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) or None.
• Used when absence is expected.
• No error information.
• Rich combinator API.

1fn first_char(s: &str) -> Option<char> {
2    s.chars().next()
3}
4
5let c = first_char("hello")
6    .map(|c| c.to_uppercase().to_string())
7    .unwrap_or("?".to_string());

Result:

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

1use std::fs;
2
3fn read_file(path: &str) -> Result<String, std::io::Error> {
4    fs::read_to_string(path)
5}
6
7fn main() -> Result<(), Box<dyn std::error::Error>> {
8    let content = read_file("config.txt")?;
9    println!("{}", content);
10    Ok(())
11}

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.
• Forgetting to handle errors.
• Using Option when error reason matters.