Struct alloc::vec::Vec

pub struct Vec<T> { /* fields omitted */ }

A contiguous growable array type, written Vec<T> but 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().cloned());

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 vec1 = Vec::with_capacity(5);
vec1.resize(5, 0);

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!

In conclusion: always check if the index you want to get really exists before doing it.

Slicing

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

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

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

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

In Rust, it's more common to pass slices as arguments rather than vectors when you just want to provide a 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.

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.

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.

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

Methods

impl<T> Vec<T>

pub const fn new() -> Vec<T>

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>

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);

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

// ...but this may make the vector reallocate
vec.push(11);

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

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).
• ptr's T needs to have the same size and alignment as it was allocated with.
• 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 and a size_t.

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;

fn main() {
    let mut v = vec![1, 2, 3];

    // 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 {
        // Cast `v` into the void: no destructor run, so we are in
        // complete control of the allocation to which `p` points.
        mem::forget(v);

        // 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]);
    }
}

pub fn capacity(&self) -> usize

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)

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 overflows usize.

Examples

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

pub fn reserve_exact(&mut self, additional: usize)

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>

🔬 This is a nightly-only experimental API. (try_reserve #48043)

new API

Tries to reserve capacity for at least additional more elements to be inserted in the given Vec<T>. The collection may reserve more space to avoid frequent reallocations. After calling 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>

🔬 This is a nightly-only experimental API. (try_reserve #48043)

new API

Tries to 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.

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 shrink_to_fit(&mut self)

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)

🔬 This is a nightly-only experimental API. (shrink_to #56431)

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.

Panics if the current capacity is smaller than the supplied minimum capacity.

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);

Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;impl<I: Iterator + Sized> Iterator for Box<I>impl<F: ?Sized + Future + Unpin> Future for Box<F> type Output = F::Output;

pub fn into_boxed_slice(self) -> Box<[T]>

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)

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]

Extracts a slice containing the entire vector.

Equivalent to &s[..].

Examples

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

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

Extracts a mutable slice of the entire vector.

Equivalent to &mut s[..].

Examples

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

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

Returns a raw pointer to the vector's buffer.

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

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

Forces the length of the vector to new_len.

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

Safety

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

Examples

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

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

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

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

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

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

Removes an element from the vector and returns it.

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

This does not preserve ordering, but is O(1).

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)

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

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, 

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]);

The exact order may be useful for tracking external state, like an index.

let mut vec = vec![1, 2, 3, 4, 5];
let keep = [false, true, true, false, true];
let mut i = 0;
vec.retain(|_| (keep[i], i += 1).0);
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, 

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

If the vector is sorted, this removes all duplicates.

Examples

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

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

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

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

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

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

If the vector is sorted, this removes all duplicates.

Examples

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

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

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

pub fn push(&mut self, value: T)

Appends an element to the back of a collection.

Panics

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

Examples

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

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

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 Self)

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, []);

Important traits for Drain<'_, T>

impl<'_, T> Iterator for Drain<'_, T> type Item = T;

pub fn drain<R>(&mut self, range: R) -> Drain<T> where
    R: RangeBounds<usize>, 

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

Note 1: The element range is removed even if the iterator is only partially consumed or not consumed at all.

Note 2: It is unspecified how many elements are removed from the vector if the Drain value is leaked.

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)

Clears the vector, removing all values.

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

Examples

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

v.clear();

assert!(v.is_empty());

pub fn len(&self) -> usize

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

Examples

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

pub fn is_empty(&self) -> bool

Returns true if the vector contains no elements.

Examples

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

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

pub fn split_off(&mut self, at: usize) -> Self

Splits the collection into two at the given index.

Returns a newly allocated Self. self contains elements [0, at), and the returned Self contains elements [at, len).

Note that the capacity of self does not change.

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, 

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 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>(vec: Vec<T>) -> &'a mut [T] where
    T: 'a, 

🔬 This is a nightly-only experimental API. (vec_leak #62195)

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.

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:

#![feature(vec_leak)]

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

impl<T: Clone> Vec<T>

pub fn resize(&mut self, new_len: usize, value: T)

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 Clone to be able clone the passed value. If you need more flexibility (or want to rely on Default instead of Clone), use 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])

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]);

impl<T: Default> Vec<T>

pub fn resize_default(&mut self, new_len: usize)

Deprecated since 1.33.0:

This is moving towards being removed in favor of .resize_with(Default::default). If you disagree, please comment in the tracking issue.

🔬 This is a nightly-only experimental API. (vec_resize_default #41758)

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 Default::default(). If new_len is less than len, the Vec is simply truncated.

This method uses Default to create new values on every push. If you'd rather Clone a given value, use resize.

Examples

#![feature(vec_resize_default)]

let mut vec = vec![1, 2, 3];
vec.resize_default(5);
assert_eq!(vec, [1, 2, 3, 0, 0]);

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

impl<T: PartialEq> Vec<T>

pub fn dedup(&mut self)

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

If the vector is sorted, this removes all duplicates.

Examples

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

vec.dedup();

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

pub fn remove_item(&mut self, item: &T) -> Option<T>

🔬 This is a nightly-only experimental API. (vec_remove_item #40062)

recently added

Removes the first instance of item from the vector if the item exists.

Examples

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

vec.remove_item(&1);

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

impl<T> Vec<T>

Important traits for Splice<'_, I>

impl<'_, I: Iterator> Iterator for Splice<'_, I> type Item = I::Item;

pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<I::IntoIter> where
    R: RangeBounds<usize>,
    I: IntoIterator<Item = T>, 

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.

The element 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 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]);

Important traits for DrainFilter<'_, T, F>

impl<'_, T, F> Iterator for DrainFilter<'_, T, F> where
    F: FnMut(&mut T) -> bool,  type Item = T;

pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<T, F> where
    F: FnMut(&mut T) -> bool, 

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

recently added

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> DerefMut for Vec<T>

fn deref_mut(&mut self) -> &mut [T]

Mutably dereferences the value.

impl<T: Ord> From<Vec<T>> for BinaryHeap<T>

fn from(vec: Vec<T>) -> BinaryHeap<T>

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

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

impl<T> From<BinaryHeap<T>> for Vec<T>

fn from(heap: BinaryHeap<T>) -> Vec<T>

Performs the conversion.

impl<T> From<Vec<T>> for VecDeque<T>

fn from(other: Vec<T>) -> Self

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.

impl<T> From<VecDeque<T>> for Vec<T>

fn from(other: VecDeque<T>) -> Self

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> From<Vec<T>> for Arc<[T]>

fn from(v: Vec<T>) -> Arc<[T]>

Performs the conversion.

impl<T> From<Vec<T>> for Rc<[T]>

fn from(v: Vec<T>) -> Rc<[T]>

Performs the conversion.

impl From<String> for Vec<u8>

fn from(string: String) -> Vec<u8>

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: Clone> From<&'_ [T]> for Vec<T>

fn from(s: &[T]) -> Vec<T>

Performs the conversion.

impl<'_, T: Clone> From<&'_ mut [T]> for Vec<T>

fn from(s: &mut [T]) -> Vec<T>

Performs the conversion.

impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where
    [T]: ToOwned<Owned = Vec<T>>, 

fn from(s: Cow<'a, [T]>) -> Vec<T>

Performs the conversion.

impl<T> From<Box<[T]>> for Vec<T>

fn from(s: Box<[T]>) -> Vec<T>

Performs the conversion.

impl<T> From<Vec<T>> for Box<[T]>

Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;impl<I: Iterator + Sized> Iterator for Box<I>impl<F: ?Sized + Future + Unpin> Future for Box<F> type Output = F::Output;

fn from(v: Vec<T>) -> Box<[T]>

Performs the conversion.

impl<'_> From<&'_ str> for Vec<u8>

fn from(s: &str) -> Vec<u8>

Performs the conversion.

impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]>

fn from(v: Vec<T>) -> Cow<'a, [T]>

Performs the conversion.

impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]>

fn from(v: &'a Vec<T>) -> Cow<'a, [T]>

Performs the conversion.

impl<A, B> PartialEq<Vec<B>> for VecDeque<A> where
    A: PartialEq<B>, 

fn eq(&self, other: &Vec<B>) -> bool

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

#[must_use] fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A, B> PartialEq<Vec<B>> for Vec<A> where
    A: PartialEq<B>, 

fn eq(&self, other: &Vec<B>) -> bool

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

fn ne(&self, other: &Vec<B>) -> bool

This method tests for !=.

impl<'_, A, B> PartialEq<&'_ [B]> for Vec<A> where
    A: PartialEq<B>, 

fn eq(&self, other: &&[B]) -> bool

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

fn ne(&self, other: &&[B]) -> bool

This method tests for !=.

impl<'_, A, B> PartialEq<&'_ mut [B]> for Vec<A> where
    A: PartialEq<B>, 

fn eq(&self, other: &&mut [B]) -> bool

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

fn ne(&self, other: &&mut [B]) -> bool

This method tests for !=.

impl<'_, A, B> PartialEq<Vec<B>> for Cow<'_, [A]> where
    A: PartialEq<B>,
    A: Clone, 

fn eq(&self, other: &Vec<B>) -> bool

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

fn ne(&self, other: &Vec<B>) -> bool

This method tests for !=.

impl<A, B, const N: usize> PartialEq<[B; N]> for Vec<A> where
    A: PartialEq<B>,
    [B; N]: LengthAtMost32, 

fn eq(&self, other: &[B; N]) -> bool

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

fn ne(&self, other: &[B; N]) -> bool

This method tests for !=.

impl<'_, A, B, const N: usize> PartialEq<&'_ [B; N]> for Vec<A> where
    A: PartialEq<B>,
    [B; N]: LengthAtMost32, 

fn eq(&self, other: &&[B; N]) -> bool

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

fn ne(&self, other: &&[B; N]) -> bool

This method tests for !=.

impl<T: Eq> Eq for Vec<T>

impl<T: Ord> Ord for Vec<T>

Implements ordering of vectors, lexicographically.

fn cmp(&self, other: &Vec<T>) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

🔬 This is a nightly-only experimental API. (clamp #44095)

Restrict a value to a certain interval.

impl<T: PartialOrd> PartialOrd<Vec<T>> for Vec<T>

Implements comparison of vectors, lexicographically.

fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering>

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

#[must_use] fn lt(&self, other: &Rhs) -> bool

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

#[must_use] fn le(&self, other: &Rhs) -> bool

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

#[must_use] fn gt(&self, other: &Rhs) -> bool

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

#[must_use] fn ge(&self, other: &Rhs) -> bool

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

impl<T: Hash> Hash for Vec<T>

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].

impl<T> Deref for Vec<T>

type Target = [T]

The resulting type after dereferencing.

fn deref(&self) -> &[T]

Dereferences the value.

impl<T> Drop for Vec<T>

fn drop(&mut self)

Executes the destructor for this type.

impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T>

type Output = I::Output

The returned type after indexing.

fn index(&self, index: I) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T>

fn index_mut(&mut self, index: I) -> &mut Self::Output

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

impl<T: Debug> Debug for Vec<T>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<T> AsRef<Vec<T>> for Vec<T>

fn as_ref(&self) -> &Vec<T>

Performs the conversion.

impl<T> AsRef<[T]> for Vec<T>

fn as_ref(&self) -> &[T]

Performs the conversion.

impl<T> AsMut<Vec<T>> for Vec<T>

fn as_mut(&mut self) -> &mut Vec<T>

Performs the conversion.

impl<T> AsMut<[T]> for Vec<T>

fn as_mut(&mut self) -> &mut [T]

Performs the conversion.

impl<T> FromIterator<T> for Vec<T>

fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T>

Creates a value from an iterator.

impl<T> IntoIterator for Vec<T>

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?

Important traits for IntoIter<T>

impl<T> Iterator for IntoIter<T> type Item = T;

fn into_iter(self) -> IntoIter<T>

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<'a, T> IntoIterator for &'a Vec<T>

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?

Important traits for Iter<'a, T>

impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;

fn into_iter(self) -> Iter<'a, T>

Creates an iterator from a value.

impl<'a, T> IntoIterator for &'a mut Vec<T>

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?

Important traits for IterMut<'a, T>

impl<'a, T> Iterator for IterMut<'a, T> type Item = &'a mut T;

fn into_iter(self) -> IterMut<'a, T>

Creates an iterator from a value.

impl<T> Extend<T> for Vec<T>

fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T>

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.

fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<T: Clone> Clone for Vec<T>

fn clone(&self) -> Vec<T>

Returns a copy of the value.

fn clone_from(&mut self, other: &Vec<T>)

Performs copy-assignment from source.

impl<T> Default for Vec<T>

fn default() -> Vec<T>

Creates an empty Vec<T>.

impl<T> Borrow<[T]> for Vec<T>

fn borrow(&self) -> &[T]

Immutably borrows from an owned value.

impl<T> BorrowMut<[T]> for Vec<T>

fn borrow_mut(&mut self) -> &mut [T]

Mutably borrows from an owned value.