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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Formats the value using the given formatter.

impl Default for ()

fn default()

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Returns the default value of ()

impl Extend<()> for ()

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

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)

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Creates a value from an iterator.

impl Hash for ()

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Feeds this value into the given Hasher.

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

where Self: Sized,

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Feeds a slice of this type into the given Hasher.

impl Ord for ()

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

This method returns an Ordering between self and other.

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

where Self: Sized,

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Compares and returns the maximum of two values.

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

where Self: Sized,

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Compares and returns the minimum of two values.

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

where Self: Sized,

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Restrict a value to a certain interval.

impl PartialEq for ()

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Tests for self and other values to be equal, and is used by ==.

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

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 item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

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

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Tests less than (for self and other) and is used by the < operator.

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

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

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

Tests greater than (for self and other) and is used by the > operator.

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

This item is validated for IEC 61508 (SIL 2) and ISO 26262 (ASIL B).

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

impl ConstParamTy_ for ()

impl Eq for ()

impl StructuralPartialEq for ()