Match with enums in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of matching enum variants with data

What is the output of this Rust program?

Rust

enum Status {
    Success(u8),
    Error(String),
    Pending,
}

fn main() {
    let s = Status::Success(200);
    match s {
        Status::Success(code) => println!("Code: {}", code),
        Status::Error(msg) => println!("Error: {}", msg),
        Status::Pending => println!("Pending..."),
    }
}

A Code: Success(200)

B Error: 200

C Pending...

D Code: 200

💡 Hint

Look at how the match extracts the inner value from the Success variant.

The match arm Status::Success(code) extracts the inner u8 value 200 and prints it with the label 'Code:'.

❓ Predict Output

intermediate

Matching nested enums with multiple patterns

What will this Rust program print?

Rust

enum Direction {
    Left,
    Right,
}

enum Command {
    Move(Direction),
    Stop,
}

fn main() {
    let cmd = Command::Move(Direction::Right);
    match cmd {
        Command::Move(Direction::Left) => println!("Moving left"),
        Command::Move(Direction::Right) => println!("Moving right"),
        Command::Stop => println!("Stopped"),
    }
}

A Moving right

B Moving left

C Stopped

D Compile error

💡 Hint

Check which Direction variant is inside the Command::Move variant.

The variable cmd is Command::Move(Direction::Right), so the match arm prints 'Moving right'.

🔧 Debug

advanced

Identify the error in matching enum with missing variant

What error will this Rust code produce when compiled?

Rust

enum Light {
    Red,
    Yellow,
    Green,
}

fn main() {
    let light = Light::Yellow;
    match light {
        Light::Red => println!("Stop"),
        Light::Green => println!("Go"),
    }
}

A Prints nothing

B Runtime panic: no matching pattern found

C Compile error: non-exhaustive patterns in match

D Compile error: unused variable 'light'

💡 Hint

Rust requires all enum variants to be matched or covered by a wildcard.

The match does not cover Light::Yellow variant, so the compiler reports a non-exhaustive patterns error.

📝 Syntax

advanced

Correct syntax for matching enum with data

Which option correctly matches and extracts data from this enum variant?

Rust

enum Message {
    Text(String),
    Quit,
}

fn main() {
    let msg = Message::Text(String::from("Hello"));
    match msg {
        // Fill in the correct pattern here
    }
}

A Message::Text(text) => println!(text),

B Message::Text(text) => println!("Text: {}", text),

C Message::Text(text) { println!("Text: {}", text); },

D Message::Text => println!("Text: {}", text),

💡 Hint

The pattern must bind the inner String to a variable and use it in println! macro.

Option B correctly matches Message::Text and binds the inner String to 'text', then prints it with a label.

🚀 Application

expert

Determine the final value after matching and updating enum

Given this Rust code, what is the final value of 'status' after the match block?

Rust

enum Status {
    Active(i32),
    Inactive,
}

fn main() {
    let mut status = Status::Active(10);
    match &mut status {
        Status::Active(ref mut val) if *val > 5 => *val += 5,
        Status::Active(_) => (),
        Status::Inactive => status = Status::Active(1),
    }
    // What is the value of status here?
}

A Status::Active(15)

B Status::Active(10)

C Status::Active(1)

D Status::Inactive

💡 Hint

The match uses a guard to check if the value is greater than 5 and updates it.

The initial value is Active(10), which matches the first arm with guard val > 5, so val is increased by 5 to 15.

Practice

1.

What does the match statement do when used with enums in Rust?

easy

A. It checks the enum variant and runs the matching code block.

B. It converts the enum into a string automatically.

C. It creates a new enum variant.

D. It deletes the enum variant from memory.

Solution

1. Step 1: Understand the purpose of match with enums

   The match statement compares the enum value against each variant.

2. Step 2: Identify what happens on a match

   When a variant matches, the corresponding code block runs.

3. Final Answer:

   It checks the enum variant and runs the matching code block. -> Option A

4. Quick Check:

   Match runs code by enum variant [OK]

Hint: Match arms correspond to enum variants directly [OK]

Common Mistakes:

• Thinking match converts enums to strings
• Assuming match creates or deletes variants
• Confusing match with if-else statements

2.

Which of the following is the correct syntax to match an enum Color with variants Red, Green, and Blue?

enum Color { Red, Green, Blue }

easy

A. match color { Color.Red => {}, Color.Green => {}, Color.Blue => {} }

B. match color { Red => {}, Green => {}, Blue => {} }

C. match color { Color::Red => {}, Color::Green => {}, Color::Blue => {} }

D. match color { 'Red' => {}, 'Green' => {}, 'Blue' => {} }

Solution

1. Step 1: Recall enum variant syntax in match

   Enum variants must be prefixed with the enum name and double colon, like Color::Red.

2. Step 2: Check each option's syntax

   Only match color { Color::Red => {}, Color::Green => {}, Color::Blue => {} } uses the correct Color::Variant syntax.

3. Final Answer:

   match color { Color::Red => {}, Color::Green => {}, Color::Blue => {} } -> Option C

4. Quick Check:

   Enum variants use EnumName::Variant [OK]

Hint: Use EnumName::Variant in match arms [OK]

Common Mistakes:

• Omitting enum name prefix
• Using dot instead of double colon
• Using strings instead of variants

3.

What will be the output of this Rust code?

enum Direction { North, South, East, West }

fn main() {
    let dir = Direction::East;
    let message = match dir {
        Direction::North => "Going up",
        Direction::South => "Going down",
        Direction::East => "Going right",
        Direction::West => "Going left",
    };
    println!("{}", message);
}

medium

A. Going right

B. Going up

C. Going left

D. Going down

Solution

1. Step 1: Identify the enum variant assigned

   The variable dir is set to Direction::East.

2. Step 2: Match dir to the correct message

   The match arm for Direction::East returns "Going right".

3. Final Answer:

   Going right -> Option A

4. Quick Check:

   Direction::East matches "Going right" [OK]

Hint: Match returns value for the exact enum variant [OK]

Common Mistakes:

• Mixing up enum variants and their messages
• Forgetting to use EnumName::Variant in match
• Assuming default or fallback arm runs

4.

Find the error in this Rust code snippet using match with enums:

enum Status { Success, Failure }

fn check(status: Status) {
    match status {
        Status::Success => println!("Success"),
        // Missing Failure arm
    }
}

medium

A. Missing semicolon after println! macro

B. Function check should return a value

C. Incorrect enum variant syntax

D. Missing match arm for Status::Failure

Solution

1. Step 1: Check completeness of match arms

   The match statement covers Status::Success but misses Status::Failure.

2. Step 2: Understand Rust's exhaustiveness requirement

   Rust requires all enum variants to be matched or a catch-all arm (_) to avoid compile errors.

3. Final Answer:

   Missing match arm for Status::Failure -> Option D

4. Quick Check:

   All enum variants must be matched [OK]

Hint: Match must cover all enum variants or use _ arm [OK]

Common Mistakes:

• Leaving out enum variants in match arms
• Assuming partial match compiles
• Confusing semicolon placement with match completeness

5.

Given this enum with data:

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
    ChangeColor(i32, i32, i32),
}

Which match arm correctly extracts the x and y values from Message::Move?

hard

A. Message::Move(x, y) => println!("x: {}, y: {}", x, y),

B. Message::Move { x, y } => println!("x: {}, y: {}", x, y),

C. Message::Move(x: x, y: y) => println!("x: {}, y: {}", x, y),

D. Message::Move(x: x, y) => println!("x: {}, y: {}", x, y),

Solution

1. Step 1: Identify the enum variant with named fields

   Move uses named fields { x: i32, y: i32 }.

2. Step 2: Match syntax for named fields

   Use Message::Move { x, y } to destructure named fields directly.

3. Final Answer:

   Message::Move { x, y } => println!("x: {}, y: {}", x, y), -> Option B

4. Quick Check:

   Named fields use braces and field names [OK]

Hint: Use braces and field names to destructure named fields [OK]

Common Mistakes:

• Using tuple pattern for struct-like variant
• Mixing colon syntax incorrectly
• Omitting braces for named fields