Option and Result

Rust has no null. A value that might be absent is wrapped in Option<T>, which is either Some(value) or None — and the compiler forces you to handle both cases before you can use the value inside, so a missing value can never be accidentally used as if it were present.

main.rs

Try it yourself →

fn find_first_even(numbers: &[i32]) -> Option<i32> {
    for &n in numbers {
        if n % 2 == 0 {
            return Some(n);
        }
    }
    None
}

fn main() {
    let numbers = vec![1, 3, 5, 4, 7];
    match find_first_even(&numbers) {
        Some(n) => println!("Found: {}", n),
        None => println!("No even number found"),
    }
}

Output

Found: 4

Result for recoverable errors

Result<T, E> represents an operation that might fail: Ok(value) on success, Err(error) on failure. There are no exceptions to throw or catch here — a function that can fail simply returns a Result, and match forces the caller to handle both outcomes explicitly.

main.rs

Try it yourself →

fn divide(a: f64, b: f64) -> Result<f64, String> {
    if b == 0.0 {
        Err(String::from("cannot divide by zero"))
    } else {
        Ok(a / b)
    }
}

fn main() {
    match divide(10.0, 2.0) {
        Ok(result) => println!("Result: {}", result),
        Err(e) => println!("Error: {}", e),
    }

    match divide(10.0, 0.0) {
        Ok(result) => println!("Result: {}", result),
        Err(e) => println!("Error: {}", e),
    }
}

Output

Result: 5
Error: cannot divide by zero

Next: functions — parameters, return types, and Rust's expression-based syntax.

Practice exercise

Write a function first_char(s: &str) -> Option<char> that returns the first character of s, or None if s is empty. Call it with "rust" and match the result, printing the character if Some, or "empty" if None.

← Enums and Pattern Matching Functions →