Enums with data in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an enum variant with a single integer value.

Rust

enum Message {
    Quit,
    Move [1] i32,
}

Drag options to blanks, or click blank then click option'

A{

B[

C(

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets or curly braces instead of parentheses for enum data.

The enum variant Move holds a single i32 value, so it needs parentheses () around the data.

2fill in blank

medium

Complete the code to create an enum variant that holds two values: an integer and a boolean.

Rust

enum Status {
    Active(i32, [1]),
    Inactive,
}

Drag options to blanks, or click blank then click option'

AString

Bchar

Cf64

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using String or other types instead of bool for boolean data.

The Active variant holds an i32 and a bool value, so the second type must be bool.

3fill in blank

hard

Fix the error in the enum variant definition that holds a named field.

Rust

enum Shape {
    Circle [1] radius: f64,
    Square { side: f64 },
}

Drag options to blanks, or click blank then click option'

A{

B[

C(

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of curly braces for named fields.

Named fields in enum variants require curly braces {} around the fields.

4fill in blank

hard

Fill both blanks to define an enum variant with named fields for width and height.

Rust

enum Rectangle {
    Rect [1] width: u32, [2] height: u32 },
}

Drag options to blanks, or click blank then click option'

A{

B:

C,

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Using colons or semicolons instead of commas between fields.

Not using curly braces to start named fields.

The variant uses curly braces {} to start named fields, and fields are separated by commas ,.

5fill in blank

hard

Fill all three blanks to create a function that matches an enum with data and returns a string describing it.

Rust

fn describe(msg: Message) -> String {
    match msg {
        Message::Quit => String::from("Quit"),
        Message::Move [1] x, y [2] => {
            format!("Move to ([3], {})", x, y)
        }
    }
}

Drag options to blanks, or click blank then click option'

A(

B)

C,

D{

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces or missing commas in the pattern.

Incorrectly placing parentheses.

The Move variant pattern uses parentheses ( ) to hold the two values x and y, separated by a comma.

Practice

1. What is the main purpose of enums with data in Rust?

easy

A. To group related values that can be different types under one name

B. To create multiple copies of the same data

C. To perform arithmetic operations on numbers

D. To store only strings in a list

Solution

1. Step 1: Understand what enums with data do

   Enums with data allow each variant to hold different types or amounts of data, grouping related but different information.

2. Step 2: Compare options with this understanding

   Only To group related values that can be different types under one name correctly describes grouping related values of different types under one name.

3. Final Answer:

   To group related values that can be different types under one name -> Option A

4. Quick Check:

   Enums with data = group different types [OK]

Hint: Enums group different data types under one name [OK]

Common Mistakes:

• Thinking enums only store one data type
• Confusing enums with arrays or vectors
• Assuming enums perform calculations

2. Which of the following is the correct syntax to define an enum variant with data in Rust?

easy

A. enum Color { Red(u8, u8, u8), Blue }

B. enum Color { Red = (u8, u8, u8), Blue }

C. enum Color { Red: (u8, u8, u8), Blue }

D. enum Color { Red -> (u8, u8, u8), Blue }

Solution

1. Step 1: Recall enum variant syntax with data

   In Rust, enum variants with data are defined by listing the variant name followed by parentheses containing the data types.

2. Step 2: Check each option

   enum Color { Red(u8, u8, u8), Blue } uses correct syntax: Red(u8, u8, u8). Options A, B, and C use invalid syntax with ->, =, or : which are incorrect for enum variant data.

3. Final Answer:

   enum Color { Red(u8, u8, u8), Blue } -> Option A

4. Quick Check:

   Variant with data uses parentheses () [OK]

Hint: Use parentheses () after variant name for data [OK]

Common Mistakes:

• Using = instead of () for variant data
• Using : or -> which are invalid here
• Forgetting parentheses for data

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

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

fn main() {
    let msg = Message::Move { x: 10, y: 20 };
    match msg {
        Message::Quit => println!("Quit"),
        Message::Move { x, y } => println!("Move to {}, {}", x, y),
        Message::Write(text) => println!("Write {}", text),
    }
}

medium

A. Compilation error

B. Quit

C. Write 10, 20

D. Move to 10, 20

Solution

1. Step 1: Identify the enum variant used

   The variable msg is assigned Message::Move with x=10 and y=20.

2. Step 2: Match arms and output

   The match statement checks msg. For Message::Move, it prints "Move to {}, {}" with x and y values, so output is "Move to 10, 20".

3. Final Answer:

   Move to 10, 20 -> Option D

4. Quick Check:

   Match Message::Move prints coordinates [OK]

Hint: Match variant and print its data fields [OK]

Common Mistakes:

• Confusing variant names
• Expecting Quit or Write output
• Thinking code won't compile

4. The following Rust code has an error. What is the problem?

enum Shape {
    Circle(f64),
    Rectangle { width: f64, height: f64 },
}

fn area(shape: Shape) -> f64 {
    match shape {
        Shape::Circle(radius) => 3.14 * radius * radius,
        Shape::Rectangle(width, height) => width * height,
    }
}

medium

A. Missing semicolon after match arms

B. Circle variant should have named fields

C. Incorrect pattern for Rectangle variant in match

D. Function return type should be i32

Solution

1. Step 1: Check enum variant definitions

   Circle has tuple data (f64), Rectangle has named fields { width, height }.

2. Step 2: Check match patterns

   Circle pattern is correct. Rectangle pattern uses (width, height) which is wrong; it should use { width, height } to match named fields.

3. Final Answer:

   Incorrect pattern for Rectangle variant in match -> Option C

4. Quick Check:

   Match named fields with braces {} [OK]

Hint: Match named fields with braces {}, tuple fields with () [OK]

Common Mistakes:

• Using parentheses for named fields
• Ignoring pattern mismatch errors
• Changing return type unnecessarily

5. Given this enum and function, what is the output?

enum Event {
    Click { x: i32, y: i32 },
    KeyPress(char),
    Resize(u32, u32),
}

fn describe(event: Event) -> String {
    match event {
        Event::Click { x, y } if x > 0 && y > 0 => format!("Clicked at positive coords: {}, {}", x, y),
        Event::Click { .. } => "Clicked at non-positive coords".to_string(),
        Event::KeyPress(c) if c.is_alphabetic() => format!("Key pressed: {}", c),
        Event::KeyPress(_) => "Non-alphabetic key pressed".to_string(),
        Event::Resize(w, h) if w == h => "Resized to square".to_string(),
        Event::Resize(_, _) => "Resized to rectangle".to_string(),
    }
}

fn main() {
    let e = Event::Resize(100, 100);
    println!("{}", describe(e));
}

hard

A. Clicked at positive coords: 100, 100

B. Resized to square

C. Resized to rectangle

D. Non-alphabetic key pressed

Solution

1. Step 1: Identify the enum variant and values

   The event is Event::Resize with width=100 and height=100.

2. Step 2: Match arms with conditions

   The Resize arm with condition w == h matches because 100 == 100, so it returns "Resized to square".

3. Final Answer:

   Resized to square -> Option B

4. Quick Check:

   Resize with equal sides = square [OK]

Hint: Check match guards (if conditions) carefully [OK]

Common Mistakes:

• Ignoring if conditions in match arms
• Confusing Resize with Click variant
• Assuming default arm without conditions