Primitive Type unit

The () type, sometimes called "unit" or "nil".

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 Hash for ()

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

Feeds this value into the given [Hasher].

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

Feeds a slice of this type into the given [Hasher].

impl Default for ()

fn default()

Returns the default value of ()

impl Ord for ()

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

This method returns an Ordering between self and other.

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

Compares and returns the maximum of two values.

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

Compares and returns the minimum of two values.

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

🔬 This is a nightly-only experimental API. (clamp #44095)

Returns max if self is greater than max, and min if self is less than min. Otherwise this will return self. Panics if min > max.

impl Eq for ()

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 !=.

impl PartialOrd<()> for ()

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

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

#[must_use]

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

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

#[must_use]

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

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

#[must_use]

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

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

#[must_use]

default 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 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 Debug for ()

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

Formats the value using the given formatter.

impl Extend<()> for ()

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

Extends a collection with the contents of an iterator.

impl Termination for ()

fn report(self) -> i32

🔬 This is a nightly-only experimental API. (termination_trait_lib #43301)

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