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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 Extend<()> for ()[src]1.28.0

impl Default for ()[src]

fn default()[src]

Returns the default value of ()

impl Hash for ()[src]

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

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

impl Eq for ()[src]

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

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

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

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

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

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

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 Ord for ()[src]

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

Compares and returns the maximum of two values. Read more

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

Compares and returns the minimum of two values. Read more

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 Debug for ()[src]

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

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

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());

impl Termination for ()[src]

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/primitive.unit.html