`Option` and `Result`

The types represent optional data:

fn main() {
    let numbers = vec![10, 20, 30];
    let first: Option<&i8> = numbers.first();
    println!("first: {first:?}");

    let idx: Result<usize, usize> = numbers.binary_search(&10);
    println!("idx: {idx:?}");
}

Option and Result are widely used not just in the standard library.
Option<&T> has zero space overhead compared to &T.
Result is the standard type to implement error handling as we will see on Day 3.
binary_search returns Result<usize, usize>.
- If found, Result::Ok holds the index where the element is found.
- Otherwise, Result::Err contains the index where such an element should be inserted.