Computed properties in Swift - Mini Project: Build & Apply

Computed Properties in Swift

📖 Scenario: You are creating a simple app to manage rectangles. You want to store the width and height, and also calculate the area automatically whenever needed.

🎯 Goal: Build a Swift struct called Rectangle with stored properties for width and height, and a computed property for area.

📋 What You'll Learn

Create a struct named Rectangle

Add stored properties width and height of type Double

Add a computed property area that returns the product of width and height

Create an instance of Rectangle with width 5.0 and height 3.0

Print the area of the rectangle

💡 Why This Matters

🌍 Real World

Computed properties help keep data consistent and up-to-date without storing extra values. For example, calculating area or volume on demand.

💼 Career

Understanding computed properties is essential for Swift developers building apps that manage dynamic data efficiently.

1

Create the Rectangle struct with width and height

Create a struct called Rectangle with two stored properties: width and height, both of type Double. Set no initial values.

Swift

struct Rectangle {
    // Your code here
}

Need a hint?

Use struct Rectangle { var width: Double; var height: Double } to define the shape.

2

Add a computed property for area

Inside the Rectangle struct, add a computed property called area of type Double that returns the product of width and height.

Swift

struct Rectangle {
    var width: Double
    var height: Double
    // Your code here
}

Need a hint?

Computed properties use { return ... } to calculate values on the fly.

3

Create an instance of Rectangle

Create a constant called myRect and assign it a Rectangle instance with width 5.0 and height 3.0.

Swift

struct Rectangle {
    var width: Double
    var height: Double
    var area: Double {
        return width * height
    }
}

// Your code here

Need a hint?

Use let myRect = Rectangle(width: 5.0, height: 3.0) to create the rectangle.

4

Print the area of the rectangle

Write a print statement to display the area of myRect.

Swift

struct Rectangle {
    var width: Double
    var height: Double
    var area: Double {
        return width * height
    }
}

let myRect = Rectangle(width: 5.0, height: 3.0)

// Your code here

Need a hint?

Use print(myRect.area) to show the area.