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` 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));
}