Enum declaration and cases in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an enum in Swift?

An enum (short for enumeration) is a way to group related values under a common type. It helps organize options or choices in your code.

beginner

How do you declare an enum with cases in Swift?

Use the enum keyword, then list cases inside curly braces. For example:

enum Direction {
  case north
  case south
  case east
  case west
}

intermediate

Can enum cases have associated values in Swift?

Yes! Enum cases can store extra information called associated values. For example:

enum Barcode {
  case upc(Int, Int, Int, Int)
  case qrCode(String)
}

beginner

How do you use an enum case in Swift code?

You create a value by writing the enum name, a dot, then the case name. For example:<br><pre>let direction = Direction.north</pre>

beginner

What is the benefit of using enums instead of strings or numbers for fixed options?

Enums make your code safer and clearer. They prevent mistakes like typos and make it easy to see all possible options in one place.

How do you declare an enum named Color with cases red, green, and blue in Swift?

A enum Color { case red, green, blue }

B class Color { var red, green, blue }

C struct Color { let red, green, blue }

D enum Color = [red, green, blue]

Option A correctly declares an enum with three cases using the enum keyword and case syntax.

Which of these is a valid way to create a value of enum Direction with case east?

A let d = Direction->east

B let d = Direction.east

C let d = Direction[east]

D let d = Direction.east()

You create enum values by writing the enum name, a dot, then the case name without parentheses.

Can enum cases in Swift have extra data attached?

A Only if declared as classes

B No, enums only hold fixed names

C Yes, but only strings

D Yes, using associated values

Swift enums can have associated values of any type attached to cases.

What keyword starts an enum declaration in Swift?

A enum

B class

C struct

D case

The enum keyword is used to declare an enumeration.

Why use enums instead of strings for fixed options?

A Because enums use less memory

B Because strings are slower

C To avoid typos and improve code clarity

D Because strings cannot be compared

Enums help prevent mistakes like typos and make code easier to understand.

Explain how to declare an enum with multiple cases in Swift and how to create a value from it.

Think about the basic syntax and how you pick a case.

Describe what associated values are in Swift enums and give an example.

Imagine a case that holds more than just a name.

Practice

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

easy

A. To group related values under one name

B. To create a function

C. To declare a variable

D. To write a loop

Solution

1. Step 1: Understand what enums represent

   Enums group related values together to make code clearer and safer.

2. Step 2: Compare options with enum purpose

   Only To group related values under one name correctly describes grouping related values under one name.

3. Final Answer:

   To group related values under one name -> Option A

4. Quick Check:

   Enum purpose = Group related values [OK]

Hint: Enums group related values clearly and safely [OK]

Common Mistakes:

• Confusing enums with functions
• Thinking enums declare variables
• Mixing enums with loops

2. Which of the following is the correct way to declare an enum named Direction with cases north, south, east, and west?

easy

A. enum Direction = { north, south, east, west }

B. enum Direction: north, south, east, west {}

C. enum Direction { case north, south, east, west }

D. enum Direction { north; south; east; west }

Solution

1. Step 1: Recall Swift enum syntax

   Enums use the keyword enum, followed by the name and curly braces containing case declarations separated by commas.

2. Step 2: Check each option's syntax

   enum Direction { case north, south, east, west } uses correct syntax: enum Direction { case north, south, east, west }. Others use invalid syntax.

3. Final Answer:

   enum Direction { case north, south, east, west } -> Option C

4. Quick Check:

   Correct enum syntax = enum Direction { case north, south, east, west } [OK]

Hint: Use 'case' keyword with comma-separated values inside braces [OK]

Common Mistakes:

• Using '=' instead of braces
• Omitting 'case' keyword
• Separating cases with semicolons

3. What will be the output of this Swift code?

enum Light {
    case red, yellow, green
}

let current = Light.red
switch current {
case .red:
    print("Stop")
case .yellow:
    print("Caution")
case .green:
    print("Go")
}

medium

A. No output

B. Go

C. Caution

D. Stop

Solution

1. Step 1: Identify the enum case assigned

   The variable current is assigned Light.red.

2. Step 2: Match the switch case for current

   The switch matches .red and prints "Stop".

3. Final Answer:

   Stop -> Option D

4. Quick Check:

   Light.red triggers "Stop" output [OK]

Hint: Match enum case in switch to get output [OK]

Common Mistakes:

• Confusing enum cases with strings
• Forgetting dot prefix in switch
• Assuming default output

4. Identify the error in this enum declaration:

enum Weather {
    case sunny
    case rainy
    case windy
    case
}

medium

A. Missing case name after 'case' keyword

B. Enum name is invalid

C. Curly braces are missing

D. Enum cases should be strings

Solution

1. Step 1: Review each enum case line

   The last line has case without a case name, which is invalid syntax.

2. Step 2: Confirm other parts are correct

   Enum name and braces are correct; cases do not need to be strings.

3. Final Answer:

   Missing case name after 'case' keyword -> Option A

4. Quick Check:

   Every 'case' must have a name [OK]

Hint: Each 'case' must have a name after it [OK]

Common Mistakes:

• Leaving 'case' empty
• Thinking cases need quotes
• Missing braces around enum

5. You want to create an enum Planet with cases for mercury, venus, and earth. Then, write a function that returns a friendly message for each planet. Which code correctly implements this?

hard

A. enum Planet { mercury, venus, earth }
func message(planet: Planet) -> String {
if planet == mercury { return "Closest to the Sun" }
else if planet == venus { return "Second planet" }
else { return "Our home" }
}

B. enum Planet { case mercury, venus, earth }
func message(for planet: Planet) -> String {
switch planet {
case .mercury: return "Closest to the Sun"
case .venus: return "Second planet"
case .earth: return "Our home"
}
}

C. enum Planet { case mercury, venus, earth }
func message(planet: Planet) -> String {
if planet == mercury { return "Closest to the Sun" }
else if planet == venus { return "Second planet" }
else { return "Our home" }
}

D. enum Planet { case mercury, venus, earth }
func message(for planet: Planet) -> String {
switch planet {
case mercury: return "Closest to the Sun"
case venus: return "Second planet"
case earth: return "Our home"
}
}

Solution

1. Step 1: Check enum declaration syntax

   Options A, C, and D declare enum correctly with case keyword; B misses it, so B is invalid.

2. Step 2: Check function parameter and switch usage

   enum Planet { case mercury, venus, earth } func message(for planet: Planet) -> String { switch planet { case .mercury: return "Closest to the Sun" case .venus: return "Second planet" case .earth: return "Our home" } } uses switch with dot syntax for cases and correct function signature. enum Planet { case mercury, venus, earth } func message(planet: Planet) -> String { if planet == mercury { return "Closest to the Sun" } else if planet == venus { return "Second planet" } else { return "Our home" } } uses if-else without dot syntax (.mercury), causing compile error. enum Planet { case mercury, venus, earth } func message(for planet: Planet) -> String { switch planet { case mercury: return "Closest to the Sun" case venus: return "Second planet" case earth: return "Our home" } } misses dot prefix in switch cases, causing error.

3. Final Answer:

   enum Planet { case mercury, venus, earth } func message(for planet: Planet) -> String { switch planet { case .mercury: return "Closest to the Sun" case .venus: return "Second planet" case .earth: return "Our home" } } -> Option B

4. Quick Check:

   Enum with 'case' and switch with dot cases [OK]

Hint: Use 'case' keyword and dot prefix in switch cases [OK]

Common Mistakes:

• Omitting 'case' keyword in enum
• Missing dot prefix in switch cases
• Using if without dot prefix for enum cases