# Struct std::vec::Vec1.0.0[−][src]

``pub struct Vec<T, A = Global> where    A: Allocator,  { /* fields omitted */ }``
Expand description

A contiguous growable array type, written as `Vec<T>` and pronounced ‘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].iter().copied());

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

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);``````
Run

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]);``````
Run

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);
}``````
Run

# Indexing

The `Vec` type allows to access 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'``````
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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!``````
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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];

// ... and that's all!
// you can also do it like this:
let u: &[usize] = &v;
// or like this:
let u: &[_] = &v;``````
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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::with_capacity(0)`, 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)`, 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 `Vec`. 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

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();``
Run

Constructs a new, empty `Vec<T>` with the specified capacity.

The vector will be able to hold exactly `capacity` elements without reallocating. If `capacity` is 0, the vector will not allocate.

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

# Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

# Examples

``````let mut vec = Vec::with_capacity(10);

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

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

// ...but this may make the vector reallocate
vec.push(11);
assert_eq!(vec.len(), 11);
assert!(vec.capacity() >= 11);``````
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Creates a `Vec<T>` directly from the raw components of another vector.

# Safety

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

• `ptr` needs to have been previously allocated via `String`/`Vec<T>` (at least, it’s highly likely to be incorrect if it wasn’t).
• `T` needs to have the same size and 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.)
• `length` needs to be less than or equal to `capacity`.
• `capacity` needs to be the capacity that the pointer was allocated with.

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

``````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 as isize {
ptr::write(p.offset(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]);
}``````
Run
🔬 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);``````
Run
🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Constructs a new, empty `Vec<T, A>` with the specified capacity with the provided allocator.

The vector will be able to hold exactly `capacity` elements without reallocating. If `capacity` is 0, the vector will not allocate.

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

# Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

# Examples

``````#![feature(allocator_api)]

use std::alloc::System;

let mut vec = Vec::with_capacity_in(10, System);

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

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

// ...but this may make the vector reallocate
vec.push(11);
assert_eq!(vec.len(), 11);
assert!(vec.capacity() >= 11);``````
Run
🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Creates a `Vec<T, A>` directly from the raw components of another vector.

# Safety

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

• `ptr` needs to have been previously allocated via `String`/`Vec<T>` (at least, it’s highly likely to be incorrect if it wasn’t).
• `T` needs to have the same size and 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.)
• `length` needs to be less than or equal to `capacity`.
• `capacity` needs to be the capacity that the pointer was allocated with.

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 as isize {
ptr::write(p.offset(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]);
}``````
Run
🔬 This is a nightly-only experimental API. (`vec_into_raw_parts` #65816)

new API

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]);``````
Run
🔬 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]);``````
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Returns the number of elements the vector can hold without reallocating.

# Examples

``````let vec: Vec<i32> = Vec::with_capacity(10);
assert_eq!(vec.capacity(), 10);``````
Run

Reserves capacity for at least `additional` more elements to be inserted in the given `Vec<T>`. The collection may reserve more space to avoid frequent reallocations. After calling `reserve`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if capacity is already sufficient.

# Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

# Examples

``````let mut vec = vec![1];
vec.reserve(10);
assert!(vec.capacity() >= 11);``````
Run

Reserves the minimum capacity for exactly `additional` more elements to be inserted in the given `Vec<T>`. After calling `reserve_exact`, capacity will be greater than or equal to `self.len() + additional`. 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 `reserve` if future insertions are expected.

# Panics

Panics if the new capacity overflows `usize`.

# Examples

``````let mut vec = vec![1];
vec.reserve_exact(10);
assert!(vec.capacity() >= 11);``````
Run
🔬 This is a nightly-only experimental API. (`try_reserve` #48043)

new API

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 avoid frequent reallocations. After calling `try_reserve`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if capacity is already sufficient.

# Errors

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

# Examples

``````#![feature(try_reserve)]
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)
}``````
Run
🔬 This is a nightly-only experimental API. (`try_reserve` #48043)

new API

Tries to reserve the minimum capacity for exactly `additional` elements to be inserted in the given `Vec<T>`. 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 `reserve` if future insertions are expected.

# Errors

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

# Examples

``````#![feature(try_reserve)]
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)
}``````
Run

Shrinks the capacity of the vector as much as possible.

It will drop down as close as possible to the length but the allocator may still inform the vector that there is space for a few more elements.

# Examples

``````let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]);
assert_eq!(vec.capacity(), 10);
vec.shrink_to_fit();
assert!(vec.capacity() >= 3);``````
Run

Shrinks the capacity of the vector with a lower bound.

The capacity will remain at least as large as both the length and the supplied value.

If the current capacity is less than the lower limit, this is a no-op.

# Examples

``````let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]);
assert_eq!(vec.capacity(), 10);
vec.shrink_to(4);
assert!(vec.capacity() >= 4);
vec.shrink_to(0);
assert!(vec.capacity() >= 3);``````
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Converts the vector into `Box<[T]>`.

Note that this will drop any excess capacity.

# Examples

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

let slice = v.into_boxed_slice();``````
Run

Any excess capacity is removed:

``````let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]);

assert_eq!(vec.capacity(), 10);
let slice = vec.into_boxed_slice();
assert_eq!(slice.into_vec().capacity(), 3);``````
Run

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

If `len` is greater than 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]);``````
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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]);``````
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Truncating when `len == 0` is equivalent to calling the `clear` method.

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

Extracts a mutable slice of the entire vector.

Equivalent to `&mut s[..]`.

# Examples

``````use std::io::{self, Read};
let mut buffer = vec![0; 3];
Run

Returns a raw pointer to the vector’s buffer.

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`.

# Examples

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

unsafe {
for i in 0..x.len() {
}
}``````
Run

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

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.

# 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.set_len(size);
}
assert_eq!(&*x, &[0, 1, 2, 3]);``````
Run
🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Returns a reference to the underlying allocator.

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
}
}
}``````
Run

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);
}``````
Run

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

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).

# 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"]);``````
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Inserts an element at position `index` within the vector, shifting all elements after it to the right.

# Panics

Panics if `index > len`.

# Examples

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

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.

# 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]);``````
Run

Retains only the elements specified by the predicate.

In other words, remove all elements `e` such that `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]);``````
Run

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]);``````
Run

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]);``````
Run

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"]);``````
Run

Appends an element to the back of a collection.

# Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

# Examples

``````let mut vec = vec![1, 2];
vec.push(3);
assert_eq!(vec, [1, 2, 3]);``````
Run

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

# Examples

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

Moves all the elements of `other` into `Self`, leaving `other` empty.

# Panics

Panics if the number of elements in the vector overflows a `usize`.

# Examples

``````let mut vec = vec![1, 2, 3];
let mut vec2 = vec![4, 5, 6];
vec.append(&mut vec2);
assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
assert_eq!(vec2, []);``````
Run

Creates a draining iterator that removes the specified range in the vector and yields the removed items.

When the iterator is dropped, all elements in the range are removed from the vector, even if the iterator was not fully consumed. If the iterator is not dropped (with `mem::forget` for example), it is unspecified how many elements are removed.

# 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.

# 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
v.drain(..);
assert_eq!(v, &[]);``````
Run

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());``````
Run

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);``````
Run

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());``````
Run

Splits the collection into two at the given index.

Returns a newly allocated vector containing the elements in the range `[at, len)`. After the call, the original vector will be left containing the elements `[0, at)` with its previous capacity unchanged.

# Panics

Panics if `at > len`.

# Examples

``````let mut vec = vec![1, 2, 3];
let vec2 = vec.split_off(1);
assert_eq!(vec, [1]);
assert_eq!(vec2, [2, 3]);``````
Run

Resizes 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 the result of calling the closure `f`. The return values from `f` will end up in the `Vec` in the order they have been generated.

If `new_len` is less than `len`, the `Vec` is simply truncated.

This method uses a closure to create new values on every push. If you’d rather `Clone` a given value, use `Vec::resize`. If you want to use the `Default` trait to generate values, you can pass `Default::default` as the second argument.

# Examples

``````let mut vec = vec![1, 2, 3];
vec.resize_with(5, Default::default);
assert_eq!(vec, [1, 2, 3, 0, 0]);

let mut vec = vec![];
let mut p = 1;
vec.resize_with(4, || { p *= 2; p });
assert_eq!(vec, [2, 4, 8, 16]);``````
Run

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`.

This function is similar to the `leak` function on `Box` except that there is no way to recover the leaked memory.

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]);``````
Run
🔬 This is a nightly-only experimental API. (`vec_spare_capacity` #75017)

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

``````#![feature(vec_spare_capacity, maybe_uninit_extra)]

// 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]);``````
Run
🔬 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, maybe_uninit_extra)]

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]);``````
Run

Resizes 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`.

# Examples

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

let mut vec = vec![1, 2, 3, 4];
vec.resize(2, 0);
assert_eq!(vec, [1, 2]);``````
Run

Clones and appends 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` vector 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.extend_from_slice(&[2, 3, 4]);
assert_eq!(vec, [1, 2, 3, 4]);``````
Run

Copies elements from `src` range to the end of the vector.

## Examples

``````let mut vec = vec![0, 1, 2, 3, 4];

vec.extend_from_within(2..);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);

vec.extend_from_within(..2);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);

vec.extend_from_within(4..8);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);``````
Run

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]);``````
Run

Creates a splicing iterator that replaces the specified range in the vector with the given `replace_with` iterator and yields the removed items. `replace_with` does not need to be the same length as `range`.

`range` is removed even if the iterator is not consumed until the end.

It is unspecified how many elements are removed from the vector if the `Splice` value is leaked.

The input iterator `replace_with` is only consumed when the `Splice` value is dropped.

This is optimal if:

• The tail (elements in the vector after `range`) is empty,
• or `replace_with` yields fewer or equal elements than `range`’s length
• or the lower bound of its `size_hint()` is exact.

Otherwise, a temporary vector is allocated and the tail is moved twice.

# 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.

# Examples

``````let mut v = vec![1, 2, 3];
let new = [7, 8];
let u: Vec<_> = v.splice(..2, new).collect();
assert_eq!(v, &[7, 8, 3]);
assert_eq!(u, &[1, 2]);``````
Run
🔬 This is a nightly-only experimental API. (`drain_filter` #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.

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);
} else {
i += 1;
}
}
``````
Run

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

Note that `drain_filter` 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(drain_filter)]
let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];

let evens = numbers.drain_filter(|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]);``````
Run

## Methods from Deref<Target = [T]>

Returns the number of elements in the slice.

# Examples

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

Returns `true` if the slice has a length of 0.

# Examples

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

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());``````
Run

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]);``````
Run

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]);
}``````
Run

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]);``````
Run

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]);
}``````
Run

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]);``````
Run

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());``````
Run

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]);``````
Run

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));``````
Run

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]);``````
Run

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);
}``````
Run

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]);``````
Run

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() {
}
}``````
Run

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() {
}
}
assert_eq!(x, &[3, 4, 6]);``````
Run

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));``````
Run

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++.

Swaps two elements in the slice.

# 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"];
v.swap(1, 3);
assert!(v == ["a", "d", "c", "b"]);``````
Run

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

# Examples

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

Returns an iterator over the slice.

# 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);``````
Run

Returns an iterator that allows modifying each value.

# Examples

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

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());``````
Run

If the slice is shorter than `size`:

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

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());``````
Run

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]);``````
Run

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']);``````
Run

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]);``````
Run
🔬 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``````
Run
🔬 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']);``````
Run
🔬 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']]);``````
Run
🔬 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']);``````
Run
🔬 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``````
Run
🔬 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]);``````
Run
🔬 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]);``````
Run
🔬 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]);``````
Run
🔬 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());``````
Run

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());``````
Run

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]);``````
Run

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 `chunks`.

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']);``````
Run

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]);``````
Run
🔬 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);``````
Run

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);``````
Run
🔬 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);``````
Run

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);``````
Run

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, []);
}``````
Run

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]);``````
Run

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());``````
Run

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());``````
Run

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());``````
Run

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]);``````
Run

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());``````
Run

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());``````
Run

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]);``````
Run

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);``````
Run

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);``````
Run

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]);``````
Run

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);
}``````
Run

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

``````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]);``````
Run

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);
}``````
Run

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]);``````
Run

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

# Examples

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

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"));``````
Run

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]));``````
Run

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(&[]));``````
Run

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]));``````
Run

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(&[]));``````
Run

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()));``````
Run

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);``````
Run

Binary searches this sorted slice for a given element.

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.

# 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, });``````
Run

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.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]);``````
Run

Binary searches this sorted slice with a comparator function.

The comparator function should implement an order consistent with the sort order of the underlying slice, returning an order code that indicates whether its argument is `Less`, `Equal` or `Greater` the desired target.

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.

# 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, });``````
Run

Binary searches this sorted 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 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.

# 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, });``````
Run

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]);``````
Run

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]);``````
Run

# 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]);``````
Run

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]);``````
Run
👎 Deprecated since 1.49.0:

🔬 This is a nightly-only experimental API. (`slice_partition_at_index` #55300)

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

👎 Deprecated since 1.49.0:

🔬 This is a nightly-only experimental API. (`slice_partition_at_index` #55300)

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

👎 Deprecated since 1.49.0:

🔬 This is a nightly-only experimental API. (`slice_partition_at_index` #55300)

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

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 O(n) worst-case. This function is also/ known as “kth element” in other libraries. It returns a triplet of the following values: all elements less than the one at the given index, the value at the given index, and all elements greater than the one at the given index.

# Current implementation

The current algorithm is based on the quickselect portion of the same quicksort algorithm used for `sort_unstable`.

# 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
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]);``````
Run

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 O(n) worst-case. This function is also known as “kth element” in other libraries. It returns a triplet of the following values: all elements less than the one at the given index, the value at the given index, and all elements greater than the one at the given index, using the provided comparator function.

# Current implementation

The current algorithm is based on the quickselect portion of the same quicksort algorithm used for `sort_unstable`.

# 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
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]);``````
Run

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 O(n) worst-case. This function is also known as “kth element” in other libraries. It returns a triplet of the following values: all elements less than the one at the given index, the value at the given index, and all elements greater than the one at the given index, using the provided key extraction function.

# Current implementation

The current algorithm is based on the quickselect portion of the same quicksort algorithm used for `sort_unstable`.

# 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
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]);``````
Run
🔬 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]);``````
Run
🔬 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"]);``````
Run
🔬 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]);``````
Run

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']);``````
Run

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']);``````
Run

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']);``````
Run

Rotate 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']);``````
Run

Fills `self` with elements by cloning `value`.

# Examples

``````let mut buf = vec![0; 10];
buf.fill(1);
assert_eq!(buf, vec![1; 10]);``````
Run

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]);``````
Run

Copies the elements from `src` into `self`.

The length of `src` must be the same as `self`.

If `T` implements `Copy`, it can be more performant to use `copy_from_slice`.

# 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]);``````
Run

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!``````
Run

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]);``````
Run

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]);``````
Run

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!``````
Run

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]);``````
Run

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!");``````
Run

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]);``````
Run

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!``````
Run

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]);``````
Run

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. The method may make the middle slice the greatest length possible for a given type and input slice, but only your algorithm’s performance should depend on that, not its correctness. It is permissible for all of the input data to be returned as the prefix or suffix slice.

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);
}``````
Run

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. The method may make the middle slice the greatest length possible for a given type and input slice, but only your algorithm’s performance should depend on that, not its correctness. It is permissible for all of the input data to be returned as the prefix or suffix slice.

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);
}``````
Run
🔬 This is a nightly-only experimental API. (`is_sorted` #53485)

new API

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());``````
Run
🔬 This is a nightly-only experimental API. (`is_sorted` #53485)

new API

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.

🔬 This is a nightly-only experimental API. (`is_sorted` #53485)

new API

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()));``````
Run

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 a 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.

# 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)));``````
Run

Checks if all bytes in this slice are within the ASCII range.

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.

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`.

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`.

🔬 This is a nightly-only experimental API. (`inherent_ascii_escape` #77174)

Returns an iterator that produces an escaped version of this slice, treating it as an ASCII string.

# Examples

``````#![feature(inherent_ascii_escape)]

let s = b"0\t\r\n'\"\\\x9d";
let escaped = s.escape_ascii().to_string();
assert_eq!(escaped, "0\\t\\r\\n\\'\\\"\\\\\\x9d");``````
Run

Sorts the slice.

This sort is stable (i.e., does not reorder equal elements) and O(n * log(n)) worst-case.

When applicable, unstable sorting is preferred because it is generally faster than stable sorting and it doesn’t allocate auxiliary memory. See `sort_unstable`.

# Current implementation

The current algorithm is an adaptive, iterative merge sort inspired by timsort. It is designed to be very fast in cases where the slice is nearly sorted, or consists of two or more sorted sequences concatenated one after another.

Also, it allocates temporary storage half the size of `self`, but for short slices a non-allocating insertion sort is used instead.

# Examples

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

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

Sorts the slice with a comparator function.

This sort is stable (i.e., does not reorder equal elements) 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_by(|a, b| a.partial_cmp(b).unwrap());
assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);``````
Run

When applicable, unstable sorting is preferred because it is generally faster than stable sorting and it doesn’t allocate auxiliary memory. See `sort_unstable_by`.

# Current implementation

The current algorithm is an adaptive, iterative merge sort inspired by timsort. It is designed to be very fast in cases where the slice is nearly sorted, or consists of two or more sorted sequences concatenated one after another.

Also, it allocates temporary storage half the size of `self`, but for short slices a non-allocating insertion sort is used instead.

# Examples

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

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

Sorts the slice with a key extraction function.

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

For expensive key functions (e.g. functions that are not simple property accesses or basic operations), `sort_by_cached_key` is likely to be significantly faster, as it does not recompute element keys.

When applicable, unstable sorting is preferred because it is generally faster than stable sorting and it doesn’t allocate auxiliary memory. See `sort_unstable_by_key`.

# Current implementation

The current algorithm is an adaptive, iterative merge sort inspired by timsort. It is designed to be very fast in cases where the slice is nearly sorted, or consists of two or more sorted sequences concatenated one after another.

Also, it allocates temporary storage half the size of `self`, but for short slices a non-allocating insertion sort is used instead.

# Examples

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

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

Sorts the slice with a key extraction function.

During sorting, the key function is called only once per element.

This sort is stable (i.e., does not reorder equal elements) and O(m * n + n * log(n)) worst-case, where the key function is O(m).

For simple key functions (e.g., functions that are property accesses or basic operations), `sort_by_key` is likely to be faster.

# 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.

In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the length of the slice.

# Examples

``````let mut v = [-5i32, 4, 32, -3, 2];

v.sort_by_cached_key(|k| k.to_string());
assert!(v == [-3, -5, 2, 32, 4]);``````
Run

Copies `self` into a new `Vec`.

# Examples

``````let s = [10, 40, 30];
let x = s.to_vec();
// Here, `s` and `x` can be modified independently.``````
Run
🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Copies `self` into a new `Vec` with an allocator.

# Examples

``````#![feature(allocator_api)]

use std::alloc::System;

let s = [10, 40, 30];
let x = s.to_vec_in(System);
// Here, `s` and `x` can be modified independently.``````
Run

Creates a vector by repeating a slice `n` times.

# Panics

This function will panic if the capacity would overflow.

# Examples

Basic usage:

``assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]);``
Run

A panic upon overflow:

``````// this will panic at runtime
b"0123456789abcdef".repeat(usize::MAX);``````
Run

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]);``````
Run

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]);``````
Run
👎 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]);``````
Run

Returns a vector containing a copy of this slice where each byte is mapped to its ASCII upper case equivalent.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To uppercase the value in-place, use `make_ascii_uppercase`.

Returns a vector containing a copy of this slice where each byte is mapped to its ASCII lower case equivalent.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To lowercase the value in-place, use `make_ascii_lowercase`.

## Trait Implementations

Performs the conversion.

Performs the conversion.

Performs the conversion.

Performs the conversion.

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns a copy of the value. Read more

Performs copy-assignment from `source`. Read more

Formats the value using the given formatter. Read more

Creates an empty `Vec<T>`.

The resulting type after dereferencing.

Dereferences the value.

Mutably dereferences the value.

Executes the destructor for this type. Read more

Extend implementation that copies elements out of references before pushing them onto the Vec.

This implementation is specialized for slice iterators, where it uses `copy_from_slice` to append the entire slice at once.

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

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

Extends a collection with exactly one element.

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

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

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

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

Extends a collection with exactly one element.

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

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

Allocate a `Vec<T>` and fill it by cloning `s`’s items.

# Examples

``assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);``
Run

Allocate a `Vec<T>` and fill it by cloning `s`’s items.

# Examples

``assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);``
Run

Allocate a `Vec<u8>` and fill it with a UTF-8 string.

# Examples

``assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);``
Run

Creates a `Borrowed` variant of `Cow` from a reference to `Vec`.

This conversion does not allocate or clone the data.

Performs the conversion.

Converts a `BinaryHeap<T>` into a `Vec<T>`.

This conversion requires no data movement or allocation, and has constant time complexity.

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]);``````
Run

Converts a `CString` into a `Vec``<u8>`.

The conversion consumes the `CString`, and removes the terminating NUL byte.

Convert a clone-on-write slice into a vector.

If `s` already owns a `Vec<T>`, it will be returned directly. If `s` is borrowing a slice, a new `Vec<T>` will be allocated and filled by cloning `s`’s items into it.

# Examples

``````let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
assert_eq!(Vec::from(o), Vec::from(b));``````
Run

Converts the given `String` to a vector `Vec` that holds values of type `u8`.

# Examples

Basic usage:

``````let s1 = String::from("hello world");
let v1 = Vec::from(s1);

for b in v1 {
println!("{}", b);
}``````
Run

Converts a `Vec``<``NonZeroU8``>` into a `CString` without copying nor checking for inner null bytes.

Convert a vector into a boxed slice.

If `v` has excess capacity, its items will be moved into a newly-allocated buffer with exactly the right capacity.

# Examples

``assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());``
Run

Turn a `Vec<T>` into a `VecDeque<T>`.

This avoids reallocating where possible, but the conditions for that are strict, and subject to change, and so shouldn’t be relied upon unless the `Vec<T>` came from `From<VecDeque<T>>` and hasn’t been reallocated.

Allocate a reference-counted slice and move `v`’s items into it.

# Example

``````let original: Box<Vec<i32>> = Box::new(vec![1, 2, 3]);
let shared: Rc<Vec<i32>> = Rc::from(original);
assert_eq!(vec![1, 2, 3], *shared);``````
Run

Creates an `Owned` variant of `Cow` from an owned instance of `Vec`.

This conversion does not allocate or clone the data.

Converts a `Vec<T>` into a `BinaryHeap<T>`.

This conversion happens in-place, and has O(n) time complexity.

Allocate a reference-counted slice and move `v`’s items into it.

# Example

``````let unique: Vec<i32> = vec![1, 2, 3];
let shared: Arc<[i32]> = Arc::from(unique);
assert_eq!(&[1, 2, 3], &shared[..]);``````
Run

Turn a `VecDeque<T>` into a `Vec<T>`.

This never needs to re-allocate, but does need to do O(n) data movement if the circular buffer doesn’t happen to be at the beginning of the allocation.

# Examples

``````use std::collections::VecDeque;

// This one is *O*(1).
let deque: VecDeque<_> = (1..5).collect();
let ptr = deque.as_slices().0.as_ptr();
let vec = Vec::from(deque);
assert_eq!(vec, [1, 2, 3, 4]);
assert_eq!(vec.as_ptr(), ptr);

// This one needs data rearranging.
let mut deque: VecDeque<_> = (1..5).collect();
deque.push_front(9);
deque.push_front(8);
let ptr = deque.as_slices().1.as_ptr();
let vec = Vec::from(deque);
assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
assert_eq!(vec.as_ptr(), ptr);``````
Run

Creates a value from an iterator. Read more

The hash of a vector is the same as that of the corresponding slice, as required by the `core::borrow::Borrow` implementation.

``````#![feature(build_hasher_simple_hash_one)]
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));``````
Run

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

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

The returned type after indexing.

Performs the indexing (`container[index]`) operation. Read more

Performs the mutable indexing (`container[index]`) operation. Read more

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

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()];
for s in v.into_iter() {
// s has type String, not &String
println!("{}", s);
}``````
Run

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Implements ordering of vectors, lexicographically.

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

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

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

This method tests for `!=`.

Implements comparison of vectors, lexicographically.

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

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

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

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

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

Gets the entire contents of the `Vec<T>` as an array, if its size exactly matches that of the requested array.

# Examples

``````use std::convert::TryInto;
assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));``````
Run

If the length doesn’t match, the input comes back in `Err`:

``````use std::convert::TryInto;
let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));``````
Run

If you’re fine with just getting a prefix of the `Vec<T>`, you can call `.truncate(N)` first.

``````use std::convert::TryInto;
let mut v = String::from("hello world").into_bytes();
v.sort();
v.truncate(2);
let [a, b]: [_; 2] = v.try_into().unwrap();
assert_eq!(a, b' ');
assert_eq!(b, b'd');``````
Run

The type returned in the event of a conversion error.

Write is implemented for `Vec<u8>` by appending to the vector. The vector will grow as needed.

Write a buffer into this writer, returning how many bytes were written. Read more

Like `write`, except that it writes from a slice of buffers. Read more

🔬 This is a nightly-only experimental API. (`can_vector` #69941)

Determines if this `Write`r has an efficient `write_vectored` implementation. Read more

Attempts to write an entire buffer into this writer. Read more

Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more

🔬 This is a nightly-only experimental API. (`write_all_vectored` #70436)

Attempts to write multiple buffers into this writer. Read more

Writes a formatted string into this writer, returning any error encountered. Read more

Creates a “by reference” adapter for this instance of `Write`. Read more

## Blanket Implementations

Gets the `TypeId` of `self`. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Performs the conversion.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (`toowned_clone_into` #41263)