Primitive Type unit

The () type, also called “unit”.

The () type has exactly one value (), and is used when there is no other meaningful value that could be returned. () is most commonly seen implicitly: functions without a -> ... implicitly have return type (), that is, these are equivalent:

fn long() -> () {}

fn short() {}

The semicolon ; can be used to discard the result of an expression at the end of a block, making the expression (and thus the block) evaluate to (). For example,

fn returns_i64() -> i64 {
    1i64
}
fn returns_unit() {
    1i64;
}

let is_i64 = {
    returns_i64()
};
let is_unit = {
    returns_i64();
};

Trait Implementations

impl Clone for ()

fn clone(&self) -> Self

Returns a copy of the value.

const fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ()

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

Formats the value using the given formatter.

impl Default for ()

fn default()

Returns the default value of ()

impl Extend<()> for ()

fn extend<T: IntoIterator<Item = ()>>(&mut self, iter: T)

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, _item: ())

🔬This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one #72631)

Reserves capacity in a collection for the given number of additional elements.

impl FromIterator<()> for ()

Collapses all unit items from an iterator into one.

This is more useful when combined with higher-level abstractions, like collecting to a Result<(), E> where you only care about errors:

use std::io::*;
let data = vec![1, 2, 3, 4, 5];
let res: Result<()> = data.iter()
    .map(|x| writeln!(stdout(), "{x}"))
    .collect();
assert!(res.is_ok());

fn from_iter<I: IntoIterator<Item = ()>>(iter: I) -> Self

Creates a value from an iterator.

impl Hash for ()

fn hash<H: Hasher>(&self, _state: &mut H)

Feeds this value into the given Hasher.

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

Feeds a slice of this type into the given Hasher.

impl Ord for ()

fn cmp(&self, _other: &()) -> Ordering

This method returns an Ordering between self and other.

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

Compares and returns the maximum of two values.

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

Compares and returns the minimum of two values.

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

Restrict a value to a certain interval.

impl PartialEq<()> for ()

fn eq(&self, _other: &()) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, _other: &()) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd<()> for ()

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

This method returns an ordering between self and other values if one exists.

const fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

const fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

const fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

const fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Copy for ()

impl Eq for ()