Durata
We have already seen some use of Option<T>. It stores either a value of type T or nothing. For example, String::find returns an Option<usize>.
fn main() {
let name = "Löwe 老虎 Léopard Gepardi";
let mut position: Option<usize> = name.find('é');
println!("find returned {position:?}");
assert_eq!(position.unwrap(), 14);
position = name.find('Z');
println!("find returned {position:?}");
assert_eq!(position.expect("Character not found"), 0);
}
This slide should take about 10 minutes.
Optionis widely used, not just in the standard library.unwrapwill return the value in anOption, or panic.expectis similar but takes an error message.- You can panic on None, but you can’t “accidentally” forget to check for None.
- It’s common to
unwrap/expectall over the place when hacking something together, but production code typically handlesNonein a nicer fashion.
- The niche optimization means that
Option<T>often has the same size in memory asT.