# Struct ark_ff::vec::Vec1.0.0[−][src]

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

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]);```

The `vec!` macro is provided to make initialization more convenient:

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

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

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

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

For more information, see Capacity and Reallocation.

Use a `Vec<T>` as an efficient stack:

```let mut stack = Vec::new();

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

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

# Indexing

The `Vec` type allows 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'```

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

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

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

# Slicing

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

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

let v = vec![0, 1];

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

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

# Capacity and reallocation

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

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

# Guarantees

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

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

However, the pointer may 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` may 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 may not actually happen because the optimizer does not consider this a side-effect that must be preserved. There is one case which we will not break, however: using `unsafe` code to write to the excess capacity, and then increasing the length to match, is always valid.

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

## Implementations

### `impl<T> Vec<T, Global>`[src]

#### `pub const fn new() -> Vec<T, Global>`1.0.0 (const: 1.39.0)[src]

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

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

# Examples

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

#### `pub fn with_capacity(capacity: usize) -> Vec<T, Global>`[src]

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.

# 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);```

#### `pub unsafe fn from_raw_parts(    ptr: *mut T,     length: usize,     capacity: usize) -> Vec<T, Global>`[src]

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]);
}```

### `impl<T, A> Vec<T, A> where    A: Allocator, `[src]

#### `pub const fn new_in(alloc: A) -> Vec<T, A>`[src]

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

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

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

# Examples

```#![feature(allocator_api)]

use std::alloc::System;

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

#### `pub fn with_capacity_in(capacity: usize, alloc: A) -> Vec<T, A>`[src]

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

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.

# 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);```

#### `pub unsafe fn from_raw_parts_in(    ptr: *mut T,     length: usize,     capacity: usize,     alloc: A) -> Vec<T, A>`[src]

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

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]);
}```

#### `pub fn into_raw_parts(self) -> (*mut T, usize, usize)`[src]

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

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]);```

#### `pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A)`[src]

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

Decomposes a `Vec<T>` into its raw components.

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

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

# Examples

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

use std::alloc::System;

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

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

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

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

#### `pub fn capacity(&self) -> usize`[src]

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);```

#### `pub fn reserve(&mut self, additional: usize)`[src]

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);```

#### `pub fn reserve_exact(&mut self, additional: usize)`[src]

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);```

#### `pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>`[src]

🔬 This is a nightly-only experimental API. (`try_reserve`)

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)
}```

#### `pub fn try_reserve_exact(    &mut self,     additional: usize) -> Result<(), TryReserveError>`[src]

🔬 This is a nightly-only experimental API. (`try_reserve`)

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)
}```

#### `pub fn shrink_to_fit(&mut self)`[src]

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].iter().cloned());
assert_eq!(vec.capacity(), 10);
vec.shrink_to_fit();
assert!(vec.capacity() >= 3);```

#### `pub fn shrink_to(&mut self, min_capacity: usize)`[src]

🔬 This is a nightly-only experimental API. (`shrink_to`)

new API

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

```#![feature(shrink_to)]
let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3].iter().cloned());
assert_eq!(vec.capacity(), 10);
vec.shrink_to(4);
assert!(vec.capacity() >= 4);
vec.shrink_to(0);
assert!(vec.capacity() >= 3);```

#### `pub fn into_boxed_slice(self) -> Box<[T], A>`[src]

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();```

Any excess capacity is removed:

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

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

#### `pub fn truncate(&mut self, len: usize)`[src]

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]);```

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

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

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

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

#### `pub fn as_slice(&self) -> &[T]`1.7.0[src]

Extracts a slice containing the entire vector.

Equivalent to `&s[..]`.

# Examples

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

#### `pub fn as_mut_slice(&mut self) -> &mut [T]`1.7.0[src]

Extracts a mutable slice of the entire vector.

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

# Examples

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

#### `pub fn as_ptr(&self) -> *const T`1.37.0[src]

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() {
assert_eq!(*x_ptr.add(i), 1 << i);
}
}```

#### `pub fn as_mut_ptr(&mut self) -> *mut T`1.37.0[src]

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_ptr.add(i) = i as i32;
}
x.set_len(size);
}
assert_eq!(&*x, &[0, 1, 2, 3]);```

#### `pub fn allocator(&self) -> &A`[src]

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

Returns a reference to the underlying allocator.

#### `pub unsafe fn set_len(&mut self, new_len: usize)`[src]

Forces the length of the vector to `new_len`.

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

# Safety

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

# Examples

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

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

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

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

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

#### `pub fn swap_remove(&mut self, index: usize) -> T`[src]

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"]);```

#### `pub fn insert(&mut self, index: usize, element: T)`[src]

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]);```

#### `pub fn remove(&mut self, index: usize) -> T`[src]

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

# Panics

Panics if `index` is out of bounds.

# Examples

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

#### `pub fn retain<F>(&mut self, f: F) where    F: FnMut(&T) -> bool, `[src]

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]);```

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

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

#### `pub fn dedup_by_key<F, K>(&mut self, key: F) where    F: FnMut(&mut T) -> K,    K: PartialEq<K>, `1.16.0[src]

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

If the vector is sorted, this removes all duplicates.

# Examples

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

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

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

#### `pub fn dedup_by<F>(&mut self, same_bucket: F) where    F: FnMut(&mut T, &mut T) -> bool, `1.16.0[src]

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

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

If the vector is sorted, this removes all duplicates.

# Examples

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

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

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

#### `pub fn push(&mut self, value: T)`[src]

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]);```

#### `pub fn pop(&mut self) -> Option<T>`[src]

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]);```

#### `pub fn append(&mut self, other: &mut Vec<T, A>)`1.4.0[src]

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, []);```

#### `pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>ⓘNotable traits for Drain<'_, T, A>impl<'_, T, A> Iterator for Drain<'_, T, A> where    A: Allocator,  type Item = T; where    R: RangeBounds<usize>, `1.6.0[src]

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, &[]);```

#### `pub fn clear(&mut self)`[src]

Clears the vector, removing all values.

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

# Examples

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

v.clear();

assert!(v.is_empty());```

#### `pub fn len(&self) -> usize`[src]

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

# Examples

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

#### `pub fn is_empty(&self) -> bool`[src]

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());```

#### `#[must_use = "use `.truncate()` if you don't need the other half"]pub fn split_off(&mut self, at: usize) -> Vec<T, A> where    A: Clone, `1.4.0[src]

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]);```

#### `pub fn resize_with<F>(&mut self, new_len: usize, f: F) where    F: FnMut() -> T, `1.33.0[src]

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]);```

#### `pub fn leak<'a>(self) -> &'a mut [T] where    A: 'a, `1.47.0[src]

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]);```

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

🔬 This is a nightly-only experimental API. (`vec_spare_capacity`)

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]);```

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

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

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]);```

### `impl<T, A> Vec<T, A> where    T: Clone,    A: Allocator, `[src]

#### `pub fn resize(&mut self, new_len: usize, value: T)`1.5.0[src]

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]);```

#### `pub fn extend_from_slice(&mut self, other: &[T])`1.6.0[src]

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]);```

#### `pub fn extend_from_within<R>(&mut self, src: R) where    R: RangeBounds<usize>, `[src]

🔬 This is a nightly-only experimental API. (`vec_extend_from_within`)

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

## Examples

```#![feature(vec_extend_from_within)]

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]);```

### `impl<T, A> Vec<T, A> where    T: PartialEq<T>,    A: Allocator, `[src]

#### `pub fn dedup(&mut self)`[src]

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

If the vector is sorted, this removes all duplicates.

# Examples

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

vec.dedup();

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

### `impl<T, A> Vec<T, A> where    A: Allocator, `[src]

#### `pub fn splice<R, I>(    &mut self,     range: R,     replace_with: I) -> Splice<'_, <I as IntoIterator>::IntoIter, A>ⓘNotable traits for Splice<'_, I, A>impl<'_, I, A> Iterator for Splice<'_, I, A> where    I: Iterator,    A: Allocator,  type Item = <I as Iterator>::Item; where    R: RangeBounds<usize>,    I: IntoIterator<Item = T>, `1.21.0[src]

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.iter().cloned()).collect();
assert_eq!(v, &[7, 8, 3]);
assert_eq!(u, &[1, 2]);```

#### `pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>ⓘNotable traits for DrainFilter<'_, T, F, A>impl<'_, T, F, A> Iterator for DrainFilter<'_, T, F, A> where    F: FnMut(&mut T) -> bool,    A: Allocator,  type Item = T; where    F: FnMut(&mut T) -> bool, `[src]

🔬 This is a nightly-only experimental API. (`drain_filter`)

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);
// your code here
} else {
i += 1;
}
}
```

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]);```

## Trait Implementations

### `impl<T> Default for Vec<T, Global>`[src]

#### `pub fn default() -> Vec<T, Global>`[src]

Creates an empty `Vec<T>`.

### `impl<T, A> Deref for Vec<T, A> where    A: Allocator, `[src]

#### `type Target = [T]`

The resulting type after dereferencing.

### `impl<'a, T, A> Extend<&'a T> for Vec<T, A> where    T: 'a + Copy,    A: 'a + Allocator, `1.2.0[src]

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.

### `impl<T> From<BinaryHeap<T>> for Vec<T, Global>`1.5.0[src]

#### `pub fn from(heap: BinaryHeap<T>) -> Vec<T, Global>`[src]

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

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

### `impl From<String> for Vec<u8, Global>`1.14.0[src]

#### `pub fn from(string: String) -> Vec<u8, Global>`[src]

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);
}```

### `impl<T> From<VecDeque<T>> for Vec<T, Global>`1.10.0[src]

#### `pub fn from(other: VecDeque<T>) -> Vec<T, Global>`[src]

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);```

### `impl<T, I, A> Index<I> for Vec<T, A> where    I: SliceIndex<[T]>,    A: Allocator, `[src]

#### `type Output = <I as SliceIndex<[T]>>::Output`

The returned type after indexing.

### `impl<'a, T, A> IntoIterator for &'a Vec<T, A> where    A: Allocator, `[src]

#### `type Item = &'a T`

The type of the elements being iterated over.

#### `type IntoIter = Iter<'a, T>`

Which kind of iterator are we turning this into?

### `impl<'a, T, A> IntoIterator for &'a mut Vec<T, A> where    A: Allocator, `[src]

#### `type Item = &'a mut T`

The type of the elements being iterated over.

#### `type IntoIter = IterMut<'a, T>`

Which kind of iterator are we turning this into?

### `impl<T, A> IntoIterator for Vec<T, A> where    A: Allocator, `[src]

#### `type Item = T`

The type of the elements being iterated over.

#### `type IntoIter = IntoIter<T, A>`

Which kind of iterator are we turning this into?

#### `pub fn into_iter(self) -> IntoIter<T, A>ⓘNotable traits for IntoIter<T, A>impl<T, A> Iterator for IntoIter<T, A> where    A: Allocator,  type Item = T;`[src]

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);
}```

### `impl<T, A> Ord for Vec<T, A> where    T: Ord,    A: Allocator, `[src]

Implements ordering of vectors, lexicographically.

### `impl<T, A> PartialOrd<Vec<T, A>> for Vec<T, A> where    T: PartialOrd<T>,    A: Allocator, `[src]

Implements comparison of vectors, lexicographically.

## Blanket Implementations

### `impl<T> ToOwned for T where    T: Clone, `[src]

#### `type Owned = T`

The resulting type after obtaining ownership.

### `impl<T, U> TryFrom<U> for T where    U: Into<T>, `[src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

### `impl<T, U> TryInto<U> for T where    U: TryFrom<T>, `[src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.