Error Handling

Rust distinguishes between recoverable and unrecoverable errors, forcing the programmer to handle them explicitly.

Unrecoverable errors: panic!

Stops the program immediately. It is used for situations that should never happen.

panic!("Fatal error");

Warning

panic! terminates the program with an error message. In production, use it only for invariant violations (things that “should never happen”).

Recoverable errors: Result<T, E>

Represents the result of an operation that can fail. See Option and Result.

use std::fs;
 
let result = fs::read_to_string("file.txt");
 
match result {
    Ok(contents) => println!("{}", contents),
    Err(e) => println!("Error: {}", e),
}

The ? operator

Automatically propagates errors. If the result is Err, it returns the error from the function. If it is Ok, it extracts the value.

fn read_file(path: &str) -> Result<String, std::io::Error> {
    let contents = std::fs::read_to_string(path)?; // Returns the error if it fails
    Ok(contents)
}

Note

The ? operator can only be used in functions that return Result or Option. See Option and Result

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