1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! A contiguous growable array type with heap-allocated contents, written
12 //! `Vec<T>` but pronounced 'vector.'
14 //! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
15 //! `O(1)` pop (from the end).
19 //! You can explicitly create a `Vec<T>` with `new()`:
22 //! let v: Vec<i32> = Vec::new();
25 //! ...or by using the `vec!` macro:
28 //! let v: Vec<i32> = vec![];
30 //! let v = vec![1, 2, 3, 4, 5];
32 //! let v = vec![0; 10]; // ten zeroes
35 //! You can `push` values onto the end of a vector (which will grow the vector
39 //! let mut v = vec![1, 2];
44 //! Popping values works in much the same way:
47 //! let mut v = vec![1, 2];
49 //! let two = v.pop();
52 //! Vectors also support indexing (through the `Index` and `IndexMut` traits):
55 //! let mut v = vec![1, 2, 3];
60 #![stable(feature = "rust1", since = "1.0.0")]
62 use alloc::boxed::Box;
63 use alloc::heap::EMPTY;
64 use alloc::raw_vec::RawVec;
67 use core::cmp::Ordering;
69 use core::hash::{self, Hash};
70 use core::intrinsics::{arith_offset, assume};
71 use core::iter::FromIterator;
73 use core::ops::{Index, IndexMut};
78 use super::SpecExtend;
79 use super::range::RangeArgument;
81 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector.'
86 /// let mut vec = Vec::new();
90 /// assert_eq!(vec.len(), 2);
91 /// assert_eq!(vec[0], 1);
93 /// assert_eq!(vec.pop(), Some(2));
94 /// assert_eq!(vec.len(), 1);
97 /// assert_eq!(vec[0], 7);
99 /// vec.extend([1, 2, 3].iter().cloned());
102 /// println!("{}", x);
104 /// assert_eq!(vec, [7, 1, 2, 3]);
107 /// The `vec!` macro is provided to make initialization more convenient:
110 /// let mut vec = vec![1, 2, 3];
112 /// assert_eq!(vec, [1, 2, 3, 4]);
115 /// It can also initialize each element of a `Vec<T>` with a given value:
118 /// let vec = vec![0; 5];
119 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
122 /// Use a `Vec<T>` as an efficient stack:
125 /// let mut stack = Vec::new();
131 /// while let Some(top) = stack.pop() {
132 /// // Prints 3, 2, 1
133 /// println!("{}", top);
139 /// The Vec type allows to access values by index, because it implements the
140 /// `Index` trait. An example will be more explicit:
143 /// let v = vec!(0, 2, 4, 6);
144 /// println!("{}", v[1]); // it will display '2'
147 /// However be careful: if you try to access an index which isn't in the Vec,
148 /// your software will panic! You cannot do this:
151 /// let v = vec!(0, 2, 4, 6);
152 /// println!("{}", v[6]); // it will panic!
155 /// In conclusion: always check if the index you want to get really exists
160 /// A Vec can be mutable. Slices, on the other hand, are read-only objects.
161 /// To get a slice, use "&". Example:
164 /// fn read_slice(slice: &[usize]) {
168 /// let v = vec!(0, 1);
171 /// // ... and that's all!
172 /// // you can also do it like this:
173 /// let x : &[usize] = &v;
176 /// In Rust, it's more common to pass slices as arguments rather than vectors
177 /// when you just want to provide a read access. The same goes for String and
180 /// # Capacity and reallocation
182 /// The capacity of a vector is the amount of space allocated for any future
183 /// elements that will be added onto the vector. This is not to be confused with
184 /// the *length* of a vector, which specifies the number of actual elements
185 /// within the vector. If a vector's length exceeds its capacity, its capacity
186 /// will automatically be increased, but its elements will have to be
189 /// For example, a vector with capacity 10 and length 0 would be an empty vector
190 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
191 /// vector will not change its capacity or cause reallocation to occur. However,
192 /// if the vector's length is increased to 11, it will have to reallocate, which
193 /// can be slow. For this reason, it is recommended to use `Vec::with_capacity`
194 /// whenever possible to specify how big the vector is expected to get.
198 /// Due to its incredibly fundamental nature, Vec makes a lot of guarantees
199 /// about its design. This ensures that it's as low-overhead as possible in
200 /// the general case, and can be correctly manipulated in primitive ways
201 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
202 /// If additional type parameters are added (e.g. to support custom allocators),
203 /// overriding their defaults may change the behavior.
205 /// Most fundamentally, Vec is and always will be a (pointer, capacity, length)
206 /// triplet. No more, no less. The order of these fields is completely
207 /// unspecified, and you should use the appropriate methods to modify these.
208 /// The pointer will never be null, so this type is null-pointer-optimized.
210 /// However, the pointer may not actually point to allocated memory. In particular,
211 /// if you construct a Vec with capacity 0 via `Vec::new()`, `vec![]`,
212 /// `Vec::with_capacity(0)`, or by calling `shrink_to_fit()` on an empty Vec, it
213 /// will not allocate memory. Similarly, if you store zero-sized types inside
214 /// a Vec, it will not allocate space for them. *Note that in this case the
215 /// Vec may not report a `capacity()` of 0*. Vec will allocate if and only
216 /// if `mem::size_of::<T>() * capacity() > 0`. In general, Vec's allocation
217 /// details are subtle enough that it is strongly recommended that you only
218 /// free memory allocated by a Vec by creating a new Vec and dropping it.
220 /// If a Vec *has* allocated memory, then the memory it points to is on the heap
221 /// (as defined by the allocator Rust is configured to use by default), and its
222 /// pointer points to `len()` initialized elements in order (what you would see
223 /// if you coerced it to a slice), followed by `capacity() - len()` logically
224 /// uninitialized elements.
226 /// Vec will never perform a "small optimization" where elements are actually
227 /// stored on the stack for two reasons:
229 /// * It would make it more difficult for unsafe code to correctly manipulate
230 /// a Vec. The contents of a Vec wouldn't have a stable address if it were
231 /// only moved, and it would be more difficult to determine if a Vec had
232 /// actually allocated memory.
234 /// * It would penalize the general case, incurring an additional branch
237 /// Vec will never automatically shrink itself, even if completely empty. This
238 /// ensures no unnecessary allocations or deallocations occur. Emptying a Vec
239 /// and then filling it back up to the same `len()` should incur no calls to
240 /// the allocator. If you wish to free up unused memory, use `shrink_to_fit`.
242 /// `push` and `insert` will never (re)allocate if the reported capacity is
243 /// sufficient. `push` and `insert` *will* (re)allocate if `len() == capacity()`.
244 /// That is, the reported capacity is completely accurate, and can be relied on.
245 /// It can even be used to manually free the memory allocated by a Vec if
246 /// desired. Bulk insertion methods *may* reallocate, even when not necessary.
248 /// Vec does not guarantee any particular growth strategy when reallocating
249 /// when full, nor when `reserve` is called. The current strategy is basic
250 /// and it may prove desirable to use a non-constant growth factor. Whatever
251 /// strategy is used will of course guarantee `O(1)` amortized `push`.
253 /// `vec![x; n]`, `vec![a, b, c, d]`, and `Vec::with_capacity(n)`, will all
254 /// produce a Vec with exactly the requested capacity. If `len() == capacity()`,
255 /// (as is the case for the `vec!` macro), then a `Vec<T>` can be converted
256 /// to and from a `Box<[T]>` without reallocating or moving the elements.
258 /// Vec will not specifically overwrite any data that is removed from it,
259 /// but also won't specifically preserve it. Its uninitialized memory is
260 /// scratch space that it may use however it wants. It will generally just do
261 /// whatever is most efficient or otherwise easy to implement. Do not rely on
262 /// removed data to be erased for security purposes. Even if you drop a Vec, its
263 /// buffer may simply be reused by another Vec. Even if you zero a Vec's memory
264 /// first, that may not actually happen because the optimizer does not consider
265 /// this a side-effect that must be preserved.
267 /// Vec does not currently guarantee the order in which elements are dropped
268 /// (the order has changed in the past, and may change again).
270 #[unsafe_no_drop_flag]
271 #[stable(feature = "rust1", since = "1.0.0")]
277 ////////////////////////////////////////////////////////////////////////////////
279 ////////////////////////////////////////////////////////////////////////////////
282 /// Constructs a new, empty `Vec<T>`.
284 /// The vector will not allocate until elements are pushed onto it.
289 /// # #![allow(unused_mut)]
290 /// let mut vec: Vec<i32> = Vec::new();
293 #[stable(feature = "rust1", since = "1.0.0")]
294 pub fn new() -> Vec<T> {
301 /// Constructs a new, empty `Vec<T>` with the specified capacity.
303 /// The vector will be able to hold exactly `capacity` elements without
304 /// reallocating. If `capacity` is 0, the vector will not allocate.
306 /// It is important to note that this function does not specify the *length*
307 /// of the returned vector, but only the *capacity*. (For an explanation of
308 /// the difference between length and capacity, see the main `Vec<T>` docs
309 /// above, 'Capacity and reallocation'.)
314 /// let mut vec = Vec::with_capacity(10);
316 /// // The vector contains no items, even though it has capacity for more
317 /// assert_eq!(vec.len(), 0);
319 /// // These are all done without reallocating...
324 /// // ...but this may make the vector reallocate
328 #[stable(feature = "rust1", since = "1.0.0")]
329 pub fn with_capacity(capacity: usize) -> Vec<T> {
331 buf: RawVec::with_capacity(capacity),
336 /// Creates a `Vec<T>` directly from the raw components of another vector.
340 /// This is highly unsafe, due to the number of invariants that aren't
343 /// * `ptr` needs to have been previously allocated via `String`/`Vec<T>`
344 /// (at least, it's highly likely to be incorrect if it wasn't).
345 /// * `length` needs to be less than or equal to `capacity`.
346 /// * `capacity` needs to be the capacity that the pointer was allocated with.
348 /// Violating these may cause problems like corrupting the allocator's
349 /// internal datastructures.
351 /// The ownership of `ptr` is effectively transferred to the
352 /// `Vec<T>` which may then deallocate, reallocate or change the
353 /// contents of memory pointed to by the pointer at will. Ensure
354 /// that nothing else uses the pointer after calling this
364 /// let mut v = vec![1, 2, 3];
366 /// // Pull out the various important pieces of information about `v`
367 /// let p = v.as_mut_ptr();
368 /// let len = v.len();
369 /// let cap = v.capacity();
372 /// // Cast `v` into the void: no destructor run, so we are in
373 /// // complete control of the allocation to which `p` points.
376 /// // Overwrite memory with 4, 5, 6
377 /// for i in 0..len as isize {
378 /// ptr::write(p.offset(i), 4 + i);
381 /// // Put everything back together into a Vec
382 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
383 /// assert_eq!(rebuilt, [4, 5, 6]);
387 #[stable(feature = "rust1", since = "1.0.0")]
388 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
390 buf: RawVec::from_raw_parts(ptr, capacity),
395 /// Returns the number of elements the vector can hold without
401 /// let vec: Vec<i32> = Vec::with_capacity(10);
402 /// assert_eq!(vec.capacity(), 10);
405 #[stable(feature = "rust1", since = "1.0.0")]
406 pub fn capacity(&self) -> usize {
410 /// Reserves capacity for at least `additional` more elements to be inserted
411 /// in the given `Vec<T>`. The collection may reserve more space to avoid
412 /// frequent reallocations.
416 /// Panics if the new capacity overflows `usize`.
421 /// let mut vec = vec![1];
423 /// assert!(vec.capacity() >= 11);
425 #[stable(feature = "rust1", since = "1.0.0")]
426 pub fn reserve(&mut self, additional: usize) {
427 self.buf.reserve(self.len, additional);
430 /// Reserves the minimum capacity for exactly `additional` more elements to
431 /// be inserted in the given `Vec<T>`. Does nothing if the capacity is already
434 /// Note that the allocator may give the collection more space than it
435 /// requests. Therefore capacity can not be relied upon to be precisely
436 /// minimal. Prefer `reserve` if future insertions are expected.
440 /// Panics if the new capacity overflows `usize`.
445 /// let mut vec = vec![1];
446 /// vec.reserve_exact(10);
447 /// assert!(vec.capacity() >= 11);
449 #[stable(feature = "rust1", since = "1.0.0")]
450 pub fn reserve_exact(&mut self, additional: usize) {
451 self.buf.reserve_exact(self.len, additional);
454 /// Shrinks the capacity of the vector as much as possible.
456 /// It will drop down as close as possible to the length but the allocator
457 /// may still inform the vector that there is space for a few more elements.
462 /// let mut vec = Vec::with_capacity(10);
463 /// vec.extend([1, 2, 3].iter().cloned());
464 /// assert_eq!(vec.capacity(), 10);
465 /// vec.shrink_to_fit();
466 /// assert!(vec.capacity() >= 3);
468 #[stable(feature = "rust1", since = "1.0.0")]
469 pub fn shrink_to_fit(&mut self) {
470 self.buf.shrink_to_fit(self.len);
473 /// Converts the vector into Box<[T]>.
475 /// Note that this will drop any excess capacity. Calling this and
476 /// converting back to a vector with `into_vec()` is equivalent to calling
477 /// `shrink_to_fit()`.
478 #[stable(feature = "rust1", since = "1.0.0")]
479 pub fn into_boxed_slice(mut self) -> Box<[T]> {
481 self.shrink_to_fit();
482 let buf = ptr::read(&self.buf);
488 /// Shortens the vector, keeping the first `len` elements and dropping
491 /// If `len` is greater than the vector's current length, this has no
494 /// The [`drain`] method can emulate `truncate`, but causes the excess
495 /// elements to be returned instead of dropped.
499 /// Truncating a five element vector to two elements:
502 /// let mut vec = vec![1, 2, 3, 4, 5];
504 /// assert_eq!(vec, [1, 2]);
507 /// No truncation occurs when `len` is greater than the vector's current
511 /// let mut vec = vec![1, 2, 3];
513 /// assert_eq!(vec, [1, 2, 3]);
516 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
520 /// let mut vec = vec![1, 2, 3];
522 /// assert_eq!(vec, []);
525 /// [`clear`]: #method.clear
526 /// [`drain`]: #method.drain
527 #[stable(feature = "rust1", since = "1.0.0")]
528 pub fn truncate(&mut self, len: usize) {
530 // drop any extra elements
531 while len < self.len {
532 // decrement len before the drop_in_place(), so a panic on Drop
533 // doesn't re-drop the just-failed value.
536 ptr::drop_in_place(self.get_unchecked_mut(len));
541 /// Extracts a slice containing the entire vector.
543 /// Equivalent to `&s[..]`.
548 /// use std::io::{self, Write};
549 /// let buffer = vec![1, 2, 3, 5, 8];
550 /// io::sink().write(buffer.as_slice()).unwrap();
553 #[stable(feature = "vec_as_slice", since = "1.7.0")]
554 pub fn as_slice(&self) -> &[T] {
558 /// Extracts a mutable slice of the entire vector.
560 /// Equivalent to `&mut s[..]`.
565 /// use std::io::{self, Read};
566 /// let mut buffer = vec![0; 3];
567 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
570 #[stable(feature = "vec_as_slice", since = "1.7.0")]
571 pub fn as_mut_slice(&mut self) -> &mut [T] {
575 /// Sets the length of a vector.
577 /// This will explicitly set the size of the vector, without actually
578 /// modifying its buffers, so it is up to the caller to ensure that the
579 /// vector is actually the specified size.
586 /// let mut vec = vec!['r', 'u', 's', 't'];
589 /// ptr::drop_in_place(&mut vec[3]);
592 /// assert_eq!(vec, ['r', 'u', 's']);
595 /// In this example, there is a memory leak since the memory locations
596 /// owned by the vector were not freed prior to the `set_len` call:
599 /// let mut vec = vec!['r', 'u', 's', 't'];
606 /// In this example, the vector gets expanded from zero to four items
607 /// without any memory allocations occurring, resulting in vector
608 /// values of unallocated memory:
611 /// let mut vec: Vec<char> = Vec::new();
618 #[stable(feature = "rust1", since = "1.0.0")]
619 pub unsafe fn set_len(&mut self, len: usize) {
623 /// Removes an element from anywhere in the vector and return it, replacing
624 /// it with the last element.
626 /// This does not preserve ordering, but is O(1).
630 /// Panics if `index` is out of bounds.
635 /// let mut v = vec!["foo", "bar", "baz", "qux"];
637 /// assert_eq!(v.swap_remove(1), "bar");
638 /// assert_eq!(v, ["foo", "qux", "baz"]);
640 /// assert_eq!(v.swap_remove(0), "foo");
641 /// assert_eq!(v, ["baz", "qux"]);
644 #[stable(feature = "rust1", since = "1.0.0")]
645 pub fn swap_remove(&mut self, index: usize) -> T {
646 let length = self.len();
647 self.swap(index, length - 1);
651 /// Inserts an element at position `index` within the vector, shifting all
652 /// elements after it to the right.
656 /// Panics if `index` is greater than the vector's length.
661 /// let mut vec = vec![1, 2, 3];
662 /// vec.insert(1, 4);
663 /// assert_eq!(vec, [1, 4, 2, 3]);
664 /// vec.insert(4, 5);
665 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
667 #[stable(feature = "rust1", since = "1.0.0")]
668 pub fn insert(&mut self, index: usize, element: T) {
669 let len = self.len();
670 assert!(index <= len);
672 // space for the new element
673 if len == self.buf.cap() {
679 // The spot to put the new value
681 let p = self.as_mut_ptr().offset(index as isize);
682 // Shift everything over to make space. (Duplicating the
683 // `index`th element into two consecutive places.)
684 ptr::copy(p, p.offset(1), len - index);
685 // Write it in, overwriting the first copy of the `index`th
687 ptr::write(p, element);
689 self.set_len(len + 1);
693 /// Removes and returns the element at position `index` within the vector,
694 /// shifting all elements after it to the left.
698 /// Panics if `index` is out of bounds.
703 /// let mut v = vec![1, 2, 3];
704 /// assert_eq!(v.remove(1), 2);
705 /// assert_eq!(v, [1, 3]);
707 #[stable(feature = "rust1", since = "1.0.0")]
708 pub fn remove(&mut self, index: usize) -> T {
709 let len = self.len();
710 assert!(index < len);
715 // the place we are taking from.
716 let ptr = self.as_mut_ptr().offset(index as isize);
717 // copy it out, unsafely having a copy of the value on
718 // the stack and in the vector at the same time.
719 ret = ptr::read(ptr);
721 // Shift everything down to fill in that spot.
722 ptr::copy(ptr.offset(1), ptr, len - index - 1);
724 self.set_len(len - 1);
729 /// Retains only the elements specified by the predicate.
731 /// In other words, remove all elements `e` such that `f(&e)` returns false.
732 /// This method operates in place and preserves the order of the retained
738 /// let mut vec = vec![1, 2, 3, 4];
739 /// vec.retain(|&x| x%2 == 0);
740 /// assert_eq!(vec, [2, 4]);
742 #[stable(feature = "rust1", since = "1.0.0")]
743 pub fn retain<F>(&mut self, mut f: F)
744 where F: FnMut(&T) -> bool
746 let len = self.len();
760 self.truncate(len - del);
764 /// Appends an element to the back of a collection.
768 /// Panics if the number of elements in the vector overflows a `usize`.
773 /// let mut vec = vec![1, 2];
775 /// assert_eq!(vec, [1, 2, 3]);
778 #[stable(feature = "rust1", since = "1.0.0")]
779 pub fn push(&mut self, value: T) {
780 // This will panic or abort if we would allocate > isize::MAX bytes
781 // or if the length increment would overflow for zero-sized types.
782 if self.len == self.buf.cap() {
786 let end = self.as_mut_ptr().offset(self.len as isize);
787 ptr::write(end, value);
792 /// Removes the last element from a vector and returns it, or `None` if it
798 /// let mut vec = vec![1, 2, 3];
799 /// assert_eq!(vec.pop(), Some(3));
800 /// assert_eq!(vec, [1, 2]);
803 #[stable(feature = "rust1", since = "1.0.0")]
804 pub fn pop(&mut self) -> Option<T> {
810 Some(ptr::read(self.get_unchecked(self.len())))
815 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
819 /// Panics if the number of elements in the vector overflows a `usize`.
824 /// let mut vec = vec![1, 2, 3];
825 /// let mut vec2 = vec![4, 5, 6];
826 /// vec.append(&mut vec2);
827 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
828 /// assert_eq!(vec2, []);
831 #[stable(feature = "append", since = "1.4.0")]
832 pub fn append(&mut self, other: &mut Self) {
833 self.reserve(other.len());
834 let len = self.len();
836 ptr::copy_nonoverlapping(other.as_ptr(), self.get_unchecked_mut(len), other.len());
839 self.len += other.len();
845 /// Create a draining iterator that removes the specified range in the vector
846 /// and yields the removed items.
848 /// Note 1: The element range is removed even if the iterator is not
849 /// consumed until the end.
851 /// Note 2: It is unspecified how many elements are removed from the vector,
852 /// if the `Drain` value is leaked.
856 /// Panics if the starting point is greater than the end point or if
857 /// the end point is greater than the length of the vector.
862 /// let mut v = vec![1, 2, 3];
863 /// let u: Vec<_> = v.drain(1..).collect();
864 /// assert_eq!(v, &[1]);
865 /// assert_eq!(u, &[2, 3]);
867 /// // A full range clears the vector
869 /// assert_eq!(v, &[]);
871 #[stable(feature = "drain", since = "1.6.0")]
872 pub fn drain<R>(&mut self, range: R) -> Drain<T>
873 where R: RangeArgument<usize>
877 // When the Drain is first created, it shortens the length of
878 // the source vector to make sure no uninitalized or moved-from elements
879 // are accessible at all if the Drain's destructor never gets to run.
881 // Drain will ptr::read out the values to remove.
882 // When finished, remaining tail of the vec is copied back to cover
883 // the hole, and the vector length is restored to the new length.
885 let len = self.len();
886 let start = *range.start().unwrap_or(&0);
887 let end = *range.end().unwrap_or(&len);
888 assert!(start <= end);
892 // set self.vec length's to start, to be safe in case Drain is leaked
894 // Use the borrow in the IterMut to indicate borrowing behavior of the
895 // whole Drain iterator (like &mut T).
896 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().offset(start as isize),
901 iter: range_slice.iter_mut(),
907 /// Clears the vector, removing all values.
912 /// let mut v = vec![1, 2, 3];
916 /// assert!(v.is_empty());
919 #[stable(feature = "rust1", since = "1.0.0")]
920 pub fn clear(&mut self) {
924 /// Returns the number of elements in the vector.
929 /// let a = vec![1, 2, 3];
930 /// assert_eq!(a.len(), 3);
933 #[stable(feature = "rust1", since = "1.0.0")]
934 pub fn len(&self) -> usize {
938 /// Returns `true` if the vector contains no elements.
943 /// let mut v = Vec::new();
944 /// assert!(v.is_empty());
947 /// assert!(!v.is_empty());
949 #[stable(feature = "rust1", since = "1.0.0")]
950 pub fn is_empty(&self) -> bool {
954 /// Splits the collection into two at the given index.
956 /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
957 /// and the returned `Self` contains elements `[at, len)`.
959 /// Note that the capacity of `self` does not change.
963 /// Panics if `at > len`.
968 /// let mut vec = vec![1,2,3];
969 /// let vec2 = vec.split_off(1);
970 /// assert_eq!(vec, [1]);
971 /// assert_eq!(vec2, [2, 3]);
974 #[stable(feature = "split_off", since = "1.4.0")]
975 pub fn split_off(&mut self, at: usize) -> Self {
976 assert!(at <= self.len(), "`at` out of bounds");
978 let other_len = self.len - at;
979 let mut other = Vec::with_capacity(other_len);
981 // Unsafely `set_len` and copy items to `other`.
984 other.set_len(other_len);
986 ptr::copy_nonoverlapping(self.as_ptr().offset(at as isize),
994 impl<T: Clone> Vec<T> {
995 /// Resizes the `Vec` in-place so that `len()` is equal to `new_len`.
997 /// If `new_len` is greater than `len()`, the `Vec` is extended by the
998 /// difference, with each additional slot filled with `value`.
999 /// If `new_len` is less than `len()`, the `Vec` is simply truncated.
1004 /// let mut vec = vec!["hello"];
1005 /// vec.resize(3, "world");
1006 /// assert_eq!(vec, ["hello", "world", "world"]);
1008 /// let mut vec = vec![1, 2, 3, 4];
1009 /// vec.resize(2, 0);
1010 /// assert_eq!(vec, [1, 2]);
1012 #[stable(feature = "vec_resize", since = "1.5.0")]
1013 pub fn resize(&mut self, new_len: usize, value: T) {
1014 let len = self.len();
1017 self.extend_with_element(new_len - len, value);
1019 self.truncate(new_len);
1023 /// Extend the vector by `n` additional clones of `value`.
1024 fn extend_with_element(&mut self, n: usize, value: T) {
1028 let len = self.len();
1029 let mut ptr = self.as_mut_ptr().offset(len as isize);
1030 // Write all elements except the last one
1032 ptr::write(ptr, value.clone());
1033 ptr = ptr.offset(1);
1034 // Increment the length in every step in case clone() panics
1035 self.set_len(len + i);
1039 // We can write the last element directly without cloning needlessly
1040 ptr::write(ptr, value);
1041 self.set_len(len + n);
1046 /// Clones and appends all elements in a slice to the `Vec`.
1048 /// Iterates over the slice `other`, clones each element, and then appends
1049 /// it to this `Vec`. The `other` vector is traversed in-order.
1051 /// Note that this function is same as `extend` except that it is
1052 /// specialized to work with slices instead. If and when Rust gets
1053 /// specialization this function will likely be deprecated (but still
1059 /// let mut vec = vec![1];
1060 /// vec.extend_from_slice(&[2, 3, 4]);
1061 /// assert_eq!(vec, [1, 2, 3, 4]);
1063 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1064 pub fn extend_from_slice(&mut self, other: &[T]) {
1065 self.reserve(other.len());
1067 for i in 0..other.len() {
1068 let len = self.len();
1070 // Unsafe code so this can be optimised to a memcpy (or something
1071 // similarly fast) when T is Copy. LLVM is easily confused, so any
1072 // extra operations during the loop can prevent this optimisation.
1074 ptr::write(self.get_unchecked_mut(len), other.get_unchecked(i).clone());
1075 self.set_len(len + 1);
1081 impl<T: PartialEq> Vec<T> {
1082 /// Removes consecutive repeated elements in the vector.
1084 /// If the vector is sorted, this removes all duplicates.
1089 /// let mut vec = vec![1, 2, 2, 3, 2];
1093 /// assert_eq!(vec, [1, 2, 3, 2]);
1095 #[stable(feature = "rust1", since = "1.0.0")]
1096 pub fn dedup(&mut self) {
1098 // Although we have a mutable reference to `self`, we cannot make
1099 // *arbitrary* changes. The `PartialEq` comparisons could panic, so we
1100 // must ensure that the vector is in a valid state at all time.
1102 // The way that we handle this is by using swaps; we iterate
1103 // over all the elements, swapping as we go so that at the end
1104 // the elements we wish to keep are in the front, and those we
1105 // wish to reject are at the back. We can then truncate the
1106 // vector. This operation is still O(n).
1108 // Example: We start in this state, where `r` represents "next
1109 // read" and `w` represents "next_write`.
1112 // +---+---+---+---+---+---+
1113 // | 0 | 1 | 1 | 2 | 3 | 3 |
1114 // +---+---+---+---+---+---+
1117 // Comparing self[r] against self[w-1], this is not a duplicate, so
1118 // we swap self[r] and self[w] (no effect as r==w) and then increment both
1119 // r and w, leaving us with:
1122 // +---+---+---+---+---+---+
1123 // | 0 | 1 | 1 | 2 | 3 | 3 |
1124 // +---+---+---+---+---+---+
1127 // Comparing self[r] against self[w-1], this value is a duplicate,
1128 // so we increment `r` but leave everything else unchanged:
1131 // +---+---+---+---+---+---+
1132 // | 0 | 1 | 1 | 2 | 3 | 3 |
1133 // +---+---+---+---+---+---+
1136 // Comparing self[r] against self[w-1], this is not a duplicate,
1137 // so swap self[r] and self[w] and advance r and w:
1140 // +---+---+---+---+---+---+
1141 // | 0 | 1 | 2 | 1 | 3 | 3 |
1142 // +---+---+---+---+---+---+
1145 // Not a duplicate, repeat:
1148 // +---+---+---+---+---+---+
1149 // | 0 | 1 | 2 | 3 | 1 | 3 |
1150 // +---+---+---+---+---+---+
1153 // Duplicate, advance r. End of vec. Truncate to w.
1155 let ln = self.len();
1160 // Avoid bounds checks by using raw pointers.
1161 let p = self.as_mut_ptr();
1162 let mut r: usize = 1;
1163 let mut w: usize = 1;
1166 let p_r = p.offset(r as isize);
1167 let p_wm1 = p.offset((w - 1) as isize);
1170 let p_w = p_wm1.offset(1);
1171 mem::swap(&mut *p_r, &mut *p_w);
1183 ////////////////////////////////////////////////////////////////////////////////
1184 // Internal methods and functions
1185 ////////////////////////////////////////////////////////////////////////////////
1188 #[stable(feature = "rust1", since = "1.0.0")]
1189 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1190 let mut v = Vec::with_capacity(n);
1191 v.extend_with_element(n, elem);
1195 ////////////////////////////////////////////////////////////////////////////////
1196 // Common trait implementations for Vec
1197 ////////////////////////////////////////////////////////////////////////////////
1199 #[stable(feature = "rust1", since = "1.0.0")]
1200 impl<T: Clone> Clone for Vec<T> {
1202 fn clone(&self) -> Vec<T> {
1203 <[T]>::to_vec(&**self)
1206 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1207 // required for this method definition, is not available. Instead use the
1208 // `slice::to_vec` function which is only available with cfg(test)
1209 // NB see the slice::hack module in slice.rs for more information
1211 fn clone(&self) -> Vec<T> {
1212 ::slice::to_vec(&**self)
1215 fn clone_from(&mut self, other: &Vec<T>) {
1216 // drop anything in self that will not be overwritten
1217 self.truncate(other.len());
1218 let len = self.len();
1220 // reuse the contained values' allocations/resources.
1221 self.clone_from_slice(&other[..len]);
1223 // self.len <= other.len due to the truncate above, so the
1224 // slice here is always in-bounds.
1225 self.extend_from_slice(&other[len..]);
1229 #[stable(feature = "rust1", since = "1.0.0")]
1230 impl<T: Hash> Hash for Vec<T> {
1232 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1233 Hash::hash(&**self, state)
1237 #[stable(feature = "rust1", since = "1.0.0")]
1238 impl<T> Index<usize> for Vec<T> {
1242 fn index(&self, index: usize) -> &T {
1243 // NB built-in indexing via `&[T]`
1248 #[stable(feature = "rust1", since = "1.0.0")]
1249 impl<T> IndexMut<usize> for Vec<T> {
1251 fn index_mut(&mut self, index: usize) -> &mut T {
1252 // NB built-in indexing via `&mut [T]`
1253 &mut (**self)[index]
1258 #[stable(feature = "rust1", since = "1.0.0")]
1259 impl<T> ops::Index<ops::Range<usize>> for Vec<T> {
1263 fn index(&self, index: ops::Range<usize>) -> &[T] {
1264 Index::index(&**self, index)
1267 #[stable(feature = "rust1", since = "1.0.0")]
1268 impl<T> ops::Index<ops::RangeTo<usize>> for Vec<T> {
1272 fn index(&self, index: ops::RangeTo<usize>) -> &[T] {
1273 Index::index(&**self, index)
1276 #[stable(feature = "rust1", since = "1.0.0")]
1277 impl<T> ops::Index<ops::RangeFrom<usize>> for Vec<T> {
1281 fn index(&self, index: ops::RangeFrom<usize>) -> &[T] {
1282 Index::index(&**self, index)
1285 #[stable(feature = "rust1", since = "1.0.0")]
1286 impl<T> ops::Index<ops::RangeFull> for Vec<T> {
1290 fn index(&self, _index: ops::RangeFull) -> &[T] {
1294 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1295 impl<T> ops::Index<ops::RangeInclusive<usize>> for Vec<T> {
1299 fn index(&self, index: ops::RangeInclusive<usize>) -> &[T] {
1300 Index::index(&**self, index)
1303 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1304 impl<T> ops::Index<ops::RangeToInclusive<usize>> for Vec<T> {
1308 fn index(&self, index: ops::RangeToInclusive<usize>) -> &[T] {
1309 Index::index(&**self, index)
1313 #[stable(feature = "rust1", since = "1.0.0")]
1314 impl<T> ops::IndexMut<ops::Range<usize>> for Vec<T> {
1316 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut [T] {
1317 IndexMut::index_mut(&mut **self, index)
1320 #[stable(feature = "rust1", since = "1.0.0")]
1321 impl<T> ops::IndexMut<ops::RangeTo<usize>> for Vec<T> {
1323 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut [T] {
1324 IndexMut::index_mut(&mut **self, index)
1327 #[stable(feature = "rust1", since = "1.0.0")]
1328 impl<T> ops::IndexMut<ops::RangeFrom<usize>> for Vec<T> {
1330 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut [T] {
1331 IndexMut::index_mut(&mut **self, index)
1334 #[stable(feature = "rust1", since = "1.0.0")]
1335 impl<T> ops::IndexMut<ops::RangeFull> for Vec<T> {
1337 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut [T] {
1341 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1342 impl<T> ops::IndexMut<ops::RangeInclusive<usize>> for Vec<T> {
1344 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut [T] {
1345 IndexMut::index_mut(&mut **self, index)
1348 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1349 impl<T> ops::IndexMut<ops::RangeToInclusive<usize>> for Vec<T> {
1351 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut [T] {
1352 IndexMut::index_mut(&mut **self, index)
1356 #[stable(feature = "rust1", since = "1.0.0")]
1357 impl<T> ops::Deref for Vec<T> {
1360 fn deref(&self) -> &[T] {
1362 let p = self.buf.ptr();
1363 assume(!p.is_null());
1364 slice::from_raw_parts(p, self.len)
1369 #[stable(feature = "rust1", since = "1.0.0")]
1370 impl<T> ops::DerefMut for Vec<T> {
1371 fn deref_mut(&mut self) -> &mut [T] {
1373 let ptr = self.buf.ptr();
1374 assume(!ptr.is_null());
1375 slice::from_raw_parts_mut(ptr, self.len)
1380 #[stable(feature = "rust1", since = "1.0.0")]
1381 impl<T> FromIterator<T> for Vec<T> {
1383 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1384 // Unroll the first iteration, as the vector is going to be
1385 // expanded on this iteration in every case when the iterable is not
1386 // empty, but the loop in extend_desugared() is not going to see the
1387 // vector being full in the few subsequent loop iterations.
1388 // So we get better branch prediction.
1389 let mut iterator = iter.into_iter();
1390 let mut vector = match iterator.next() {
1391 None => return Vec::new(),
1393 let (lower, _) = iterator.size_hint();
1394 let mut vector = Vec::with_capacity(lower.saturating_add(1));
1396 ptr::write(vector.get_unchecked_mut(0), element);
1402 vector.extend_desugared(iterator);
1407 #[stable(feature = "rust1", since = "1.0.0")]
1408 impl<T> IntoIterator for Vec<T> {
1410 type IntoIter = IntoIter<T>;
1412 /// Creates a consuming iterator, that is, one that moves each value out of
1413 /// the vector (from start to end). The vector cannot be used after calling
1419 /// let v = vec!["a".to_string(), "b".to_string()];
1420 /// for s in v.into_iter() {
1421 /// // s has type String, not &String
1422 /// println!("{}", s);
1426 fn into_iter(mut self) -> IntoIter<T> {
1428 let ptr = self.as_mut_ptr();
1429 assume(!ptr.is_null());
1430 let begin = ptr as *const T;
1431 let end = if mem::size_of::<T>() == 0 {
1432 arith_offset(ptr as *const i8, self.len() as isize) as *const T
1434 ptr.offset(self.len() as isize) as *const T
1436 let buf = ptr::read(&self.buf);
1447 #[stable(feature = "rust1", since = "1.0.0")]
1448 impl<'a, T> IntoIterator for &'a Vec<T> {
1450 type IntoIter = slice::Iter<'a, T>;
1452 fn into_iter(self) -> slice::Iter<'a, T> {
1457 #[stable(feature = "rust1", since = "1.0.0")]
1458 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1459 type Item = &'a mut T;
1460 type IntoIter = slice::IterMut<'a, T>;
1462 fn into_iter(mut self) -> slice::IterMut<'a, T> {
1467 #[stable(feature = "rust1", since = "1.0.0")]
1468 impl<T> Extend<T> for Vec<T> {
1470 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1471 <Self as SpecExtend<I>>::spec_extend(self, iter);
1475 impl<I: IntoIterator> SpecExtend<I> for Vec<I::Item> {
1476 default fn spec_extend(&mut self, iter: I) {
1477 self.extend_desugared(iter.into_iter())
1481 impl<T> SpecExtend<Vec<T>> for Vec<T> {
1482 fn spec_extend(&mut self, ref mut other: Vec<T>) {
1488 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
1489 // This function should be the moral equivalent of:
1491 // for item in iterator {
1494 while let Some(element) = iterator.next() {
1495 let len = self.len();
1496 if len == self.capacity() {
1497 let (lower, _) = iterator.size_hint();
1498 self.reserve(lower.saturating_add(1));
1501 ptr::write(self.get_unchecked_mut(len), element);
1502 // NB can't overflow since we would have had to alloc the address space
1503 self.set_len(len + 1);
1509 #[stable(feature = "extend_ref", since = "1.2.0")]
1510 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
1511 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
1512 self.extend(iter.into_iter().cloned());
1516 macro_rules! __impl_slice_eq1 {
1517 ($Lhs: ty, $Rhs: ty) => {
1518 __impl_slice_eq1! { $Lhs, $Rhs, Sized }
1520 ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
1521 #[stable(feature = "rust1", since = "1.0.0")]
1522 impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
1524 fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
1526 fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
1531 __impl_slice_eq1! { Vec<A>, Vec<B> }
1532 __impl_slice_eq1! { Vec<A>, &'b [B] }
1533 __impl_slice_eq1! { Vec<A>, &'b mut [B] }
1534 __impl_slice_eq1! { Cow<'a, [A]>, &'b [B], Clone }
1535 __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B], Clone }
1536 __impl_slice_eq1! { Cow<'a, [A]>, Vec<B>, Clone }
1538 macro_rules! array_impls {
1541 // NOTE: some less important impls are omitted to reduce code bloat
1542 __impl_slice_eq1! { Vec<A>, [B; $N] }
1543 __impl_slice_eq1! { Vec<A>, &'b [B; $N] }
1544 // __impl_slice_eq1! { Vec<A>, &'b mut [B; $N] }
1545 // __impl_slice_eq1! { Cow<'a, [A]>, [B; $N], Clone }
1546 // __impl_slice_eq1! { Cow<'a, [A]>, &'b [B; $N], Clone }
1547 // __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B; $N], Clone }
1554 10 11 12 13 14 15 16 17 18 19
1555 20 21 22 23 24 25 26 27 28 29
1559 #[stable(feature = "rust1", since = "1.0.0")]
1560 impl<T: PartialOrd> PartialOrd for Vec<T> {
1562 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
1563 PartialOrd::partial_cmp(&**self, &**other)
1567 #[stable(feature = "rust1", since = "1.0.0")]
1568 impl<T: Eq> Eq for Vec<T> {}
1570 #[stable(feature = "rust1", since = "1.0.0")]
1571 impl<T: Ord> Ord for Vec<T> {
1573 fn cmp(&self, other: &Vec<T>) -> Ordering {
1574 Ord::cmp(&**self, &**other)
1578 #[stable(feature = "rust1", since = "1.0.0")]
1579 impl<T> Drop for Vec<T> {
1580 #[unsafe_destructor_blind_to_params]
1581 fn drop(&mut self) {
1582 if self.buf.unsafe_no_drop_flag_needs_drop() {
1585 ptr::drop_in_place(&mut self[..]);
1588 // RawVec handles deallocation
1592 #[stable(feature = "rust1", since = "1.0.0")]
1593 impl<T> Default for Vec<T> {
1594 fn default() -> Vec<T> {
1599 #[stable(feature = "rust1", since = "1.0.0")]
1600 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
1601 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1602 fmt::Debug::fmt(&**self, f)
1606 #[stable(feature = "rust1", since = "1.0.0")]
1607 impl<T> AsRef<Vec<T>> for Vec<T> {
1608 fn as_ref(&self) -> &Vec<T> {
1613 #[stable(feature = "vec_as_mut", since = "1.5.0")]
1614 impl<T> AsMut<Vec<T>> for Vec<T> {
1615 fn as_mut(&mut self) -> &mut Vec<T> {
1620 #[stable(feature = "rust1", since = "1.0.0")]
1621 impl<T> AsRef<[T]> for Vec<T> {
1622 fn as_ref(&self) -> &[T] {
1627 #[stable(feature = "vec_as_mut", since = "1.5.0")]
1628 impl<T> AsMut<[T]> for Vec<T> {
1629 fn as_mut(&mut self) -> &mut [T] {
1634 #[stable(feature = "rust1", since = "1.0.0")]
1635 impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
1637 fn from(s: &'a [T]) -> Vec<T> {
1641 fn from(s: &'a [T]) -> Vec<T> {
1646 #[stable(feature = "rust1", since = "1.0.0")]
1647 impl<'a> From<&'a str> for Vec<u8> {
1648 fn from(s: &'a str) -> Vec<u8> {
1649 From::from(s.as_bytes())
1653 ////////////////////////////////////////////////////////////////////////////////
1655 ////////////////////////////////////////////////////////////////////////////////
1657 #[stable(feature = "cow_from_vec", since = "1.7.0")]
1658 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
1659 fn from(s: &'a [T]) -> Cow<'a, [T]> {
1664 #[stable(feature = "cow_from_vec", since = "1.7.0")]
1665 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
1666 fn from(v: Vec<T>) -> Cow<'a, [T]> {
1671 #[stable(feature = "rust1", since = "1.0.0")]
1672 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
1673 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
1674 Cow::Owned(FromIterator::from_iter(it))
1678 ////////////////////////////////////////////////////////////////////////////////
1680 ////////////////////////////////////////////////////////////////////////////////
1682 /// An iterator that moves out of a vector.
1684 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
1685 /// by the [`IntoIterator`] trait).
1687 /// [`Vec`]: struct.Vec.html
1688 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
1689 #[stable(feature = "rust1", since = "1.0.0")]
1690 pub struct IntoIter<T> {
1696 #[stable(feature = "rust1", since = "1.0.0")]
1697 unsafe impl<T: Send> Send for IntoIter<T> {}
1698 #[stable(feature = "rust1", since = "1.0.0")]
1699 unsafe impl<T: Sync> Sync for IntoIter<T> {}
1701 #[stable(feature = "rust1", since = "1.0.0")]
1702 impl<T> Iterator for IntoIter<T> {
1706 fn next(&mut self) -> Option<T> {
1708 if self.ptr == self.end {
1711 if mem::size_of::<T>() == 0 {
1712 // purposefully don't use 'ptr.offset' because for
1713 // vectors with 0-size elements this would return the
1715 self.ptr = arith_offset(self.ptr as *const i8, 1) as *const T;
1717 // Use a non-null pointer value
1718 Some(ptr::read(EMPTY as *mut T))
1721 self.ptr = self.ptr.offset(1);
1723 Some(ptr::read(old))
1730 fn size_hint(&self) -> (usize, Option<usize>) {
1731 let diff = (self.end as usize) - (self.ptr as usize);
1732 let size = mem::size_of::<T>();
1739 (exact, Some(exact))
1743 fn count(self) -> usize {
1748 #[stable(feature = "rust1", since = "1.0.0")]
1749 impl<T> DoubleEndedIterator for IntoIter<T> {
1751 fn next_back(&mut self) -> Option<T> {
1753 if self.end == self.ptr {
1756 if mem::size_of::<T>() == 0 {
1757 // See above for why 'ptr.offset' isn't used
1758 self.end = arith_offset(self.end as *const i8, -1) as *const T;
1760 // Use a non-null pointer value
1761 Some(ptr::read(EMPTY as *mut T))
1763 self.end = self.end.offset(-1);
1765 Some(ptr::read(self.end))
1772 #[stable(feature = "rust1", since = "1.0.0")]
1773 impl<T> ExactSizeIterator for IntoIter<T> {}
1775 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
1776 impl<T: Clone> Clone for IntoIter<T> {
1777 fn clone(&self) -> IntoIter<T> {
1779 slice::from_raw_parts(self.ptr, self.len()).to_owned().into_iter()
1784 #[stable(feature = "rust1", since = "1.0.0")]
1785 impl<T> Drop for IntoIter<T> {
1786 #[unsafe_destructor_blind_to_params]
1787 fn drop(&mut self) {
1788 // destroy the remaining elements
1791 // RawVec handles deallocation
1795 /// A draining iterator for `Vec<T>`.
1797 /// This `struct` is created by the [`drain`] method on [`Vec`].
1799 /// [`drain`]: struct.Vec.html#method.drain
1800 /// [`Vec`]: struct.Vec.html
1801 #[stable(feature = "drain", since = "1.6.0")]
1802 pub struct Drain<'a, T: 'a> {
1803 /// Index of tail to preserve
1807 /// Current remaining range to remove
1808 iter: slice::IterMut<'a, T>,
1812 #[stable(feature = "drain", since = "1.6.0")]
1813 unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
1814 #[stable(feature = "drain", since = "1.6.0")]
1815 unsafe impl<'a, T: Send> Send for Drain<'a, T> {}
1817 #[stable(feature = "rust1", since = "1.0.0")]
1818 impl<'a, T> Iterator for Drain<'a, T> {
1822 fn next(&mut self) -> Option<T> {
1823 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
1826 fn size_hint(&self) -> (usize, Option<usize>) {
1827 self.iter.size_hint()
1831 #[stable(feature = "rust1", since = "1.0.0")]
1832 impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
1834 fn next_back(&mut self) -> Option<T> {
1835 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
1839 #[stable(feature = "rust1", since = "1.0.0")]
1840 impl<'a, T> Drop for Drain<'a, T> {
1841 fn drop(&mut self) {
1842 // exhaust self first
1843 while let Some(_) = self.next() {}
1845 if self.tail_len > 0 {
1847 let source_vec = &mut *self.vec;
1848 // memmove back untouched tail, update to new length
1849 let start = source_vec.len();
1850 let tail = self.tail_start;
1851 let src = source_vec.as_ptr().offset(tail as isize);
1852 let dst = source_vec.as_mut_ptr().offset(start as isize);
1853 ptr::copy(src, dst, self.tail_len);
1854 source_vec.set_len(start + self.tail_len);
1861 #[stable(feature = "rust1", since = "1.0.0")]
1862 impl<'a, T> ExactSizeIterator for Drain<'a, T> {}