Raw values for enums in Swift

Introduction

Raw values let you give each option in an enum a fixed, simple value like a number or a word. This helps you connect enum options to real data easily.

When you want to assign a specific number or string to each choice in a list.

When you need to save or load enum values from files or databases.

When you want to compare enum options with simple values.

When you want to print or show enum options as readable text.

When you want to convert between enum options and their raw values quickly.

Syntax

Swift

enum EnumName: RawValueType {
    case option1 = rawValue1
    case option2 = rawValue2
    // more cases
}

The RawValueType can be Int, String, or other simple types.

Each case must have a unique raw value of the specified type.

Examples

Each direction has a short string as its raw value.

Swift

enum Direction: String {
    case north = "N"
    case south = "S"
    case east = "E"
    case west = "W"
}

Raw values start at 1 for Monday and automatically increase by 1 for the next days.

Swift

enum Weekday: Int {
    case monday = 1
    case tuesday
    case wednesday
    case thursday
    case friday
}

Sample Program

This program shows how to get the raw value from an enum case and how to create an enum case from a raw value.

Swift

enum Fruit: String {
    case apple = "A"
    case banana = "B"
    case cherry = "C"
}

let favorite = Fruit.banana
print("My favorite fruit raw value is \(favorite.rawValue)")

if let fruitFromRaw = Fruit(rawValue: "C") {
    print("Fruit from raw value 'C' is \(fruitFromRaw.rawValue)")
} else {
    print("No fruit found for that raw value")
}

Important Notes

You can create an enum case from a raw value using the initializer EnumName(rawValue: value). It returns an optional because the raw value might not match any case.

If you don't assign raw values explicitly for Int enums, Swift assigns them starting from 0 by default.

Summary

Raw values give enum cases fixed simple values like strings or numbers.

They help convert between enum cases and data easily.

Use raw values when you want to save, compare, or display enum options clearly.

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