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:

• Two variants: Some(T) (value present) or None (value absent).
• Used when absence is normal, not exceptional.
• No error information — just "there" or "not there".
• Methods: .unwrap(), .unwrap_or(), .map(), .and_then().

1fn find_user(id: u32) -> Option<String> {
2    if id == 1 {
3        Some("Alice".to_string())
4    } else {
5        None
6    }
7}
8
9match find_user(2) {
10    Some(name) => println!("Found: {}", name),
11    None => println!("User not found"),
12}

Result:

• Two variants: Ok(T) (success) or Err(E) (failure with error info).
• Used for operations that can fail (I/O, parsing, network).
• Carries an error type for debugging/logging.
• The ? operator propagates errors up the call stack.

1use std::fs;
2
3fn read_config() -> Result<String, std::io::Error> {
4    let content = fs::read_to_string("config.toml")?;
5    Ok(content)
6}
7
8fn main() {
9    match read_config() {
10        Ok(config) => println!("{}", config),
11        Err(e) => eprintln!("Error: {}", e),
12    }
13}

When to use:

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

Common mistakes:

• Using unwrap() in production — can panic on None/Err.
• Forgetting to handle the error case — use ? or explicit matching.
• Confusing Option and Result — Result must carry an error type.