unit - Rust
Description: API documentation for the Rust `unit` primitive in crate `std`.
Keywords: rust, rustlang, rust-lang, unit

# 1.0.0[−]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() {}

Run

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();
    };

Run

## Trait Implementations

### `impl Debug for ()`[src]

#### `fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

### `impl Default for ()`[src]

#### `fn default()`[src]

Returns the default value of `()`

### `impl Eq for ()`[src]

### `impl Extend<()> for ()`1.28.0[src]

#### `fn extend<T>(&mut self, iter: T) where
T: IntoIterator<Item = ()>,` [src]

Extends a collection with the contents of an iterator. Read more

#### `fn extend_one(&mut self, _item: ())`[src]

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

Extends a collection with exactly one element.

#### `fn extend_reserve(&mut self, additional: usize)`[src]

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

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

### `impl FromIterator<()> for ()`1.23.0[src]

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());

Run

#### `fn from_iter<I>(iter: I) where
I: IntoIterator<Item = ()>,` [src]

Creates a value from an iterator. Read more

### `impl Hash for ()`[src]

#### `fn hash<H>(&self, _state: &mut H) where
H: Hasher,` [src]

Feeds this value into the given `Hasher`. Read more

#### `fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,` 1.3.0[src]

Feeds a slice of this type into the given `Hasher`. Read more

### `impl Ord for ()`[src]

#### `fn cmp(&self, _other: &()) -> Ordering`[src]

This method returns an `Ordering` between `self` and `other`. Read more

#### `#[must_use]fn max(self, other: Self) -> Self`1.21.0[src]

Compares and returns the maximum of two values. Read more

#### `#[must_use]fn min(self, other: Self) -> Self`1.21.0[src]

Compares and returns the minimum of two values. Read more

#### `#[must_use]fn clamp(self, min: Self, max: Self) -> Self`[src]

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

Restrict a value to a certain interval. Read more

### `impl PartialEq<()> for ()`[src]

#### `fn eq(&self, _other: &()) -> bool`[src]

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

#### `fn ne(&self, _other: &()) -> bool`[src]

This method tests for `!=`.

### `impl PartialOrd<()> for ()`[src]

#### `fn partial_cmp(&self, &()) -> Option<Ordering>`[src]

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

#### `#[must_use]fn lt(&self, other: &Rhs) -> bool`[src]

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

#### `#[must_use]fn le(&self, other: &Rhs) -> bool`[src]

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

#### `#[must_use]fn gt(&self, other: &Rhs) -> bool`[src]

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

#### `#[must_use]fn ge(&self, other: &Rhs) -> bool`[src]

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

### `impl Termination for ()`[src]

#### `fn report(self) -> i32`[src]

🔬 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. Read more