Rust by Example

Unpacking options with ?

You can unpack Options 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) -> Option {

// 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?;

Some(format!("Next year I will be {}", next_age))

}

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You can chain many ?s together to make your code much more readable.

struct Person {

job: Option,

}

#[derive(Clone, Copy)]

struct Job {

phone_number: Option,

}

#[derive(Clone, Copy)]

struct PhoneNumber {

area_code: Option,

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 {

// 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));

}

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