Raw values for enums in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a raw value in a Swift enum?

A raw value is a constant value of a specific type (like String or Int) that each enum case can have. It lets you assign a fixed value to each case.

beginner

How do you declare an enum with raw values in Swift?

You add a type after the enum name, like enum Direction: String, then assign raw values to each case, e.g., case north = "N".

intermediate

Can raw values be of any type in Swift enums?

No, raw values must be of a literal type like String, Int, or Character. You cannot use complex types like arrays or dictionaries as raw values.

beginner

How do you access the raw value of an enum case?

Use the .rawValue property on the enum case. For example, Direction.north.rawValue returns the raw value assigned to north.

intermediate

How can you create an enum case from a raw value?

Use the initializer EnumType(rawValue: value). It returns an optional enum case matching the raw value or nil if no match is found.

Which of these is a valid raw value type for a Swift enum?

A Array

B String

C Dictionary

D Class

Raw values must be literal types like String, Int, or Character. Arrays, dictionaries, and classes are not allowed.

How do you declare an enum with Int raw values starting from 1?

A enum Number: String { case one = "1", two, three }

B enum Number { case one = 1, two, three }

C enum Number: Int { case one = 1, two, three }

D enum Number: Int { case one, two, three }

You specify the raw value type after the enum name and assign the first case a raw value. The rest auto-increment.

What does Direction(rawValue: "N") return if Direction enum has a case with raw value "N"?

A The enum case matching "N"

B nil

C A string "N"

D An error

The initializer returns the enum case that has the raw value "N" or nil if none matches.

What is the type of Direction.north.rawValue if Direction is declared as enum Direction: String?

A String

B Direction

C Int

D Optional String

The rawValue property returns the raw value type, which is String in this case.

Can you assign different raw value types to different cases in the same enum?

A Only if the enum is generic

B Yes, each case can have its own type

C Only if you use associated values

D No, all cases must have the same raw value type

All enum cases must share the same raw value type declared for the enum.

Explain what raw values are in Swift enums and how to use them.

Think about fixed values assigned to enum cases.

Describe the difference between raw values and associated values in Swift enums.

Consider how each enum case stores data.

Practice

1. What is the purpose of raw values in Swift enums?

easy

A. To allow enums to inherit from classes

B. To assign fixed simple values like strings or numbers to enum cases

C. To make enums mutable after declaration

D. To create functions inside enums

Solution

1. Step 1: Understand what raw values are

   Raw values are fixed values assigned to enum cases, like strings or numbers.

2. Step 2: Identify the purpose of raw values

   They help convert enum cases to simple data types for saving or displaying.

3. Final Answer:

   To assign fixed simple values like strings or numbers to enum cases -> Option B

4. Quick Check:

   Raw values = fixed simple values [OK]

Hint: Raw values give enums fixed simple data like strings or numbers [OK]

Common Mistakes:

• Thinking raw values make enums mutable
• Confusing raw values with associated values
• Believing enums can inherit from classes

2. Which of the following is the correct syntax to declare an enum with raw values in Swift?

easy

A. enum Direction: Int { case north; case south }

B. enum Direction { case north = "N" case south = "S" }

C. enum Direction: String { case north = "N" case south = "S" }

D. enum Direction: String { north = "N", south = "S" }

Solution

1. Step 1: Check enum declaration with raw values

   Raw values require specifying the type after enum name, e.g., : String.

2. Step 2: Verify correct case syntax

   Cases use 'case name = value' syntax, separated by new lines or semicolons.

3. Final Answer:

   enum Direction: String { case north = "N" case south = "S" } -> Option C

4. Quick Check:

   Raw value enum syntax = enum Direction: String { case north = "N" case south = "S" } [OK]

Hint: Raw value enums need type after name and '=' for values [OK]

Common Mistakes:

• Omitting the raw value type after enum name
• Using commas instead of separate case lines
• Assigning raw values without specifying type

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

enum Weekday: Int {
    case monday = 1
    case tuesday
    case wednesday
}
print(Weekday.tuesday.rawValue)

medium

A. 1

B. Error: rawValue not found

C. 3

D. 2

Solution

1. Step 1: Understand raw value auto-increment

   When the first case has a raw value (1), following cases auto-increment by 1.

2. Step 2: Identify raw value of 'tuesday'

   Since monday = 1, tuesday = 2, wednesday = 3.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Auto-increment raw values = 2 [OK]

Hint: Raw Int values auto-increment from first assigned value [OK]

Common Mistakes:

• Assuming all raw values must be explicitly assigned
• Confusing rawValue with case index
• Expecting an error when accessing rawValue

4. Identify the error in this enum declaration:

enum Color: String {
    case red = 1
    case green = "Green"
    case blue = "Blue"
}

medium

A. Raw values must all be of the declared type String

B. Enum cases cannot have raw values

C. Raw values must be integers only

D. Missing semicolon after each case

Solution

1. Step 1: Check raw value type consistency

   The enum declares raw type String, so all raw values must be strings.

2. Step 2: Identify the incorrect raw value

   Case 'red' has raw value 1 (an Int), which conflicts with String type.

3. Final Answer:

   Raw values must all be of the declared type String -> Option A

4. Quick Check:

   Raw values must match enum type [OK]

Hint: All raw values must match enum's declared raw type [OK]

Common Mistakes:

• Mixing raw value types in one enum
• Thinking semicolons are required after cases
• Believing enums can't have raw values

5. Given this enum:

enum StatusCode: Int {
    case success = 200
    case notFound = 404
    case serverError = 500
}

func message(for code: Int) -> String {
    if let status = StatusCode(rawValue: code) {
        switch status {
        case .success: return "OK"
        case .notFound: return "Not Found"
        case .serverError: return "Server Error"
        }
    } else {
        return "Unknown"
    }
}

print(message(for: 404))
print(message(for: 201))

What is the output?

hard

A. Not Found
Unknown

B. OK
Unknown

C. Not Found
Server Error

D. Error at runtime

Solution

1. Step 1: Understand rawValue initializer

   StatusCode(rawValue: 404) returns .notFound; 201 returns nil.

2. Step 2: Trace function output for each input

   For 404, returns "Not Found"; for 201, returns "Unknown".

3. Final Answer:

   Not Found Unknown -> Option A

4. Quick Check:

   Raw value init maps code to enum or nil [OK]

Hint: Raw value init returns nil if no matching case [OK]

Common Mistakes:

• Assuming rawValue init always returns a case
• Confusing rawValue with case index
• Expecting runtime error for unknown raw value