Enum methods and computed properties in Swift - Mini Project: Build & Apply

Enum methods and computed properties

📖 Scenario: You are creating a simple app that shows different types of fruits and their colors.

🎯 Goal: Build a Swift enum called Fruit with a method and a computed property to get the fruit's color and description.

📋 What You'll Learn

Create an enum called Fruit with cases apple, banana, and cherry

Add a computed property called color that returns the color of each fruit as a String

Add a method called description() that returns a sentence describing the fruit and its color

Print the description of each fruit

💡 Why This Matters

🌍 Real World

Enums with methods and computed properties help organize related data and behavior, like representing fruit types and their details in an app.

💼 Career

Understanding enums with methods and computed properties is important for writing clean, maintainable Swift code in iOS app development.

1

Create the Fruit enum

Create an enum called Fruit with cases apple, banana, and cherry.

Swift

// Your code here

Hint

Use the enum keyword to define Fruit and list the cases inside curly braces.

2

Add a computed property for color

Add a computed property called color inside the Fruit enum that returns a String with the color for each fruit: "Red" for apple, "Yellow" for banana, and "Red" for cherry.

Swift

enum Fruit {
    case apple
    case banana
    case cherry

    // Your code here
}

Hint

Use a var with a switch on self to return the correct color.

3

Add a method to describe the fruit

Add a method called description() inside the Fruit enum that returns a String describing the fruit and its color, like "An apple is Red." Use the color computed property inside this method.

Swift

enum Fruit {
    case apple
    case banana
    case cherry

    var color: String {
        switch self {
        case .apple: return "Red"
        case .banana: return "Yellow"
        case .cherry: return "Red"
        }
    }

    // Your code here
}

Hint

Define a function that returns a string using self and the color property with string interpolation.

4

Print descriptions of all fruits

Create constants apple, banana, and cherry of type Fruit. Then print the result of calling description() on each constant.

Swift

enum Fruit {
    case apple
    case banana
    case cherry

    var color: String {
        switch self {
        case .apple: return "Red"
        case .banana: return "Yellow"
        case .cherry: return "Red"
        }
    }

    func description() -> String {
        return "An \(self) is \(color)."
    }
}

// Your code here

Hint

Create constants for each fruit case and print their descriptions using the description() method.

Practice

1. What is the purpose of adding methods to an enum in Swift?

easy

A. To inherit properties from other enums

B. To store additional data inside enum cases

C. To perform actions or calculations related to enum cases

D. To convert enums into classes automatically

Solution

1. Step 1: Understand enum methods

   Enum methods allow you to add functions that perform tasks related to the enum's cases.

2. Step 2: Differentiate from other enum features

   Enums do not store extra data like classes; methods help organize related actions.

3. Final Answer:

   To perform actions or calculations related to enum cases -> Option C

4. Quick Check:

   Enum methods = perform actions [OK]

Hint: Methods in enums perform actions tied to cases [OK]

Common Mistakes:

• Thinking enums can inherit from other enums
• Confusing methods with stored properties
• Assuming enums convert to classes automatically

2. Which of the following is the correct syntax to declare a computed property inside an enum in Swift?

easy

A. static var description: String = "Example"

B. func description() -> String { return "Example" }

C. let description = "Example"

D. var description: String { return "Example" }

Solution

1. Step 1: Identify computed property syntax

   Computed properties use var with a code block returning a value, like var name: Type { ... }.

2. Step 2: Check options

   var description: String { return "Example" } matches computed property syntax; B is a method, C is a stored property, D is a static stored property.

3. Final Answer:

   var description: String { return "Example" } -> Option D

4. Quick Check:

   Computed property syntax = var with braces [OK]

Hint: Computed properties use var with braces returning a value [OK]

Common Mistakes:

• Using func instead of var for computed properties
• Declaring computed properties as let constants
• Confusing static stored properties with computed ones

3. Consider this Swift enum with a computed property and method:

enum Direction {
    case north, south, east, west

    var isVertical: Bool {
        return self == .north || self == .south
    }

    func description() -> String {
        switch self {
        case .north: return "Up"
        case .south: return "Down"
        case .east: return "Right"
        case .west: return "Left"
        }
    }
}

let dir = Direction.east
print(dir.isVertical)
print(dir.description())

What is the output?

medium

A. false
Right

B. true
Right

C. false
East

D. true
East

Solution

1. Step 1: Evaluate computed property isVertical

   For Direction.east, isVertical checks if east == north or south, which is false.

2. Step 2: Evaluate description() method

   Switch on east returns "Right" string.

3. Final Answer:

   false Right -> Option A

4. Quick Check:

   east isVertical = false, description = Right [OK]

Hint: Check enum case matches in computed property and switch [OK]

Common Mistakes:

• Assuming east is vertical
• Confusing method return values with case names
• Forgetting to call method with parentheses

4. This Swift enum code has an error:

enum Status {
    case success, failure

    var message: String {
        switch self {
        case .success:
            return "Success"
        case .failure
            return "Failure"
        }
    }
}

What is the error and how to fix it?

medium

A. Computed property must be a function; change to func message() -> String

B. Missing colon after case .failure; add ':' after .failure

C. Enum cases must have raw values; add raw values to cases

D. Return statements are not allowed in computed properties; remove returns

Solution

1. Step 1: Identify syntax error in switch cases

   Case .failure is missing a colon ':' after it, causing a syntax error.

2. Step 2: Fix the syntax

   Add ':' after case .failure to correct the switch syntax.

3. Final Answer:

   Missing colon after case .failure; add ':' after .failure -> Option B

4. Quick Check:

   Switch case syntax requires ':' [OK]

Hint: Switch cases must end with a colon ':' [OK]

Common Mistakes:

• Thinking computed properties need func keyword
• Adding raw values unnecessarily
• Removing return statements inside computed properties

5. You want to create an enum Light with cases red, yellow, and green. Add a computed property time that returns the duration in seconds for each light: red = 30, yellow = 5, green = 25. Also add a method next() that returns the next light in the traffic cycle (red -> green -> yellow -> red). Which implementation is correct?

hard

A. enum Light {
case red, yellow, green

var time: Int {
switch self {
case .red: return 30
case .yellow: return 5
case .green: return 25
}
}

func next() -> Light {
switch self {
case .red: return .green
case .green: return .yellow
case .yellow: return .red
}
}
}

B. enum Light {
case red, yellow, green

func time() -> Int {
if self == .red { return 30 }
else if self == .yellow { return 5 }
else { return 25 }
}

func next() -> Light {
if self == .red { return .yellow }
else if self == .yellow { return .green }
else { return .red }
}
}

C. enum Light {
case red, yellow, green

var time: Int {
if self == .red { return 30 }
else if self == .yellow { return 5 }
else { return 25 }
}

func next() -> Light {
switch self {
case .red: return .yellow
case .yellow: return .green
case .green: return .red
}
}
}

D. enum Light {
case red, yellow, green

var time: Int {
switch self {
case .red: return 25
case .yellow: return 30
case .green: return 5
}
}

func next() -> Light {
switch self {
case .red: return .green
case .green: return .yellow
case .yellow: return .red
}
}
}

Solution

1. Step 1: Check computed property time values

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } correctly returns 30 for red, 5 for yellow, and 25 for green as required.

2. Step 2: Check next() method cycle order

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } cycles red -> green -> yellow -> red, matching the problem statement.

3. Final Answer:

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } -> Option A

4. Quick Check:

   Correct time values and cycle order = enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } [OK]

Hint: Match switch cases exactly to problem requirements [OK]

Common Mistakes:

• Mixing up time values for colors
• Incorrect next() cycle order
• Using func instead of computed property for time