Struct alloc::vec::Vec

pub struct Vec<T, A: Allocator = Global> { /* private fields */ }

A contiguous growable array type, written as Vec<T>, short for ‘vector’.

Examples

let mut vec = Vec::new();
vec.push(1);
vec.push(2);

assert_eq!(vec.len(), 2);
assert_eq!(vec[0], 1);

assert_eq!(vec.pop(), Some(2));
assert_eq!(vec.len(), 1);

vec[0] = 7;
assert_eq!(vec[0], 7);

vec.extend([1, 2, 3]);

for x in &vec {
    println!("{x}");
}
assert_eq!(vec, [7, 1, 2, 3]);

The [vec!] macro is provided for convenient initialization:

let mut vec1 = vec![1, 2, 3];
vec1.push(4);
let vec2 = Vec::from([1, 2, 3, 4]);
assert_eq!(vec1, vec2);

It can also initialize each element of a Vec<T> with a given value. This may be more efficient than performing allocation and initialization in separate steps, especially when initializing a vector of zeros:

let vec = vec![0; 5];
assert_eq!(vec, [0, 0, 0, 0, 0]);

// The following is equivalent, but potentially slower:
let mut vec = Vec::with_capacity(5);
vec.resize(5, 0);
assert_eq!(vec, [0, 0, 0, 0, 0]);

For more information, see Capacity and Reallocation.

Use a Vec<T> as an efficient stack:

let mut stack = Vec::new();

stack.push(1);
stack.push(2);
stack.push(3);

while let Some(top) = stack.pop() {
    // Prints 3, 2, 1
    println!("{top}");
}

Indexing

The Vec type allows access to values by index, because it implements the Index trait. An example will be more explicit:

let v = vec![0, 2, 4, 6];
println!("{}", v[1]); // it will display '2'

However be careful: if you try to access an index which isn’t in the Vec, your software will panic! You cannot do this:

let v = vec![0, 2, 4, 6];
println!("{}", v[6]); // it will panic!

Use get and get_mut if you want to check whether the index is in the Vec.

Slicing

A Vec can be mutable. On the other hand, slices are read-only objects. To get a slice, use &. Example:

fn read_slice(slice: &[usize]) {
    // ...
}

let v = vec![0, 1];
read_slice(&v);

// ... and that's all!
// you can also do it like this:
let u: &[usize] = &v;
// or like this:
let u: &[_] = &v;

In Rust, it’s more common to pass slices as arguments rather than vectors when you just want to provide read access. The same goes for String and &str.

Capacity and reallocation

The capacity of a vector is the amount of space allocated for any future elements that will be added onto the vector. This is not to be confused with the length of a vector, which specifies the number of actual elements within the vector. If a vector’s length exceeds its capacity, its capacity will automatically be increased, but its elements will have to be reallocated.

For example, a vector with capacity 10 and length 0 would be an empty vector with space for 10 more elements. Pushing 10 or fewer elements onto the vector will not change its capacity or cause reallocation to occur. However, if the vector’s length is increased to 11, it will have to reallocate, which can be slow. For this reason, it is recommended to use [Vec::with_capacity] whenever possible to specify how big the vector is expected to get.

Guarantees

Due to its incredibly fundamental nature, Vec makes a lot of guarantees about its design. This ensures that it’s as low-overhead as possible in the general case, and can be correctly manipulated in primitive ways by unsafe code. Note that these guarantees refer to an unqualified Vec<T>. If additional type parameters are added (e.g., to support custom allocators), overriding their defaults may change the behavior.

Most fundamentally, Vec is and always will be a (pointer, capacity, length) triplet. No more, no less. The order of these fields is completely unspecified, and you should use the appropriate methods to modify these. The pointer will never be null, so this type is null-pointer-optimized.

However, the pointer might not actually point to allocated memory. In particular, if you construct a Vec with capacity 0 via Vec::new, [vec![]][vec!], [Vec::with_capacity(0)][Vec::with_capacity], or by calling shrink_to_fit on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized types inside a Vec, it will not allocate space for them. Note that in this case the Vec might not report a capacity of 0. Vec will allocate if and only if mem::size_of::<T>() * capacity() > 0. In general, Vec’s allocation details are very subtle — if you intend to allocate memory using a Vec and use it for something else (either to pass to unsafe code, or to build your own memory-backed collection), be sure to deallocate this memory by using from_raw_parts to recover the Vec and then dropping it.

If a Vec has allocated memory, then the memory it points to is on the heap (as defined by the allocator Rust is configured to use by default), and its pointer points to len initialized, contiguous elements in order (what you would see if you coerced it to a slice), followed by capacity - len logically uninitialized, contiguous elements.

A vector containing the elements 'a' and 'b' with capacity 4 can be visualized as below. The top part is the Vec struct, it contains a pointer to the head of the allocation in the heap, length and capacity. The bottom part is the allocation on the heap, a contiguous memory block.

            ptr      len  capacity
       +--------+--------+--------+
       | 0x0123 |      2 |      4 |
       +--------+--------+--------+
            |
            v
Heap   +--------+--------+--------+--------+
       |    'a' |    'b' | uninit | uninit |
       +--------+--------+--------+--------+

• uninit represents memory that is not initialized, see MaybeUninit.
• Note: the ABI is not stable and Vec makes no guarantees about its memory layout (including the order of fields).

Vec will never perform a “small optimization” where elements are actually stored on the stack for two reasons:

• It would make it more difficult for unsafe code to correctly manipulate a Vec. The contents of a Vec wouldn’t have a stable address if it were only moved, and it would be more difficult to determine if a Vec had actually allocated memory.

• It would penalize the general case, incurring an additional branch on every access.

Vec will never automatically shrink itself, even if completely empty. This ensures no unnecessary allocations or deallocations occur. Emptying a Vec and then filling it back up to the same len should incur no calls to the allocator. If you wish to free up unused memory, use shrink_to_fit or shrink_to.

push and insert will never (re)allocate if the reported capacity is sufficient. push and insert will (re)allocate if len == capacity. That is, the reported capacity is completely accurate, and can be relied on. It can even be used to manually free the memory allocated by a Vec if desired. Bulk insertion methods may reallocate, even when not necessary.

Vec does not guarantee any particular growth strategy when reallocating when full, nor when reserve is called. The current strategy is basic and it may prove desirable to use a non-constant growth factor. Whatever strategy is used will of course guarantee O(1) amortized push.

vec![x; n], vec![a, b, c, d], and [Vec::with_capacity(n)][Vec::with_capacity], will all produce a Vec with exactly the requested capacity. If len == capacity, (as is the case for the [vec!] macro), then a Vec<T> can be converted to and from a Box<[T]> without reallocating or moving the elements.

Vec will not specifically overwrite any data that is removed from it, but also won’t specifically preserve it. Its uninitialized memory is scratch space that it may use however it wants. It will generally just do whatever is most efficient or otherwise easy to implement. Do not rely on removed data to be erased for security purposes. Even if you drop a Vec, its buffer may simply be reused by another allocation. Even if you zero a Vec’s memory first, that might not actually happen because the optimizer does not consider this a side-effect that must be preserved. There is one case which we will not break, however: using unsafe code to write to the excess capacity, and then increasing the length to match, is always valid.

Currently, Vec does not guarantee the order in which elements are dropped. The order has changed in the past and may change again.

Implementations

impl<T> Vec<T>

pub const fn new() -> Self

Constructs a new, empty Vec<T>.

The vector will not allocate until elements are pushed onto it.

Examples

let mut vec: Vec<i32> = Vec::new();

pub fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError>

Tries to construct a new, empty Vec<T> with at least the specified capacity.

The vector will be able to hold at least capacity elements without reallocating. This method is allowed to allocate for more elements than capacity. If capacity is 0, the vector will not allocate.

It is important to note that although the returned vector has the minimum capacity specified, the vector will have a zero length. For an explanation of the difference between length and capacity, see Capacity and reallocation.

If it is important to know the exact allocated capacity of a Vec, always use the capacity method after construction.

For Vec<T> where T is a zero-sized type, there will be no allocation and the capacity will always be usize::MAX.

Examples

let mut vec = Vec::try_with_capacity(10).unwrap();

// The vector contains no items, even though it has capacity for more
assert_eq!(vec.len(), 0);
assert!(vec.capacity() >= 10);

// These are all done without reallocating...
for i in 0..10 {
    vec.push(i);
}
assert_eq!(vec.len(), 10);
assert!(vec.capacity() >= 10);

// ...but this may make the vector reallocate
vec.push(11);
assert_eq!(vec.len(), 11);
assert!(vec.capacity() >= 11);

let mut result = Vec::try_with_capacity(usize::MAX);
assert!(result.is_err());

// A vector of a zero-sized type will always over-allocate, since no
// allocation is necessary
let vec_units = Vec::<()>::try_with_capacity(10).unwrap();
assert_eq!(vec_units.capacity(), usize::MAX);

pub unsafe fn from_raw_parts( ptr: *mut T, length: usize, capacity: usize ) -> Self

Creates a Vec<T> directly from a pointer, a capacity, and a length.

Safety

This is highly unsafe, due to the number of invariants that aren’t checked:

• ptr must have been allocated using the global allocator, such as via the alloc::alloc function.
• T needs to have the same alignment as what ptr was allocated with. (T having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the dealloc requirement that memory must be allocated and deallocated with the same layout.)
• The size of T times the capacity (ie. the allocated size in bytes) needs to be the same size as the pointer was allocated with. (Because similar to alignment, dealloc must be called with the same layout size.)
• length needs to be less than or equal to capacity.
• The first length values must be properly initialized values of type T.
• capacity needs to be the capacity that the pointer was allocated with.
• The allocated size in bytes must be no larger than isize::MAX. See the safety documentation of pointer::offset.

These requirements are always upheld by any ptr that has been allocated via Vec<T>. Other allocation sources are allowed if the invariants are upheld.

Violating these may cause problems like corrupting the allocator’s internal data structures. For example it is normally not safe to build a Vec<u8> from a pointer to a C char array with length size_t, doing so is only safe if the array was initially allocated by a Vec or String. It’s also not safe to build one from a Vec<u16> and its length, because the allocator cares about the alignment, and these two types have different alignments. The buffer was allocated with alignment 2 (for u16), but after turning it into a Vec<u8> it’ll be deallocated with alignment 1. To avoid these issues, it is often preferable to do casting/transmuting using slice::from_raw_parts instead.

The ownership of ptr is effectively transferred to the Vec<T> which may then deallocate, reallocate or change the contents of memory pointed to by the pointer at will. Ensure that nothing else uses the pointer after calling this function.

Examples

use std::ptr;
use std::mem;

let v = vec![1, 2, 3];

// Prevent running `v`'s destructor so we are in complete control
// of the allocation.
let mut v = mem::ManuallyDrop::new(v);

// Pull out the various important pieces of information about `v`
let p = v.as_mut_ptr();
let len = v.len();
let cap = v.capacity();

unsafe {
    // Overwrite memory with 4, 5, 6
    for i in 0..len {
        ptr::write(p.add(i), 4 + i);
    }

    // Put everything back together into a Vec
    let rebuilt = Vec::from_raw_parts(p, len, cap);
    assert_eq!(rebuilt, [4, 5, 6]);
}

Using memory that was allocated elsewhere:

use std::alloc::{alloc, Layout};

fn main() {
    let layout = Layout::array::<u32>(16).expect("overflow cannot happen");

    let vec = unsafe {
        let mem = alloc(layout).cast::<u32>();
        if mem.is_null() {
            return;
        }

        mem.write(1_000_000);

        Vec::from_raw_parts(mem, 1, 16)
    };

    assert_eq!(vec, &[1_000_000]);
    assert_eq!(vec.capacity(), 16);
}

impl<T, A: Allocator> Vec<T, A>

pub const fn new_in(alloc: A) -> Self

🔬This is a nightly-only experimental API. (allocator_api #32838)

Constructs a new, empty Vec<T, A>.

The vector will not allocate until elements are pushed onto it.

Examples

#![feature(allocator_api)]

use std::alloc::System;

let mut vec: Vec<i32, _> = Vec::new_in(System);

pub fn try_with_capacity_in( capacity: usize, alloc: A ) -> Result<Self, TryReserveError>

Tries to construct a new, empty Vec<T, A> with at least the specified capacity with the provided allocator.

The vector will be able to hold at least capacity elements without reallocating. This method is allowed to allocate for more elements than capacity. If capacity is 0, the vector will not allocate.

It is important to note that although the returned vector has the minimum capacity specified, the vector will have a zero length. For an explanation of the difference between length and capacity, see Capacity and reallocation.

If it is important to know the exact allocated capacity of a Vec, always use the capacity method after construction.

For Vec<T, A> where T is a zero-sized type, there will be no allocation and the capacity will always be usize::MAX.

Examples

#![feature(allocator_api)]

use std::alloc::System;

let mut vec = Vec::try_with_capacity_in(10, System).unwrap();

// The vector contains no items, even though it has capacity for more
assert_eq!(vec.len(), 0);
assert!(vec.capacity() >= 10);

// These are all done without reallocating...
for i in 0..10 {
    vec.push(i);
}
assert_eq!(vec.len(), 10);
assert!(vec.capacity() >= 10);

// ...but this may make the vector reallocate
vec.push(11);
assert_eq!(vec.len(), 11);
assert!(vec.capacity() >= 11);

let mut result = Vec::try_with_capacity_in(usize::MAX, System);
assert!(result.is_err());

// A vector of a zero-sized type will always over-allocate, since no
// allocation is necessary
let vec_units = Vec::<(), System>::try_with_capacity_in(10, System).unwrap();
assert_eq!(vec_units.capacity(), usize::MAX);

pub unsafe fn from_raw_parts_in( ptr: *mut T, length: usize, capacity: usize, alloc: A ) -> Self

🔬This is a nightly-only experimental API. (allocator_api #32838)

Creates a Vec<T, A> directly from a pointer, a capacity, a length, and an allocator.

Safety

This is highly unsafe, due to the number of invariants that aren’t checked:

• ptr must be currently allocated via the given allocator alloc.
• T needs to have the same alignment as what ptr was allocated with. (T having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the dealloc requirement that memory must be allocated and deallocated with the same layout.)
• The size of T times the capacity (ie. the allocated size in bytes) needs to be the same size as the pointer was allocated with. (Because similar to alignment, dealloc must be called with the same layout size.)
• length needs to be less than or equal to capacity.
• The first length values must be properly initialized values of type T.
• capacity needs to fit the layout size that the pointer was allocated with.
• The allocated size in bytes must be no larger than isize::MAX. See the safety documentation of pointer::offset.

These requirements are always upheld by any ptr that has been allocated via Vec<T, A>. Other allocation sources are allowed if the invariants are upheld.

Violating these may cause problems like corrupting the allocator’s internal data structures. For example it is not safe to build a Vec<u8> from a pointer to a C char array with length size_t. It’s also not safe to build one from a Vec<u16> and its length, because the allocator cares about the alignment, and these two types have different alignments. The buffer was allocated with alignment 2 (for u16), but after turning it into a Vec<u8> it’ll be deallocated with alignment 1.

The ownership of ptr is effectively transferred to the Vec<T> which may then deallocate, reallocate or change the contents of memory pointed to by the pointer at will. Ensure that nothing else uses the pointer after calling this function.

Examples

#![feature(allocator_api)]

use std::alloc::System;

use std::ptr;
use std::mem;

let mut v = Vec::with_capacity_in(3, System);
v.push(1);
v.push(2);
v.push(3);

// Prevent running `v`'s destructor so we are in complete control
// of the allocation.
let mut v = mem::ManuallyDrop::new(v);

// Pull out the various important pieces of information about `v`
let p = v.as_mut_ptr();
let len = v.len();
let cap = v.capacity();
let alloc = v.allocator();

unsafe {
    // Overwrite memory with 4, 5, 6
    for i in 0..len {
        ptr::write(p.add(i), 4 + i);
    }

    // Put everything back together into a Vec
    let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
    assert_eq!(rebuilt, [4, 5, 6]);
}

Using memory that was allocated elsewhere:

#![feature(allocator_api)]

use std::alloc::{AllocError, Allocator, Global, Layout};

fn main() {
    let layout = Layout::array::<u32>(16).expect("overflow cannot happen");

    let vec = unsafe {
        let mem = match Global.allocate(layout) {
            Ok(mem) => mem.cast::<u32>().as_ptr(),
            Err(AllocError) => return,
        };

        mem.write(1_000_000);

        Vec::from_raw_parts_in(mem, 1, 16, Global)
    };

    assert_eq!(vec, &[1_000_000]);
    assert_eq!(vec.capacity(), 16);
}

pub fn into_raw_parts(self) -> (*mut T, usize, usize)

🔬This is a nightly-only experimental API. (vec_into_raw_parts #65816)

Decomposes a Vec<T> into its raw components.

Returns the raw pointer to the underlying data, the length of the vector (in elements), and the allocated capacity of the data (in elements). These are the same arguments in the same order as the arguments to from_raw_parts.

After calling this function, the caller is responsible for the memory previously managed by the Vec. The only way to do this is to convert the raw pointer, length, and capacity back into a Vec with the from_raw_parts function, allowing the destructor to perform the cleanup.

Examples

#![feature(vec_into_raw_parts)]
let v: Vec<i32> = vec![-1, 0, 1];

let (ptr, len, cap) = v.into_raw_parts();

let rebuilt = unsafe {
    // We can now make changes to the components, such as
    // transmuting the raw pointer to a compatible type.
    let ptr = ptr as *mut u32;

    Vec::from_raw_parts(ptr, len, cap)
};
assert_eq!(rebuilt, [4294967295, 0, 1]);

pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A)

🔬This is a nightly-only experimental API. (allocator_api #32838)

Decomposes a Vec<T> into its raw components.

Returns the raw pointer to the underlying data, the length of the vector (in elements), the allocated capacity of the data (in elements), and the allocator. These are the same arguments in the same order as the arguments to from_raw_parts_in.

After calling this function, the caller is responsible for the memory previously managed by the Vec. The only way to do this is to convert the raw pointer, length, and capacity back into a Vec with the from_raw_parts_in function, allowing the destructor to perform the cleanup.

Examples

#![feature(allocator_api, vec_into_raw_parts)]

use std::alloc::System;

let mut v: Vec<i32, System> = Vec::new_in(System);
v.push(-1);
v.push(0);
v.push(1);

let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();

let rebuilt = unsafe {
    // We can now make changes to the components, such as
    // transmuting the raw pointer to a compatible type.
    let ptr = ptr as *mut u32;

    Vec::from_raw_parts_in(ptr, len, cap, alloc)
};
assert_eq!(rebuilt, [4294967295, 0, 1]);

pub fn capacity(&self) -> usize

Returns the total number of elements the vector can hold without reallocating.

Examples

let mut vec: Vec<i32> = Vec::with_capacity(10);
vec.push(42);
assert!(vec.capacity() >= 10);

pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

Tries to reserve capacity for at least additional more elements to be inserted in the given Vec<T>. The collection may reserve more space to speculatively avoid frequent reallocations. After calling try_reserve, capacity will be greater than or equal to self.len() + additional if it returns Ok(()). Does nothing if capacity is already sufficient. This method preserves the contents even if an error occurs.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

Examples

use std::collections::TryReserveError;

fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
    let mut output = Vec::new();

    // Pre-reserve the memory, exiting if we can't
    output.try_reserve(data.len())?;

    // Now we know this can't OOM in the middle of our complex work
    output.extend(data.iter().map(|&val| {
        val * 2 + 5 // very complicated
    }));

    Ok(output)
}

pub fn try_reserve_exact( &mut self, additional: usize ) -> Result<(), TryReserveError>

Tries to reserve the minimum capacity for at least additional elements to be inserted in the given Vec<T>. Unlike try_reserve, this will not deliberately over-allocate to speculatively avoid frequent allocations. After calling try_reserve_exact, capacity will be greater than or equal to self.len() + additional if it returns Ok(()). Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer try_reserve if future insertions are expected.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

Examples

use std::collections::TryReserveError;

fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
    let mut output = Vec::new();

    // Pre-reserve the memory, exiting if we can't
    output.try_reserve_exact(data.len())?;

    // Now we know this can't OOM in the middle of our complex work
    output.extend(data.iter().map(|&val| {
        val * 2 + 5 // very complicated
    }));

    Ok(output)
}

pub fn truncate(&mut self, len: usize)

Shortens the vector, keeping the first len elements and dropping the rest.

If len is greater or equal to the vector’s current length, this has no effect.

The drain method can emulate truncate, but causes the excess elements to be returned instead of dropped.

Note that this method has no effect on the allocated capacity of the vector.

Examples

Truncating a five element vector to two elements:

let mut vec = vec![1, 2, 3, 4, 5];
vec.truncate(2);
assert_eq!(vec, [1, 2]);

No truncation occurs when len is greater than the vector’s current length:

let mut vec = vec![1, 2, 3];
vec.truncate(8);
assert_eq!(vec, [1, 2, 3]);

Truncating when len == 0 is equivalent to calling the clear method.

let mut vec = vec![1, 2, 3];
vec.truncate(0);
assert_eq!(vec, []);

pub fn as_slice(&self) -> &[T]

Extracts a slice containing the entire vector.

Equivalent to &s[..].

Examples

use std::io::{self, Write};
let buffer = vec![1, 2, 3, 5, 8];
io::sink().write(buffer.as_slice()).unwrap();

pub fn as_mut_slice(&mut self) -> &mut [T]

Extracts a mutable slice of the entire vector.

Equivalent to &mut s[..].

Examples

use std::io::{self, Read};
let mut buffer = vec![0; 3];
io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();

pub fn as_ptr(&self) -> *const T

Returns a raw pointer to the vector’s buffer, or a dangling raw pointer valid for zero sized reads if the vector didn’t allocate.

The caller must ensure that the vector outlives the pointer this function returns, or else it will end up pointing to garbage. Modifying the vector may cause its buffer to be reallocated, which would also make any pointers to it invalid.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an UnsafeCell) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use as_mut_ptr.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying slice, and thus the returned pointer will remain valid when mixed with other calls to as_ptr and as_mut_ptr. Note that calling other methods that materialize mutable references to the slice, or mutable references to specific elements you are planning on accessing through this pointer, as well as writing to those elements, may still invalidate this pointer. See the second example below for how this guarantee can be used.

Examples

let x = vec![1, 2, 4];
let x_ptr = x.as_ptr();

unsafe {
    for i in 0..x.len() {
        assert_eq!(*x_ptr.add(i), 1 << i);
    }
}

Due to the aliasing guarantee, the following code is legal:

unsafe {
    let mut v = vec![0, 1, 2];
    let ptr1 = v.as_ptr();
    let _ = ptr1.read();
    let ptr2 = v.as_mut_ptr().offset(2);
    ptr2.write(2);
    // Notably, the write to `ptr2` did *not* invalidate `ptr1`
    // because it mutated a different element:
    let _ = ptr1.read();
}

pub fn as_mut_ptr(&mut self) -> *mut T

Returns an unsafe mutable pointer to the vector’s buffer, or a dangling raw pointer valid for zero sized reads if the vector didn’t allocate.

The caller must ensure that the vector outlives the pointer this function returns, or else it will end up pointing to garbage. Modifying the vector may cause its buffer to be reallocated, which would also make any pointers to it invalid.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying slice, and thus the returned pointer will remain valid when mixed with other calls to as_ptr and as_mut_ptr. Note that calling other methods that materialize references to the slice, or references to specific elements you are planning on accessing through this pointer, may still invalidate this pointer. See the second example below for how this guarantee can be used.

Examples

// Allocate vector big enough for 4 elements.
let size = 4;
let mut x: Vec<i32> = Vec::with_capacity(size);
let x_ptr = x.as_mut_ptr();

// Initialize elements via raw pointer writes, then set length.
unsafe {
    for i in 0..size {
        *x_ptr.add(i) = i as i32;
    }
    x.set_len(size);
}
assert_eq!(&*x, &[0, 1, 2, 3]);

Due to the aliasing guarantee, the following code is legal:

unsafe {
    let mut v = vec![0];
    let ptr1 = v.as_mut_ptr();
    ptr1.write(1);
    let ptr2 = v.as_mut_ptr();
    ptr2.write(2);
    // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
    ptr1.write(3);
}

pub fn allocator(&self) -> &A

🔬This is a nightly-only experimental API. (allocator_api #32838)

Returns a reference to the underlying allocator.

pub unsafe fn set_len(&mut self, new_len: usize)

Forces the length of the vector to new_len.

This is a low-level operation that maintains none of the normal invariants of the type. Normally changing the length of a vector is done using one of the safe operations instead, such as truncate, resize, extend, or clear.

Safety

• new_len must be less than or equal to capacity().
• The elements at old_len..new_len must be initialized.

Examples

This method can be useful for situations in which the vector is serving as a buffer for other code, particularly over FFI:

pub fn get_dictionary(&self) -> Option<Vec<u8>> {
    // Per the FFI method's docs, "32768 bytes is always enough".
    let mut dict = Vec::with_capacity(32_768);
    let mut dict_length = 0;
    // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
    // 1. `dict_length` elements were initialized.
    // 2. `dict_length` <= the capacity (32_768)
    // which makes `set_len` safe to call.
    unsafe {
        // Make the FFI call...
        let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
        if r == Z_OK {
            // ...and update the length to what was initialized.
            dict.set_len(dict_length);
            Some(dict)
        } else {
            None
        }
    }
}

While the following example is sound, there is a memory leak since the inner vectors were not freed prior to the set_len call:

let mut vec = vec![vec![1, 0, 0],
                   vec![0, 1, 0],
                   vec![0, 0, 1]];
// SAFETY:
// 1. `old_len..0` is empty so no elements need to be initialized.
// 2. `0 <= capacity` always holds whatever `capacity` is.
unsafe {
    vec.set_len(0);
}

Normally, here, one would use clear instead to correctly drop the contents and thus not leak memory.

pub fn swap_remove(&mut self, index: usize) -> T

Removes an element from the vector and returns it.

The removed element is replaced by the last element of the vector.

This does not preserve ordering, but is O(1). If you need to preserve the element order, use remove instead.

Panics

Panics if index is out of bounds.

Examples

let mut v = vec!["foo", "bar", "baz", "qux"];

assert_eq!(v.swap_remove(1), "bar");
assert_eq!(v, ["foo", "qux", "baz"]);

assert_eq!(v.swap_remove(0), "foo");
assert_eq!(v, ["baz", "qux"]);

pub fn remove(&mut self, index: usize) -> T

Removes and returns the element at position index within the vector, shifting all elements after it to the left.

Note: Because this shifts over the remaining elements, it has a worst-case performance of O(n). If you don’t need the order of elements to be preserved, use swap_remove instead. If you’d like to remove elements from the beginning of the Vec, consider using VecDeque::pop_front instead.

Panics

Panics if index is out of bounds.

Examples

let mut v = vec![1, 2, 3];
assert_eq!(v.remove(1), 2);
assert_eq!(v, [1, 3]);

pub fn retain<F>(&mut self, f: F)where F: FnMut(&T) -> bool,

Retains only the elements specified by the predicate.

In other words, remove all elements e for which f(&e) returns false. This method operates in place, visiting each element exactly once in the original order, and preserves the order of the retained elements.

Examples

let mut vec = vec![1, 2, 3, 4];
vec.retain(|&x| x % 2 == 0);
assert_eq!(vec, [2, 4]);

Because the elements are visited exactly once in the original order, external state may be used to decide which elements to keep.

let mut vec = vec![1, 2, 3, 4, 5];
let keep = [false, true, true, false, true];
let mut iter = keep.iter();
vec.retain(|_| *iter.next().unwrap());
assert_eq!(vec, [2, 3, 5]);

pub fn retain_mut<F>(&mut self, f: F)where F: FnMut(&mut T) -> bool,

Retains only the elements specified by the predicate, passing a mutable reference to it.

In other words, remove all elements e such that f(&mut e) returns false. This method operates in place, visiting each element exactly once in the original order, and preserves the order of the retained elements.

Examples

let mut vec = vec![1, 2, 3, 4];
vec.retain_mut(|x| if *x <= 3 {
    *x += 1;
    true
} else {
    false
});
assert_eq!(vec, [2, 3, 4]);

pub fn dedup_by_key<F, K>(&mut self, key: F)where F: FnMut(&mut T) -> K, K: PartialEq,

Removes all but the first of consecutive elements in the vector that resolve to the same key.

If the vector is sorted, this removes all duplicates.

Examples

let mut vec = vec![10, 20, 21, 30, 20];

vec.dedup_by_key(|i| *i / 10);

assert_eq!(vec, [10, 20, 30, 20]);

pub fn dedup_by<F>(&mut self, same_bucket: F)where F: FnMut(&mut T, &mut T) -> bool,

Removes all but the first of consecutive elements in the vector satisfying a given equality relation.

The same_bucket function is passed references to two elements from the vector and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if same_bucket(a, b) returns true, a is removed.

If the vector is sorted, this removes all duplicates.

Examples

let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];

vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));

assert_eq!(vec, ["foo", "bar", "baz", "bar"]);

pub fn try_push(&mut self, value: T) -> Result<(), TryReserveError>

Tries to append an element to the back of a collection.

Examples

let mut vec = vec![1, 2];
vec.try_push(3).unwrap();
assert_eq!(vec, [1, 2, 3]);

pub fn push_within_capacity(&mut self, value: T) -> Result<(), T>

🔬This is a nightly-only experimental API. (vec_push_within_capacity #100486)

Appends an element if there is sufficient spare capacity, otherwise an error is returned with the element.

Unlike push this method will not reallocate when there’s insufficient capacity. The caller should use reserve or try_reserve to ensure that there is enough capacity.

Examples

A manual, panic-free alternative to FromIterator:

#![feature(vec_push_within_capacity)]

use std::collections::TryReserveError;
fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
    let mut vec = Vec::new();
    for value in iter {
        if let Err(value) = vec.push_within_capacity(value) {
            vec.try_reserve(1)?;
            // this cannot fail, the previous line either returned or added at least 1 free slot
            let _ = vec.push_within_capacity(value);
        }
    }
    Ok(vec)
}
assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));

pub fn pop(&mut self) -> Option<T>

Removes the last element from a vector and returns it, or None if it is empty.

If you’d like to pop the first element, consider using VecDeque::pop_front instead.

Examples

let mut vec = vec![1, 2, 3];
assert_eq!(vec.pop(), Some(3));
assert_eq!(vec, [1, 2]);

pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A> where R: RangeBounds<usize>,

Removes the specified range from the vector in bulk, returning all removed elements as an iterator. If the iterator is dropped before being fully consumed, it drops the remaining removed elements.

The returned iterator keeps a mutable borrow on the vector to optimize its implementation.

Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

Leaking

If the returned iterator goes out of scope without being dropped (due to mem::forget, for example), the vector may have lost and leaked elements arbitrarily, including elements outside the range.

Examples

let mut v = vec![1, 2, 3];
let u: Vec<_> = v.drain(1..).collect();
assert_eq!(v, &[1]);
assert_eq!(u, &[2, 3]);

// A full range clears the vector, like `clear()` does
v.drain(..);
assert_eq!(v, &[]);

pub fn clear(&mut self)

Clears the vector, removing all values.

Note that this method has no effect on the allocated capacity of the vector.

Examples

let mut v = vec![1, 2, 3];

v.clear();

assert!(v.is_empty());

pub fn len(&self) -> usize

Returns the number of elements in the vector, also referred to as its ‘length’.

Examples

let a = vec![1, 2, 3];
assert_eq!(a.len(), 3);

pub fn is_empty(&self) -> bool

Returns true if the vector contains no elements.

Examples

let mut v = Vec::new();
assert!(v.is_empty());

v.push(1);
assert!(!v.is_empty());

pub fn leak<'a>(self) -> &'a mut [T]where A: 'a,

Consumes and leaks the Vec, returning a mutable reference to the contents, &'a mut [T]. Note that the type T must outlive the chosen lifetime 'a. If the type has only static references, or none at all, then this may be chosen to be 'static.

As of Rust 1.57, this method does not reallocate or shrink the Vec, so the leaked allocation may include unused capacity that is not part of the returned slice.

This function is mainly useful for data that lives for the remainder of the program’s life. Dropping the returned reference will cause a memory leak.

Examples

Simple usage:

let x = vec![1, 2, 3];
let static_ref: &'static mut [usize] = x.leak();
static_ref[0] += 1;
assert_eq!(static_ref, &[2, 2, 3]);

pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>]

Returns the remaining spare capacity of the vector as a slice of MaybeUninit<T>.

The returned slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the set_len method.

Examples

// Allocate vector big enough for 10 elements.
let mut v = Vec::with_capacity(10);

// Fill in the first 3 elements.
let uninit = v.spare_capacity_mut();
uninit[0].write(0);
uninit[1].write(1);
uninit[2].write(2);

// Mark the first 3 elements of the vector as being initialized.
unsafe {
    v.set_len(3);
}

assert_eq!(&v, &[0, 1, 2]);

pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>])

🔬This is a nightly-only experimental API. (vec_split_at_spare #81944)

Returns vector content as a slice of T, along with the remaining spare capacity of the vector as a slice of MaybeUninit<T>.

The returned spare capacity slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the set_len method.

Note that this is a low-level API, which should be used with care for optimization purposes. If you need to append data to a Vec you can use push, extend, extend_from_slice, extend_from_within, insert, append, resize or resize_with, depending on your exact needs.

Examples

#![feature(vec_split_at_spare)]

let mut v = vec![1, 1, 2];

// Reserve additional space big enough for 10 elements.
v.reserve(10);

let (init, uninit) = v.split_at_spare_mut();
let sum = init.iter().copied().sum::<u32>();

// Fill in the next 4 elements.
uninit[0].write(sum);
uninit[1].write(sum * 2);
uninit[2].write(sum * 3);
uninit[3].write(sum * 4);

// Mark the 4 elements of the vector as being initialized.
unsafe {
    let len = v.len();
    v.set_len(len + 4);
}

assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);

impl<T: Clone, A: Allocator> Vec<T, A>

pub fn try_resize( &mut self, new_len: usize, value: T ) -> Result<(), TryReserveError>

Tries to resize the Vec in-place so that len is equal to new_len.

If new_len is greater than len, the Vec is extended by the difference, with each additional slot filled with value. If new_len is less than len, the Vec is simply truncated.

This method requires T to implement Clone, in order to be able to clone the passed value. If you need more flexibility (or want to rely on Default instead of Clone), use [Vec::resize_with]. If you only need to resize to a smaller size, use Vec::truncate.

Examples

let mut vec = vec!["hello"];
vec.try_resize(3, "world").unwrap();
assert_eq!(vec, ["hello", "world", "world"]);

let mut vec = vec![1, 2, 3, 4];
vec.try_resize(2, 0).unwrap();
assert_eq!(vec, [1, 2]);

let mut vec = vec![42];
let result = vec.try_resize(usize::MAX, 0);
assert!(result.is_err());

pub fn try_extend_from_slice( &mut self, other: &[T] ) -> Result<(), TryReserveError>

Tries to clone and append all elements in a slice to the Vec.

Iterates over the slice other, clones each element, and then appends it to this Vec. The other slice is traversed in-order.

Note that this function is same as extend except that it is specialized to work with slices instead. If and when Rust gets specialization this function will likely be deprecated (but still available).

Examples

let mut vec = vec![1];
vec.try_extend_from_slice(&[2, 3, 4]).unwrap();
assert_eq!(vec, [1, 2, 3, 4]);

impl<T, A: Allocator, const N: usize> Vec<[T; N], A>

pub fn into_flattened(self) -> Vec<T, A>

🔬This is a nightly-only experimental API. (slice_flatten #95629)

Takes a Vec<[T; N]> and flattens it into a Vec<T>.

Panics

Panics if the length of the resulting vector would overflow a usize.

This is only possible when flattening a vector of arrays of zero-sized types, and thus tends to be irrelevant in practice. If size_of::<T>() > 0, this will never panic.

Examples

#![feature(slice_flatten)]

let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
assert_eq!(vec.pop(), Some([7, 8, 9]));

let mut flattened = vec.into_flattened();
assert_eq!(flattened.pop(), Some(6));

impl<T: PartialEq, A: Allocator> Vec<T, A>

pub fn dedup(&mut self)

Removes consecutive repeated elements in the vector according to the PartialEq trait implementation.

If the vector is sorted, this removes all duplicates.

Examples

let mut vec = vec![1, 2, 2, 3, 2];

vec.dedup();

assert_eq!(vec, [1, 2, 3, 2]);

impl<T, A: Allocator> Vec<T, A>

pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A> where F: FnMut(&mut T) -> bool,

🔬This is a nightly-only experimental API. (extract_if #43244)

Creates an iterator which uses a closure to determine if an element should be removed.

If the closure returns true, then the element is removed and yielded. If the closure returns false, the element will remain in the vector and will not be yielded by the iterator.

If the returned ExtractIf is not exhausted, e.g. because it is dropped without iterating or the iteration short-circuits, then the remaining elements will be retained. Use retain with a negated predicate if you do not need the returned iterator.

Using this method is equivalent to the following code:

let mut i = 0;
while i < vec.len() {
    if some_predicate(&mut vec[i]) {
        let val = vec.remove(i);
        // your code here
    } else {
        i += 1;
    }
}

But extract_if is easier to use. extract_if is also more efficient, because it can backshift the elements of the array in bulk.

Note that extract_if also lets you mutate every element in the filter closure, regardless of whether you choose to keep or remove it.

Examples

Splitting an array into evens and odds, reusing the original allocation:

#![feature(extract_if)]
let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];

let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
let odds = numbers;

assert_eq!(evens, vec![2, 4, 6, 8, 14]);
assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);

Methods from Deref<Target = [T]>

pub fn concat<Item: ?Sized>(&self) -> <Self as Concat<Item>>::Outputwhere Self: Concat<Item>,

Flattens a slice of T into a single value Self::Output.

Examples

assert_eq!(["hello", "world"].concat(), "helloworld");
assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);

pub fn join<Separator>( &self, sep: Separator ) -> <Self as Join<Separator>>::Outputwhere Self: Join<Separator>,

Flattens a slice of T into a single value Self::Output, placing a given separator between each.

Examples

assert_eq!(["hello", "world"].join(" "), "hello world");
assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]);

pub fn connect<Separator>( &self, sep: Separator ) -> <Self as Join<Separator>>::Outputwhere Self: Join<Separator>,

👎Deprecated since 1.3.0: renamed to join

Flattens a slice of T into a single value Self::Output, placing a given separator between each.

Examples

assert_eq!(["hello", "world"].connect(" "), "hello world");
assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]);

pub fn len(&self) -> usize

Returns the number of elements in the slice.

Examples

let a = [1, 2, 3];
assert_eq!(a.len(), 3);

pub fn is_empty(&self) -> bool

Returns true if the slice has a length of 0.

Examples

let a = [1, 2, 3];
assert!(!a.is_empty());

pub fn first(&self) -> Option<&T>

Returns the first element of the slice, or None if it is empty.

Examples

let v = [10, 40, 30];
assert_eq!(Some(&10), v.first());

let w: &[i32] = &[];
assert_eq!(None, w.first());

pub fn first_mut(&mut self) -> Option<&mut T>

Returns a mutable pointer to the first element of the slice, or None if it is empty.

Examples

let x = &mut [0, 1, 2];

if let Some(first) = x.first_mut() {
    *first = 5;
}
assert_eq!(x, &[5, 1, 2]);

pub fn split_first(&self) -> Option<(&T, &[T])>

Returns the first and all the rest of the elements of the slice, or None if it is empty.

Examples

let x = &[0, 1, 2];

if let Some((first, elements)) = x.split_first() {
    assert_eq!(first, &0);
    assert_eq!(elements, &[1, 2]);
}

pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])>

Returns the first and all the rest of the elements of the slice, or None if it is empty.

Examples

let x = &mut [0, 1, 2];

if let Some((first, elements)) = x.split_first_mut() {
    *first = 3;
    elements[0] = 4;
    elements[1] = 5;
}
assert_eq!(x, &[3, 4, 5]);

pub fn split_last(&self) -> Option<(&T, &[T])>

Returns the last and all the rest of the elements of the slice, or None if it is empty.

Examples

let x = &[0, 1, 2];

if let Some((last, elements)) = x.split_last() {
    assert_eq!(last, &2);
    assert_eq!(elements, &[0, 1]);
}

pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])>

Returns the last and all the rest of the elements of the slice, or None if it is empty.

Examples

let x = &mut [0, 1, 2];

if let Some((last, elements)) = x.split_last_mut() {
    *last = 3;
    elements[0] = 4;
    elements[1] = 5;
}
assert_eq!(x, &[4, 5, 3]);

pub fn last(&self) -> Option<&T>

Returns the last element of the slice, or None if it is empty.

Examples

let v = [10, 40, 30];
assert_eq!(Some(&30), v.last());

let w: &[i32] = &[];
assert_eq!(None, w.last());

pub fn last_mut(&mut self) -> Option<&mut T>

Returns a mutable pointer to the last item in the slice.

Examples

let x = &mut [0, 1, 2];

if let Some(last) = x.last_mut() {
    *last = 10;
}
assert_eq!(x, &[0, 1, 10]);

pub fn first_chunk<const N: usize>(&self) -> Option<&[T; N]>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns the first N elements of the slice, or None if it has fewer than N elements.

Examples

#![feature(slice_first_last_chunk)]

let u = [10, 40, 30];
assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());

let v: &[i32] = &[10];
assert_eq!(None, v.first_chunk::<2>());

let w: &[i32] = &[];
assert_eq!(Some(&[]), w.first_chunk::<0>());

pub fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns a mutable reference to the first N elements of the slice, or None if it has fewer than N elements.

Examples

#![feature(slice_first_last_chunk)]

let x = &mut [0, 1, 2];

if let Some(first) = x.first_chunk_mut::<2>() {
    first[0] = 5;
    first[1] = 4;
}
assert_eq!(x, &[5, 4, 2]);

pub fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns the first N elements of the slice and the remainder, or None if it has fewer than N elements.

Examples

#![feature(slice_first_last_chunk)]

let x = &[0, 1, 2];

if let Some((first, elements)) = x.split_first_chunk::<2>() {
    assert_eq!(first, &[0, 1]);
    assert_eq!(elements, &[2]);
}

pub fn split_first_chunk_mut<const N: usize>( &mut self ) -> Option<(&mut [T; N], &mut [T])>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns a mutable reference to the first N elements of the slice and the remainder, or None if it has fewer than N elements.

Examples

#![feature(slice_first_last_chunk)]

let x = &mut [0, 1, 2];

if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
    first[0] = 3;
    first[1] = 4;
    elements[0] = 5;
}
assert_eq!(x, &[3, 4, 5]);

pub fn split_last_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns the last N elements of the slice and the remainder, or None if it has fewer than N elements.

Examples

#![feature(slice_first_last_chunk)]

let x = &[0, 1, 2];

if let Some((last, elements)) = x.split_last_chunk::<2>() {
    assert_eq!(last, &[1, 2]);
    assert_eq!(elements, &[0]);
}

pub fn split_last_chunk_mut<const N: usize>( &mut self ) -> Option<(&mut [T; N], &mut [T])>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns the last and all the rest of the elements of the slice, or None if it is empty.

Examples

#![feature(slice_first_last_chunk)]

let x = &mut [0, 1, 2];

if let Some((last, elements)) = x.split_last_chunk_mut::<2>() {
    last[0] = 3;
    last[1] = 4;
    elements[0] = 5;
}
assert_eq!(x, &[5, 3, 4]);

pub fn last_chunk<const N: usize>(&self) -> Option<&[T; N]>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns the last element of the slice, or None if it is empty.

Examples

#![feature(slice_first_last_chunk)]

let u = [10, 40, 30];
assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());

let v: &[i32] = &[10];
assert_eq!(None, v.last_chunk::<2>());

let w: &[i32] = &[];
assert_eq!(Some(&[]), w.last_chunk::<0>());

pub fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>

🔬This is a nightly-only experimental API. (slice_first_last_chunk #111774)

Returns a mutable pointer to the last item in the slice.

Examples

#![feature(slice_first_last_chunk)]

let x = &mut [0, 1, 2];

if let Some(last) = x.last_chunk_mut::<2>() {
    last[0] = 10;
    last[1] = 20;
}
assert_eq!(x, &[0, 10, 20]);

pub fn get<I>(&self, index: I) -> Option<&<I as SliceIndex<[T]>>::Output>where I: SliceIndex<[T]>,

Returns a reference to an element or subslice depending on the type of index.

• If given a position, returns a reference to the element at that position or None if out of bounds.
• If given a range, returns the subslice corresponding to that range, or None if out of bounds.

Examples

let v = [10, 40, 30];
assert_eq!(Some(&40), v.get(1));
assert_eq!(Some(&[10, 40][..]), v.get(0..2));
assert_eq!(None, v.get(3));
assert_eq!(None, v.get(0..4));

pub fn get_mut<I>( &mut self, index: I ) -> Option<&mut <I as SliceIndex<[T]>>::Output>where I: SliceIndex<[T]>,

Returns a mutable reference to an element or subslice depending on the type of index (see get) or None if the index is out of bounds.

Examples

let x = &mut [0, 1, 2];

if let Some(elem) = x.get_mut(1) {
    *elem = 42;
}
assert_eq!(x, &[0, 42, 2]);

pub unsafe fn get_unchecked<I>( &self, index: I ) -> &<I as SliceIndex<[T]>>::Outputwhere I: SliceIndex<[T]>,

Returns a reference to an element or subslice, without doing bounds checking.

For a safe alternative see get.

Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

Examples

let x = &[1, 2, 4];

unsafe {
    assert_eq!(x.get_unchecked(1), &2);
}

pub unsafe fn get_unchecked_mut<I>( &mut self, index: I ) -> &mut <I as SliceIndex<[T]>>::Outputwhere I: SliceIndex<[T]>,

Returns a mutable reference to an element or subslice, without doing bounds checking.

For a safe alternative see get_mut.

Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

Examples

let x = &mut [1, 2, 4];

unsafe {
    let elem = x.get_unchecked_mut(1);
    *elem = 13;
}
assert_eq!(x, &[1, 13, 4]);

pub fn as_ptr(&self) -> *const T

Returns a raw pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an UnsafeCell) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use as_mut_ptr.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

Examples

let x = &[1, 2, 4];
let x_ptr = x.as_ptr();

unsafe {
    for i in 0..x.len() {
        assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
    }
}

pub fn as_mut_ptr(&mut self) -> *mut T

Returns an unsafe mutable pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

Examples

let x = &mut [1, 2, 4];
let x_ptr = x.as_mut_ptr();

unsafe {
    for i in 0..x.len() {
        *x_ptr.add(i) += 2;
    }
}
assert_eq!(x, &[3, 4, 6]);

pub fn as_ptr_range(&self) -> Range<*const T>

Returns the two raw pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See as_ptr for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

It can also be useful to check if a pointer to an element refers to an element of this slice:

let a = [1, 2, 3];
let x = &a[1] as *const _;
let y = &5 as *const _;

assert!(a.as_ptr_range().contains(&x));
assert!(!a.as_ptr_range().contains(&y));

pub fn as_mut_ptr_range(&mut self) -> Range<*mut T>

Returns the two unsafe mutable pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See as_mut_ptr for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

pub fn swap(&mut self, a: usize, b: usize)

Swaps two elements in the slice.

If a equals to b, it’s guaranteed that elements won’t change value.

Arguments

• a - The index of the first element
• b - The index of the second element

Panics

Panics if a or b are out of bounds.

Examples

let mut v = ["a", "b", "c", "d", "e"];
v.swap(2, 4);
assert!(v == ["a", "b", "e", "d", "c"]);

pub unsafe fn swap_unchecked(&mut self, a: usize, b: usize)

🔬This is a nightly-only experimental API. (slice_swap_unchecked #88539)

Swaps two elements in the slice, without doing bounds checking.

For a safe alternative see swap.

Arguments

• a - The index of the first element
• b - The index of the second element

Safety

Calling this method with an out-of-bounds index is undefined behavior. The caller has to ensure that a < self.len() and b < self.len().

Examples

#![feature(slice_swap_unchecked)]

let mut v = ["a", "b", "c", "d"];
// SAFETY: we know that 1 and 3 are both indices of the slice
unsafe { v.swap_unchecked(1, 3) };
assert!(v == ["a", "d", "c", "b"]);

pub fn reverse(&mut self)

Reverses the order of elements in the slice, in place.

Examples

let mut v = [1, 2, 3];
v.reverse();
assert!(v == [3, 2, 1]);

pub fn iter(&self) -> Iter<'_, T>

Returns an iterator over the slice.

The iterator yields all items from start to end.

Examples

let x = &[1, 2, 4];
let mut iterator = x.iter();

assert_eq!(iterator.next(), Some(&1));
assert_eq!(iterator.next(), Some(&2));
assert_eq!(iterator.next(), Some(&4));
assert_eq!(iterator.next(), None);

pub fn iter_mut(&mut self) -> IterMut<'_, T>

Returns an iterator that allows modifying each value.

The iterator yields all items from start to end.

Examples

let x = &mut [1, 2, 4];
for elem in x.iter_mut() {
    *elem += 2;
}
assert_eq!(x, &[3, 4, 6]);

pub fn windows(&self, size: usize) -> Windows<'_, T>

Returns an iterator over all contiguous windows of length size. The windows overlap. If the slice is shorter than size, the iterator returns no values.

Panics

Panics if size is 0.

Examples

let slice = ['r', 'u', 's', 't'];
let mut iter = slice.windows(2);
assert_eq!(iter.next().unwrap(), &['r', 'u']);
assert_eq!(iter.next().unwrap(), &['u', 's']);
assert_eq!(iter.next().unwrap(), &['s', 't']);
assert!(iter.next().is_none());

If the slice is shorter than size:

let slice = ['f', 'o', 'o'];
let mut iter = slice.windows(4);
assert!(iter.next().is_none());

There’s no windows_mut, as that existing would let safe code violate the “only one &mut at a time to the same thing” rule. However, you can sometimes use Cell::as_slice_of_cells in conjunction with windows to accomplish something similar:

use std::cell::Cell;

let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
let slice = &mut array[..];
let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
for w in slice_of_cells.windows(3) {
    Cell::swap(&w[0], &w[2]);
}
assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);

pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See chunks_exact for a variant of this iterator that returns chunks of always exactly chunk_size elements, and rchunks for the same iterator but starting at the end of the slice.

Panics

Panics if chunk_size is 0.

Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.chunks(2);
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert_eq!(iter.next().unwrap(), &['m']);
assert!(iter.next().is_none());

pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See chunks_exact_mut for a variant of this iterator that returns chunks of always exactly chunk_size elements, and rchunks_mut for the same iterator but starting at the end of the slice.

Panics

Panics if chunk_size is 0.

Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.chunks_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 3]);

pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks.

See chunks for a variant of this iterator that also returns the remainder as a smaller chunk, and rchunks_exact for the same iterator but starting at the end of the slice.

Panics

Panics if chunk_size is 0.

Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.chunks_exact(2);
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert!(iter.next().is_none());
assert_eq!(iter.remainder(), &['m']);

pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the into_remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks_mut.

See chunks_mut for a variant of this iterator that also returns the remainder as a smaller chunk, and rchunks_exact_mut for the same iterator but starting at the end of the slice.

Panics

Panics if chunk_size is 0.

Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.chunks_exact_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 0]);

pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]]

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, assuming that there’s no remainder.

Safety

This may only be called when

• The slice splits exactly into N-element chunks (aka self.len() % N == 0).
• N != 0.

Examples

#![feature(slice_as_chunks)]
let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
let chunks: &[[char; 1]] =
    // SAFETY: 1-element chunks never have remainder
    unsafe { slice.as_chunks_unchecked() };
assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
let chunks: &[[char; 3]] =
    // SAFETY: The slice length (6) is a multiple of 3
    unsafe { slice.as_chunks_unchecked() };
assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);

// These would be unsound:
// let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
// let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed

pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T])

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than N.

Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

Examples

#![feature(slice_as_chunks)]
let slice = ['l', 'o', 'r', 'e', 'm'];
let (chunks, remainder) = slice.as_chunks();
assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
assert_eq!(remainder, &['m']);

If you expect the slice to be an exact multiple, you can combine let-else with an empty slice pattern:

#![feature(slice_as_chunks)]
let slice = ['R', 'u', 's', 't'];
let (chunks, []) = slice.as_chunks::<2>() else {
    panic!("slice didn't have even length")
};
assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);

pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]])

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than N.

Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

Examples

#![feature(slice_as_chunks)]
let slice = ['l', 'o', 'r', 'e', 'm'];
let (remainder, chunks) = slice.as_rchunks();
assert_eq!(remainder, &['l']);
assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);

pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N>

🔬This is a nightly-only experimental API. (array_chunks #74985)

Returns an iterator over N elements of the slice at a time, starting at the beginning of the slice.

The chunks are array references and do not overlap. If N does not divide the length of the slice, then the last up to N-1 elements will be omitted and can be retrieved from the remainder function of the iterator.

This method is the const generic equivalent of chunks_exact.

Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

Examples

#![feature(array_chunks)]
let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.array_chunks();
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert!(iter.next().is_none());
assert_eq!(iter.remainder(), &['m']);

pub unsafe fn as_chunks_unchecked_mut<const N: usize>( &mut self ) -> &mut [[T; N]]

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, assuming that there’s no remainder.

Safety

This may only be called when

• The slice splits exactly into N-element chunks (aka self.len() % N == 0).
• N != 0.

Examples

#![feature(slice_as_chunks)]
let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
let chunks: &mut [[char; 1]] =
    // SAFETY: 1-element chunks never have remainder
    unsafe { slice.as_chunks_unchecked_mut() };
chunks[0] = ['L'];
assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
let chunks: &mut [[char; 3]] =
    // SAFETY: The slice length (6) is a multiple of 3
    unsafe { slice.as_chunks_unchecked_mut() };
chunks[1] = ['a', 'x', '?'];
assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);

// These would be unsound:
// let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
// let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed

pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T])

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than N.

Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

Examples

#![feature(slice_as_chunks)]
let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

let (chunks, remainder) = v.as_chunks_mut();
remainder[0] = 9;
for chunk in chunks {
    *chunk = [count; 2];
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 9]);

pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]])

🔬This is a nightly-only experimental API. (slice_as_chunks #74985)

Splits the slice into a slice of N-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than N.

Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

Examples

#![feature(slice_as_chunks)]
let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

let (remainder, chunks) = v.as_rchunks_mut();
remainder[0] = 9;
for chunk in chunks {
    *chunk = [count; 2];
    count += 1;
}
assert_eq!(v, &[9, 1, 1, 2, 2]);

pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N>

🔬This is a nightly-only experimental API. (array_chunks #74985)

Returns an iterator over N elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable array references and do not overlap. If N does not divide the length of the slice, then the last up to N-1 elements will be omitted and can be retrieved from the into_remainder function of the iterator.

This method is the const generic equivalent of chunks_exact_mut.

Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

Examples

#![feature(array_chunks)]
let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.array_chunks_mut() {
    *chunk = [count; 2];
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 0]);

pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N>

🔬This is a nightly-only experimental API. (array_windows #75027)

Returns an iterator over overlapping windows of N elements of a slice, starting at the beginning of the slice.

This is the const generic equivalent of windows.

If N is greater than the size of the slice, it will return no windows.

Panics

Panics if N is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

Examples

#![feature(array_windows)]
let slice = [0, 1, 2, 3];
let mut iter = slice.array_windows();
assert_eq!(iter.next().unwrap(), &[0, 1]);
assert_eq!(iter.next().unwrap(), &[1, 2]);
assert_eq!(iter.next().unwrap(), &[2, 3]);
assert!(iter.next().is_none());

pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See rchunks_exact for a variant of this iterator that returns chunks of always exactly chunk_size elements, and chunks for the same iterator but starting at the beginning of the slice.

Panics

Panics if chunk_size is 0.

Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.rchunks(2);
assert_eq!(iter.next().unwrap(), &['e', 'm']);
assert_eq!(iter.next().unwrap(), &['o', 'r']);
assert_eq!(iter.next().unwrap(), &['l']);
assert!(iter.next().is_none());

pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

See rchunks_exact_mut for a variant of this iterator that returns chunks of always exactly chunk_size elements, and chunks_mut for the same iterator but starting at the beginning of the slice.

Panics

Panics if chunk_size is 0.

Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.rchunks_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[3, 2, 2, 1, 1]);

pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of rchunks.

See rchunks for a variant of this iterator that also returns the remainder as a smaller chunk, and chunks_exact for the same iterator but starting at the beginning of the slice.

Panics

Panics if chunk_size is 0.

Examples

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.rchunks_exact(2);
assert_eq!(iter.next().unwrap(), &['e', 'm']);
assert_eq!(iter.next().unwrap(), &['o', 'r']);
assert!(iter.next().is_none());
assert_eq!(iter.remainder(), &['l']);

pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T>

Returns an iterator over chunk_size elements of the slice at a time, starting at the end of the slice.

The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last up to chunk_size-1 elements will be omitted and can be retrieved from the into_remainder function of the iterator.

Due to each chunk having exactly chunk_size elements, the compiler can often optimize the resulting code better than in the case of chunks_mut.

See rchunks_mut for a variant of this iterator that also returns the remainder as a smaller chunk, and chunks_exact_mut for the same iterator but starting at the beginning of the slice.

Panics

Panics if chunk_size is 0.

Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.rchunks_exact_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[0, 2, 2, 1, 1]);

pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F> where F: FnMut(&T, &T) -> bool,

🔬This is a nightly-only experimental API. (slice_group_by #80552)

Returns an iterator over the slice producing non-overlapping runs of elements using the predicate to separate them.

The predicate is called on two elements following themselves, it means the predicate is called on slice[0] and slice[1] then on slice[1] and slice[2] and so on.

Examples

#![feature(slice_group_by)]

let slice = &[1, 1, 1, 3, 3, 2, 2, 2];

let mut iter = slice.group_by(|a, b| a == b);

assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
assert_eq!(iter.next(), Some(&[3, 3][..]));
assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
assert_eq!(iter.next(), None);

This method can be used to extract the sorted subslices:

#![feature(slice_group_by)]

let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];

let mut iter = slice.group_by(|a, b| a <= b);

assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
assert_eq!(iter.next(), None);

pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F> where F: FnMut(&T, &T) -> bool,

🔬This is a nightly-only experimental API. (slice_group_by #80552)

Returns an iterator over the slice producing non-overlapping mutable runs of elements using the predicate to separate them.

The predicate is called on two elements following themselves, it means the predicate is called on slice[0] and slice[1] then on slice[1] and slice[2] and so on.

Examples

#![feature(slice_group_by)]

let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];

let mut iter = slice.group_by_mut(|a, b| a == b);

assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
assert_eq!(iter.next(), Some(&mut [3, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
assert_eq!(iter.next(), None);

This method can be used to extract the sorted subslices:

#![feature(slice_group_by)]

let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];

let mut iter = slice.group_by_mut(|a, b| a <= b);

assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 3][..]));
assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
assert_eq!(iter.next(), None);

pub fn split_at(&self, mid: usize) -> (&[T], &[T])

Divides one slice into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

Panics

Panics if mid > len.

Examples

let v = [1, 2, 3, 4, 5, 6];

{
   let (left, right) = v.split_at(0);
   assert_eq!(left, []);
   assert_eq!(right, [1, 2, 3, 4, 5, 6]);
}

{
    let (left, right) = v.split_at(2);
    assert_eq!(left, [1, 2]);
    assert_eq!(right, [3, 4, 5, 6]);
}

{
    let (left, right) = v.split_at(6);
    assert_eq!(left, [1, 2, 3, 4, 5, 6]);
    assert_eq!(right, []);
}

pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T])

Divides one mutable slice into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

Panics

Panics if mid > len.

Examples

let mut v = [1, 0, 3, 0, 5, 6];
let (left, right) = v.split_at_mut(2);
assert_eq!(left, [1, 0]);
assert_eq!(right, [3, 0, 5, 6]);
left[1] = 2;
right[1] = 4;
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T])

🔬This is a nightly-only experimental API. (slice_split_at_unchecked #76014)

Divides one slice into two at an index, without doing bounds checking.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

For a safe alternative see split_at.

Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that 0 <= mid <= self.len().

Examples

#![feature(slice_split_at_unchecked)]

let v = [1, 2, 3, 4, 5, 6];

unsafe {
   let (left, right) = v.split_at_unchecked(0);
   assert_eq!(left, []);
   assert_eq!(right, [1, 2, 3, 4, 5, 6]);
}

unsafe {
    let (left, right) = v.split_at_unchecked(2);
    assert_eq!(left, [1, 2]);
    assert_eq!(right, [3, 4, 5, 6]);
}

unsafe {
    let (left, right) = v.split_at_unchecked(6);
    assert_eq!(left, [1, 2, 3, 4, 5, 6]);
    assert_eq!(right, []);
}

pub unsafe fn split_at_mut_unchecked( &mut self, mid: usize ) -> (&mut [T], &mut [T])

🔬This is a nightly-only experimental API. (slice_split_at_unchecked #76014)

Divides one mutable slice into two at an index, without doing bounds checking.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

For a safe alternative see split_at_mut.

Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that 0 <= mid <= self.len().

Examples

#![feature(slice_split_at_unchecked)]

let mut v = [1, 0, 3, 0, 5, 6];
// scoped to restrict the lifetime of the borrows
unsafe {
    let (left, right) = v.split_at_mut_unchecked(2);
    assert_eq!(left, [1, 0]);
    assert_eq!(right, [3, 0, 5, 6]);
    left[1] = 2;
    right[1] = 4;
}
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T])

🔬This is a nightly-only experimental API. (split_array #90091)

Divides one slice into an array and a remainder slice at an index.

The array will contain all indices from [0, N) (excluding the index N itself) and the slice will contain all indices from [N, len) (excluding the index len itself).

Panics

Panics if N > len.

Examples

#![feature(split_array)]

let v = &[1, 2, 3, 4, 5, 6][..];

{
   let (left, right) = v.split_array_ref::<0>();
   assert_eq!(left, &[]);
   assert_eq!(right, [1, 2, 3, 4, 5, 6]);
}

{
    let (left, right) = v.split_array_ref::<2>();
    assert_eq!(left, &[1, 2]);
    assert_eq!(right, [3, 4, 5, 6]);
}

{
    let (left, right) = v.split_array_ref::<6>();
    assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
    assert_eq!(right, []);
}

pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T])

🔬This is a nightly-only experimental API. (split_array #90091)

Divides one mutable slice into an array and a remainder slice at an index.

The array will contain all indices from [0, N) (excluding the index N itself) and the slice will contain all indices from [N, len) (excluding the index len itself).

Panics

Panics if N > len.

Examples

#![feature(split_array)]

let mut v = &mut [1, 0, 3, 0, 5, 6][..];
let (left, right) = v.split_array_mut::<2>();
assert_eq!(left, &mut [1, 0]);
assert_eq!(right, [3, 0, 5, 6]);
left[1] = 2;
right[1] = 4;
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N])

🔬This is a nightly-only experimental API. (split_array #90091)

Divides one slice into an array and a remainder slice at an index from the end.

The slice will contain all indices from [0, len - N) (excluding the index len - N itself) and the array will contain all indices from [len - N, len) (excluding the index len itself).

Panics

Panics if N > len.

Examples

#![feature(split_array)]

let v = &[1, 2, 3, 4, 5, 6][..];

{
   let (left, right) = v.rsplit_array_ref::<0>();
   assert_eq!(left, [1, 2, 3, 4, 5, 6]);
   assert_eq!(right, &[]);
}

{
    let (left, right) = v.rsplit_array_ref::<2>();
    assert_eq!(left, [1, 2, 3, 4]);
    assert_eq!(right, &[5, 6]);
}

{
    let (left, right) = v.rsplit_array_ref::<6>();
    assert_eq!(left, []);
    assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
}

pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N])

🔬This is a nightly-only experimental API. (split_array #90091)

Divides one mutable slice into an array and a remainder slice at an index from the end.

The slice will contain all indices from [0, len - N) (excluding the index N itself) and the array will contain all indices from [len - N, len) (excluding the index len itself).

Panics

Panics if N > len.

Examples

#![feature(split_array)]

let mut v = &mut [1, 0, 3, 0, 5, 6][..];
let (left, right) = v.rsplit_array_mut::<4>();
assert_eq!(left, [1, 0]);
assert_eq!(right, &mut [3, 0, 5, 6]);
left[1] = 2;
right[1] = 4;
assert_eq!(v, [1, 2, 3, 4, 5, 6]);

pub fn split<F>(&self, pred: F) -> Split<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match pred. The matched element is not contained in the subslices.

Examples

let slice = [10, 40, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

If the first element is matched, an empty slice will be the first item returned by the iterator. Similarly, if the last element in the slice is matched, an empty slice will be the last item returned by the iterator:

let slice = [10, 40, 33];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[]);
assert!(iter.next().is_none());

If two matched elements are directly adjacent, an empty slice will be present between them:

let slice = [10, 6, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10]);
assert_eq!(iter.next().unwrap(), &[]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match pred. The matched element is not contained in the subslices.

Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.split_mut(|num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 1]);

pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match pred. The matched element is contained in the end of the previous subslice as a terminator.

Examples

let slice = [10, 40, 33, 20];
let mut iter = slice.split_inclusive(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

If the last element of the slice is matched, that element will be considered the terminator of the preceding slice. That slice will be the last item returned by the iterator.

let slice = [3, 10, 40, 33];
let mut iter = slice.split_inclusive(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[3]);
assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
assert!(iter.next().is_none());

pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match pred. The matched element is contained in the previous subslice as a terminator.

Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
    let terminator_idx = group.len()-1;
    group[terminator_idx] = 1;
}
assert_eq!(v, [10, 40, 1, 20, 1, 1]);

pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match pred, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

Examples

let slice = [11, 22, 33, 0, 44, 55];
let mut iter = slice.rsplit(|num| *num == 0);

assert_eq!(iter.next().unwrap(), &[44, 55]);
assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
assert_eq!(iter.next(), None);

As with split(), if the first or last element is matched, an empty slice will be the first (or last) item returned by the iterator.

let v = &[0, 1, 1, 2, 3, 5, 8];
let mut it = v.rsplit(|n| *n % 2 == 0);
assert_eq!(it.next().unwrap(), &[]);
assert_eq!(it.next().unwrap(), &[3, 5]);
assert_eq!(it.next().unwrap(), &[1, 1]);
assert_eq!(it.next().unwrap(), &[]);
assert_eq!(it.next(), None);

pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match pred, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

Examples

let mut v = [100, 400, 300, 200, 600, 500];

let mut count = 0;
for group in v.rsplit_mut(|num| *num % 3 == 0) {
    count += 1;
    group[0] = count;
}
assert_eq!(v, [3, 400, 300, 2, 600, 1]);

pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

Examples

Print the slice split once by numbers divisible by 3 (i.e., [10, 40], [20, 60, 50]):

let v = [10, 40, 30, 20, 60, 50];

for group in v.splitn(2, |num| *num % 3 == 0) {
    println!("{group:?}");
}

pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.splitn_mut(2, |num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 50]);

pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match pred limited to returning at most n items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

Examples

Print the slice split once, starting from the end, by numbers divisible by 3 (i.e., [50], [10, 40, 30, 20]):

let v = [10, 40, 30, 20, 60, 50];

for group in v.rsplitn(2, |num| *num % 3 == 0) {
    println!("{group:?}");
}

pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F> where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match pred limited to returning at most n items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

Examples

let mut s = [10, 40, 30, 20, 60, 50];

for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(s, [1, 40, 30, 20, 60, 1]);

pub fn contains(&self, x: &T) -> boolwhere T: PartialEq<T>,

Returns true if the slice contains an element with the given value.

This operation is O(n).

Note that if you have a sorted slice, binary_search may be faster.

Examples

let v = [10, 40, 30];
assert!(v.contains(&30));
assert!(!v.contains(&50));

If you do not have a &T, but some other value that you can compare with one (for example, String implements PartialEq<str>), you can use iter().any:

let v = [String::from("hello"), String::from("world")]; // slice of `String`
assert!(v.iter().any(|e| e == "hello")); // search with `&str`
assert!(!v.iter().any(|e| e == "hi"));

pub fn starts_with(&self, needle: &[T]) -> boolwhere T: PartialEq<T>,

Returns true if needle is a prefix of the slice.

Examples

let v = [10, 40, 30];
assert!(v.starts_with(&[10]));
assert!(v.starts_with(&[10, 40]));
assert!(!v.starts_with(&[50]));
assert!(!v.starts_with(&[10, 50]));

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.starts_with(&[]));
let v: &[u8] = &[];
assert!(v.starts_with(&[]));

pub fn ends_with(&self, needle: &[T]) -> boolwhere T: PartialEq<T>,

Returns true if needle is a suffix of the slice.

Examples

let v = [10, 40, 30];
assert!(v.ends_with(&[30]));
assert!(v.ends_with(&[40, 30]));
assert!(!v.ends_with(&[50]));
assert!(!v.ends_with(&[50, 30]));

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.ends_with(&[]));
let v: &[u8] = &[];
assert!(v.ends_with(&[]));

pub fn strip_prefix<P>(&self, prefix: &P) -> Option<&[T]>where P: SlicePattern<Item = T> + ?Sized, T: PartialEq<T>,

Returns a subslice with the prefix removed.

If the slice starts with prefix, returns the subslice after the prefix, wrapped in Some. If prefix is empty, simply returns the original slice.

If the slice does not start with prefix, returns None.

Examples

let v = &[10, 40, 30];
assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
assert_eq!(v.strip_prefix(&[50]), None);
assert_eq!(v.strip_prefix(&[10, 50]), None);

let prefix : &str = "he";
assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
           Some(b"llo".as_ref()));

pub fn strip_suffix<P>(&self, suffix: &P) -> Option<&[T]>where P: SlicePattern<Item = T> + ?Sized, T: PartialEq<T>,

Returns a subslice with the suffix removed.

If the slice ends with suffix, returns the subslice before the suffix, wrapped in Some. If suffix is empty, simply returns the original slice.

If the slice does not end with suffix, returns None.

Examples

let v = &[10, 40, 30];
assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
assert_eq!(v.strip_suffix(&[50]), None);
assert_eq!(v.strip_suffix(&[50, 30]), None);

pub fn binary_search(&self, x: &T) -> Result<usize, usize>where T: Ord,

Binary searches this slice for a given element. If the slice is not sorted, the returned result is unspecified and meaningless.

If the value is found then Result::Ok is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then Result::Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also binary_search_by, binary_search_by_key, and partition_point.

Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

assert_eq!(s.binary_search(&13),  Ok(9));
assert_eq!(s.binary_search(&4),   Err(7));
assert_eq!(s.binary_search(&100), Err(13));
let r = s.binary_search(&1);
assert!(match r { Ok(1..=4) => true, _ => false, });

If you want to find that whole range of matching items, rather than an arbitrary matching one, that can be done using partition_point:

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

let low = s.partition_point(|x| x < &1);
assert_eq!(low, 1);
let high = s.partition_point(|x| x <= &1);
assert_eq!(high, 5);
let r = s.binary_search(&1);
assert!((low..high).contains(&r.unwrap()));

assert!(s[..low].iter().all(|&x| x < 1));
assert!(s[low..high].iter().all(|&x| x == 1));
assert!(s[high..].iter().all(|&x| x > 1));

// For something not found, the "range" of equal items is empty
assert_eq!(s.partition_point(|x| x < &11), 9);
assert_eq!(s.partition_point(|x| x <= &11), 9);
assert_eq!(s.binary_search(&11), Err(9));

If you want to insert an item to a sorted vector, while maintaining sort order, consider using partition_point:

let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
let num = 42;
let idx = s.partition_point(|&x| x < num);
// The above is equivalent to `let idx = s.binary_search(&num).unwrap_or_else(|x| x);`
s.insert(idx, num);
assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

pub fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize>where F: FnMut(&'a T) -> Ordering,

Binary searches this slice with a comparator function.

The comparator function should return an order code that indicates whether its argument is Less, Equal or Greater the desired target. If the slice is not sorted or if the comparator function does not implement an order consistent with the sort order of the underlying slice, the returned result is unspecified and meaningless.

If the value is found then Result::Ok is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then Result::Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also binary_search, binary_search_by_key, and partition_point.

Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

let seek = 13;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
let seek = 4;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
let seek = 100;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
let seek = 1;
let r = s.binary_search_by(|probe| probe.cmp(&seek));
assert!(match r { Ok(1..=4) => true, _ => false, });

pub fn binary_search_by_key<'a, B, F>( &'a self, b: &B, f: F ) -> Result<usize, usize>where F: FnMut(&'a T) -> B, B: Ord,

Binary searches this slice with a key extraction function.

Assumes that the slice is sorted by the key, for instance with sort_by_key using the same key extraction function. If the slice is not sorted by the key, the returned result is unspecified and meaningless.

If the value is found then Result::Ok is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then Result::Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also binary_search, binary_search_by, and partition_point.

Examples

Looks up a series of four elements in a slice of pairs sorted by their second elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
         (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
         (1, 21), (2, 34), (4, 55)];

assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b),  Ok(9));
assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b),   Err(7));
assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
let r = s.binary_search_by_key(&1, |&(a, b)| b);
assert!(match r { Ok(1..=4) => true, _ => false, });

pub fn sort_unstable(&mut self)where T: Ord,

Sorts the slice, but might not preserve the order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

Current implementation

The current algorithm is based on pattern-defeating quicksort by Orson Peters, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on slices with certain patterns. It uses some randomization to avoid degenerate cases, but with a fixed seed to always provide deterministic behavior.

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice consists of several concatenated sorted sequences.

Examples

let mut v = [-5, 4, 1, -3, 2];

v.sort_unstable();
assert!(v == [-5, -3, 1, 2, 4]);

pub fn sort_unstable_by<F>(&mut self, compare: F)where F: FnMut(&T, &T) -> Ordering,

Sorts the slice with a comparator function, but might not preserve the order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

The comparator function must define a total ordering for the elements in the slice. If the ordering is not total, the order of the elements is unspecified. An order is a total order if it is (for all a, b and c):

• total and antisymmetric: exactly one of a < b, a == b or a > b is true, and
• transitive, a < b and b < c implies a < c. The same must hold for both == and >.

For example, while f64 doesn’t implement Ord because NaN != NaN, we can use partial_cmp as our sort function when we know the slice doesn’t contain a NaN.

let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);

Current implementation

The current algorithm is based on pattern-defeating quicksort by Orson Peters, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on slices with certain patterns. It uses some randomization to avoid degenerate cases, but with a fixed seed to always provide deterministic behavior.

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice consists of several concatenated sorted sequences.

Examples

let mut v = [5, 4, 1, 3, 2];
v.sort_unstable_by(|a, b| a.cmp(b));
assert!(v == [1, 2, 3, 4, 5]);

// reverse sorting
v.sort_unstable_by(|a, b| b.cmp(a));
assert!(v == [5, 4, 3, 2, 1]);

pub fn sort_unstable_by_key<K, F>(&mut self, f: F)where F: FnMut(&T) -> K, K: Ord,

Sorts the slice with a key extraction function, but might not preserve the order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(m * n * log(n)) worst-case, where the key function is O(m).

Current implementation

The current algorithm is based on pattern-defeating quicksort by Orson Peters, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on slices with certain patterns. It uses some randomization to avoid degenerate cases, but with a fixed seed to always provide deterministic behavior.

Due to its key calling strategy, sort_unstable_by_key is likely to be slower than sort_by_cached_key in cases where the key function is expensive.

Examples

let mut v = [-5i32, 4, 1, -3, 2];

v.sort_unstable_by_key(|k| k.abs());
assert!(v == [1, 2, -3, 4, -5]);

pub fn select_nth_unstable( &mut self, index: usize ) -> (&mut [T], &mut T, &mut [T])where T: Ord,

Reorder the slice such that the element at index is at its final sorted position.

This reordering has the additional property that any value at position i < index will be less than or equal to any value at a position j > index. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position index), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the reordered slice: the subslice prior to index, the element at index, and the subslice after index; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at index.

Current implementation

The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also the basis for sort_unstable. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

Panics

Panics when index >= len(), meaning it always panics on empty slices.

Examples

let mut v = [-5i32, 4, 1, -3, 2];

// Find the median
v.select_nth_unstable(2);

// We are only guaranteed the slice will be one of the following, based on the way we sort
// about the specified index.
assert!(v == [-3, -5, 1, 2, 4] ||
        v == [-5, -3, 1, 2, 4] ||
        v == [-3, -5, 1, 4, 2] ||
        v == [-5, -3, 1, 4, 2]);

pub fn select_nth_unstable_by<F>( &mut self, index: usize, compare: F ) -> (&mut [T], &mut T, &mut [T])where F: FnMut(&T, &T) -> Ordering,

Reorder the slice with a comparator function such that the element at index is at its final sorted position.

This reordering has the additional property that any value at position i < index will be less than or equal to any value at a position j > index using the comparator function. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position index), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the slice reordered according to the provided comparator function: the subslice prior to index, the element at index, and the subslice after index; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at index.

Current implementation

The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also the basis for sort_unstable. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

Panics

Panics when index >= len(), meaning it always panics on empty slices.

Examples

let mut v = [-5i32, 4, 1, -3, 2];

// Find the median as if the slice were sorted in descending order.
v.select_nth_unstable_by(2, |a, b| b.cmp(a));

// We are only guaranteed the slice will be one of the following, based on the way we sort
// about the specified index.
assert!(v == [2, 4, 1, -5, -3] ||
        v == [2, 4, 1, -3, -5] ||
        v == [4, 2, 1, -5, -3] ||
        v == [4, 2, 1, -3, -5]);

pub fn select_nth_unstable_by_key<K, F>( &mut self, index: usize, f: F ) -> (&mut [T], &mut T, &mut [T])where F: FnMut(&T) -> K, K: Ord,

Reorder the slice with a key extraction function such that the element at index is at its final sorted position.

This reordering has the additional property that any value at position i < index will be less than or equal to any value at a position j > index using the key extraction function. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position index), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the slice reordered according to the provided key extraction function: the subslice prior to index, the element at index, and the subslice after index; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at index.

Current implementation

The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also the basis for sort_unstable. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

Panics

Panics when index >= len(), meaning it always panics on empty slices.

Examples

let mut v = [-5i32, 4, 1, -3, 2];

// Return the median as if the array were sorted according to absolute value.
v.select_nth_unstable_by_key(2, |a| a.abs());

// We are only guaranteed the slice will be one of the following, based on the way we sort
// about the specified index.
assert!(v == [1, 2, -3, 4, -5] ||
        v == [1, 2, -3, -5, 4] ||
        v == [2, 1, -3, 4, -5] ||
        v == [2, 1, -3, -5, 4]);

pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])where T: PartialEq<T>,

🔬This is a nightly-only experimental API. (slice_partition_dedup #54279)

Moves all consecutive repeated elements to the end of the slice according to the PartialEq trait implementation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

Examples

#![feature(slice_partition_dedup)]

let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];

let (dedup, duplicates) = slice.partition_dedup();

assert_eq!(dedup, [1, 2, 3, 2, 1]);
assert_eq!(duplicates, [2, 3, 1]);

pub fn partition_dedup_by<F>(&mut self, same_bucket: F) -> (&mut [T], &mut [T])where F: FnMut(&mut T, &mut T) -> bool,

🔬This is a nightly-only experimental API. (slice_partition_dedup #54279)

Moves all but the first of consecutive elements to the end of the slice satisfying a given equality relation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

The same_bucket function is passed references to two elements from the slice and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if same_bucket(a, b) returns true, a is moved at the end of the slice.

If the slice is sorted, the first returned slice contains no duplicates.

Examples

#![feature(slice_partition_dedup)]

let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];

let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));

assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);

pub fn partition_dedup_by_key<K, F>(&mut self, key: F) -> (&mut [T], &mut [T])where F: FnMut(&mut T) -> K, K: PartialEq<K>,

🔬This is a nightly-only experimental API. (slice_partition_dedup #54279)

Moves all but the first of consecutive elements to the end of the slice that resolve to the same key.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

Examples

#![feature(slice_partition_dedup)]

let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];

let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);

assert_eq!(dedup, [10, 20, 30, 20, 11]);
assert_eq!(duplicates, [21, 30, 13]);

pub fn rotate_left(&mut self, mid: usize)

Rotates the slice in-place such that the first mid elements of the slice move to the end while the last self.len() - mid elements move to the front. After calling rotate_left, the element previously at index mid will become the first element in the slice.

Panics

This function will panic if mid is greater than the length of the slice. Note that mid == self.len() does not panic and is a no-op rotation.

Complexity

Takes linear (in self.len()) time.

Examples

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a.rotate_left(2);
assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);

Rotating a subslice:

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a[1..5].rotate_left(1);
assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);

pub fn rotate_right(&mut self, k: usize)

Rotates the slice in-place such that the first self.len() - k elements of the slice move to the end while the last k elements move to the front. After calling rotate_right, the element previously at index self.len() - k will become the first element in the slice.

Panics

This function will panic if k is greater than the length of the slice. Note that k == self.len() does not panic and is a no-op rotation.

Complexity

Takes linear (in self.len()) time.

Examples

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a.rotate_right(2);
assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);

Rotating a subslice:

let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
a[1..5].rotate_right(1);
assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);

pub fn fill(&mut self, value: T)where T: Clone,

Fills self with elements by cloning value.

Examples

let mut buf = vec![0; 10];
buf.fill(1);
assert_eq!(buf, vec![1; 10]);

pub fn fill_with<F>(&mut self, f: F)where F: FnMut() -> T,

Fills self with elements returned by calling a closure repeatedly.

This method uses a closure to create new values. If you’d rather Clone a given value, use fill. If you want to use the Default trait to generate values, you can pass Default::default as the argument.

Examples

let mut buf = vec![1; 10];
buf.fill_with(Default::default);
assert_eq!(buf, vec![0; 10]);

pub fn clone_from_slice(&mut self, src: &[T])where T: Clone,

Copies the elements from src into self.

The length of src must be the same as self.

Panics

This function will panic if the two slices have different lengths.

Examples

Cloning two elements from a slice into another:

let src = [1, 2, 3, 4];
let mut dst = [0, 0];

// Because the slices have to be the same length,
// we slice the source slice from four elements
// to two. It will panic if we don't do this.
dst.clone_from_slice(&src[2..]);

assert_eq!(src, [1, 2, 3, 4]);
assert_eq!(dst, [3, 4]);

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use clone_from_slice on a single slice will result in a compile failure:

let mut slice = [1, 2, 3, 4, 5];

slice[..2].clone_from_slice(&slice[3..]); // compile fail!

To work around this, we can use split_at_mut to create two distinct sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5];

{
    let (left, right) = slice.split_at_mut(2);
    left.clone_from_slice(&right[1..]);
}

assert_eq!(slice, [4, 5, 3, 4, 5]);

pub fn copy_from_slice(&mut self, src: &[T])where T: Copy,

Copies all elements from src into self, using a memcpy.

The length of src must be the same as self.

If T does not implement Copy, use clone_from_slice.

Panics

This function will panic if the two slices have different lengths.

Examples

Copying two elements from a slice into another:

let src = [1, 2, 3, 4];
let mut dst = [0, 0];

// Because the slices have to be the same length,
// we slice the source slice from four elements
// to two. It will panic if we don't do this.
dst.copy_from_slice(&src[2..]);

assert_eq!(src, [1, 2, 3, 4]);
assert_eq!(dst, [3, 4]);

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use copy_from_slice on a single slice will result in a compile failure:

let mut slice = [1, 2, 3, 4, 5];

slice[..2].copy_from_slice(&slice[3..]); // compile fail!

To work around this, we can use split_at_mut to create two distinct sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5];

{
    let (left, right) = slice.split_at_mut(2);
    left.copy_from_slice(&right[1..]);
}

assert_eq!(slice, [4, 5, 3, 4, 5]);

pub fn copy_within<R>(&mut self, src: R, dest: usize)where R: RangeBounds<usize>, T: Copy,

Copies elements from one part of the slice to another part of itself, using a memmove.

src is the range within self to copy from. dest is the starting index of the range within self to copy to, which will have the same length as src. The two ranges may overlap. The ends of the two ranges must be less than or equal to self.len().

Panics

This function will panic if either range exceeds the end of the slice, or if the end of src is before the start.

Examples

Copying four bytes within a slice:

let mut bytes = *b"Hello, World!";

bytes.copy_within(1..5, 8);

assert_eq!(&bytes, b"Hello, Wello!");

pub fn swap_with_slice(&mut self, other: &mut [T])

Swaps all elements in self with those in other.

The length of other must be the same as self.

Panics

This function will panic if the two slices have different lengths.

Example

Swapping two elements across slices:

let mut slice1 = [0, 0];
let mut slice2 = [1, 2, 3, 4];

slice1.swap_with_slice(&mut slice2[2..]);

assert_eq!(slice1, [3, 4]);
assert_eq!(slice2, [1, 2, 0, 0]);

Rust enforces that there can only be one mutable reference to a particular piece of data in a particular scope. Because of this, attempting to use swap_with_slice on a single slice will result in a compile failure:

let mut slice = [1, 2, 3, 4, 5];
slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!

To work around this, we can use split_at_mut to create two distinct mutable sub-slices from a slice:

let mut slice = [1, 2, 3, 4, 5];

{
    let (left, right) = slice.split_at_mut(2);
    left.swap_with_slice(&mut right[1..]);
}

assert_eq!(slice, [4, 5, 3, 1, 2]);

pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T])

Transmute the slice to a slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. How exactly the slice is split up is not specified; the middle part may be smaller than necessary. However, if this fails to return a maximal middle part, that is because code is running in a context where performance does not matter, such as a sanitizer attempting to find alignment bugs. Regular code running in a default (debug or release) execution will return a maximal middle part.

This method has no purpose when either input element T or output element U are zero-sized and will return the original slice without splitting anything.

Safety

This method is essentially a transmute with respect to the elements in the returned middle slice, so all the usual caveats pertaining to transmute::<T, U> also apply here.

Examples

Basic usage:

unsafe {
    let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
    let (prefix, shorts, suffix) = bytes.align_to::<u16>();
    // less_efficient_algorithm_for_bytes(prefix);
    // more_efficient_algorithm_for_aligned_shorts(shorts);
    // less_efficient_algorithm_for_bytes(suffix);
}

pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T])

Transmute the mutable slice to a mutable slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. How exactly the slice is split up is not specified; the middle part may be smaller than necessary. However, if this fails to return a maximal middle part, that is because code is running in a context where performance does not matter, such as a sanitizer attempting to find alignment bugs. Regular code running in a default (debug or release) execution will return a maximal middle part.

This method has no purpose when either input element T or output element U are zero-sized and will return the original slice without splitting anything.

Safety

This method is essentially a transmute with respect to the elements in the returned middle slice, so all the usual caveats pertaining to transmute::<T, U> also apply here.

Examples

Basic usage:

unsafe {
    let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
    let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
    // less_efficient_algorithm_for_bytes(prefix);
    // more_efficient_algorithm_for_aligned_shorts(shorts);
    // less_efficient_algorithm_for_bytes(suffix);
}

pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])where Simd<T, LANES>: AsRef<[T; LANES]>, T: SimdElement, LaneCount<LANES>: SupportedLaneCount,

🔬This is a nightly-only experimental API. (portable_simd #86656)

Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.

This is a safe wrapper around slice::align_to, so has the same weak postconditions as that method. You’re only assured that self.len() == prefix.len() + middle.len() * LANES + suffix.len().

Notably, all of the following are possible:

• prefix.len() >= LANES.
• middle.is_empty() despite self.len() >= 3 * LANES.
• suffix.len() >= LANES.

That said, this is a safe method, so if you’re only writing safe code, then this can at most cause incorrect logic, not unsoundness.

Panics

This will panic if the size of the SIMD type is different from LANES times that of the scalar.

At the time of writing, the trait restrictions on Simd<T, LANES> keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like LANES == 3.

Examples

#![feature(portable_simd)]
use core::simd::SimdFloat;

let short = &[1, 2, 3];
let (prefix, middle, suffix) = short.as_simd::<4>();
assert_eq!(middle, []); // Not enough elements for anything in the middle

// They might be split in any possible way between prefix and suffix
let it = prefix.iter().chain(suffix).copied();
assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);

fn basic_simd_sum(x: &[f32]) -> f32 {
    use std::ops::Add;
    use std::simd::f32x4;
    let (prefix, middle, suffix) = x.as_simd();
    let sums = f32x4::from_array([
        prefix.iter().copied().sum(),
        0.0,
        0.0,
        suffix.iter().copied().sum(),
    ]);
    let sums = middle.iter().copied().fold(sums, f32x4::add);
    sums.reduce_sum()
}

let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);

pub fn as_simd_mut<const LANES: usize>( &mut self ) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])where Simd<T, LANES>: AsMut<[T; LANES]>, T: SimdElement, LaneCount<LANES>: SupportedLaneCount,

🔬This is a nightly-only experimental API. (portable_simd #86656)

Split a mutable slice into a mutable prefix, a middle of aligned SIMD types, and a mutable suffix.

This is a safe wrapper around slice::align_to_mut, so has the same weak postconditions as that method. You’re only assured that self.len() == prefix.len() + middle.len() * LANES + suffix.len().

Notably, all of the following are possible:

• prefix.len() >= LANES.
• middle.is_empty() despite self.len() >= 3 * LANES.
• suffix.len() >= LANES.

That said, this is a safe method, so if you’re only writing safe code, then this can at most cause incorrect logic, not unsoundness.

This is the mutable version of slice::as_simd; see that for examples.

Panics

This will panic if the size of the SIMD type is different from LANES times that of the scalar.

At the time of writing, the trait restrictions on Simd<T, LANES> keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like LANES == 3.

pub fn is_sorted(&self) -> boolwhere T: PartialOrd<T>,

🔬This is a nightly-only experimental API. (is_sorted #53485)

Checks if the elements of this slice are sorted.

That is, for each element a and its following element b, a <= b must hold. If the slice yields exactly zero or one element, true is returned.

Note that if Self::Item is only PartialOrd, but not Ord, the above definition implies that this function returns false if any two consecutive items are not comparable.

Examples

#![feature(is_sorted)]
let empty: [i32; 0] = [];

assert!([1, 2, 2, 9].is_sorted());
assert!(![1, 3, 2, 4].is_sorted());
assert!([0].is_sorted());
assert!(empty.is_sorted());
assert!(![0.0, 1.0, f32::NAN].is_sorted());

pub fn is_sorted_by<'a, F>(&'a self, compare: F) -> boolwhere F: FnMut(&'a T, &'a T) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (is_sorted #53485)

Checks if the elements of this slice are sorted using the given comparator function.

Instead of using PartialOrd::partial_cmp, this function uses the given compare function to determine the ordering of two elements. Apart from that, it’s equivalent to is_sorted; see its documentation for more information.

pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> boolwhere F: FnMut(&'a T) -> K, K: PartialOrd<K>,

🔬This is a nightly-only experimental API. (is_sorted #53485)

Checks if the elements of this slice are sorted using the given key extraction function.

Instead of comparing the slice’s elements directly, this function compares the keys of the elements, as determined by f. Apart from that, it’s equivalent to is_sorted; see its documentation for more information.

Examples

#![feature(is_sorted)]

assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));

pub fn partition_point<P>(&self, pred: P) -> usizewhere P: FnMut(&T) -> bool,

Returns the index of the partition point according to the given predicate (the index of the first element of the second partition).

The slice is assumed to be partitioned according to the given predicate. This means that all elements for which the predicate returns true are at the start of the slice and all elements for which the predicate returns false are at the end. For example, [7, 15, 3, 5, 4, 12, 6] is partitioned under the predicate x % 2 != 0 (all odd numbers are at the start, all even at the end).

If this slice is not partitioned, the returned result is unspecified and meaningless, as this method performs a kind of binary search.

See also binary_search, binary_search_by, and binary_search_by_key.

Examples

let v = [1, 2, 3, 3, 5, 6, 7];
let i = v.partition_point(|&x| x < 5);

assert_eq!(i, 4);
assert!(v[..i].iter().all(|&x| x < 5));
assert!(v[i..].iter().all(|&x| !(x < 5)));

If all elements of the slice match the predicate, including if the slice is empty, then the length of the slice will be returned:

let a = [2, 4, 8];
assert_eq!(a.partition_point(|x| x < &100), a.len());
let a: [i32; 0] = [];
assert_eq!(a.partition_point(|x| x < &100), 0);

If you want to insert an item to a sorted vector, while maintaining sort order:

let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
let num = 42;
let idx = s.partition_point(|&x| x < num);
s.insert(idx, num);
assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

pub fn take<R, 'a>(self: &mut &'a [T], range: R) -> Option<&'a [T]>where R: OneSidedRange<usize>,

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the subslice corresponding to the given range and returns a reference to it.

Returns None and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as 2.. or ..6, but not 2..6.

Examples

Taking the first three elements of a slice:

#![feature(slice_take)]

let mut slice: &[_] = &['a', 'b', 'c', 'd'];
let mut first_three = slice.take(..3).unwrap();

assert_eq!(slice, &['d']);
assert_eq!(first_three, &['a', 'b', 'c']);

Taking the last two elements of a slice:

#![feature(slice_take)]

let mut slice: &[_] = &['a', 'b', 'c', 'd'];
let mut tail = slice.take(2..).unwrap();

assert_eq!(slice, &['a', 'b']);
assert_eq!(tail, &['c', 'd']);

Getting None when range is out of bounds:

#![feature(slice_take)]

let mut slice: &[_] = &['a', 'b', 'c', 'd'];

assert_eq!(None, slice.take(5..));
assert_eq!(None, slice.take(..5));
assert_eq!(None, slice.take(..=4));
let expected: &[char] = &['a', 'b', 'c', 'd'];
assert_eq!(Some(expected), slice.take(..4));

pub fn take_mut<R, 'a>(self: &mut &'a mut [T], range: R) -> Option<&'a mut [T]>where R: OneSidedRange<usize>,

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the subslice corresponding to the given range and returns a mutable reference to it.

Returns None and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as 2.. or ..6, but not 2..6.

Examples

Taking the first three elements of a slice:

#![feature(slice_take)]

let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
let mut first_three = slice.take_mut(..3).unwrap();

assert_eq!(slice, &mut ['d']);
assert_eq!(first_three, &mut ['a', 'b', 'c']);

Taking the last two elements of a slice:

#![feature(slice_take)]

let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
let mut tail = slice.take_mut(2..).unwrap();

assert_eq!(slice, &mut ['a', 'b']);
assert_eq!(tail, &mut ['c', 'd']);

Getting None when range is out of bounds:

#![feature(slice_take)]

let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];

assert_eq!(None, slice.take_mut(5..));
assert_eq!(None, slice.take_mut(..5));
assert_eq!(None, slice.take_mut(..=4));
let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
assert_eq!(Some(expected), slice.take_mut(..4));

pub fn take_first<'a>(self: &mut &'a [T]) -> Option<&'a T>

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the first element of the slice and returns a reference to it.

Returns None if the slice is empty.

Examples

#![feature(slice_take)]

let mut slice: &[_] = &['a', 'b', 'c'];
let first = slice.take_first().unwrap();

assert_eq!(slice, &['b', 'c']);
assert_eq!(first, &'a');

pub fn take_first_mut<'a>(self: &mut &'a mut [T]) -> Option<&'a mut T>

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the first element of the slice and returns a mutable reference to it.

Returns None if the slice is empty.

Examples

#![feature(slice_take)]

let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
let first = slice.take_first_mut().unwrap();
*first = 'd';

assert_eq!(slice, &['b', 'c']);
assert_eq!(first, &'d');

pub fn take_last<'a>(self: &mut &'a [T]) -> Option<&'a T>

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the last element of the slice and returns a reference to it.

Returns None if the slice is empty.

Examples

#![feature(slice_take)]

let mut slice: &[_] = &['a', 'b', 'c'];
let last = slice.take_last().unwrap();

assert_eq!(slice, &['a', 'b']);
assert_eq!(last, &'c');

pub fn take_last_mut<'a>(self: &mut &'a mut [T]) -> Option<&'a mut T>

🔬This is a nightly-only experimental API. (slice_take #62280)

Removes the last element of the slice and returns a mutable reference to it.

Returns None if the slice is empty.

Examples

#![feature(slice_take)]

let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
let last = slice.take_last_mut().unwrap();
*last = 'd';

assert_eq!(slice, &['a', 'b']);
assert_eq!(last, &'d');

pub unsafe fn get_many_unchecked_mut<const N: usize>( &mut self, indices: [usize; N] ) -> [&mut T; N]

🔬This is a nightly-only experimental API. (get_many_mut #104642)

Returns mutable references to many indices at once, without doing any checks.

For a safe alternative see get_many_mut.

Safety

Calling this method with overlapping or out-of-bounds indices is undefined behavior even if the resulting references are not used.

Examples

#![feature(get_many_mut)]

let x = &mut [1, 2, 4];

unsafe {
    let [a, b] = x.get_many_unchecked_mut([0, 2]);
    *a *= 10;
    *b *= 100;
}
assert_eq!(x, &[10, 2, 400]);

pub fn get_many_mut<const N: usize>( &mut self, indices: [usize; N] ) -> Result<[&mut T; N], GetManyMutError<N>>

🔬This is a nightly-only experimental API. (get_many_mut #104642)

Returns mutable references to many indices at once.

Returns an error if any index is out-of-bounds, or if the same index was passed more than once.

Examples

#![feature(get_many_mut)]

let v = &mut [1, 2, 3];
if let Ok([a, b]) = v.get_many_mut([0, 2]) {
    *a = 413;
    *b = 612;
}
assert_eq!(v, &[413, 2, 612]);

pub fn sort_floats(&mut self)

🔬This is a nightly-only experimental API. (sort_floats #93396)

Sorts the slice of floats.

This sort is in-place (i.e. does not allocate), O(n * log(n)) worst-case, and uses the ordering defined by f64::total_cmp.

Current implementation

This uses the same sorting algorithm as sort_unstable_by.

Examples

#![feature(sort_floats)]
let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];

v.sort_floats();
let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
assert_eq!(&v[..8], &sorted[..8]);
assert!(v[8].is_nan());

pub fn flatten(&self) -> &[T]

🔬This is a nightly-only experimental API. (slice_flatten #95629)

Takes a &[[T; N]], and flattens it to a &[T].

Panics

This panics if the length of the resulting slice would overflow a usize.

This is only possible when flattening a slice of arrays of zero-sized types, and thus tends to be irrelevant in practice. If size_of::<T>() > 0, this will never panic.

Examples

#![feature(slice_flatten)]

assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]);

assert_eq!(
    [[1, 2, 3], [4, 5, 6]].flatten(),
    [[1, 2], [3, 4], [5, 6]].flatten(),
);

let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
assert!(slice_of_empty_arrays.flatten().is_empty());

let empty_slice_of_arrays: &[[u32; 10]] = &[];
assert!(empty_slice_of_arrays.flatten().is_empty());

pub fn flatten_mut(&mut self) -> &mut [T]

🔬This is a nightly-only experimental API. (slice_flatten #95629)

Takes a &mut [[T; N]], and flattens it to a &mut [T].

Panics

This panics if the length of the resulting slice would overflow a usize.

This is only possible when flattening a slice of arrays of zero-sized types, and thus tends to be irrelevant in practice. If size_of::<T>() > 0, this will never panic.

Examples

#![feature(slice_flatten)]

fn add_5_to_all(slice: &mut [i32]) {
    for i in slice {
        *i += 5;
    }
}

let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
add_5_to_all(array.flatten_mut());
assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);

pub fn is_ascii(&self) -> bool

Checks if all bytes in this slice are within the ASCII range.

pub fn as_ascii(&self) -> Option<&[AsciiChar]>

🔬This is a nightly-only experimental API. (ascii_char #110998)

If this slice is_ascii, returns it as a slice of ASCII characters, otherwise returns None.

pub unsafe fn as_ascii_unchecked(&self) -> &[AsciiChar]

🔬This is a nightly-only experimental API. (ascii_char #110998)

Converts this slice of bytes into a slice of ASCII characters, without checking whether they’re valid.

Safety

Every byte in the slice must be in 0..=127, or else this is UB.

pub fn eq_ignore_ascii_case(&self, other: &[u8]) -> bool

Checks that two slices are an ASCII case-insensitive match.

Same as to_ascii_lowercase(a) == to_ascii_lowercase(b), but without allocating and copying temporaries.

pub fn make_ascii_uppercase(&mut self)

Converts this slice to its ASCII upper case equivalent in-place.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To return a new uppercased value without modifying the existing one, use to_ascii_uppercase.

pub fn make_ascii_lowercase(&mut self)

Converts this slice to its ASCII lower case equivalent in-place.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To return a new lowercased value without modifying the existing one, use to_ascii_lowercase.

pub fn escape_ascii(&self) -> EscapeAscii<'_>

Returns an iterator that produces an escaped version of this slice, treating it as an ASCII string.

Examples

let s = b"0\t\r\n'\"\\\x9d";
let escaped = s.escape_ascii().to_string();
assert_eq!(escaped, "0\\t\\r\\n\\'\\\"\\\\\\x9d");

pub fn trim_ascii_start(&self) -> &[u8]

🔬This is a nightly-only experimental API. (byte_slice_trim_ascii #94035)

Returns a byte slice with leading ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

Examples

#![feature(byte_slice_trim_ascii)]

assert_eq!(b" \t hello world\n".trim_ascii_start(), b"hello world\n");
assert_eq!(b"  ".trim_ascii_start(), b"");
assert_eq!(b"".trim_ascii_start(), b"");

pub fn trim_ascii_end(&self) -> &[u8]

🔬This is a nightly-only experimental API. (byte_slice_trim_ascii #94035)

Returns a byte slice with trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

Examples

#![feature(byte_slice_trim_ascii)]

assert_eq!(b"\r hello world\n ".trim_ascii_end(), b"\r hello world");
assert_eq!(b"  ".trim_ascii_end(), b"");
assert_eq!(b"".trim_ascii_end(), b"");

pub fn trim_ascii(&self) -> &[u8]

🔬This is a nightly-only experimental API. (byte_slice_trim_ascii #94035)

Returns a byte slice with leading and trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

Examples

#![feature(byte_slice_trim_ascii)]

assert_eq!(b"\r hello world\n ".trim_ascii(), b"hello world");
assert_eq!(b"  ".trim_ascii(), b"");
assert_eq!(b"".trim_ascii(), b"");

pub fn as_str(&self) -> &str

🔬This is a nightly-only experimental API. (ascii_char #110998)

Views this slice of ASCII characters as a UTF-8 str.

pub fn as_bytes(&self) -> &[u8]

🔬This is a nightly-only experimental API. (ascii_char #110998)

Views this slice of ASCII characters as a slice of u8 bytes.

pub fn sort_floats(&mut self)

🔬This is a nightly-only experimental API. (sort_floats #93396)

Sorts the slice of floats.

This sort is in-place (i.e. does not allocate), O(n * log(n)) worst-case, and uses the ordering defined by f32::total_cmp.

Current implementation

This uses the same sorting algorithm as sort_unstable_by.

Examples

#![feature(sort_floats)]
let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];

v.sort_floats();
let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
assert_eq!(&v[..8], &sorted[..8]);
assert!(v[8].is_nan());

Trait Implementations

impl<T, A: Allocator> AsMut<[T]> for Vec<T, A>

fn as_mut(&mut self) -> &mut [T]

Converts this type into a mutable reference of the (usually inferred) input type.

impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A>

fn as_mut(&mut self) -> &mut Vec<T, A>

Converts this type into a mutable reference of the (usually inferred) input type.

impl<T, A: Allocator> AsRef<[T]> for Vec<T, A>

fn as_ref(&self) -> &[T]

Converts this type into a shared reference of the (usually inferred) input type.

impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A>

fn as_ref(&self) -> &Vec<T, A>

Converts this type into a shared reference of the (usually inferred) input type.

impl<T, A: Allocator> Borrow<[T]> for Vec<T, A>

fn borrow(&self) -> &[T]

Immutably borrows from an owned value.

impl<T, A: Allocator> BorrowMut<[T]> for Vec<T, A>

fn borrow_mut(&mut self) -> &mut [T]

Mutably borrows from an owned value.

impl<T: Debug, A: Allocator> Debug for Vec<T, A>

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

Formats the value using the given formatter.

impl<T> Default for Vec<T>

fn default() -> Vec<T>

Creates an empty Vec<T>.

The vector will not allocate until elements are pushed onto it.

impl<T, A: Allocator> Deref for Vec<T, A>

type Target = [T]

The resulting type after dereferencing.

fn deref(&self) -> &[T]

Dereferences the value.

impl<T, A: Allocator> DerefMut for Vec<T, A>

fn deref_mut(&mut self) -> &mut [T]

Mutably dereferences the value.

impl<T, A: Allocator> Drop for Vec<T, A>

fn drop(&mut self)

Executes the destructor for this type.

impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A>

fn from(s: Box<[T], A>) -> Self

Convert a boxed slice into a vector by transferring ownership of the existing heap allocation.

Examples

let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
assert_eq!(Vec::from(b), vec![1, 2, 3]);

impl<T: Hash, A: Allocator> Hash for Vec<T, A>

The hash of a vector is the same as that of the corresponding slice, as required by the core::borrow::Borrow implementation.

use std::hash::BuildHasher;

let b = std::collections::hash_map::RandomState::new();
let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
let s: &[u8] = &[0xa8, 0x3c, 0x09];
assert_eq!(b.hash_one(v), b.hash_one(s));

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

Feeds this value into the given Hasher.

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

Feeds a slice of this type into the given Hasher.

impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A>

type Output = <I as SliceIndex<[T]>>::Output

The returned type after indexing.

fn index(&self, index: I) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A>

fn index_mut(&mut self, index: I) -> &mut Self::Output

Performs the mutable indexing (container[index]) operation.

impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A>

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?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A>

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?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<T, A: Allocator> IntoIterator for Vec<T, A>

fn into_iter(self) -> Self::IntoIter

Creates a consuming iterator, that is, one that moves each value out of the vector (from start to end). The vector cannot be used after calling this.

Examples

let v = vec!["a".to_string(), "b".to_string()];
let mut v_iter = v.into_iter();

let first_element: Option<String> = v_iter.next();

assert_eq!(first_element, Some("a".to_string()));
assert_eq!(v_iter.next(), Some("b".to_string()));
assert_eq!(v_iter.next(), None);

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T, A>

Which kind of iterator are we turning this into?

impl<T: Ord, A: Allocator> Ord for Vec<T, A>

Implements ordering of vectors, lexicographically.

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

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

Compares and returns the maximum of two values.

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

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval.

impl<T, U, A: Allocator> PartialEq<&[U]> for Vec<T, A>where T: PartialEq<U>,

fn eq(&self, other: &&[U]) -> bool

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

fn ne(&self, other: &&[U]) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A: Allocator, const N: usize> PartialEq<&[U; N]> for Vec<T, A>where T: PartialEq<U>,

fn eq(&self, other: &&[U; N]) -> bool

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

fn ne(&self, other: &&[U; N]) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A: Allocator> PartialEq<&mut [U]> for Vec<T, A>where T: PartialEq<U>,

fn eq(&self, other: &&mut [U]) -> bool

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

fn ne(&self, other: &&mut [U]) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A: Allocator> PartialEq<[U]> for Vec<T, A>where T: PartialEq<U>,

fn eq(&self, other: &[U]) -> bool

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

fn ne(&self, other: &[U]) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A: Allocator, const N: usize> PartialEq<[U; N]> for Vec<T, A>where T: PartialEq<U>,

fn eq(&self, other: &[U; N]) -> bool

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

fn ne(&self, other: &[U; N]) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A: Allocator> PartialEq<Vec<U, A>> for &[T]where T: PartialEq<U>,

fn eq(&self, other: &Vec<U, A>) -> bool

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

fn ne(&self, other: &Vec<U, A>) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A: Allocator> PartialEq<Vec<U, A>> for &mut [T]where T: PartialEq<U>,

fn eq(&self, other: &Vec<U, A>) -> bool

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

fn ne(&self, other: &Vec<U, A>) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A: Allocator> PartialEq<Vec<U, A>> for [T]where T: PartialEq<U>,

fn eq(&self, other: &Vec<U, A>) -> bool

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

fn ne(&self, other: &Vec<U, A>) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, U, A1: Allocator, A2: Allocator> PartialEq<Vec<U, A2>> for Vec<T, A1>where T: PartialEq<U>,

fn eq(&self, other: &Vec<U, A2>) -> bool

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

fn ne(&self, other: &Vec<U, A2>) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, A1, A2> PartialOrd<Vec<T, A2>> for Vec<T, A1>where T: PartialOrd, A1: Allocator, A2: Allocator,

Implements comparison of vectors, lexicographically.

fn partial_cmp(&self, other: &Vec<T, A2>) -> Option<Ordering>

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

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

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

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

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

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

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

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

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

impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N]

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

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:

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.

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.

impl<T: Eq, A: Allocator> Eq for Vec<T, A>