Option

enum Option<T>

An optional value: either Some(value) or None.

Option is auto-imported into every file. Construct it with Option::Some(x) and Option::None; bare Some / None also work while no other enum in scope has a case with the same name.

Take it apart with match, the coalesce operator ?? (use a default when the value is None), the try operator ? (return None early from a function that itself returns an Option) or optional access a?.field. Vec::pop and Vec::remove return Option.

Variants#

None#

No value.

Some(T)#

Some value of type T.

Methods#

Trait implementations#

• Arbitrary for Option<T: Arbitrary>

Examples#

use tests::assert;
fn find(Vec<int> xs, int wanted) -> Option<int> {
    let i = 0;
    while i < xs.len() {
        if xs[i] == wanted {
            return Option::Some(i);
        }
        i = i + 1;
    }
    return Option::None;
}

fn main() {
    let xs: Vec<int> = [4, 8, 15];
    let at = match find(xs, 8) {
        Option::Some(i) => i,
        Option::None => -1,
    };
    assert!(at == 1);
    assert!((find(xs, 99) ?? -1) == -1);
}

See also#

• Vec::pop
• Vec::remove
• Result: The outcome of an operation that can fail: Ok(value) or Err(error).