Rust: What is the difference between Option and Result?

Option — value may or may not exist (no error info). Result — operation succeeded or failed (carries error info).

Option:

• Some(T) for present, None for absent.
• Used when absence is expected.
• No error information.
• Rich combinator API for chaining.

1fn divide(a: f64, b: f64) -> Option<f64> {
2    if b == 0.0 {
3        None
4    } else {
5        Some(a / b)
6    }
7}
8
9let result = divide(10.0, 2.0)
10    .map(|x| x * 100.0)
11    .unwrap_or(0.0);

Result:

• Ok(T) for success, Err(E) for failure.
• Used for fallible operations.
• Carries an error type.
• ? operator propagates errors.

1use std::num::ParseIntError;
2
3fn parse_number(s: &str) -> Result<i32, ParseIntError> {
4    s.parse::<i32>()
5}
6
7fn main() {
8    match parse_number("42") {
9        Ok(n) => println!("Got: {}", n),
10        Err(e) => eprintln!("Error: {}", e),
11    }
12}

When to use:

• Option for: lookups, optional fields, nullable values.
• Result for: I/O, parsing, network, any fallible operation.

Common mistakes:

• Using unwrap() in production — can panic.
• Forgetting to handle errors — use ? or match.
• Using Option when error reason matters — use Result.