Custom error types in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a custom error enum named MyError.

Rust

#[derive(Debug)]
enum MyError {
    [1]
}

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AIoError(std::io::Error)

BError(String)

CMyErrorType

DCustomError

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variant name without data when a message is needed

Trying to use a type name as a variant

The enum variant Error(String) defines a custom error variant holding a string message.

2fill in blank

medium

Complete the code to implement the Display trait for MyError.

Rust

impl std::fmt::Display for MyError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            MyError::Error(msg) => write!(f, [1], msg),
        }
    }
}

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A"{}"

B"MyError: {}"

C"Error: {}"

D"Error occurred: {}"

Attempts:

3 left

💡 Hint

Common Mistakes

Adding extra text that is not needed

Forgetting to include the placeholder {}

The format string "{}" directly prints the error message string.

3fill in blank

hard

Fix the error in the From trait implementation to convert std::io::Error into MyError.

Rust

impl From<std::io::Error> for MyError {
    fn from(err: std::io::Error) -> MyError {
        MyError::[1](err.to_string())
    }
}

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AIoError

BCustomError

CError

DMyErrorType

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variant name that does not exist

Passing the error type directly instead of converting to string

The variant Error holds a String, so we convert the io::Error to string and wrap it.

4fill in blank

hard

Fill in the blank to implement the std::error::Error trait for MyError.

Rust

impl std::error::Error for MyError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        [1]
    }
}

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ANone

B"Custom error"

CSome(self)

D"MyError occurred"

Attempts:

3 left

💡 Hint

Common Mistakes

Returning Some(self) in source which causes lifetime issues

The source method returns None because this error has no underlying cause.

5fill in blank

hard

Fill all three blanks to create a function that returns a Result with MyError and uses the ? operator.

Rust

fn read_file(path: &str) -> Result<String, MyError> {
    let content = std::fs::read_to_string(path)[1];
    Ok([2])
}

fn main() {
    match read_file("file.txt") {
        Ok(data) => println!("File content: {}", [3]),
        Err(e) => println!("Error: {}", e),
    }
}

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A?

Bcontent

Cdata

D.unwrap()

Attempts:

3 left

💡 Hint

Common Mistakes

Using .unwrap() which panics on error

Printing the wrong variable in main

The ? operator propagates errors. The variable content holds the file data, and data is used in the print statement.