# Primitive Type unit

1.0.0
Expand description

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§

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### impl Debug for ()

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

Formats the value using the given formatter. Read more
1.0.0 (const: unstable) · Source§

### impl Default for ()

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#### fn default()

Returns the default value of `()`

1.28.0 · Source§

### impl Extend<()> for ()

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

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, _item: ())

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
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#### 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. Read more
1.23.0 · Source§

### 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());

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#### fn from_iter<I>(iter: I)
where I: IntoIterator<Item = ()>,

Creates a value from an iterator. Read more
1.0.0 · Source§

### impl Hash for ()

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

Feeds this value into the given `Hasher`. Read more
1.3.0 · Source§

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

Feeds a slice of this type into the given `Hasher`. Read more
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### impl Ord for ()

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

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 · Source§

#### fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · Source§

#### fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · Source§

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

Restrict a value to a certain interval. Read more
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### impl PartialEq for ()

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

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, _other: &()) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialOrd for ()

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

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

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

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 · Source§

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

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 · Source§

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

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 · Source§

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

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
1.61.0 · Source§

### impl Termination for ()

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#### 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.
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### impl ConstParamTy_ for ()

1.0.0 · Source§

### impl Eq for ()

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### impl StructuralPartialEq for ()

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### impl UnsizedConstParamTy for ()

## Auto Trait Implementations§

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### impl Freeze for ()

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### impl RefUnwindSafe for ()

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### impl Send for ()

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### impl Sync for ()

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### impl Unpin for ()

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### impl UnwindSafe for ()

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.