Primitive Type array
A fixed-size array, denoted [T; N]
, for the element type, T
, and the non-negative compile-time constant size, N
.
There are two syntactic forms for creating an array:
- A list with each element, i.e.,
[x, y, z]
. - A repeat expression
[x; N]
, which produces an array withN
copies ofx
. The type ofx
must beCopy
.
Note that [expr; 0]
is allowed, and produces an empty array. This will still evaluate expr
, however, and immediately drop the resulting value, so be mindful of side effects.
Arrays of any size implement the following traits if the element type allows it:
Copy
Clone
Debug
-
IntoIterator
(implemented for[T; N]
,&[T; N]
and&mut [T; N]
) -
PartialEq
,PartialOrd
,Eq
,Ord
Hash
-
AsRef
,AsMut
-
Borrow
,BorrowMut
Arrays of sizes from 0 to 32 (inclusive) implement the Default
trait if the element type allows it. As a stopgap, trait implementations are statically generated up to size 32.
Arrays coerce to slices ([T]
), so a slice method may be called on an array. Indeed, this provides most of the API for working with arrays. Slices have a dynamic size and do not coerce to arrays.
You can move elements out of an array with a slice pattern. If you want one element, see mem::replace
.
Examples
let mut array: [i32; 3] = [0; 3]; array[1] = 1; array[2] = 2; assert_eq!([1, 2], &array[1..]); // This loop prints: 0 1 2 for x in array { print!("{} ", x); }
You can also iterate over reference to the array’s elements:
let array: [i32; 3] = [0; 3]; for x in &array { }
You can use a slice pattern to move elements out of an array:
fn move_away(_: String) { /* Do interesting things. */ } let [john, roa] = ["John".to_string(), "Roa".to_string()]; move_away(john); move_away(roa);
Editions
Prior to Rust 1.53, arrays did not implement IntoIterator
by value, so the method call array.into_iter()
auto-referenced into a slice iterator. Right now, the old behavior is preserved in the 2015 and 2018 editions of Rust for compatibility, ignoring IntoIterator
by value. In the future, the behavior on the 2015 and 2018 edition might be made consistent to the behavior of later editions.
// Rust 2015 and 2018: let array: [i32; 3] = [0; 3]; // This creates a slice iterator, producing references to each value. for item in array.into_iter().enumerate() { let (i, x): (usize, &i32) = item; println!("array[{}] = {}", i, x); } // The `array_into_iter` lint suggests this change for future compatibility: for item in array.iter().enumerate() { let (i, x): (usize, &i32) = item; println!("array[{}] = {}", i, x); } // You can explicitly iterate an array by value using // `IntoIterator::into_iter` or `std::array::IntoIter::new`: for item in IntoIterator::into_iter(array).enumerate() { let (i, x): (usize, i32) = item; println!("array[{}] = {}", i, x); }
Starting in the 2021 edition, array.into_iter()
uses IntoIterator
normally to iterate by value, and iter()
should be used to iterate by reference like previous editions.
// Rust 2021: let array: [i32; 3] = [0; 3]; // This iterates by reference: for item in array.iter().enumerate() { let (i, x): (usize, &i32) = item; println!("array[{}] = {}", i, x); } // This iterates by value: for item in array.into_iter().enumerate() { let (i, x): (usize, i32) = item; println!("array[{}] = {}", i, x); }
Future language versions might start treating the array.into_iter()
syntax on editions 2015 and 2018 the same as on edition 2021. So code using those older editions should still be written with this change in mind, to prevent breakage in the future. The safest way to accomplish this is to avoid the into_iter
syntax on those editions. If an edition update is not viable/desired, there are multiple alternatives:
- use
iter
, equivalent to the old behavior, creating references - use
IntoIterator::into_iter
, equivalent to the post-2021 behavior (Rust 1.53+) - replace
for ... in array.into_iter() {
withfor ... in array {
, equivalent to the post-2021 behavior (Rust 1.53+)
// Rust 2015 and 2018: let array: [i32; 3] = [0; 3]; // This iterates by reference: for item in array.iter() { let x: &i32 = item; println!("{}", x); } // This iterates by value: for item in IntoIterator::into_iter(array) { let x: i32 = item; println!("{}", x); } // This iterates by value: for item in array { let x: i32 = item; println!("{}", x); } // IntoIter can also start a chain. // This iterates by value: for item in IntoIterator::into_iter(array).enumerate() { let (i, x): (usize, i32) = item; println!("array[{}] = {}", i, x); }
Implementations
impl<T, const N: usize> [T; N]
Returns an array of the same size as self
, with function f
applied to each element in order.
If you don’t necessarily need a new fixed-size array, consider using Iterator::map
instead.
Note on performance and stack usage
Unfortunately, usages of this method are currently not always optimized as well as they could be. This mainly concerns large arrays, as mapping over small arrays seem to be optimized just fine. Also note that in debug mode (i.e. without any optimizations), this method can use a lot of stack space (a few times the size of the array or more).
Therefore, in performance-critical code, try to avoid using this method on large arrays or check the emitted code. Also try to avoid chained maps (e.g. arr.map(...).map(...)
).
In many cases, you can instead use Iterator::map
by calling .iter()
or .into_iter()
on your array. [T; N]::map
is only necessary if you really need a new array of the same size as the result. Rust’s lazy iterators tend to get optimized very well.
Examples
let x = [1, 2, 3]; let y = x.map(|v| v + 1); assert_eq!(y, [2, 3, 4]); let x = [1, 2, 3]; let mut temp = 0; let y = x.map(|v| { temp += 1; v * temp }); assert_eq!(y, [1, 4, 9]); let x = ["Ferris", "Bueller's", "Day", "Off"]; let y = x.map(|v| v.len()); assert_eq!(y, [6, 9, 3, 3]);
pub fn zip<U>(self, rhs: [U; N]) -> [(T, U); N]
‘Zips up’ two arrays into a single array of pairs.
zip()
returns a new array where every element is a tuple where the first element comes from the first array, and the second element comes from the second array. In other words, it zips two arrays together, into a single one.
Examples
#![feature(array_zip)] let x = [1, 2, 3]; let y = [4, 5, 6]; let z = x.zip(y); assert_eq!(z, [(1, 4), (2, 5), (3, 6)]);
pub fn as_slice(&self) -> &[T]
Returns a slice containing the entire array. Equivalent to &s[..]
.
pub fn as_mut_slice(&mut self) -> &mut [T]
Returns a mutable slice containing the entire array. Equivalent to &mut s[..]
.
pub fn each_ref(&self) -> [&T; N]
Borrows each element and returns an array of references with the same size as self
.
Example
#![feature(array_methods)] let floats = [3.1, 2.7, -1.0]; let float_refs: [&f64; 3] = floats.each_ref(); assert_eq!(float_refs, [&3.1, &2.7, &-1.0]);
This method is particularly useful if combined with other methods, like map
. This way, you can avoid moving the original array if its elements are not Copy
.
#![feature(array_methods)] let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()]; let is_ascii = strings.each_ref().map(|s| s.is_ascii()); assert_eq!(is_ascii, [true, false, true]); // We can still access the original array: it has not been moved. assert_eq!(strings.len(), 3);
pub fn each_mut(&mut self) -> [&mut T; N]
Borrows each element mutably and returns an array of mutable references with the same size as self
.
Example
#![feature(array_methods)] let mut floats = [3.1, 2.7, -1.0]; let float_refs: [&mut f64; 3] = floats.each_mut(); *float_refs[0] = 0.0; assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]); assert_eq!(floats, [0.0, 2.7, -1.0]);
Trait Implementations
impl<T, const N: usize> AsMut<[T]> for [T; N]
pub fn as_mut(&mut self) -> &mut [T]
Performs the conversion.
impl<T, const N: usize> AsRef<[T]> for [T; N]
pub fn as_ref(&self) -> &[T]
Performs the conversion.
impl<T, const N: usize> Borrow<[T]> for [T; N]
pub fn borrow(&self) -> &[T]
Immutably borrows from an owned value. Read more
impl<T, const N: usize> BorrowMut<[T]> for [T; N]
pub fn borrow_mut(&mut self) -> &mut [T]
Mutably borrows from an owned value. Read more
pub fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>
Formats the value using the given formatter. Read more
The hash of an array is the same as that of the corresponding slice, as required by the Borrow
implementation.
#![feature(build_hasher_simple_hash_one)] use std::hash::BuildHasher; let b = std::collections::hash_map::RandomState::new(); let a: [u8; 3] = [0xa8, 0x3c, 0x09]; let s: &[u8] = &[0xa8, 0x3c, 0x09]; assert_eq!(b.hash_one(a), b.hash_one(s));
type Output = <[T] as Index<I>>::Output
The returned type after indexing.
pub fn index(&self, index: I) -> &<[T; N] as Index<I>>::Output
Performs the indexing (container[index]
) operation. Read more
pub fn index_mut(&mut self, index: I) -> &mut <[T; N] as Index<I>>::Output
Performs the mutable indexing (container[index]
) operation. Read more
impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N]
type Item = &'a mut T
The type of the elements being iterated over.
type IntoIter = IterMut<'a, T>
Which kind of iterator are we turning this into?
pub fn into_iter(self) -> IterMut<'a, T>
impl<'a, T> Iterator for IterMut<'a, T> type Item = &'a mut T;
Creates an iterator from a value. Read more
impl<'a, T, const N: usize> IntoIterator for &'a [T; N]
type Item = &'a T
The type of the elements being iterated over.
type IntoIter = Iter<'a, T>
Which kind of iterator are we turning this into?
pub fn into_iter(self) -> Iter<'a, T>
impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;
Creates an iterator from a value. Read more
impl<T, const N: usize> IntoIterator for [T; N]
pub fn into_iter(self) -> <[T; N] as IntoIterator>::IntoIter
Creates a consuming iterator, that is, one that moves each value out of the array (from start to end). The array cannot be used after calling this unless T
implements Copy
, so the whole array is copied.
Arrays have special behavior when calling .into_iter()
prior to the 2021 edition – see the array Editions section for more information.
type Item = T
The type of the elements being iterated over.
type IntoIter = IntoIter<T, N>
Which kind of iterator are we turning this into?
Implements comparison of arrays lexicographically.
pub fn cmp(&self, other: &[T; N]) -> Ordering
fn max(self, other: Self) -> Self
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self
Compares and returns the minimum of two values. Read more
fn clamp(self, min: Self, max: Self) -> Self
Restrict a value to a certain interval. Read more
pub fn eq(&self, other: &&[B]) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
pub fn ne(&self, other: &&[B]) -> bool
This method tests for !=
.
pub fn eq(&self, other: &&mut [B]) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
pub fn ne(&self, other: &&mut [B]) -> bool
This method tests for !=
.
pub fn eq(&self, other: &[B; N]) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
pub fn ne(&self, other: &[B; N]) -> bool
This method tests for !=
.
pub fn eq(&self, other: &[B]) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
pub fn ne(&self, other: &[B]) -> bool
This method tests for !=
.
impl<T, const N: usize> PartialOrd<[T; N]> for [T; N] where
T: PartialOrd<T>,
pub fn partial_cmp(&self, other: &[T; N]) -> Option<Ordering>
This method returns an ordering between self
and other
values if one exists. Read more
pub fn lt(&self, other: &[T; N]) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
pub fn le(&self, other: &[T; N]) -> bool
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
pub fn ge(&self, other: &[T; N]) -> bool
This method tests greater than or equal to (for self
and other
) and is used by the >=
operator. Read more
pub fn gt(&self, other: &[T; N]) -> bool
This method tests greater than (for self
and other
) and is used by the >
operator. Read more
impl<T, const N: usize> SlicePattern for [T; N]
type Item = T
slice_pattern
#56345)stopgap trait for slice patterns
The element type of the slice being matched on.
pub fn as_slice(&self) -> &[<[T; N] as SlicePattern>::Item]
slice_pattern
#56345)stopgap trait for slice patterns
Currently, the consumers of SlicePattern
need a slice.
type Error = TryFromSliceError
The type returned in the event of a conversion error.
pub fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError>
Performs the conversion.
impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N]
type Error = TryFromSliceError
The type returned in the event of a conversion error.
pub fn try_from(slice: &[T]) -> Result<&[T; N], TryFromSliceError>
Performs the conversion.
impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N]
type Error = TryFromSliceError
The type returned in the event of a conversion error.
pub fn try_from(slice: &mut [T]) -> Result<&mut [T; N], TryFromSliceError>
Performs the conversion.
pub fn try_from(vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>>
Gets the entire contents of the Vec<T>
as an array, if its size exactly matches that of the requested array.
Examples
use std::convert::TryInto; assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3])); assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
If the length doesn’t match, the input comes back in Err
:
use std::convert::TryInto; let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into(); assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
If you’re fine with just getting a prefix of the Vec<T>
, you can call .truncate(N)
first.
use std::convert::TryInto; let mut v = String::from("hello world").into_bytes(); v.sort(); v.truncate(2); let [a, b]: [_; 2] = v.try_into().unwrap(); assert_eq!(a, b' '); assert_eq!(b, b'd');
type Error = Vec<T, A>
The type returned in the event of a conversion error.
Auto Trait Implementations
impl<T, const N: usize> RefUnwindSafe for [T; N] where
T: RefUnwindSafe,
impl<T, const N: usize> Send for [T; N] where
T: Send,
impl<T, const N: usize> Sync for [T; N] where
T: Sync,
impl<T, const N: usize> Unpin for [T; N] where
T: Unpin,
impl<T, const N: usize> UnwindSafe for [T; N] where
T: UnwindSafe,
Blanket Implementations
impl<T> From<T> for T
pub fn from(t: T) -> T
Performs the conversion.
pub fn into(self) -> U
Performs the conversion.
type Owned = T
The resulting type after obtaining ownership.
pub fn to_owned(&self) -> T
Creates owned data from borrowed data, usually by cloning. Read more
pub fn clone_into(&self, target: &mut T)
toowned_clone_into
#41263)recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.
© 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.array.html