Enum serde::lib::option::Option

1.0.0 · source ·
pub enum Option<T> {
    None,
    Some(T),
}
Expand description

The Option type. See the module level documentation for more.

Variants§

§

None

No value.

§

Some(T)

Some value of type T.

Implementations§

source§

impl<T> Option<T>

const: 1.48.0 · source

pub const fn is_some(&self) -> bool

Returns true if the option is a Some value.

Examples
let x: Option<u32> = Some(2);
assert_eq!(x.is_some(), true);

let x: Option<u32> = None;
assert_eq!(x.is_some(), false);
source

pub fn is_some_and(self, f: impl FnOnce(T) -> bool) -> bool

🔬This is a nightly-only experimental API. (is_some_and)

Returns true if the option is a Some and the value inside of it matches a predicate.

Examples
#![feature(is_some_and)]

let x: Option<u32> = Some(2);
assert_eq!(x.is_some_and(|x| x > 1), true);

let x: Option<u32> = Some(0);
assert_eq!(x.is_some_and(|x| x > 1), false);

let x: Option<u32> = None;
assert_eq!(x.is_some_and(|x| x > 1), false);
const: 1.48.0 · source

pub const fn is_none(&self) -> bool

Returns true if the option is a None value.

Examples
let x: Option<u32> = Some(2);
assert_eq!(x.is_none(), false);

let x: Option<u32> = None;
assert_eq!(x.is_none(), true);
const: 1.48.0 · source

pub const fn as_ref(&self) -> Option<&T>

Converts from &Option<T> to Option<&T>.

Examples

Calculates the length of an Option<String> as an Option<usize> without moving the String. The map method takes the self argument by value, consuming the original, so this technique uses as_ref to first take an Option to a reference to the value inside the original.

let text: Option<String> = Some("Hello, world!".to_string());
// First, cast `Option<String>` to `Option<&String>` with `as_ref`,
// then consume *that* with `map`, leaving `text` on the stack.
let text_length: Option<usize> = text.as_ref().map(|s| s.len());
println!("still can print text: {text:?}");
const: unstable · source

pub fn as_mut(&mut self) -> Option<&mut T>

Converts from &mut Option<T> to Option<&mut T>.

Examples
let mut x = Some(2);
match x.as_mut() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));
1.33.0 (const: unstable) · source

pub fn as_pin_ref(self: Pin<&Option<T>>) -> Option<Pin<&T>>

Converts from Pin<&Option<T>> to Option<Pin<&T>>.

1.33.0 (const: unstable) · source

pub fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&mut T>>

Converts from Pin<&mut Option<T>> to Option<Pin<&mut T>>.

const: unstable · source

pub fn expect(self, msg: &str) -> T

Returns the contained Some value, consuming the self value.

Panics

Panics if the value is a None with a custom panic message provided by msg.

Examples
let x = Some("value");
assert_eq!(x.expect("fruits are healthy"), "value");
let x: Option<&str> = None;
x.expect("fruits are healthy"); // panics with `fruits are healthy`

We recommend that expect messages are used to describe the reason you expect the Option should be Some.

let item = slice.get(0)
    .expect("slice should not be empty");

Hint: If you’re having trouble remembering how to phrase expect error messages remember to focus on the word “should” as in “env variable should be set by blah” or “the given binary should be available and executable by the current user”.

For more detail on expect message styles and the reasoning behind our recommendation please refer to the section on “Common Message Styles” in the std::error module docs.

const: unstable · source

pub fn unwrap(self) -> T

Returns the contained Some value, consuming the self value.

Because this function may panic, its use is generally discouraged. Instead, prefer to use pattern matching and handle the None case explicitly, or call unwrap_or, unwrap_or_else, or unwrap_or_default.

Panics

Panics if the self value equals None.

Examples
let x = Some("air");
assert_eq!(x.unwrap(), "air");
let x: Option<&str> = None;
assert_eq!(x.unwrap(), "air"); // fails
const: unstable · source

pub fn unwrap_or(self, default: T) -> T

Returns the contained Some value or a provided default.

Arguments passed to unwrap_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use unwrap_or_else, which is lazily evaluated.

Examples
assert_eq!(Some("car").unwrap_or("bike"), "car");
assert_eq!(None.unwrap_or("bike"), "bike");
const: unstable · source

pub fn unwrap_or_else<F>(self, f: F) -> Twhere
    F: FnOnce() -> T,

Returns the contained Some value or computes it from a closure.

Examples
let k = 10;
assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4);
assert_eq!(None.unwrap_or_else(|| 2 * k), 20);
const: unstable · source

pub fn unwrap_or_default(self) -> Twhere
    T: Default,

Returns the contained Some value or a default.

Consumes the self argument then, if Some, returns the contained value, otherwise if None, returns the default value for that type.

Examples
let x: Option<u32> = None;
let y: Option<u32> = Some(12);

assert_eq!(x.unwrap_or_default(), 0);
assert_eq!(y.unwrap_or_default(), 12);
1.58.0 (const: unstable) · source

pub unsafe fn unwrap_unchecked(self) -> T

Returns the contained Some value, consuming the self value, without checking that the value is not None.

Safety

Calling this method on None is undefined behavior.

Examples
let x = Some("air");
assert_eq!(unsafe { x.unwrap_unchecked() }, "air");
let x: Option<&str> = None;
assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior!
const: unstable · source

pub fn map<U, F>(self, f: F) -> Option<U>where
    F: FnOnce(T) -> U,

Maps an Option<T> to Option<U> by applying a function to a contained value.

Examples

Calculates the length of an Option<String> as an Option<usize>, consuming the original:

let maybe_some_string = Some(String::from("Hello, World!"));
// `Option::map` takes self *by value*, consuming `maybe_some_string`
let maybe_some_len = maybe_some_string.map(|s| s.len());

assert_eq!(maybe_some_len, Some(13));
const: unstable · source

pub fn inspect<F>(self, f: F) -> Option<T>where
    F: FnOnce(&T),

🔬This is a nightly-only experimental API. (result_option_inspect)

Calls the provided closure with a reference to the contained value (if Some).

Examples
#![feature(result_option_inspect)]

let v = vec![1, 2, 3, 4, 5];

// prints "got: 4"
let x: Option<&usize> = v.get(3).inspect(|x| println!("got: {x}"));

// prints nothing
let x: Option<&usize> = v.get(5).inspect(|x| println!("got: {x}"));
const: unstable · source

pub fn map_or<U, F>(self, default: U, f: F) -> Uwhere
    F: FnOnce(T) -> U,

Returns the provided default result (if none), or applies a function to the contained value (if any).

Arguments passed to map_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use map_or_else, which is lazily evaluated.

Examples
let x = Some("foo");
assert_eq!(x.map_or(42, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or(42, |v| v.len()), 42);
const: unstable · source

pub fn map_or_else<U, D, F>(self, default: D, f: F) -> Uwhere
    D: FnOnce() -> U,
    F: FnOnce(T) -> U,

Computes a default function result (if none), or applies a different function to the contained value (if any).

Examples
let k = 21;

let x = Some("foo");
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42);
const: unstable · source

pub fn ok_or<E>(self, err: E) -> Result<T, E>

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err).

Arguments passed to ok_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use ok_or_else, which is lazily evaluated.

Examples
let x = Some("foo");
assert_eq!(x.ok_or(0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or(0), Err(0));
const: unstable · source

pub fn ok_or_else<E, F>(self, err: F) -> Result<T, E>where
    F: FnOnce() -> E,

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err()).

Examples
let x = Some("foo");
assert_eq!(x.ok_or_else(|| 0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or_else(|| 0), Err(0));
1.40.0 (const: unstable) · source

pub fn as_deref(&self) -> Option<&<T as Deref>::Target>where
    T: Deref,

Converts from Option<T> (or &Option<T>) to Option<&T::Target>.

Leaves the original Option in-place, creating a new one with a reference to the original one, additionally coercing the contents via Deref.

Examples
let x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref(), Some("hey"));

let x: Option<String> = None;
assert_eq!(x.as_deref(), None);
1.40.0 (const: unstable) · source

pub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::Target>where
    T: DerefMut,

Converts from Option<T> (or &mut Option<T>) to Option<&mut T::Target>.

Leaves the original Option in-place, creating a new one containing a mutable reference to the inner type’s Deref::Target type.

Examples
let mut x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref_mut().map(|x| {
    x.make_ascii_uppercase();
    x
}), Some("HEY".to_owned().as_mut_str()));
const: unstable · source

pub fn iter(&self) -> Iter<'_, T>

Returns an iterator over the possibly contained value.

Examples
let x = Some(4);
assert_eq!(x.iter().next(), Some(&4));

let x: Option<u32> = None;
assert_eq!(x.iter().next(), None);
source

pub fn iter_mut(&mut self) -> IterMut<'_, T>

Returns a mutable iterator over the possibly contained value.

Examples
let mut x = Some(4);
match x.iter_mut().next() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));

let mut x: Option<u32> = None;
assert_eq!(x.iter_mut().next(), None);
const: unstable · source

pub fn and<U>(self, optb: Option<U>) -> Option<U>

Returns None if the option is None, otherwise returns optb.

Arguments passed to and are eagerly evaluated; if you are passing the result of a function call, it is recommended to use and_then, which is lazily evaluated.

Examples
let x = Some(2);
let y: Option<&str> = None;
assert_eq!(x.and(y), None);

let x: Option<u32> = None;
let y = Some("foo");
assert_eq!(x.and(y), None);

let x = Some(2);
let y = Some("foo");
assert_eq!(x.and(y), Some("foo"));

let x: Option<u32> = None;
let y: Option<&str> = None;
assert_eq!(x.and(y), None);
const: unstable · source

pub fn and_then<U, F>(self, f: F) -> Option<U>where
    F: FnOnce(T) -> Option<U>,

Returns None if the option is None, otherwise calls f with the wrapped value and returns the result.

Some languages call this operation flatmap.

Examples
fn sq_then_to_string(x: u32) -> Option<String> {
    x.checked_mul(x).map(|sq| sq.to_string())
}

assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string()));
assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None); // overflowed!
assert_eq!(None.and_then(sq_then_to_string), None);

Often used to chain fallible operations that may return None.

let arr_2d = [["A0", "A1"], ["B0", "B1"]];

let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1));
assert_eq!(item_0_1, Some(&"A1"));

let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0));
assert_eq!(item_2_0, None);
1.27.0 (const: unstable) · source

pub fn filter<P>(self, predicate: P) -> Option<T>where
    P: FnOnce(&T) -> bool,

Returns None if the option is None, otherwise calls predicate with the wrapped value and returns:

  • Some(t) if predicate returns true (where t is the wrapped value), and
  • None if predicate returns false.

This function works similar to Iterator::filter(). You can imagine the Option<T> being an iterator over one or zero elements. filter() lets you decide which elements to keep.

Examples
fn is_even(n: &i32) -> bool {
    n % 2 == 0
}

assert_eq!(None.filter(is_even), None);
assert_eq!(Some(3).filter(is_even), None);
assert_eq!(Some(4).filter(is_even), Some(4));
const: unstable · source

pub fn or(self, optb: Option<T>) -> Option<T>

Returns the option if it contains a value, otherwise returns optb.

Arguments passed to or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use or_else, which is lazily evaluated.

Examples
let x = Some(2);
let y = None;
assert_eq!(x.or(y), Some(2));

let x = None;
let y = Some(100);
assert_eq!(x.or(y), Some(100));

let x = Some(2);
let y = Some(100);
assert_eq!(x.or(y), Some(2));

let x: Option<u32> = None;
let y = None;
assert_eq!(x.or(y), None);
const: unstable · source

pub fn or_else<F>(self, f: F) -> Option<T>where
    F: FnOnce() -> Option<T>,

Returns the option if it contains a value, otherwise calls f and returns the result.

Examples
fn nobody() -> Option<&'static str> { None }
fn vikings() -> Option<&'static str> { Some("vikings") }

assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians"));
assert_eq!(None.or_else(vikings), Some("vikings"));
assert_eq!(None.or_else(nobody), None);
1.37.0 (const: unstable) · source

pub fn xor(self, optb: Option<T>) -> Option<T>

Returns Some if exactly one of self, optb is Some, otherwise returns None.

Examples
let x = Some(2);
let y: Option<u32> = None;
assert_eq!(x.xor(y), Some(2));

let x: Option<u32> = None;
let y = Some(2);
assert_eq!(x.xor(y), Some(2));

let x = Some(2);
let y = Some(2);
assert_eq!(x.xor(y), None);

let x: Option<u32> = None;
let y: Option<u32> = None;
assert_eq!(x.xor(y), None);
1.53.0 (const: unstable) · source

pub fn insert(&mut self, value: T) -> &mut T

Inserts value into the option, then returns a mutable reference to it.

If the option already contains a value, the old value is dropped.

See also Option::get_or_insert, which doesn’t update the value if the option already contains Some.

Example
let mut opt = None;
let val = opt.insert(1);
assert_eq!(*val, 1);
assert_eq!(opt.unwrap(), 1);
let val = opt.insert(2);
assert_eq!(*val, 2);
*val = 3;
assert_eq!(opt.unwrap(), 3);
1.20.0 (const: unstable) · source

pub fn get_or_insert(&mut self, value: T) -> &mut T

Inserts value into the option if it is None, then returns a mutable reference to the contained value.

See also Option::insert, which updates the value even if the option already contains Some.

Examples
let mut x = None;

{
    let y: &mut u32 = x.get_or_insert(5);
    assert_eq!(y, &5);

    *y = 7;
}

assert_eq!(x, Some(7));
const: unstable · source

pub fn get_or_insert_default(&mut self) -> &mut Twhere
    T: Default,

🔬This is a nightly-only experimental API. (option_get_or_insert_default)

Inserts the default value into the option if it is None, then returns a mutable reference to the contained value.

Examples
#![feature(option_get_or_insert_default)]

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_default();
    assert_eq!(y, &0);

    *y = 7;
}

assert_eq!(x, Some(7));
1.20.0 (const: unstable) · source

pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut Twhere
    F: FnOnce() -> T,

Inserts a value computed from f into the option if it is None, then returns a mutable reference to the contained value.

Examples
let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_with(|| 5);
    assert_eq!(y, &5);

    *y = 7;
}

assert_eq!(x, Some(7));
const: unstable · source

pub fn take(&mut self) -> Option<T>

Takes the value out of the option, leaving a None in its place.

Examples
let mut x = Some(2);
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, Some(2));

let mut x: Option<u32> = None;
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, None);
1.31.0 (const: unstable) · source

pub fn replace(&mut self, value: T) -> Option<T>

Replaces the actual value in the option by the value given in parameter, returning the old value if present, leaving a Some in its place without deinitializing either one.

Examples
let mut x = Some(2);
let old = x.replace(5);
assert_eq!(x, Some(5));
assert_eq!(old, Some(2));

let mut x = None;
let old = x.replace(3);
assert_eq!(x, Some(3));
assert_eq!(old, None);
const: unstable · source

pub fn contains<U>(&self, x: &U) -> boolwhere
    U: PartialEq<T>,

🔬This is a nightly-only experimental API. (option_result_contains)

Returns true if the option is a Some value containing the given value.

Examples
#![feature(option_result_contains)]

let x: Option<u32> = Some(2);
assert_eq!(x.contains(&2), true);

let x: Option<u32> = Some(3);
assert_eq!(x.contains(&2), false);

let x: Option<u32> = None;
assert_eq!(x.contains(&2), false);
1.46.0 (const: unstable) · source

pub fn zip<U>(self, other: Option<U>) -> Option<(T, U)>

Zips self with another Option.

If self is Some(s) and other is Some(o), this method returns Some((s, o)). Otherwise, None is returned.

Examples
let x = Some(1);
let y = Some("hi");
let z = None::<u8>;

assert_eq!(x.zip(y), Some((1, "hi")));
assert_eq!(x.zip(z), None);
const: unstable · source

pub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>where
    F: FnOnce(T, U) -> R,

🔬This is a nightly-only experimental API. (option_zip)

Zips self and another Option with function f.

If self is Some(s) and other is Some(o), this method returns Some(f(s, o)). Otherwise, None is returned.

Examples
#![feature(option_zip)]

#[derive(Debug, PartialEq)]
struct Point {
    x: f64,
    y: f64,
}

impl Point {
    fn new(x: f64, y: f64) -> Self {
        Self { x, y }
    }
}

let x = Some(17.5);
let y = Some(42.7);

assert_eq!(x.zip_with(y, Point::new), Some(Point { x: 17.5, y: 42.7 }));
assert_eq!(x.zip_with(None, Point::new), None);
source§

impl<T, U> Option<(T, U)>

1.66.0 (const: unstable) · source

pub fn unzip(self) -> (Option<T>, Option<U>)

Unzips an option containing a tuple of two options.

If self is Some((a, b)) this method returns (Some(a), Some(b)). Otherwise, (None, None) is returned.

Examples
let x = Some((1, "hi"));
let y = None::<(u8, u32)>;

assert_eq!(x.unzip(), (Some(1), Some("hi")));
assert_eq!(y.unzip(), (None, None));
source§

impl<T> Option<&T>

1.35.0 (const: unstable) · source

pub fn copied(self) -> Option<T>where
    T: Copy,

Maps an Option<&T> to an Option<T> by copying the contents of the option.

Examples
let x = 12;
let opt_x = Some(&x);
assert_eq!(opt_x, Some(&12));
let copied = opt_x.copied();
assert_eq!(copied, Some(12));
const: unstable · source

pub fn cloned(self) -> Option<T>where
    T: Clone,

Maps an Option<&T> to an Option<T> by cloning the contents of the option.

Examples
let x = 12;
let opt_x = Some(&x);
assert_eq!(opt_x, Some(&12));
let cloned = opt_x.cloned();
assert_eq!(cloned, Some(12));
source§

impl<T> Option<&mut T>

1.35.0 (const: unstable) · source

pub fn copied(self) -> Option<T>where
    T: Copy,

Maps an Option<&mut T> to an Option<T> by copying the contents of the option.

Examples
let mut x = 12;
let opt_x = Some(&mut x);
assert_eq!(opt_x, Some(&mut 12));
let copied = opt_x.copied();
assert_eq!(copied, Some(12));
1.26.0 (const: unstable) · source

pub fn cloned(self) -> Option<T>where
    T: Clone,

Maps an Option<&mut T> to an Option<T> by cloning the contents of the option.

Examples
let mut x = 12;
let opt_x = Some(&mut x);
assert_eq!(opt_x, Some(&mut 12));
let cloned = opt_x.cloned();
assert_eq!(cloned, Some(12));
source§

impl<T, E> Option<Result<T, E>>

1.33.0 (const: unstable) · source

pub fn transpose(self) -> Result<Option<T>, E>

Transposes an Option of a Result into a Result of an Option.

None will be mapped to Ok(None). Some(Ok(_)) and Some(Err(_)) will be mapped to Ok(Some(_)) and Err(_).

Examples
#[derive(Debug, Eq, PartialEq)]
struct SomeErr;

let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
assert_eq!(x, y.transpose());
source§

impl<T> Option<Option<T>>

1.40.0 (const: unstable) · source

pub fn flatten(self) -> Option<T>

Converts from Option<Option<T>> to Option<T>.

Examples

Basic usage:

let x: Option<Option<u32>> = Some(Some(6));
assert_eq!(Some(6), x.flatten());

let x: Option<Option<u32>> = Some(None);
assert_eq!(None, x.flatten());

let x: Option<Option<u32>> = None;
assert_eq!(None, x.flatten());

Flattening only removes one level of nesting at a time:

let x: Option<Option<Option<u32>>> = Some(Some(Some(6)));
assert_eq!(Some(Some(6)), x.flatten());
assert_eq!(Some(6), x.flatten().flatten());

Trait Implementations§

const: unstable · source§

impl<T> Clone for Option<T>where
    T: Clone,

const: unstable · source§

fn clone(&self) -> Option<T>

Returns a copy of the value. Read more
const: unstable · source§

fn clone_from(&mut self, source: &Option<T>)

Performs copy-assignment from source. Read more
source§

impl<T> Debug for Option<T>where
    T: Debug,

source§

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
const: unstable · source§

impl<T> Default for Option<T>

const: unstable · source§

fn default() -> Option<T>

Returns None.

Examples
let opt: Option<u32> = Option::default();
assert!(opt.is_none());
source§

impl<'de, T> Deserialize<'de> for Option<T>where
    T: Deserialize<'de>,

source§

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>where
    D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer. Read more
1.30.0 (const: unstable) · source§

impl<'a, T> From<&'a Option<T>> for Option<&'a T>

const: unstable · source§

fn from(o: &'a Option<T>) -> Option<&'a T>

Converts from &Option<T> to Option<&T>.

Examples

Converts an Option<String> into an Option<usize>, preserving the original. The map method takes the self argument by value, consuming the original, so this technique uses from to first take an Option to a reference to the value inside the original.

let s: Option<String> = Some(String::from("Hello, Rustaceans!"));
let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len());

println!("Can still print s: {s:?}");

assert_eq!(o, Some(18));
1.30.0 (const: unstable) · source§

impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>

const: unstable · source§

fn from(o: &'a mut Option<T>) -> Option<&'a mut T>

Converts from &mut Option<T> to Option<&mut T>

Examples
let mut s = Some(String::from("Hello"));
let o: Option<&mut String> = Option::from(&mut s);

match o {
    Some(t) => *t = String::from("Hello, Rustaceans!"),
    None => (),
}

assert_eq!(s, Some(String::from("Hello, Rustaceans!")));
1.12.0 (const: unstable) · source§

impl<T> From<T> for Option<T>

const: unstable · source§

fn from(val: T) -> Option<T>

Moves val into a new Some.

Examples
let o: Option<u8> = Option::from(67);

assert_eq!(Some(67), o);
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impl<A, V> FromIterator<Option<A>> for Option<V>where
    V: FromIterator<A>,

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fn from_iter<I>(iter: I) -> Option<V>where
    I: IntoIterator<Item = Option<A>>,

Takes each element in the Iterator: if it is None, no further elements are taken, and the None is returned. Should no None occur, a container of type V containing the values of each Option is returned.

Examples

Here is an example which increments every integer in a vector. We use the checked variant of add that returns None when the calculation would result in an overflow.

let items = vec![0_u16, 1, 2];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_add(1))
    .collect();

assert_eq!(res, Some(vec![1, 2, 3]));

As you can see, this will return the expected, valid items.

Here is another example that tries to subtract one from another list of integers, this time checking for underflow:

let items = vec![2_u16, 1, 0];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_sub(1))
    .collect();

assert_eq!(res, None);

Since the last element is zero, it would underflow. Thus, the resulting value is None.

Here is a variation on the previous example, showing that no further elements are taken from iter after the first None.

let items = vec![3_u16, 2, 1, 10];

let mut shared = 0;

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| { shared += x; x.checked_sub(2) })
    .collect();

assert_eq!(res, None);
assert_eq!(shared, 6);

Since the third element caused an underflow, no further elements were taken, so the final value of shared is 6 (= 3 + 2 + 1), not 16.

const: unstable · source§

impl<T> FromResidual<<Option<T> as Try>::Residual> for Option<T>

const: unstable · source§

fn from_residual(residual: Option<Infallible>) -> Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2)
Constructs the type from a compatible Residual type. Read more
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impl<T> FromResidual<Yeet<()>> for Option<T>

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fn from_residual(_: Yeet<()>) -> Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2)
Constructs the type from a compatible Residual type. Read more
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impl<T> Hash for Option<T>where
    T: Hash,

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fn hash<__H>(&self, state: &mut __H)where
    __H: Hasher,

Feeds this value into the given Hasher. Read more
1.3.0 · source§

fn hash_slice<H>(data: &[Self], state: &mut H)where
    H: Hasher,
    Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
1.4.0 · source§

impl<'a, T> IntoIterator for &'a Option<T>

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type Item = &'a T

The type of the elements being iterated over.
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type IntoIter = Iter<'a, T>

Which kind of iterator are we turning this into?
source§

fn into_iter(self) -> Iter<'a, T>

Creates an iterator from a value. Read more
1.4.0 · source§

impl<'a, T> IntoIterator for &'a mut Option<T>

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type Item = &'a mut T

The type of the elements being iterated over.
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type IntoIter = IterMut<'a, T>

Which kind of iterator are we turning this into?
source§

fn into_iter(self) -> IterMut<'a, T>

Creates an iterator from a value. Read more
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impl<T> IntoIterator for Option<T>

source§

fn into_iter(self) -> IntoIter<T>

Returns a consuming iterator over the possibly contained value.

Examples
let x = Some("string");
let v: Vec<&str> = x.into_iter().collect();
assert_eq!(v, ["string"]);

let x = None;
let v: Vec<&str> = x.into_iter().collect();
assert!(v.is_empty());
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type Item = T

The type of the elements being iterated over.
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type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?
source§

impl<T> Ord for Option<T>where
    T: Ord,

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fn cmp(&self, other: &Option<T>) -> Ordering

This method returns an Ordering between self and other. Read more
1.21.0 · source§

fn max(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · source§

fn min(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · source§

fn clamp(self, min: Self, max: Self) -> Selfwhere
    Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval. Read more
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impl<T> PartialEq<Option<T>> for Option<T>where
    T: PartialEq<T>,

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fn eq(&self, other: &Option<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<T> PartialOrd<Option<T>> for Option<T>where
    T: PartialOrd<T>,

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fn partial_cmp(&self, other: &Option<T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
1.37.0 · source§

impl<T, U> Product<Option<U>> for Option<T>where
    T: Product<U>,

source§

fn product<I>(iter: I) -> Option<T>where
    I: Iterator<Item = Option<U>>,

Takes each element in the Iterator: if it is a None, no further elements are taken, and the None is returned. Should no None occur, the product of all elements is returned.

const: unstable · source§

impl<T> Residual<T> for Option<Infallible>

§

type TryType = Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2_residual)
The “return” type of this meta-function.
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impl<T> Serialize for Option<T>where
    T: Serialize,

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fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>where
    S: Serializer,

Serialize this value into the given Serde serializer. Read more
1.37.0 · source§

impl<T, U> Sum<Option<U>> for Option<T>where
    T: Sum<U>,

source§

fn sum<I>(iter: I) -> Option<T>where
    I: Iterator<Item = Option<U>>,

Takes each element in the Iterator: if it is a None, no further elements are taken, and the None is returned. Should no None occur, the sum of all elements is returned.

Examples

This sums up the position of the character ‘a’ in a vector of strings, if a word did not have the character ‘a’ the operation returns None:

let words = vec!["have", "a", "great", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, Some(5));
const: unstable · source§

impl<T> Try for Option<T>

§

type Output = T

🔬This is a nightly-only experimental API. (try_trait_v2)
The type of the value produced by ? when not short-circuiting.
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type Residual = Option<Infallible>

🔬This is a nightly-only experimental API. (try_trait_v2)
The type of the value passed to FromResidual::from_residual as part of ? when short-circuiting. Read more
const: unstable · source§

fn from_output(output: <Option<T> as Try>::Output) -> Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2)
Constructs the type from its Output type. Read more
const: unstable · source§

fn branch(
    self
) -> ControlFlow<<Option<T> as Try>::Residual, <Option<T> as Try>::Output>

🔬This is a nightly-only experimental API. (try_trait_v2)
Used in ? to decide whether the operator should produce a value (because this returned ControlFlow::Continue) or propagate a value back to the caller (because this returned ControlFlow::Break). Read more
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impl<T> Copy for Option<T>where
    T: Copy,

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impl<T> Eq for Option<T>where
    T: Eq,

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impl<T> StructuralEq for Option<T>

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impl<T> StructuralPartialEq for Option<T>

Auto Trait Implementations§

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impl<T> RefUnwindSafe for Option<T>where
    T: RefUnwindSafe,

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impl<T> Send for Option<T>where
    T: Send,

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impl<T> Sync for Option<T>where
    T: Sync,

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impl<T> Unpin for Option<T>where
    T: Unpin,

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impl<T> UnwindSafe for Option<T>where
    T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for Twhere
    T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for Twhere
    T: ?Sized,

const: unstable · source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere
    T: ?Sized,

const: unstable · source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<!> for T

const: unstable · source§

fn from(t: !) -> T

Converts to this type from the input type.
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impl<T> From<T> for T

const: unstable · source§

fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for Twhere
    U: From<T>,

const: unstable · source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for Twhere
    T: Clone,

§

type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for Twhere
    U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
const: unstable · source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for Twhere
    U: TryFrom<T>,

§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
const: unstable · source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<T> DeserializeOwned for Twhere
    T: for<'de> Deserialize<'de>,