Rust: What is the difference between Option<T> and Result<T, E>?

Option<T> — optional value. Result<T, E> — success or error.

Option<T>:

• Some or None.
• No error info.
• For nullable values.

Result<T, E>:

• Ok or Err.
• Error info.
• For operations that can fail.

1// Option
2fn find_user(id: u32) -> Option<User> {
3    if id == 1 {
4        Some(User { name: "Alice".into() })
5    } else {
6        None
7    }
8}
9
10// Result
11fn parse_number(s: &str) -> Result<i32, ParseIntError> {
12    s.parse()
13}

Key: Option for existence, Result for success/failure.