methods, initializers, and even conforming to protocols. The primary purpose of extensions is to extend the capabilities of existing types without modifying their original source code.

The purpose of this extension is to add a computed property timeFormatted to the TimeModel type. This property provides a string representation of the remaining time in a formatted "MM:SS" format.

Example Usage

Assuming timeRemaining is a property of TimeModel, you can use the timeFormatted property like this:

let timeModel = TimeModel()
timeModel.timeRemaining = 125 // for example
print(timeModel.timeFormatted) // Output: "02:05"

Summary

• Extension: Allows you to add new functionality to existing types without modifying their original implementation.

This feature is useful for enhancing types with additional functionality while keeping your code organized and modular.