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/Rust

Struct std::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:

let vec = vec![0; 5];
assert_eq!(vec, [0, 0, 0, 0, 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 subtle enough that it is strongly recommended that you only free memory allocated by a Vec by creating a new Vec and 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 elements in order (what you would see if you coerced it to a slice), followed by capacity()-len() logically uninitialized 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.

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>` [src]

`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();

`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 this function does not specify the length of the returned vector, but only the capacity. 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);

`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).
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 datastructures. 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]);
    }
}

`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);

`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.

Panics

Panics if the new capacity overflows usize.

Examples

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

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

Reserves the minimum capacity for exactly additional more elements to be inserted in the given Vec<T>. 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);

`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);

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

Converts the vector into Box<[T]>.

Note that this will drop any excess capacity. Calling this and converting back to a vector with into_vec() is equivalent to calling shrink_to_fit().

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);

`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.

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, []);

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

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();

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

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();

`unsafe fn set_len(&mut self, len: usize)`

Sets the length of a vector.

This will explicitly set the size of the vector, without actually modifying its buffers, so it is up to the caller to ensure that the vector is actually the specified size.

Examples

use std::ptr;

let mut vec = vec!['r', 'u', 's', 't'];

unsafe {
    ptr::drop_in_place(&mut vec[3]);
    vec.set_len(3);
}
assert_eq!(vec, ['r', 'u', 's']);

In this example, there is a memory leak since the memory locations owned by 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]];
unsafe {
    vec.set_len(0);
}

In this example, the vector gets expanded from zero to four items without any memory allocations occurring, resulting in vector values of unallocated memory:

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

unsafe {
    vec.set_len(4);
}

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

Removes an element from anywhere in the vector and return it, replacing it with the last element.

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"]);

`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 is out of bounds.

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]);

`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]);

`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 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]);

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

Removes 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]);

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

Removes consecutive elements in the vector that resolve to the same key.

If the vector is sorted, this removes all duplicates.

Examples

use std::ascii::AsciiExt;

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"]);

`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]);

`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]);

`fn append(&mut self, other: &mut Vec<T>)`
1.4.0

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, []);

`fn drain<R>(&mut self, range: R) -> Drain<T> where R: RangeArgument<usize>`
1.6.0

Create 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, &[]);

`fn clear(&mut self)`

Clears the vector, removing all values.

Examples

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

v.clear();

assert!(v.is_empty());

`fn len(&self) -> usize`

Returns the number of elements in the vector.

Examples

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

`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());

`fn split_off(&mut self, at: usize) -> Vec<T>`
1.4.0

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]);

`impl<T> Vec<T> where T: Clone` [src]

`fn resize(&mut self, new_len: usize, value: T)`
1.5.0

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.

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]);

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

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]);

`fn place_back(&mut self) -> PlaceBack<T>`

🔬 This is a nightly-only experimental API. (collection_placement #30172)placement protocol is subject to change

Returns a place for insertion at the back of the Vec.

Using this method with placement syntax is equivalent to push, but may be more efficient.

Examples

#![feature(collection_placement)]
#![feature(placement_in_syntax)]

let mut vec = vec![1, 2];
vec.place_back() <- 3;
vec.place_back() <- 4;
assert_eq!(&vec, &[1, 2, 3, 4]);

`impl<T> Vec<T> where T: PartialEq<T>` [src]

`fn dedup(&mut self)`

Removes consecutive repeated elements in the vector.

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]);

Methods from Deref<Target=[T]>

`fn len(&self) -> usize`

Returns the number of elements in the slice.

Example

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

`fn is_empty(&self) -> bool`

Returns true if the slice has a length of 0.

Example

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

`fn first(&self) -> Option<&T>`

Returns the first element of a slice, or None if it is empty.

Examples

let v = [10, 40, 30];
assert_eq!(Some(&10), v.first());

let w: &[i32] = &[];
assert_eq!(None, w.first());

`fn first_mut(&mut self) -> Option<&mut T>`

Returns a mutable pointer to the first element of a slice, or None if it is empty.

Examples

let x = &mut [0, 1, 2];

if let Some(first) = x.first_mut() {
    *first = 5;
}
assert_eq!(x, &[5, 1, 2]);

`fn split_first(&self) -> Option<(&T, &[T])>`
1.5.0

Returns the first and all the rest of the elements of a slice.

Examples

let x = &[0, 1, 2];

if let Some((first, elements)) = x.split_first() {
    assert_eq!(first, &0);
    assert_eq!(elements, &[1, 2]);
}

`fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])>`
1.5.0

Returns the first and all the rest of the elements of a slice.

Examples

let x = &mut [0, 1, 2];

if let Some((first, elements)) = x.split_first_mut() {
    *first = 3;
    elements[0] = 4;
    elements[1] = 5;
}
assert_eq!(x, &[3, 4, 5]);

`fn split_last(&self) -> Option<(&T, &[T])>`
1.5.0

Returns the last and all the rest of the elements of a slice.

Examples

let x = &[0, 1, 2];

if let Some((last, elements)) = x.split_last() {
    assert_eq!(last, &2);
    assert_eq!(elements, &[0, 1]);
}

`fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])>`
1.5.0

Returns the last and all the rest of the elements of a slice.

Examples

let x = &mut [0, 1, 2];

if let Some((last, elements)) = x.split_last_mut() {
    *last = 3;
    elements[0] = 4;
    elements[1] = 5;
}
assert_eq!(x, &[4, 5, 3]);

`fn last(&self) -> Option<&T>`

Returns the last element of a slice, or None if it is empty.

Examples

let v = [10, 40, 30];
assert_eq!(Some(&30), v.last());

let w: &[i32] = &[];
assert_eq!(None, w.last());

`fn last_mut(&mut self) -> Option<&mut T>`

Returns a mutable pointer to the last item in the slice.

Examples

let x = &mut [0, 1, 2];

if let Some(last) = x.last_mut() {
    *last = 10;
}
assert_eq!(x, &[0, 1, 10]);

`fn get(&self, index: I) -> Option<&I::Output> where I: SliceIndex<T>`

Returns a reference to an element or subslice depending on the type of index.

If given a position, returns a reference to the element at that position or None if out of bounds.
If given a range, returns the subslice corresponding to that range, or None if out of bounds.

Examples

let v = [10, 40, 30];
assert_eq!(Some(&40), v.get(1));
assert_eq!(Some(&[10, 40][..]), v.get(0..2));
assert_eq!(None, v.get(3));
assert_eq!(None, v.get(0..4));

`fn get_mut(&mut self, index: I) -> Option<&mut I::Output> where I: SliceIndex<T>`

Returns a mutable reference to an element or subslice depending on the type of index (see get()) or None if the index is out of bounds.

Examples

let x = &mut [0, 1, 2];

if let Some(elem) = x.get_mut(1) {
    *elem = 42;
}
assert_eq!(x, &[0, 42, 2]);

`unsafe fn get_unchecked(&self, index: I) -> &I::Output where I: SliceIndex<T>`

Returns a reference to an element or subslice, without doing bounds checking. So use it very carefully!

Examples

let x = &[1, 2, 4];

unsafe {
    assert_eq!(x.get_unchecked(1), &2);
}

`unsafe fn get_unchecked_mut(&mut self, index: I) -> &mut I::Output where I: SliceIndex<T>`

Returns a mutable reference to an element or subslice, without doing bounds checking. So use it very carefully!

Examples

let x = &mut [1, 2, 4];

unsafe {
    let elem = x.get_unchecked_mut(1);
    *elem = 13;
}
assert_eq!(x, &[1, 13, 4]);

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

Returns a raw pointer to the slice's buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

Modifying the slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

Examples

let x = &[1, 2, 4];
let x_ptr = x.as_ptr();

unsafe {
    for i in 0..x.len() {
        assert_eq!(x.get_unchecked(i), &*x_ptr.offset(i as isize));
    }
}

`fn as_mut_ptr(&mut self) -> *mut T`

Returns an unsafe mutable pointer to the slice's buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

Modifying the slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

Examples

let x = &mut [1, 2, 4];
let x_ptr = x.as_mut_ptr();

unsafe {
    for i in 0..x.len() {
        *x_ptr.offset(i as isize) += 2;
    }
}
assert_eq!(x, &[3, 4, 6]);

`fn swap(&mut self, a: usize, b: usize)`

Swaps two elements in a slice.

Arguments

a - The index of the first element
b - The index of the second element

Panics

Panics if a or b are out of bounds.

Examples

let mut v = ["a", "b", "c", "d"];
v.swap(1, 3);
assert!(v == ["a", "d", "c", "b"]);

`fn reverse(&mut self)`

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

Example

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

`fn iter(&self) -> Iter<T>`

Returns an iterator over the slice.

Examples

let x = &[1, 2, 4];
let mut iterator = x.iter();

assert_eq!(iterator.next(), Some(&1));
assert_eq!(iterator.next(), Some(&2));
assert_eq!(iterator.next(), Some(&4));
assert_eq!(iterator.next(), None);

`fn iter_mut(&mut self) -> IterMut<T>`

Returns an iterator that allows modifying each value.

Examples

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

`fn windows(&self, size: usize) -> Windows<T>`

Returns an iterator over all contiguous windows of length size. The windows overlap. If the slice is shorter than size, the iterator returns no values.

Panics

Panics if size is 0.

Example

let slice = ['r', 'u', 's', 't'];
let mut iter = slice.windows(2);
assert_eq!(iter.next().unwrap(), &['r', 'u']);
assert_eq!(iter.next().unwrap(), &['u', 's']);
assert_eq!(iter.next().unwrap(), &['s', 't']);
assert!(iter.next().is_none());

If the slice is shorter than size:

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

`fn chunks(&self, size: usize) -> Chunks<T>`

Returns an iterator over size elements of the slice at a time. The chunks are slices and do not overlap. If size does not divide the length of the slice, then the last chunk will not have length size.

Panics

Panics if size is 0.

Example

let slice = ['l', 'o', 'r', 'e', 'm'];
let mut iter = slice.chunks(2);
assert_eq!(iter.next().unwrap(), &['l', 'o']);
assert_eq!(iter.next().unwrap(), &['r', 'e']);
assert_eq!(iter.next().unwrap(), &['m']);
assert!(iter.next().is_none());

`fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<T>`

Returns an iterator over chunk_size elements of the slice at a time. The chunks are mutable slices, and do not overlap. If chunk_size does not divide the length of the slice, then the last chunk will not have length chunk_size.

Panics

Panics if chunk_size is 0.

Examples

let v = &mut [0, 0, 0, 0, 0];
let mut count = 1;

for chunk in v.chunks_mut(2) {
    for elem in chunk.iter_mut() {
        *elem += count;
    }
    count += 1;
}
assert_eq!(v, &[1, 1, 2, 2, 3]);

`fn split_at(&self, mid: usize) -> (&[T], &[T])`

Divides one slice into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

Panics

Panics if mid > len.

Examples

let v = [10, 40, 30, 20, 50];
let (v1, v2) = v.split_at(2);
assert_eq!([10, 40], v1);
assert_eq!([30, 20, 50], v2);

`fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T])`

Divides one &mut into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

Panics

Panics if mid > len.

Examples

let mut v = [1, 2, 3, 4, 5, 6];

// scoped to restrict the lifetime of the borrows
{
   let (left, right) = v.split_at_mut(0);
   assert!(left == []);
   assert!(right == [1, 2, 3, 4, 5, 6]);
}

{
    let (left, right) = v.split_at_mut(2);
    assert!(left == [1, 2]);
    assert!(right == [3, 4, 5, 6]);
}

{
    let (left, right) = v.split_at_mut(6);
    assert!(left == [1, 2, 3, 4, 5, 6]);
    assert!(right == []);
}

`fn split<F>(&self, pred: F) -> Split<T, F> where F: FnMut(&T) -> bool`

Returns an iterator over subslices separated by elements that match pred. The matched element is not contained in the subslices.

Examples

let slice = [10, 40, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

If the first element is matched, an empty slice will be the first item returned by the iterator. Similarly, if the last element in the slice is matched, an empty slice will be the last item returned by the iterator:

let slice = [10, 40, 33];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10, 40]);
assert_eq!(iter.next().unwrap(), &[]);
assert!(iter.next().is_none());

If two matched elements are directly adjacent, an empty slice will be present between them:

let slice = [10, 6, 33, 20];
let mut iter = slice.split(|num| num % 3 == 0);

assert_eq!(iter.next().unwrap(), &[10]);
assert_eq!(iter.next().unwrap(), &[]);
assert_eq!(iter.next().unwrap(), &[20]);
assert!(iter.next().is_none());

`fn split_mut<F>(&mut self, pred: F) -> SplitMut<T, F> where F: FnMut(&T) -> bool`

Returns an iterator over mutable subslices separated by elements that match pred. The matched element is not contained in the subslices.

Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.split_mut(|num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 1]);

`fn splitn<F>(&self, n: usize, pred: F) -> SplitN<T, F> where F: FnMut(&T) -> bool`

Returns an iterator over subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

Examples

Print the slice split once by numbers divisible by 3 (i.e. [10, 40], [20, 60, 50]):

let v = [10, 40, 30, 20, 60, 50];

for group in v.splitn(2, |num| *num % 3 == 0) {
    println!("{:?}", group);
}

`fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<T, F> where F: FnMut(&T) -> bool`

Returns an iterator over subslices separated by elements that match pred, limited to returning at most n items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

Examples

let mut v = [10, 40, 30, 20, 60, 50];

for group in v.splitn_mut(2, |num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(v, [1, 40, 30, 1, 60, 50]);

`fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<T, F> where F: FnMut(&T) -> bool`

Returns an iterator over subslices separated by elements that match pred limited to returning at most n items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

Examples

Print the slice split once, starting from the end, by numbers divisible by 3 (i.e. [50], [10, 40, 30, 20]):

let v = [10, 40, 30, 20, 60, 50];

for group in v.rsplitn(2, |num| *num % 3 == 0) {
    println!("{:?}", group);
}

`fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<T, F> where F: FnMut(&T) -> bool`

The last element returned, if any, will contain the remainder of the slice.

Examples

let mut s = [10, 40, 30, 20, 60, 50];

for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
    group[0] = 1;
}
assert_eq!(s, [1, 40, 30, 20, 60, 1]);

`fn contains(&self, x: &T) -> bool where T: PartialEq<T>`

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

Examples

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

`fn starts_with(&self, needle: &[T]) -> bool where T: PartialEq<T>`

Returns true if needle is a prefix of the slice.

Examples

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

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.starts_with(&[]));
let v: &[u8] = &[];
assert!(v.starts_with(&[]));

`fn ends_with(&self, needle: &[T]) -> bool where T: PartialEq<T>`

Returns true if needle is a suffix of the slice.

Examples

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

Always returns true if needle is an empty slice:

let v = &[10, 40, 30];
assert!(v.ends_with(&[]));
let v: &[u8] = &[];
assert!(v.ends_with(&[]));

`fn binary_search(&self, x: &T) -> Result<usize, usize> where T: Ord`

Binary search a sorted slice for a given element.

If the value is found then Ok is returned, containing the index of the matching element; if the value is not found then Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

Example

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

assert_eq!(s.binary_search(&13),  Ok(9));
assert_eq!(s.binary_search(&4),   Err(7));
assert_eq!(s.binary_search(&100), Err(13));
let r = s.binary_search(&1);
assert!(match r { Ok(1...4) => true, _ => false, });

`fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize> where F: FnMut(&'a T) -> Ordering`

Binary search a sorted slice with a comparator function.

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

If a matching value is found then returns Ok, containing the index for the matched element; if no match is found then Err is returned, containing the index where a matching element could be inserted while maintaining sorted order.

Example

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

let seek = 13;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
let seek = 4;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
let seek = 100;
assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
let seek = 1;
let r = s.binary_search_by(|probe| probe.cmp(&seek));
assert!(match r { Ok(1...4) => true, _ => false, });

`fn binary_search_by_key<'a, B, F>(&'a self, b: &B, f: F) -> Result<usize, usize> where B: Ord, F: FnMut(&'a T) -> B`
1.10.0

Binary search a sorted slice with a key extraction function.

Assumes that the slice is sorted by the key, for instance with sort_by_key using the same key extraction function.

Examples

Looks up a series of four elements in a slice of pairs sorted by their second elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in [1, 4].

let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
         (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
         (1, 21), (2, 34), (4, 55)];

assert_eq!(s.binary_search_by_key(&13, |&(a,b)| b),  Ok(9));
assert_eq!(s.binary_search_by_key(&4, |&(a,b)| b),   Err(7));
assert_eq!(s.binary_search_by_key(&100, |&(a,b)| b), Err(13));
let r = s.binary_search_by_key(&1, |&(a,b)| b);
assert!(match r { Ok(1...4) => true, _ => false, });

`fn sort(&mut self) where T: Ord`

Sorts the slice.

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

Current implementation

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

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

Examples

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

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

`fn sort_by_key<B, F>(&mut self, f: F) where B: Ord, F: FnMut(&T) -> B`
1.7.0

Sorts the slice using f to extract a key to compare elements by.

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

Current implementation

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

Examples

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

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

`fn sort_by<F>(&mut self, compare: F) where F: FnMut(&T, &T) -> Ordering`

Sorts the slice using compare to compare elements.

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

Current implementation

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

Examples

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

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

`fn clone_from_slice(&mut self, src: &[T]) where T: Clone`
1.7.0

Copies the elements from src into self.

The length of src must be the same as self.

Panics

This function will panic if the two slices have different lengths.

Example

let mut dst = [0, 0, 0];
let src = [1, 2, 3];

dst.clone_from_slice(&src);
assert!(dst == [1, 2, 3]);

`fn copy_from_slice(&mut self, src: &[T]) where T: Copy`
1.9.0

Copies all elements from src into self, using a memcpy.

The length of src must be the same as self.

Panics

This function will panic if the two slices have different lengths.

Example

let mut dst = [0, 0, 0];
let src = [1, 2, 3];

dst.copy_from_slice(&src);
assert_eq!(src, dst);

`fn to_vec(&self) -> Vec<T> where T: Clone`

Copies self into a new Vec.

Examples

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

`fn into_vec(self: Box<[T]>) -> Vec<T>`

Converts self into a vector without clones or allocation.

Examples

let s: Box<[i32]> = Box::new([10, 40, 30]);
let x = s.into_vec();
// `s` cannot be used anymore because it has been converted into `x`.

assert_eq!(x, vec![10, 40, 30]);

Trait Implementations

`impl<T> Extend<T> for Vec<T>` [src]

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

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

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

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

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

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

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

Mutably borrows from an owned value. Read more

`impl<T> DerefMut for Vec<T>` [src]

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

The method called to mutably dereference a value

`impl<T> PartialOrd<Vec<T>> for Vec<T> where T: PartialOrd<T>` [src]

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

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

`fn lt(&self, other: &Rhs) -> bool`

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

`fn le(&self, other: &Rhs) -> bool`

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

`fn gt(&self, other: &Rhs) -> bool`

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

`fn ge(&self, other: &Rhs) -> bool`

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

`impl<T> Hash for Vec<T> where T: Hash` [src]

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

Feeds this value into the state given, updating the hasher as necessary.

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

Feeds a slice of this type into the state provided.

`impl<T> Eq for Vec<T> where T: Eq` [src]

`impl<T> From<BinaryHeap<T>> for Vec<T>` [src]

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

Performs the conversion.

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

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

Performs the conversion.

`impl<'a, T> From<&'a [T]> for Vec<T> where T: Clone` [src]

`fn from(s: &'a [T]) -> Vec<T>`

Performs the conversion.

`impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned, [T]::Owned == Vec<T>`
1.14.0
[src]

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

Performs the conversion.

`impl<'a> From<&'a str> for Vec<u8>` [src]

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

Performs the conversion.

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

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

Performs the conversion.

`impl<T> Ord for Vec<T> where T: Ord` [src]

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

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

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

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

Performs the conversion.

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

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

Performs the conversion.

`impl<T> IntoIterator for Vec<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>`

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>` [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>`

Creates an iterator from a value. Read more

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

Creates an iterator from a value. Read more

`impl<T> IndexMut<usize> for Vec<T>` [src]

`fn index_mut(&mut self, index: usize) -> &mut T`

The method for the mutable indexing (container[index]) operation

`impl<T> IndexMut<Range<usize>> for Vec<T>` [src]

`fn index_mut(&mut self, index: Range<usize>) -> &mut [T]`

The method for the mutable indexing (container[index]) operation

`impl<T> IndexMut<RangeTo<usize>> for Vec<T>` [src]

`fn index_mut(&mut self, index: RangeTo<usize>) -> &mut [T]`

The method for the mutable indexing (container[index]) operation

`impl<T> IndexMut<RangeFrom<usize>> for Vec<T>` [src]

`fn index_mut(&mut self, index: RangeFrom<usize>) -> &mut [T]`

The method for the mutable indexing (container[index]) operation

`impl<T> IndexMut<RangeFull> for Vec<T>` [src]

`fn index_mut(&mut self, _index: RangeFull) -> &mut [T]`

The method for the mutable indexing (container[index]) operation

`impl<T> IndexMut<RangeInclusive<usize>> for Vec<T>` [src]

`fn index_mut(&mut self, index: RangeInclusive<usize>) -> &mut [T]`

The method for the mutable indexing (container[index]) operation

`impl<T> IndexMut<RangeToInclusive<usize>> for Vec<T>` [src]

`fn index_mut(&mut self, index: RangeToInclusive<usize>) -> &mut [T]`

The method for the mutable indexing (container[index]) operation

`impl<T> Clone for Vec<T> where T: Clone` [src]

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

Returns a copy of the value. Read more

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

Performs copy-assignment from source. Read more

`impl<T> Debug for Vec<T> where T: Debug` [src]

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

Formats the value using the given formatter.

`impl<T> Default for Vec<T>` [src]

`fn default() -> Vec<T>`

Creates an empty Vec<T>.

`impl<T> FromIterator<T> for Vec<T>` [src]

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

Creates a value from an iterator. Read more

`impl<T> Drop for Vec<T>` [src]

`fn drop(&mut self)`

A method called when the value goes out of scope. Read more

`impl<T> Deref for Vec<T>` [src]

`type Target = [T]`

The resulting type after dereferencing

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

The method called to dereference a value

`impl<T> Index<usize> for Vec<T>` [src]

`type Output = T`

The returned type after indexing

`fn index(&self, index: usize) -> &T`

The method for the indexing (container[index]) operation

`impl<T> Index<Range<usize>> for Vec<T>` [src]

`type Output = [T]`

The returned type after indexing

`fn index(&self, index: Range<usize>) -> &[T]`

The method for the indexing (container[index]) operation

`impl<T> Index<RangeTo<usize>> for Vec<T>` [src]

`type Output = [T]`

The returned type after indexing

`fn index(&self, index: RangeTo<usize>) -> &[T]`

The method for the indexing (container[index]) operation

`impl<T> Index<RangeFrom<usize>> for Vec<T>` [src]

`type Output = [T]`

The returned type after indexing

`fn index(&self, index: RangeFrom<usize>) -> &[T]`

The method for the indexing (container[index]) operation

`impl<T> Index<RangeFull> for Vec<T>` [src]

`type Output = [T]`

The returned type after indexing

`fn index(&self, _index: RangeFull) -> &[T]`

The method for the indexing (container[index]) operation

`impl<T> Index<RangeInclusive<usize>> for Vec<T>` [src]

`type Output = [T]`

The returned type after indexing

`fn index(&self, index: RangeInclusive<usize>) -> &[T]`

The method for the indexing (container[index]) operation

`impl<T> Index<RangeToInclusive<usize>> for Vec<T>` [src]

`type Output = [T]`

The returned type after indexing