std::collections::VecDeque - Rust
Description: API documentation for the Rust `VecDeque` struct in crate `std`.
Keywords: rust, rustlang, rust-lang, VecDeque

# 1.0.0[−][src]Struct std::collections::VecDeque

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

A double-ended queue implemented with a growable ring buffer.

The "default" usage of this type as a queue is to use `push_back` to add to the queue, and `pop_front` to remove from the queue. `extend` and `append` push onto the back in this manner, and iterating over `VecDeque` goes front to back.

## Implementations

### `impl<T> VecDeque<T>`[src]

#### `pub fn new() -> VecDeque<T>`[src]

Creates an empty `VecDeque`.

# Examples

    use std::collections::VecDeque;

    let vector: VecDeque<u32> = VecDeque::new();

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

Creates an empty `VecDeque` with space for at least `capacity` elements.

# Examples

    use std::collections::VecDeque;

    let vector: VecDeque<u32> = VecDeque::with_capacity(10);

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#### `pub fn get(&self, index: usize) -> Option<&T>`[src]

Provides a reference to the element at the given index.

Element at index 0 is the front of the queue.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(3);
    buf.push_back(4);
    buf.push_back(5);
    assert_eq!(buf.get(1), Some(&4));

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

Provides a mutable reference to the element at the given index.

Element at index 0 is the front of the queue.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(3);
    buf.push_back(4);
    buf.push_back(5);
    if let Some(elem) = buf.get_mut(1) {
        *elem = 7;
    }

    assert_eq!(buf[1], 7);

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#### `pub fn swap(&mut self, i: usize, j: usize)`[src]

Swaps elements at indices `i` and `j`.

`i` and `j` may be equal.

Element at index 0 is the front of the queue.

# Panics

Panics if either index is out of bounds.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(3);
    buf.push_back(4);
    buf.push_back(5);
    assert_eq!(buf, [3, 4, 5]);
    buf.swap(0, 2);
    assert_eq!(buf, [5, 4, 3]);

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

Returns the number of elements the `VecDeque` can hold without reallocating.

# Examples

    use std::collections::VecDeque;

    let buf: VecDeque<i32> = VecDeque::with_capacity(10);
    assert!(buf.capacity() >= 10);

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

Reserves the minimum capacity for exactly `additional` more elements to be inserted in the given `VecDeque`. 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

    use std::collections::VecDeque;

    let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
    buf.reserve_exact(10);
    assert!(buf.capacity() >= 11);

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

Reserves capacity for at least `additional` more elements to be inserted in the given `VecDeque`. The collection may reserve more space to avoid frequent reallocations.

# Panics

Panics if the new capacity overflows `usize`.

# Examples

    use std::collections::VecDeque;

    let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
    buf.reserve(10);
    assert!(buf.capacity() >= 11);

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

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

new API

Tries to reserve the minimum capacity for exactly `additional` more elements to be inserted in the given `VecDeque<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 `usize`, or the allocator reports a failure, then an error is returned.

# Examples

    #![feature(try_reserve)]
    use std::collections::TryReserveError;
    use std::collections::VecDeque;

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

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

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

        Ok(output)
    }

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

🔬 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 `VecDeque<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 `usize`, or the allocator reports a failure, then an error is returned.

# Examples

    #![feature(try_reserve)]
    use std::collections::TryReserveError;
    use std::collections::VecDeque;

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

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#### `pub fn shrink_to_fit(&mut self)`1.5.0[src]

Shrinks the capacity of the `VecDeque` as much as possible.

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

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::with_capacity(15);
    buf.extend(0..4);
    assert_eq!(buf.capacity(), 15);
    buf.shrink_to_fit();
    assert!(buf.capacity() >= 4);

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

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

new API

Shrinks the capacity of the `VecDeque` 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)]
    use std::collections::VecDeque;

    let mut buf = VecDeque::with_capacity(15);
    buf.extend(0..4);
    assert_eq!(buf.capacity(), 15);
    buf.shrink_to(6);
    assert!(buf.capacity() >= 6);
    buf.shrink_to(0);
    assert!(buf.capacity() >= 4);

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#### `pub fn truncate(&mut self, len: usize)`1.16.0[src]

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

If `len` is greater than the `VecDeque`'s current length, this has no effect.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(5);
    buf.push_back(10);
    buf.push_back(15);
    assert_eq!(buf, [5, 10, 15]);
    buf.truncate(1);
    assert_eq!(buf, [5]);

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#### `pub fn iter(&self) -> Iter<T>`[src]

Returns a front-to-back iterator.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(5);
    buf.push_back(3);
    buf.push_back(4);
    let b: &[_] = &[&5, &3, &4];
    let c: Vec<&i32> = buf.iter().collect();
    assert_eq!(&c[..], b);

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

Returns a front-to-back iterator that returns mutable references.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(5);
    buf.push_back(3);
    buf.push_back(4);
    for num in buf.iter_mut() {
        *num = *num - 2;
    }
    let b: &[_] = &[&mut 3, &mut 1, &mut 2];
    assert_eq!(&buf.iter_mut().collect::<Vec<&mut i32>>()[..], b);

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#### `pub fn as_slices(&self) -> (&[T], &[T])`1.5.0[src]

Returns a pair of slices which contain, in order, the contents of the `VecDeque`.

If `make_contiguous` was previously called, all elements of the `VecDeque` will be in the first slice and the second slice will be empty.

# Examples

    use std::collections::VecDeque;

    let mut vector = VecDeque::new();

    vector.push_back(0);
    vector.push_back(1);
    vector.push_back(2);

    assert_eq!(vector.as_slices(), (&[0, 1, 2][..], &[][..]));

    vector.push_front(10);
    vector.push_front(9);

    assert_eq!(vector.as_slices(), (&[9, 10][..], &[0, 1, 2][..]));

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#### `pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T])`1.5.0[src]

Returns a pair of slices which contain, in order, the contents of the `VecDeque`.

If `make_contiguous` was previously called, all elements of the `VecDeque` will be in the first slice and the second slice will be empty.

# Examples

    use std::collections::VecDeque;

    let mut vector = VecDeque::new();

    vector.push_back(0);
    vector.push_back(1);

    vector.push_front(10);
    vector.push_front(9);

    vector.as_mut_slices().0[0] = 42;
    vector.as_mut_slices().1[0] = 24;
    assert_eq!(vector.as_slices(), (&[42, 10][..], &[24, 1][..]));

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

Returns the number of elements in the `VecDeque`.

# Examples

    use std::collections::VecDeque;

    let mut v = VecDeque::new();
    assert_eq!(v.len(), 0);
    v.push_back(1);
    assert_eq!(v.len(), 1);

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

Returns `true` if the `VecDeque` is empty.

# Examples

    use std::collections::VecDeque;

    let mut v = VecDeque::new();
    assert!(v.is_empty());
    v.push_front(1);
    assert!(!v.is_empty());

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#### `pub fn range<R>(&self, range: R) -> Iter<T> where
R: RangeBounds<usize>,` [src]

🔬 This is a nightly-only experimental API. (`deque_range` #74217)

Creates an iterator that covers the specified range in the `VecDeque`.

# 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

    #![feature(deque_range)]

    use std::collections::VecDeque;

    let v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
    let range = v.range(2..).copied().collect::<VecDeque<_>>();
    assert_eq!(range, [3]);

    // A full range covers all contents
    let all = v.range(..);
    assert_eq!(all.len(), 3);

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#### `pub fn range_mut<R>(&mut self, range: R) -> IterMut<T> where
R: RangeBounds<usize>,` [src]

🔬 This is a nightly-only experimental API. (`deque_range` #74217)

Creates an iterator that covers the specified mutable range in the `VecDeque`.

# 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

    #![feature(deque_range)]

    use std::collections::VecDeque;

    let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
    for v in v.range_mut(2..) {
      *v *= 2;
    }
    assert_eq!(v, vec![1, 2, 6]);

    // A full range covers all contents
    for v in v.range_mut(..) {
      *v *= 2;
    }
    assert_eq!(v, vec![2, 4, 12]);

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#### `pub fn drain<R>(&mut self, range: R) -> Drain<T> where
R: RangeBounds<usize>,` 1.6.0[src]

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

Note 1: The element range is removed even if the iterator is not consumed until the end.

Note 2: It is unspecified how many elements are removed from the deque, if the `Drain` value is not dropped, but the borrow it holds expires (e.g., due to `mem::forget`).

# 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

    use std::collections::VecDeque;

    let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
    let drained = v.drain(2..).collect::<VecDeque<_>>();
    assert_eq!(drained, [3]);
    assert_eq!(v, [1, 2]);

    // A full range clears all contents
    v.drain(..);
    assert!(v.is_empty());

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

Clears the `VecDeque`, removing all values.

# Examples

    use std::collections::VecDeque;

    let mut v = VecDeque::new();
    v.push_back(1);
    v.clear();
    assert!(v.is_empty());

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#### `pub fn contains(&self, x: &T) -> bool where
T: PartialEq<T>,` 1.12.0[src]

Returns `true` if the `VecDeque` contains an element equal to the given value.

# Examples

    use std::collections::VecDeque;

    let mut vector: VecDeque<u32> = VecDeque::new();

    vector.push_back(0);
    vector.push_back(1);

    assert_eq!(vector.contains(&1), true);
    assert_eq!(vector.contains(&10), false);

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

Provides a reference to the front element, or `None` if the `VecDeque` is empty.

# Examples

    use std::collections::VecDeque;

    let mut d = VecDeque::new();
    assert_eq!(d.front(), None);

    d.push_back(1);
    d.push_back(2);
    assert_eq!(d.front(), Some(&1));

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

Provides a mutable reference to the front element, or `None` if the `VecDeque` is empty.

# Examples

    use std::collections::VecDeque;

    let mut d = VecDeque::new();
    assert_eq!(d.front_mut(), None);

    d.push_back(1);
    d.push_back(2);
    match d.front_mut() {
        Some(x) => *x = 9,
        None => (),
    }
    assert_eq!(d.front(), Some(&9));

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

Provides a reference to the back element, or `None` if the `VecDeque` is empty.

# Examples

    use std::collections::VecDeque;

    let mut d = VecDeque::new();
    assert_eq!(d.back(), None);

    d.push_back(1);
    d.push_back(2);
    assert_eq!(d.back(), Some(&2));

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

Provides a mutable reference to the back element, or `None` if the `VecDeque` is empty.

# Examples

    use std::collections::VecDeque;

    let mut d = VecDeque::new();
    assert_eq!(d.back(), None);

    d.push_back(1);
    d.push_back(2);
    match d.back_mut() {
        Some(x) => *x = 9,
        None => (),
    }
    assert_eq!(d.back(), Some(&9));

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

Removes the first element and returns it, or `None` if the `VecDeque` is empty.

# Examples

    use std::collections::VecDeque;

    let mut d = VecDeque::new();
    d.push_back(1);
    d.push_back(2);

    assert_eq!(d.pop_front(), Some(1));
    assert_eq!(d.pop_front(), Some(2));
    assert_eq!(d.pop_front(), None);

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

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

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    assert_eq!(buf.pop_back(), None);
    buf.push_back(1);
    buf.push_back(3);
    assert_eq!(buf.pop_back(), Some(3));

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

Prepends an element to the `VecDeque`.

# Examples

    use std::collections::VecDeque;

    let mut d = VecDeque::new();
    d.push_front(1);
    d.push_front(2);
    assert_eq!(d.front(), Some(&2));

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

Appends an element to the back of the `VecDeque`.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(1);
    buf.push_back(3);
    assert_eq!(3, *buf.back().unwrap());

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#### `pub fn swap_remove_front(&mut self, index: usize) -> Option<T>`1.5.0[src]

Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the first element.

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

Returns `None` if `index` is out of bounds.

Element at index 0 is the front of the queue.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    assert_eq!(buf.swap_remove_front(0), None);
    buf.push_back(1);
    buf.push_back(2);
    buf.push_back(3);
    assert_eq!(buf, [1, 2, 3]);

    assert_eq!(buf.swap_remove_front(2), Some(3));
    assert_eq!(buf, [2, 1]);

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#### `pub fn swap_remove_back(&mut self, index: usize) -> Option<T>`1.5.0[src]

Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the last element.

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

Returns `None` if `index` is out of bounds.

Element at index 0 is the front of the queue.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    assert_eq!(buf.swap_remove_back(0), None);
    buf.push_back(1);
    buf.push_back(2);
    buf.push_back(3);
    assert_eq!(buf, [1, 2, 3]);

    assert_eq!(buf.swap_remove_back(0), Some(1));
    assert_eq!(buf, [3, 2]);

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

Inserts an element at `index` within the `VecDeque`, shifting all elements with indices greater than or equal to `index` towards the back.

Element at index 0 is the front of the queue.

# Panics

Panics if `index` is greater than `VecDeque`'s length

# Examples

    use std::collections::VecDeque;

    let mut vec_deque = VecDeque::new();
    vec_deque.push_back('a');
    vec_deque.push_back('b');
    vec_deque.push_back('c');
    assert_eq!(vec_deque, &['a', 'b', 'c']);

    vec_deque.insert(1, 'd');
    assert_eq!(vec_deque, &['a', 'd', 'b', 'c']);

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

Removes and returns the element at `index` from the `VecDeque`. Whichever end is closer to the removal point will be moved to make room, and all the affected elements will be moved to new positions. Returns `None` if `index` is out of bounds.

Element at index 0 is the front of the queue.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(1);
    buf.push_back(2);
    buf.push_back(3);
    assert_eq!(buf, [1, 2, 3]);

    assert_eq!(buf.remove(1), Some(2));
    assert_eq!(buf, [1, 3]);

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

Splits the `VecDeque` into two at the given index.

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

Note that the capacity of `self` does not change.

Element at index 0 is the front of the queue.

# Panics

Panics if `at > len`.

# Examples

    use std::collections::VecDeque;

    let mut buf: VecDeque<_> = vec![1,2,3].into_iter().collect();
    let buf2 = buf.split_off(1);
    assert_eq!(buf, [1]);
    assert_eq!(buf2, [2, 3]);

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

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

# Panics

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

# Examples

    use std::collections::VecDeque;

    let mut buf: VecDeque<_> = vec![1, 2].into_iter().collect();
    let mut buf2: VecDeque<_> = vec![3, 4].into_iter().collect();
    buf.append(&mut buf2);
    assert_eq!(buf, [1, 2, 3, 4]);
    assert_eq!(buf2, []);

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#### `pub fn retain<F>(&mut self, f: F) where
F: FnMut(&T) -> bool,` 1.4.0[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

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.extend(1..5);
    buf.retain(|&x| x % 2 == 0);
    assert_eq!(buf, [2, 4]);

Run

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

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.extend(1..6);

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

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#### `pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut() -> T)`1.33.0[src]

Modifies the `VecDeque` in-place so that `len()` is equal to `new_len`, either by removing excess elements from the back or by appending elements generated by calling `generator` to the back.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(5);
    buf.push_back(10);
    buf.push_back(15);
    assert_eq!(buf, [5, 10, 15]);

    buf.resize_with(5, Default::default);
    assert_eq!(buf, [5, 10, 15, 0, 0]);

    buf.resize_with(2, || unreachable!());
    assert_eq!(buf, [5, 10]);

    let mut state = 100;
    buf.resize_with(5, || { state += 1; state });
    assert_eq!(buf, [5, 10, 101, 102, 103]);

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

🔬 This is a nightly-only experimental API. (`deque_make_contiguous` #70929)

Rearranges the internal storage of this deque so it is one contiguous slice, which is then returned.

This method does not allocate and does not change the order of the inserted elements. As it returns a mutable slice, this can be used to sort or binary search a deque.

Once the internal storage is contiguous, the `as_slices` and `as_mut_slices` methods will return the entire contents of the `VecDeque` in a single slice.

# Examples

Sorting the content of a deque.

    #![feature(deque_make_contiguous)]

    use std::collections::VecDeque;

    let mut buf = VecDeque::with_capacity(15);

    buf.push_back(2);
    buf.push_back(1);
    buf.push_front(3);

    // sorting the deque
    buf.make_contiguous().sort();
    assert_eq!(buf.as_slices(), (&[1, 2, 3] as &[_], &[] as &[_]));

    // sorting it in reverse order
    buf.make_contiguous().sort_by(|a, b| b.cmp(a));
    assert_eq!(buf.as_slices(), (&[3, 2, 1] as &[_], &[] as &[_]));

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Getting immutable access to the contiguous slice.

    #![feature(deque_make_contiguous)]

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();

    buf.push_back(2);
    buf.push_back(1);
    buf.push_front(3);

    buf.make_contiguous();
    if let (slice, &[]) = buf.as_slices() {
        // we can now be sure that `slice` contains all elements of the deque,
        // while still having immutable access to `buf`.
        assert_eq!(buf.len(), slice.len());
        assert_eq!(slice, &[3, 2, 1] as &[_]);
    }

Run

#### `pub fn rotate_left(&mut self, mid: usize)`1.36.0[src]

Rotates the double-ended queue `mid` places to the left.

Equivalently,

- Rotates item `mid` into the first position.
- Pops the first `mid` items and pushes them to the end.
- Rotates `len() - mid` places to the right.

# Panics

If `mid` is greater than `len()`. Note that `mid == len()` does not panic and is a no-op rotation.

# Complexity

Takes `O(min(mid, len() - mid))` time and no extra space.

# Examples

    use std::collections::VecDeque;

    let mut buf: VecDeque<_> = (0..10).collect();

    buf.rotate_left(3);
    assert_eq!(buf, [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]);

    for i in 1..10 {
        assert_eq!(i * 3 % 10, buf[0]);
        buf.rotate_left(3);
    }
    assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

Run

#### `pub fn rotate_right(&mut self, k: usize)`1.36.0[src]

Rotates the double-ended queue `k` places to the right.

Equivalently,

- Rotates the first item into position `k`.
- Pops the last `k` items and pushes them to the front.
- Rotates `len() - k` places to the left.

# Panics

If `k` is greater than `len()`. Note that `k == len()` does not panic and is a no-op rotation.

# Complexity

Takes `O(min(k, len() - k))` time and no extra space.

# Examples

    use std::collections::VecDeque;

    let mut buf: VecDeque<_> = (0..10).collect();

    buf.rotate_right(3);
    assert_eq!(buf, [7, 8, 9, 0, 1, 2, 3, 4, 5, 6]);

    for i in 1..10 {
        assert_eq!(0, buf[i * 3 % 10]);
        buf.rotate_right(3);
    }
    assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

Run

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

#### `pub fn resize(&mut self, new_len: usize, value: T)`1.16.0[src]

Modifies the `VecDeque` in-place so that `len()` is equal to new_len, either by removing excess elements from the back or by appending clones of `value` to the back.

# Examples

    use std::collections::VecDeque;

    let mut buf = VecDeque::new();
    buf.push_back(5);
    buf.push_back(10);
    buf.push_back(15);
    assert_eq!(buf, [5, 10, 15]);

    buf.resize(2, 0);
    assert_eq!(buf, [5, 10]);

    buf.resize(5, 20);
    assert_eq!(buf, [5, 10, 20, 20, 20]);

Run

## Trait Implementations

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

#### `fn clone(&self) -> VecDeque<T>`[src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, other: &VecDeque<T>)`[src]

Performs copy-assignment from `source`. Read more

### `impl<T> Debug for VecDeque<T> where
T: Debug,` [src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

### `impl<T> Default for VecDeque<T>`[src]

#### `fn default() -> VecDeque<T>`[src]

Creates an empty `VecDeque<T>`.

### `impl<T> Drop for VecDeque<T>`[src]

#### `fn drop(&mut self)`[src]

Executes the destructor for this type. Read more

### `impl<A> Eq for VecDeque<A> where
A: Eq,` [src]

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

#### `fn extend<I>(&mut self, iter: I) where
I: IntoIterator<Item = &'a T>,` [src]

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

#### `fn extend_one(&mut self, &T)`[src]

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

Extends a collection with exactly one element.

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

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

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

### `impl<A> Extend<A> for VecDeque<A>`[src]

#### `fn extend<T>(&mut self, iter: T) where
T: IntoIterator<Item = A>,` [src]

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

#### `fn extend_one(&mut self, elem: A)`[src]

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

Extends a collection with exactly one element.

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

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

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

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

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

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>`1.10.0[src]

#### `fn from(other: VecDeque<T>) -> Vec<T>`[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);

Run

### `impl<A> FromIterator<A> for VecDeque<A>`[src]

#### `fn from_iter<T>(iter: T) -> VecDeque<A> where
T: IntoIterator<Item = A>,` [src]

Creates a value from an iterator. Read more

### `impl<A> Hash for VecDeque<A> where
A: Hash,` [src]

#### `fn hash<H>(&self, state: &mut H) where
H: Hasher,` [src]

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

#### `fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,` 1.3.0[src]

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

### `impl<A> Index<usize> for VecDeque<A>`[src]

#### `type Output = A`

The returned type after indexing.

#### `fn index(&self, index: usize) -> &A`[src]

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

### `impl<A> IndexMut<usize> for VecDeque<A>`[src]

#### `fn index_mut(&mut self, index: usize) -> &mut A`[src]

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

### `impl<'a, T> IntoIterator for &'a mut VecDeque<T>`[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?

#### `fn into_iter(self) -> IterMut<'a, T>`[src]

Creates an iterator from a value. Read more

### `impl<'a, T> IntoIterator for &'a VecDeque<T>`[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?

#### `fn into_iter(self) -> Iter<'a, T>`[src]

Creates an iterator from a value. Read more

### `impl<T> IntoIterator for VecDeque<T>`[src]

#### `type Item = T`

The type of the elements being iterated over.

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

Which kind of iterator are we turning this into?

#### `fn into_iter(self) -> IntoIter<T>`[src]

Consumes the `VecDeque` into a front-to-back iterator yielding elements by value.

### `impl<A> Ord for VecDeque<A> where
A: Ord,` [src]

#### `fn cmp(&self, other: &VecDeque<A>) -> Ordering`[src]

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

#### `#[must_use]fn max(self, other: Self) -> Self`1.21.0[src]

Compares and returns the maximum of two values. Read more

#### `#[must_use]fn min(self, other: Self) -> Self`1.21.0[src]

Compares and returns the minimum of two values. Read more

#### `#[must_use]fn clamp(self, min: Self, max: Self) -> Self`[src]

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

Restrict a value to a certain interval. Read more

### `impl<'_, const N: usize, A, B> PartialEq<&'_ [B; N]> for VecDeque<A> where
A: PartialEq<B>,
[B; N]: LengthAtMost32,` 1.17.0[src]

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

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

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

This method tests for `!=`.

### `impl<'_, A, B> PartialEq<&'_ [B]> for VecDeque<A> where
A: PartialEq<B>,` 1.17.0[src]

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

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

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

This method tests for `!=`.

### `impl<'_, const N: usize, A, B> PartialEq<&'_ mut [B; N]> for VecDeque<A> where
A: PartialEq<B>,
[B; N]: LengthAtMost32,` 1.17.0[src]

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

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

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

This method tests for `!=`.

### `impl<'_, A, B> PartialEq<&'_ mut [B]> for VecDeque<A> where
A: PartialEq<B>,` 1.17.0[src]

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

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

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

This method tests for `!=`.

### `impl<const N: usize, A, B> PartialEq<[B; N]> for VecDeque<A> where
A: PartialEq<B>,
[B; N]: LengthAtMost32,` 1.17.0[src]

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

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

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

This method tests for `!=`.

### `impl<A, B> PartialEq<Vec<B>> for VecDeque<A> where
A: PartialEq<B>,` 1.17.0[src]

#### `fn eq(&self, other: &Vec<B>) -> bool`[src]

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

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

This method tests for `!=`.

### `impl<A> PartialEq<VecDeque<A>> for VecDeque<A> where
A: PartialEq<A>,` [src]

#### `fn eq(&self, other: &VecDeque<A>) -> bool`[src]

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

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

This method tests for `!=`.

### `impl<A> PartialOrd<VecDeque<A>> for VecDeque<A> where
A: PartialOrd<A>,` [src]

#### `fn partial_cmp(&self, other: &VecDeque<A>) -> Option<Ordering>`[src]

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

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

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

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

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

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

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

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

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

## Auto Trait Implementations

### `impl<T> RefUnwindSafe for VecDeque<T> where
T: RefUnwindSafe,`

### `impl<T> Send for VecDeque<T> where
T: Send,`

### `impl<T> Sync for VecDeque<T> where
T: Sync,`

### `impl<T> Unpin for VecDeque<T> where
T: Unpin,`

### `impl<T> UnwindSafe for VecDeque<T> where
T: UnwindSafe,`

## Blanket Implementations

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `fn type_id(&self) -> TypeId`[src]

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

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `fn borrow(&self) -> &T`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

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

Mutably borrows from an owned value. Read more

### `impl<T> From<T> for T`[src]

#### `fn from(t: T) -> T`[src]

Performs the conversion.

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

#### `fn into(self) -> U`[src]

Performs the conversion.

### `impl<I> IntoIterator for I where
I: Iterator,` [src]

#### `type Item = <I as Iterator>::Item`

The type of the elements being iterated over.

#### `type IntoIter = I`

Which kind of iterator are we turning this into?

#### `fn into_iter(self) -> I`[src]

Creates an iterator from a value. Read more

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

#### `type Owned = T`

The resulting type after obtaining ownership.

#### `fn to_owned(&self) -> T`[src]

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

#### `fn clone_into(&self, target: &mut T)`[src]

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

recently added

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

### `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.

#### `fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `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.

#### `fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.