Enum methods and computed properties in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an enum method in Swift?

An enum method is a function defined inside an enum that can perform actions or return values related to the enum cases. It helps organize behavior specific to the enum.

beginner

What is a computed property in a Swift enum?

A computed property calculates and returns a value each time it is accessed, instead of storing a value. In enums, it can provide extra information based on the current case.

intermediate

How do you define a computed property inside a Swift enum?

You define it like a variable with the keyword var and provide a get block or just return a value directly without storing it.

intermediate

Can enum methods in Swift modify the enum's cases?

No, enum methods cannot change the enum's cases because enums are value types and their cases are fixed. Methods can return new values or perform calculations but not alter the case itself.

beginner

Give an example of a computed property in a Swift enum that returns a description string.

Example:

enum Direction {
  case north, south, east, west
  var description: String {
    switch self {
    case .north: return "Up"
    case .south: return "Down"
    case .east: return "Right"
    case .west: return "Left"
    }
  }
}

What keyword is used to define a computed property in a Swift enum?

A var

B let

C func

D enum

Computed properties are defined using the var keyword because they behave like variables that compute their value.

Can enum methods in Swift change the enum case itself?

A Only for raw value enums

B Yes, always

C Only if marked mutating

D No, enum cases are fixed

Enum cases are fixed and cannot be changed by methods. Methods can return new values but cannot modify the enum case.

Which of the following is a valid use of a computed property in an enum?

A Calculating a value based on the current case

B Changing the enum case

C Storing a value permanently

D Defining a new enum case

Computed properties calculate and return values dynamically based on the enum's current case.

How do you access a computed property in a Swift enum?

A By using square brackets

B By calling it like a function with parentheses

C By using dot notation without parentheses

D By importing a special library

Computed properties are accessed like variables using dot notation without parentheses.

What is the purpose of adding methods inside a Swift enum?

A To store extra data permanently

B To add behavior related to enum cases

C To change the enum's raw values

D To create new enum cases dynamically

Methods inside enums help organize behavior and actions related to the enum cases.

Explain how computed properties work inside Swift enums and give an example.

Think about a variable that calculates its value each time you ask for it.

Describe the role of methods inside Swift enums and why they are useful.

Consider how you might add actions related to each enum case.

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