Struct collections::vec::Vec
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pub struct Vec<T> {
// some fields omitted
}A growable list type, written Vec<T> but pronounced 'vector.'
Examples
fn main() { 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]); }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); }
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.
Methods
impl<T> Vec<T>
fn new() -> Vec<T>
Constructs a new, empty Vec<T>.
The vector will not allocate until elements are pushed onto it.
Examples
fn main() { let mut vec: Vec<i32> = Vec::new(); }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 the main Vec<T> docs
above, 'Capacity and reallocation'.)
Examples
fn main() { 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); }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.
Unsafety
This is highly unsafe, due to the number of invariants that aren't checked:
ptrneeds to have been previously allocated viaString/Vec<T>(at least, it's highly likely to be incorrect if it wasn't).lengthneeds to be the length that less than or equal tocapacity.capacityneeds to be the capacity that the pointer was allocated with.
Violating these may cause problems like corrupting the allocator's internal datastructures.
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]); } }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
fn main() { let vec: Vec<i32> = Vec::with_capacity(10); assert_eq!(vec.capacity(), 10); }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
fn main() { let mut vec = vec![1]; vec.reserve(10); assert!(vec.capacity() >= 11); }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
fn main() { let mut vec = vec![1]; vec.reserve_exact(10); assert!(vec.capacity() >= 11); }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
fn main() { 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); }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().
fn truncate(&mut self, len: usize)
Shorten a vector, dropping excess elements.
If len is greater than the vector's current length, this has no
effect.
Examples
fn main() { let mut vec = vec![1, 2, 3, 4]; vec.truncate(2); assert_eq!(vec, [1, 2]); }let mut vec = vec![1, 2, 3, 4]; vec.truncate(2); assert_eq!(vec, [1, 2]);
fn as_slice(&self) -> &[T]
Extracts a slice containing the entire vector.
Equivalent to &s[..].
fn as_mut_slice(&mut self) -> &mut [T]
Extracts a mutable slice of the entire vector.
Equivalent to &mut s[..].
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
fn main() { let mut v = vec![1, 2, 3, 4]; unsafe { v.set_len(1); } }let mut v = vec![1, 2, 3, 4]; unsafe { v.set_len(1); }
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
fn main() { 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"]); }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 position i one position to the right.
Panics
Panics if index is greater than the vector's length.
Examples
fn main() { 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]); }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 position index one position to the left.
Panics
Panics if index is out of bounds.
Examples
fn main() { let mut v = vec![1, 2, 3]; assert_eq!(v.remove(1), 2); assert_eq!(v, [1, 3]); }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
fn main() { let mut vec = vec![1, 2, 3, 4]; vec.retain(|&x| x%2 == 0); assert_eq!(vec, [2, 4]); }let mut vec = vec![1, 2, 3, 4]; vec.retain(|&x| x%2 == 0); assert_eq!(vec, [2, 4]);
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
fn main() { let mut vec = vec![1, 2]; vec.push(3); assert_eq!(vec, [1, 2, 3]); }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
fn main() { let mut vec = vec![1, 2, 3]; assert_eq!(vec.pop(), Some(3)); assert_eq!(vec, [1, 2]); }let mut vec = vec![1, 2, 3]; assert_eq!(vec.pop(), Some(3)); assert_eq!(vec, [1, 2]);
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
#![feature(append)] fn main() { 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, []); }#![feature(append)] 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>
Create a draining iterator that removes the specified range in the vector and yields the removed items from start to end. The element range is removed even if the iterator is not consumed until the end.
Note: 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
#![feature(drain)] fn main() { // Draining using `..` clears the whole vector. let mut v = vec![1, 2, 3]; let u: Vec<_> = v.drain(..).collect(); assert_eq!(v, &[]); assert_eq!(u, &[1, 2, 3]); }#![feature(drain)] // Draining using `..` clears the whole vector. let mut v = vec![1, 2, 3]; let u: Vec<_> = v.drain(..).collect(); assert_eq!(v, &[]); assert_eq!(u, &[1, 2, 3]);
fn clear(&mut self)
Clears the vector, removing all values.
Examples
fn main() { let mut v = vec![1, 2, 3]; v.clear(); assert!(v.is_empty()); }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
fn main() { let a = vec![1, 2, 3]; assert_eq!(a.len(), 3); }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
fn main() { let mut v = Vec::new(); assert!(v.is_empty()); v.push(1); assert!(!v.is_empty()); }let mut v = Vec::new(); assert!(v.is_empty()); v.push(1); assert!(!v.is_empty());
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
#![feature(split_off)] fn main() { let mut vec = vec![1,2,3]; let vec2 = vec.split_off(1); assert_eq!(vec, [1]); assert_eq!(vec2, [2, 3]); }#![feature(split_off)] let mut vec = vec![1,2,3]; let vec2 = vec.split_off(1); assert_eq!(vec, [1]); assert_eq!(vec2, [2, 3]);
impl<T: Clone> Vec<T>
fn resize(&mut self, new_len: usize, value: T)
Resizes the Vec in-place so that len() is equal to new_len.
Calls either extend() or truncate() depending on whether new_len
is larger than the current value of len() or not.
Examples
#![feature(vec_resize)] fn main() { 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]); }#![feature(vec_resize)] 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 push_all(&mut self, other: &[T])
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.
Examples
#![feature(vec_push_all)] fn main() { let mut vec = vec![1]; vec.push_all(&[2, 3, 4]); assert_eq!(vec, [1, 2, 3, 4]); }#![feature(vec_push_all)] let mut vec = vec![1]; vec.push_all(&[2, 3, 4]); assert_eq!(vec, [1, 2, 3, 4]);
impl<T: PartialEq> Vec<T>
fn dedup(&mut self)
Removes consecutive repeated elements in the vector.
If the vector is sorted, this removes all duplicates.
Examples
fn main() { let mut vec = vec![1, 2, 2, 3, 2]; vec.dedup(); assert_eq!(vec, [1, 2, 3, 2]); }let mut vec = vec![1, 2, 2, 3, 2]; vec.dedup(); assert_eq!(vec, [1, 2, 3, 2]);