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 Debug for ()

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

Formats the value using the given formatter.

impl Default for ()

fn default()

Returns the default value of ()

impl Extend<()> for ()

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

where T: IntoIterator<Item = ()>,

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>(iter: I)

where I: IntoIterator<Item = ()>,

Creates a value from an iterator.

impl Hash for ()

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

where H: Hasher,

Feeds this value into the given Hasher.

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

where H: Hasher, 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.

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

where Self: Sized,

Compares and returns the maximum of two values.

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

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized + 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.

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

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

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

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

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

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

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 Termination for ()

fn report(self) -> ExitCode

Is called to get the representation of the value as status code. This status code is returned to the operating system.

impl ConstParamTy for ()

impl Eq for ()

impl StructuralPartialEq for ()