Unpacking options with ?
You can unpack Option
s by using match
statements, but it's often easier to
use the ?
operator. If x
is an Option
, then evaluating x?
will return
the underlying value if x
is Some
, otherwise it will terminate whatever
function is being executed and return None
.
fn next_birthday(current_age: Option<u8>) -> Option<String> { // If `current_age` is `None`, this returns `None`. // If `current_age` is `Some`, the inner `u8` value + 1 // gets assigned to `next_age` let next_age: u8 = current_age? + 1; Some(format!("Next year I will be {}", next_age)) }
You can chain many ?
s together to make your code much more readable.
struct Person { job: Option<Job>, } #[derive(Clone, Copy)] struct Job { phone_number: Option<PhoneNumber>, } #[derive(Clone, Copy)] struct PhoneNumber { area_code: Option<u8>, number: u32, } impl Person { // Gets the area code of the phone number of the person's job, if it exists. fn work_phone_area_code(&self) -> Option<u8> { // This would need many nested `match` statements without the `?` operator. // It would take a lot more code - try writing it yourself and see which // is easier. self.job?.phone_number?.area_code } } fn main() { let p = Person { job: Some(Job { phone_number: Some(PhoneNumber { area_code: Some(61), number: 439222222, }), }), }; assert_eq!(p.work_phone_area_code(), Some(61)); }