Why Raw values for enums in Swift? - Purpose & Use Cases

The Big Idea

What if you could stop juggling confusing numbers and let your code remember them perfectly for you?

The Scenario

Imagine you have a list of colors, and you want to assign each color a number or a string to identify it. You write separate variables for each color and its value. When you want to check or use these values, you have to remember each one and write extra code to match them.

The Problem

This manual way is slow and confusing. If you add or change a color, you must update many places. It's easy to make mistakes, like mixing up numbers or forgetting to update a value. Your code becomes messy and hard to read.

The Solution

Using raw values for enums lets you group related values together with clear names and automatic links to their raw data. You write less code, avoid errors, and your program understands the connection between names and values easily.

Before vs After

✗ Before

let red = 1
let green = 2
let blue = 3
// Need to remember these numbers everywhere

✓ After

enum Color: Int {
    case red = 1
    case green = 2
    case blue = 3
}
// Use Color.red.rawValue to get 1

What It Enables

This makes your code cleaner and lets you easily convert between names and values, making your programs smarter and less error-prone.

Real Life Example

Think of a traffic light system where each light color has a number code. Using raw values in enums helps you manage these codes clearly and safely in your app.

Key Takeaways

Manual value management is slow and error-prone.

Raw values in enums link names to values automatically.

This simplifies code and reduces mistakes.

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