# Struct alloc::vec::Vec

1.0.0 · source · []
``pub struct Vec<T, A: Allocator = Global> { /* private fields */ }``
Expand description

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

## Examples

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

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

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

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

vec.extend([1, 2, 3].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 allocation. Even if you zero a `Vec`’s memory first, that might not actually happen because the optimizer does not consider this a side-effect that must be preserved. There is one case which we will not break, however: using `unsafe` code to write to the excess capacity, and then increasing the length to match, is always valid.

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

## Implementations

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);``````
Run

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 alignment as what `ptr` was allocated with. (`T` having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the `dealloc` requirement that memory must be allocated and deallocated with the same layout.)
• The size of `T` times the `capacity` (ie. the allocated size in bytes) needs to be the same size as the pointer was allocated with. (Because similar to alignment, `dealloc` must be called with the same layout `size`.)
• `length` needs to be less than or equal to `capacity`.

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. To avoid these issues, it is often preferable to do casting/transmuting using `slice::from_raw_parts` instead.

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

##### Examples
``````use std::ptr;
use std::mem;

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

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

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

unsafe {
// Overwrite memory with 4, 5, 6
for i in 0..len 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);``````
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🔬 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)

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 exceeds `isize::MAX` bytes.

##### Examples
``````let mut vec = vec![1];
vec.reserve_exact(10);
assert!(vec.capacity() >= 11);``````
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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
``````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

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 `try_reserve` if future insertions are expected.

##### Errors

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

##### Examples
``````use std::collections::TryReserveError;

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

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

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

Ok(output)
}``````
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);``````
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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();``````
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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);``````
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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();``````
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Extracts a mutable slice of the entire vector.

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

##### Examples
``````use std::io::{self, Read};
let mut buffer = vec![0; 3];
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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() {
}
}``````
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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
}
}
}``````
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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);
}``````
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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). If you need to preserve the element order, use `remove` instead.

##### Panics

Panics if `index` is out of bounds.

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

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

assert_eq!(v.swap_remove(0), "foo");
assert_eq!(v, ["baz", "qux"]);``````
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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. If you’d like to remove elements from the beginning of the `Vec`, consider using `VecDeque::pop_front` instead.

##### Panics

Panics if `index` is out of bounds.

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

Retains only the elements specified by the predicate.

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

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

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

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

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

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

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

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

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

##### Panics

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

##### Leaking

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

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

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

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

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

##### Examples

Simple usage:

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

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

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

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

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

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

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

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`. If you only need to resize to a smaller size, use `Vec::truncate`.

##### 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` slice is traversed in-order.

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

##### Examples
``````let mut vec = vec![1];
vec.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.

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

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

##### Panics

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

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

##### Examples
``````#![feature(slice_flatten)]

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

let mut flattened = vec.into_flattened();
assert_eq!(flattened.pop(), Some(6));``````
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, 4];
let new = [7, 8, 9];
let u: Vec<_> = v.splice(1..3, new).collect();
assert_eq!(v, &[1, 7, 8, 9, 4]);
assert_eq!(u, &[2, 3]);``````
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]>

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 at most once per element, by using temporary storage to remember the results of key evaluation. The order of calls to the key function is unspecified and may change in future versions of the standard library.

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

Converts this type into a mutable reference of the (usually inferred) input type.

Converts this type into a mutable reference of the (usually inferred) input type.

Converts this type into a shared reference of the (usually inferred) input type.

Converts this type into a shared reference of the (usually inferred) input type.

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(b"raw"), vec![b'r', b'a', b'w']);``
Run

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<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.

Allocate a `Vec<T>` and move `s`’s items into it.

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

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

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

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.

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

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 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

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

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

This conversion does not allocate or clone the data.

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

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?

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

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
``````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`:

``````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.

``````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.

## 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

Returns the argument unchanged.

Calls `U::from(self)`.

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

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)

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.