Option and Result

Option for maybe values

Some(v) holds a value; None means absent. No null pointer.

fn first(nums: &[i32]) -> Option<i32> {
    nums.first().copied()
}

match first(&[10, 20]) {
    Some(n) => println!("{n}"),
    None => println!("empty"),
}

Result for success or error

Ok(v) is success; Err(e) is failure.

use std::fs;

fn read_hello() -> Result<String, std::io::Error> {
    fs::read_to_string("hello.txt")
}

Unwrap carefully

unwrap panics on None/Err. Prefer match, ?, or unwrap_or while learning.

let n = first(&[]).unwrap_or(0);
println!("{n}");

Everyday pattern

• Return Option when absence is normal
• Return Result when failure needs an error value
• Use ? to propagate errors in functions that return Result
• Avoid unchecked unwrap in library code