Raw values for enums in Swift - Mini Project: Build & Apply

Raw values for enums

📖 Scenario: Imagine you are creating a simple app that needs to represent different types of fruits with specific codes. You want to use Swift enums with raw values to assign each fruit a unique code.

🎯 Goal: Build a Swift program that defines an enum with raw values for fruits and prints the raw value of a selected fruit.

📋 What You'll Learn

Create an enum called Fruit with raw values of type String

Include these fruits with exact raw values: apple = "A01", banana = "B02", cherry = "C03"

Create a variable called selectedFruit and assign it the enum case .banana

Print the raw value of selectedFruit using print

💡 Why This Matters

🌍 Real World

Enums with raw values are useful for representing fixed sets of related values with associated codes, like product categories, error codes, or status flags.

💼 Career

Understanding enums with raw values is important for Swift developers working on iOS apps, as it helps organize data clearly and safely.

1

Create the Fruit enum with raw values

Create an enum called Fruit with raw values of type String. Add these cases with exact raw values: apple = "A01", banana = "B02", cherry = "C03".

Swift

# Your code here to create the Fruit enum with raw String raw values

Hint

Use enum Fruit: String and assign raw values with =.

2

Create a variable for the selected fruit

Create a variable called selectedFruit and assign it the enum case .banana from the Fruit enum.

Swift

enum Fruit: String {
    case apple = "A01"
    case banana = "B02"
    case cherry = "C03"
}

# Your code here to create selectedFruit variable assigned to .banana

Hint

Use var selectedFruit = Fruit.banana to assign the enum case.

3

Access the raw value of the selected fruit

Create a constant called fruitCode and assign it the raw value of selectedFruit using the rawValue property.

Swift

enum Fruit: String {
    case apple = "A01"
    case banana = "B02"
    case cherry = "C03"
}

var selectedFruit = Fruit.banana

# Your code here to create fruitCode constant with selectedFruit.rawValue

Hint

Use let fruitCode = selectedFruit.rawValue to get the raw value string.

4

Print the raw value of the selected fruit

Use print to display the value of fruitCode.

Swift

enum Fruit: String {
    case apple = "A01"
    case banana = "B02"
    case cherry = "C03"
}

var selectedFruit = Fruit.banana

let fruitCode = selectedFruit.rawValue

# Your code here to print fruitCode

Hint

Use print(fruitCode) to show the raw value.

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