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
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 //! [`Vec<T>`]: ../../std/vec/struct.Vec.html
61 //! [`new`]: ../../std/vec/struct.Vec.html#method.new
62 //! [`push`]: ../../std/vec/struct.Vec.html#method.push
63 //! [`Index`]: ../../std/ops/trait.Index.html
64 //! [`IndexMut`]: ../../std/ops/trait.IndexMut.html
65 //! [`vec!`]: ../../std/macro.vec.html
67 #![stable(feature = "rust1", since = "1.0.0")]
69 use core::cmp::Ordering;
71 use core::hash::{self, Hash};
72 use core::intrinsics::{arith_offset, assume};
73 use core::iter::{FromIterator, FusedIterator, TrustedLen};
77 use core::ops::{InPlace, Index, IndexMut, Place, Placer};
80 use core::ptr::Shared;
87 use super::range::RangeArgument;
88 use Bound::{Excluded, Included, Unbounded};
90 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
95 /// let mut vec = Vec::new();
99 /// assert_eq!(vec.len(), 2);
100 /// assert_eq!(vec[0], 1);
102 /// assert_eq!(vec.pop(), Some(2));
103 /// assert_eq!(vec.len(), 1);
106 /// assert_eq!(vec[0], 7);
108 /// vec.extend([1, 2, 3].iter().cloned());
111 /// println!("{}", x);
113 /// assert_eq!(vec, [7, 1, 2, 3]);
116 /// The [`vec!`] macro is provided to make initialization more convenient:
119 /// let mut vec = vec![1, 2, 3];
121 /// assert_eq!(vec, [1, 2, 3, 4]);
124 /// It can also initialize each element of a `Vec<T>` with a given value:
127 /// let vec = vec![0; 5];
128 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
131 /// Use a `Vec<T>` as an efficient stack:
134 /// let mut stack = Vec::new();
140 /// while let Some(top) = stack.pop() {
141 /// // Prints 3, 2, 1
142 /// println!("{}", top);
148 /// The `Vec` type allows to access values by index, because it implements the
149 /// [`Index`] trait. An example will be more explicit:
152 /// let v = vec![0, 2, 4, 6];
153 /// println!("{}", v[1]); // it will display '2'
156 /// However be careful: if you try to access an index which isn't in the `Vec`,
157 /// your software will panic! You cannot do this:
160 /// let v = vec![0, 2, 4, 6];
161 /// println!("{}", v[6]); // it will panic!
164 /// In conclusion: always check if the index you want to get really exists
169 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
170 /// To get a slice, use `&`. Example:
173 /// fn read_slice(slice: &[usize]) {
177 /// let v = vec![0, 1];
180 /// // ... and that's all!
181 /// // you can also do it like this:
182 /// let x : &[usize] = &v;
185 /// In Rust, it's more common to pass slices as arguments rather than vectors
186 /// when you just want to provide a read access. The same goes for [`String`] and
189 /// # Capacity and reallocation
191 /// The capacity of a vector is the amount of space allocated for any future
192 /// elements that will be added onto the vector. This is not to be confused with
193 /// the *length* of a vector, which specifies the number of actual elements
194 /// within the vector. If a vector's length exceeds its capacity, its capacity
195 /// will automatically be increased, but its elements will have to be
198 /// For example, a vector with capacity 10 and length 0 would be an empty vector
199 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
200 /// vector will not change its capacity or cause reallocation to occur. However,
201 /// if the vector's length is increased to 11, it will have to reallocate, which
202 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
203 /// whenever possible to specify how big the vector is expected to get.
207 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
208 /// about its design. This ensures that it's as low-overhead as possible in
209 /// the general case, and can be correctly manipulated in primitive ways
210 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
211 /// If additional type parameters are added (e.g. to support custom allocators),
212 /// overriding their defaults may change the behavior.
214 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
215 /// triplet. No more, no less. The order of these fields is completely
216 /// unspecified, and you should use the appropriate methods to modify these.
217 /// The pointer will never be null, so this type is null-pointer-optimized.
219 /// However, the pointer may not actually point to allocated memory. In particular,
220 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
221 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
222 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
223 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
224 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
225 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
226 /// details are subtle enough that it is strongly recommended that you only
227 /// free memory allocated by a `Vec` by creating a new `Vec` and dropping it.
229 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
230 /// (as defined by the allocator Rust is configured to use by default), and its
231 /// pointer points to [`len`] initialized elements in order (what you would see
232 /// if you coerced it to a slice), followed by [`capacity`]` - `[`len`]
233 /// logically uninitialized elements.
235 /// `Vec` will never perform a "small optimization" where elements are actually
236 /// stored on the stack for two reasons:
238 /// * It would make it more difficult for unsafe code to correctly manipulate
239 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
240 /// only moved, and it would be more difficult to determine if a `Vec` had
241 /// actually allocated memory.
243 /// * It would penalize the general case, incurring an additional branch
246 /// `Vec` will never automatically shrink itself, even if completely empty. This
247 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
248 /// and then filling it back up to the same [`len`] should incur no calls to
249 /// the allocator. If you wish to free up unused memory, use
250 /// [`shrink_to_fit`][`shrink_to_fit`].
252 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
253 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
254 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
255 /// accurate, and can be relied on. It can even be used to manually free the memory
256 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
257 /// when not necessary.
259 /// `Vec` does not guarantee any particular growth strategy when reallocating
260 /// when full, nor when [`reserve`] is called. The current strategy is basic
261 /// and it may prove desirable to use a non-constant growth factor. Whatever
262 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
264 /// `vec![x; n]`, `vec![a, b, c, d]`, and
265 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
266 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
267 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
268 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
270 /// `Vec` will not specifically overwrite any data that is removed from it,
271 /// but also won't specifically preserve it. Its uninitialized memory is
272 /// scratch space that it may use however it wants. It will generally just do
273 /// whatever is most efficient or otherwise easy to implement. Do not rely on
274 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
275 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
276 /// first, that may not actually happen because the optimizer does not consider
277 /// this a side-effect that must be preserved. There is one case which we will
278 /// not break, however: using `unsafe` code to write to the excess capacity,
279 /// and then increasing the length to match, is always valid.
281 /// `Vec` does not currently guarantee the order in which elements are dropped
282 /// (the order has changed in the past, and may change again).
284 /// [`vec!`]: ../../std/macro.vec.html
285 /// [`Index`]: ../../std/ops/trait.Index.html
286 /// [`String`]: ../../std/string/struct.String.html
287 /// [`&str`]: ../../std/primitive.str.html
288 /// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
289 /// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
290 /// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
291 /// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
292 /// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
293 /// [`len`]: ../../std/vec/struct.Vec.html#method.len
294 /// [`push`]: ../../std/vec/struct.Vec.html#method.push
295 /// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
296 /// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
297 /// [owned slice]: ../../std/boxed/struct.Box.html
298 #[stable(feature = "rust1", since = "1.0.0")]
304 ////////////////////////////////////////////////////////////////////////////////
306 ////////////////////////////////////////////////////////////////////////////////
309 /// Constructs a new, empty `Vec<T>`.
311 /// The vector will not allocate until elements are pushed onto it.
316 /// # #![allow(unused_mut)]
317 /// let mut vec: Vec<i32> = Vec::new();
320 #[stable(feature = "rust1", since = "1.0.0")]
321 pub fn new() -> Vec<T> {
328 /// Constructs a new, empty `Vec<T>` with the specified capacity.
330 /// The vector will be able to hold exactly `capacity` elements without
331 /// reallocating. If `capacity` is 0, the vector will not allocate.
333 /// It is important to note that this function does not specify the *length*
334 /// of the returned vector, but only the *capacity*. For an explanation of
335 /// the difference between length and capacity, see *[Capacity and reallocation]*.
337 /// [Capacity and reallocation]: #capacity-and-reallocation
342 /// let mut vec = Vec::with_capacity(10);
344 /// // The vector contains no items, even though it has capacity for more
345 /// assert_eq!(vec.len(), 0);
347 /// // These are all done without reallocating...
352 /// // ...but this may make the vector reallocate
356 #[stable(feature = "rust1", since = "1.0.0")]
357 pub fn with_capacity(capacity: usize) -> Vec<T> {
359 buf: RawVec::with_capacity(capacity),
364 /// Creates a `Vec<T>` directly from the raw components of another vector.
368 /// This is highly unsafe, due to the number of invariants that aren't
371 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
372 /// (at least, it's highly likely to be incorrect if it wasn't).
373 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
374 /// * `length` needs to be less than or equal to `capacity`.
375 /// * `capacity` needs to be the capacity that the pointer was allocated with.
377 /// Violating these may cause problems like corrupting the allocator's
378 /// internal data structures. For example it is **not** safe
379 /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
381 /// The ownership of `ptr` is effectively transferred to the
382 /// `Vec<T>` which may then deallocate, reallocate or change the
383 /// contents of memory pointed to by the pointer at will. Ensure
384 /// that nothing else uses the pointer after calling this
387 /// [`String`]: ../../std/string/struct.String.html
396 /// let mut v = vec![1, 2, 3];
398 /// // Pull out the various important pieces of information about `v`
399 /// let p = v.as_mut_ptr();
400 /// let len = v.len();
401 /// let cap = v.capacity();
404 /// // Cast `v` into the void: no destructor run, so we are in
405 /// // complete control of the allocation to which `p` points.
408 /// // Overwrite memory with 4, 5, 6
409 /// for i in 0..len as isize {
410 /// ptr::write(p.offset(i), 4 + i);
413 /// // Put everything back together into a Vec
414 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
415 /// assert_eq!(rebuilt, [4, 5, 6]);
419 #[stable(feature = "rust1", since = "1.0.0")]
420 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
422 buf: RawVec::from_raw_parts(ptr, capacity),
427 /// Returns the number of elements the vector can hold without
433 /// let vec: Vec<i32> = Vec::with_capacity(10);
434 /// assert_eq!(vec.capacity(), 10);
437 #[stable(feature = "rust1", since = "1.0.0")]
438 pub fn capacity(&self) -> usize {
442 /// Reserves capacity for at least `additional` more elements to be inserted
443 /// in the given `Vec<T>`. The collection may reserve more space to avoid
444 /// frequent reallocations. After calling `reserve`, capacity will be
445 /// greater than or equal to `self.len() + additional`. Does nothing if
446 /// capacity is already sufficient.
450 /// Panics if the new capacity overflows `usize`.
455 /// let mut vec = vec![1];
457 /// assert!(vec.capacity() >= 11);
459 #[stable(feature = "rust1", since = "1.0.0")]
460 pub fn reserve(&mut self, additional: usize) {
461 self.buf.reserve(self.len, additional);
464 /// Reserves the minimum capacity for exactly `additional` more elements to
465 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
466 /// capacity will be greater than or equal to `self.len() + additional`.
467 /// Does nothing if the capacity is already sufficient.
469 /// Note that the allocator may give the collection more space than it
470 /// requests. Therefore capacity can not be relied upon to be precisely
471 /// minimal. Prefer `reserve` if future insertions are expected.
475 /// Panics if the new capacity overflows `usize`.
480 /// let mut vec = vec![1];
481 /// vec.reserve_exact(10);
482 /// assert!(vec.capacity() >= 11);
484 #[stable(feature = "rust1", since = "1.0.0")]
485 pub fn reserve_exact(&mut self, additional: usize) {
486 self.buf.reserve_exact(self.len, additional);
489 /// Shrinks the capacity of the vector as much as possible.
491 /// It will drop down as close as possible to the length but the allocator
492 /// may still inform the vector that there is space for a few more elements.
497 /// let mut vec = Vec::with_capacity(10);
498 /// vec.extend([1, 2, 3].iter().cloned());
499 /// assert_eq!(vec.capacity(), 10);
500 /// vec.shrink_to_fit();
501 /// assert!(vec.capacity() >= 3);
503 #[stable(feature = "rust1", since = "1.0.0")]
504 pub fn shrink_to_fit(&mut self) {
505 self.buf.shrink_to_fit(self.len);
508 /// Converts the vector into [`Box<[T]>`][owned slice].
510 /// Note that this will drop any excess capacity.
512 /// [owned slice]: ../../std/boxed/struct.Box.html
517 /// let v = vec![1, 2, 3];
519 /// let slice = v.into_boxed_slice();
522 /// Any excess capacity is removed:
525 /// let mut vec = Vec::with_capacity(10);
526 /// vec.extend([1, 2, 3].iter().cloned());
528 /// assert_eq!(vec.capacity(), 10);
529 /// let slice = vec.into_boxed_slice();
530 /// assert_eq!(slice.into_vec().capacity(), 3);
532 #[stable(feature = "rust1", since = "1.0.0")]
533 pub fn into_boxed_slice(mut self) -> Box<[T]> {
535 self.shrink_to_fit();
536 let buf = ptr::read(&self.buf);
542 /// Shortens the vector, keeping the first `len` elements and dropping
545 /// If `len` is greater than the vector's current length, this has no
548 /// The [`drain`] method can emulate `truncate`, but causes the excess
549 /// elements to be returned instead of dropped.
551 /// Note that this method has no effect on the allocated capacity
556 /// Truncating a five element vector to two elements:
559 /// let mut vec = vec![1, 2, 3, 4, 5];
561 /// assert_eq!(vec, [1, 2]);
564 /// No truncation occurs when `len` is greater than the vector's current
568 /// let mut vec = vec![1, 2, 3];
570 /// assert_eq!(vec, [1, 2, 3]);
573 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
577 /// let mut vec = vec![1, 2, 3];
579 /// assert_eq!(vec, []);
582 /// [`clear`]: #method.clear
583 /// [`drain`]: #method.drain
584 #[stable(feature = "rust1", since = "1.0.0")]
585 pub fn truncate(&mut self, len: usize) {
587 // drop any extra elements
588 while len < self.len {
589 // decrement len before the drop_in_place(), so a panic on Drop
590 // doesn't re-drop the just-failed value.
593 ptr::drop_in_place(self.get_unchecked_mut(len));
598 /// Extracts a slice containing the entire vector.
600 /// Equivalent to `&s[..]`.
605 /// use std::io::{self, Write};
606 /// let buffer = vec![1, 2, 3, 5, 8];
607 /// io::sink().write(buffer.as_slice()).unwrap();
610 #[stable(feature = "vec_as_slice", since = "1.7.0")]
611 pub fn as_slice(&self) -> &[T] {
615 /// Extracts a mutable slice of the entire vector.
617 /// Equivalent to `&mut s[..]`.
622 /// use std::io::{self, Read};
623 /// let mut buffer = vec![0; 3];
624 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
627 #[stable(feature = "vec_as_slice", since = "1.7.0")]
628 pub fn as_mut_slice(&mut self) -> &mut [T] {
632 /// Sets the length of a vector.
634 /// This will explicitly set the size of the vector, without actually
635 /// modifying its buffers, so it is up to the caller to ensure that the
636 /// vector is actually the specified size.
643 /// let mut vec = vec!['r', 'u', 's', 't'];
646 /// ptr::drop_in_place(&mut vec[3]);
649 /// assert_eq!(vec, ['r', 'u', 's']);
652 /// In this example, there is a memory leak since the memory locations
653 /// owned by the inner vectors were not freed prior to the `set_len` call:
656 /// let mut vec = vec![vec![1, 0, 0],
664 /// In this example, the vector gets expanded from zero to four items
665 /// without any memory allocations occurring, resulting in vector
666 /// values of unallocated memory:
669 /// let mut vec: Vec<char> = Vec::new();
676 #[stable(feature = "rust1", since = "1.0.0")]
677 pub unsafe fn set_len(&mut self, len: usize) {
681 /// Removes an element from the vector and returns it.
683 /// The removed element is replaced by the last element of the vector.
685 /// This does not preserve ordering, but is O(1).
689 /// Panics if `index` is out of bounds.
694 /// let mut v = vec!["foo", "bar", "baz", "qux"];
696 /// assert_eq!(v.swap_remove(1), "bar");
697 /// assert_eq!(v, ["foo", "qux", "baz"]);
699 /// assert_eq!(v.swap_remove(0), "foo");
700 /// assert_eq!(v, ["baz", "qux"]);
703 #[stable(feature = "rust1", since = "1.0.0")]
704 pub fn swap_remove(&mut self, index: usize) -> T {
705 let length = self.len();
706 self.swap(index, length - 1);
710 /// Inserts an element at position `index` within the vector, shifting all
711 /// elements after it to the right.
715 /// Panics if `index` is out of bounds.
720 /// let mut vec = vec![1, 2, 3];
721 /// vec.insert(1, 4);
722 /// assert_eq!(vec, [1, 4, 2, 3]);
723 /// vec.insert(4, 5);
724 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
726 #[stable(feature = "rust1", since = "1.0.0")]
727 pub fn insert(&mut self, index: usize, element: T) {
728 let len = self.len();
729 assert!(index <= len);
731 // space for the new element
732 if len == self.buf.cap() {
738 // The spot to put the new value
740 let p = self.as_mut_ptr().offset(index as isize);
741 // Shift everything over to make space. (Duplicating the
742 // `index`th element into two consecutive places.)
743 ptr::copy(p, p.offset(1), len - index);
744 // Write it in, overwriting the first copy of the `index`th
746 ptr::write(p, element);
748 self.set_len(len + 1);
752 /// Removes and returns the element at position `index` within the vector,
753 /// shifting all elements after it to the left.
757 /// Panics if `index` is out of bounds.
762 /// let mut v = vec![1, 2, 3];
763 /// assert_eq!(v.remove(1), 2);
764 /// assert_eq!(v, [1, 3]);
766 #[stable(feature = "rust1", since = "1.0.0")]
767 pub fn remove(&mut self, index: usize) -> T {
768 let len = self.len();
769 assert!(index < len);
774 // the place we are taking from.
775 let ptr = self.as_mut_ptr().offset(index as isize);
776 // copy it out, unsafely having a copy of the value on
777 // the stack and in the vector at the same time.
778 ret = ptr::read(ptr);
780 // Shift everything down to fill in that spot.
781 ptr::copy(ptr.offset(1), ptr, len - index - 1);
783 self.set_len(len - 1);
788 /// Retains only the elements specified by the predicate.
790 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
791 /// This method operates in place and preserves the order of the retained
797 /// let mut vec = vec![1, 2, 3, 4];
798 /// vec.retain(|&x| x%2 == 0);
799 /// assert_eq!(vec, [2, 4]);
801 #[stable(feature = "rust1", since = "1.0.0")]
802 pub fn retain<F>(&mut self, mut f: F)
803 where F: FnMut(&T) -> bool
805 let len = self.len();
819 self.truncate(len - del);
823 /// Removes all but the first of consecutive elements in the vector that resolve to the same
826 /// If the vector is sorted, this removes all duplicates.
831 /// let mut vec = vec![10, 20, 21, 30, 20];
833 /// vec.dedup_by_key(|i| *i / 10);
835 /// assert_eq!(vec, [10, 20, 30, 20]);
837 #[stable(feature = "dedup_by", since = "1.16.0")]
839 pub fn dedup_by_key<F, K>(&mut self, mut key: F) where F: FnMut(&mut T) -> K, K: PartialEq {
840 self.dedup_by(|a, b| key(a) == key(b))
843 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
846 /// The `same_bucket` function is passed references to two elements from the vector, and
847 /// returns `true` if the elements compare equal, or `false` if they do not. The elements are
848 /// passed in opposite order from their order in the vector, so if `same_bucket(a, b)` returns
849 /// `true`, `a` is removed.
851 /// If the vector is sorted, this removes all duplicates.
856 /// use std::ascii::AsciiExt;
858 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
860 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
862 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
864 #[stable(feature = "dedup_by", since = "1.16.0")]
865 pub fn dedup_by<F>(&mut self, mut same_bucket: F) where F: FnMut(&mut T, &mut T) -> bool {
867 // Although we have a mutable reference to `self`, we cannot make
868 // *arbitrary* changes. The `same_bucket` calls could panic, so we
869 // must ensure that the vector is in a valid state at all time.
871 // The way that we handle this is by using swaps; we iterate
872 // over all the elements, swapping as we go so that at the end
873 // the elements we wish to keep are in the front, and those we
874 // wish to reject are at the back. We can then truncate the
875 // vector. This operation is still O(n).
877 // Example: We start in this state, where `r` represents "next
878 // read" and `w` represents "next_write`.
881 // +---+---+---+---+---+---+
882 // | 0 | 1 | 1 | 2 | 3 | 3 |
883 // +---+---+---+---+---+---+
886 // Comparing self[r] against self[w-1], this is not a duplicate, so
887 // we swap self[r] and self[w] (no effect as r==w) and then increment both
888 // r and w, leaving us with:
891 // +---+---+---+---+---+---+
892 // | 0 | 1 | 1 | 2 | 3 | 3 |
893 // +---+---+---+---+---+---+
896 // Comparing self[r] against self[w-1], this value is a duplicate,
897 // so we increment `r` but leave everything else unchanged:
900 // +---+---+---+---+---+---+
901 // | 0 | 1 | 1 | 2 | 3 | 3 |
902 // +---+---+---+---+---+---+
905 // Comparing self[r] against self[w-1], this is not a duplicate,
906 // so swap self[r] and self[w] and advance r and w:
909 // +---+---+---+---+---+---+
910 // | 0 | 1 | 2 | 1 | 3 | 3 |
911 // +---+---+---+---+---+---+
914 // Not a duplicate, repeat:
917 // +---+---+---+---+---+---+
918 // | 0 | 1 | 2 | 3 | 1 | 3 |
919 // +---+---+---+---+---+---+
922 // Duplicate, advance r. End of vec. Truncate to w.
929 // Avoid bounds checks by using raw pointers.
930 let p = self.as_mut_ptr();
931 let mut r: usize = 1;
932 let mut w: usize = 1;
935 let p_r = p.offset(r as isize);
936 let p_wm1 = p.offset((w - 1) as isize);
937 if !same_bucket(&mut *p_r, &mut *p_wm1) {
939 let p_w = p_wm1.offset(1);
940 mem::swap(&mut *p_r, &mut *p_w);
951 /// Appends an element to the back of a collection.
955 /// Panics if the number of elements in the vector overflows a `usize`.
960 /// let mut vec = vec![1, 2];
962 /// assert_eq!(vec, [1, 2, 3]);
965 #[stable(feature = "rust1", since = "1.0.0")]
966 pub fn push(&mut self, value: T) {
967 // This will panic or abort if we would allocate > isize::MAX bytes
968 // or if the length increment would overflow for zero-sized types.
969 if self.len == self.buf.cap() {
973 let end = self.as_mut_ptr().offset(self.len as isize);
974 ptr::write(end, value);
979 /// Returns a place for insertion at the back of the `Vec`.
981 /// Using this method with placement syntax is equivalent to [`push`](#method.push),
982 /// but may be more efficient.
987 /// #![feature(collection_placement)]
988 /// #![feature(placement_in_syntax)]
990 /// let mut vec = vec![1, 2];
991 /// vec.place_back() <- 3;
992 /// vec.place_back() <- 4;
993 /// assert_eq!(&vec, &[1, 2, 3, 4]);
995 #[unstable(feature = "collection_placement",
996 reason = "placement protocol is subject to change",
998 pub fn place_back(&mut self) -> PlaceBack<T> {
999 PlaceBack { vec: self }
1002 /// Removes the last element from a vector and returns it, or [`None`] if it
1005 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1010 /// let mut vec = vec![1, 2, 3];
1011 /// assert_eq!(vec.pop(), Some(3));
1012 /// assert_eq!(vec, [1, 2]);
1015 #[stable(feature = "rust1", since = "1.0.0")]
1016 pub fn pop(&mut self) -> Option<T> {
1022 Some(ptr::read(self.get_unchecked(self.len())))
1027 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1031 /// Panics if the number of elements in the vector overflows a `usize`.
1036 /// let mut vec = vec![1, 2, 3];
1037 /// let mut vec2 = vec![4, 5, 6];
1038 /// vec.append(&mut vec2);
1039 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1040 /// assert_eq!(vec2, []);
1043 #[stable(feature = "append", since = "1.4.0")]
1044 pub fn append(&mut self, other: &mut Self) {
1046 self.append_elements(other.as_slice() as _);
1051 /// Appends elements to `Self` from other buffer.
1053 unsafe fn append_elements(&mut self, other: *const [T]) {
1054 let count = (*other).len();
1055 self.reserve(count);
1056 let len = self.len();
1057 ptr::copy_nonoverlapping(other as *const T, self.get_unchecked_mut(len), count);
1061 /// Creates a draining iterator that removes the specified range in the vector
1062 /// and yields the removed items.
1064 /// Note 1: The element range is removed even if the iterator is only
1065 /// partially consumed or not consumed at all.
1067 /// Note 2: It is unspecified how many elements are removed from the vector
1068 /// if the `Drain` value is leaked.
1072 /// Panics if the starting point is greater than the end point or if
1073 /// the end point is greater than the length of the vector.
1078 /// let mut v = vec![1, 2, 3];
1079 /// let u: Vec<_> = v.drain(1..).collect();
1080 /// assert_eq!(v, &[1]);
1081 /// assert_eq!(u, &[2, 3]);
1083 /// // A full range clears the vector
1085 /// assert_eq!(v, &[]);
1087 #[stable(feature = "drain", since = "1.6.0")]
1088 pub fn drain<R>(&mut self, range: R) -> Drain<T>
1089 where R: RangeArgument<usize>
1093 // When the Drain is first created, it shortens the length of
1094 // the source vector to make sure no uninitalized or moved-from elements
1095 // are accessible at all if the Drain's destructor never gets to run.
1097 // Drain will ptr::read out the values to remove.
1098 // When finished, remaining tail of the vec is copied back to cover
1099 // the hole, and the vector length is restored to the new length.
1101 let len = self.len();
1102 let start = match range.start() {
1104 Excluded(&n) => n + 1,
1107 let end = match range.end() {
1108 Included(&n) => n + 1,
1112 assert!(start <= end);
1113 assert!(end <= len);
1116 // set self.vec length's to start, to be safe in case Drain is leaked
1117 self.set_len(start);
1118 // Use the borrow in the IterMut to indicate borrowing behavior of the
1119 // whole Drain iterator (like &mut T).
1120 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().offset(start as isize),
1124 tail_len: len - end,
1125 iter: range_slice.iter(),
1126 vec: Shared::from(self),
1131 /// Clears the vector, removing all values.
1133 /// Note that this method has no effect on the allocated capacity
1139 /// let mut v = vec![1, 2, 3];
1143 /// assert!(v.is_empty());
1146 #[stable(feature = "rust1", since = "1.0.0")]
1147 pub fn clear(&mut self) {
1151 /// Returns the number of elements in the vector, also referred to
1152 /// as its 'length'.
1157 /// let a = vec![1, 2, 3];
1158 /// assert_eq!(a.len(), 3);
1161 #[stable(feature = "rust1", since = "1.0.0")]
1162 pub fn len(&self) -> usize {
1166 /// Returns `true` if the vector contains no elements.
1171 /// let mut v = Vec::new();
1172 /// assert!(v.is_empty());
1175 /// assert!(!v.is_empty());
1177 #[stable(feature = "rust1", since = "1.0.0")]
1178 pub fn is_empty(&self) -> bool {
1182 /// Splits the collection into two at the given index.
1184 /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
1185 /// and the returned `Self` contains elements `[at, len)`.
1187 /// Note that the capacity of `self` does not change.
1191 /// Panics if `at > len`.
1196 /// let mut vec = vec![1,2,3];
1197 /// let vec2 = vec.split_off(1);
1198 /// assert_eq!(vec, [1]);
1199 /// assert_eq!(vec2, [2, 3]);
1202 #[stable(feature = "split_off", since = "1.4.0")]
1203 pub fn split_off(&mut self, at: usize) -> Self {
1204 assert!(at <= self.len(), "`at` out of bounds");
1206 let other_len = self.len - at;
1207 let mut other = Vec::with_capacity(other_len);
1209 // Unsafely `set_len` and copy items to `other`.
1212 other.set_len(other_len);
1214 ptr::copy_nonoverlapping(self.as_ptr().offset(at as isize),
1222 impl<T: Clone> Vec<T> {
1223 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1225 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1226 /// difference, with each additional slot filled with `value`.
1227 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1229 /// This method requires `Clone` to clone the passed value. If you'd
1230 /// rather create a value with `Default` instead, see [`resize_default`].
1235 /// let mut vec = vec!["hello"];
1236 /// vec.resize(3, "world");
1237 /// assert_eq!(vec, ["hello", "world", "world"]);
1239 /// let mut vec = vec![1, 2, 3, 4];
1240 /// vec.resize(2, 0);
1241 /// assert_eq!(vec, [1, 2]);
1244 /// [`resize_default`]: #method.resize_default
1245 #[stable(feature = "vec_resize", since = "1.5.0")]
1246 pub fn resize(&mut self, new_len: usize, value: T) {
1247 let len = self.len();
1250 self.extend_with(new_len - len, ExtendElement(value))
1252 self.truncate(new_len);
1256 /// Clones and appends all elements in a slice to the `Vec`.
1258 /// Iterates over the slice `other`, clones each element, and then appends
1259 /// it to this `Vec`. The `other` vector is traversed in-order.
1261 /// Note that this function is same as `extend` except that it is
1262 /// specialized to work with slices instead. If and when Rust gets
1263 /// specialization this function will likely be deprecated (but still
1269 /// let mut vec = vec![1];
1270 /// vec.extend_from_slice(&[2, 3, 4]);
1271 /// assert_eq!(vec, [1, 2, 3, 4]);
1273 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1274 pub fn extend_from_slice(&mut self, other: &[T]) {
1275 self.spec_extend(other.iter())
1279 impl<T: Default> Vec<T> {
1280 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1282 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1283 /// difference, with each additional slot filled with `Default::default()`.
1284 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1286 /// This method uses `Default` to create new values on every push. If
1287 /// you'd rather `Clone` a given value, use [`resize`].
1293 /// #![feature(vec_resize_default)]
1295 /// let mut vec = vec![1, 2, 3];
1296 /// vec.resize_default(5);
1297 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1299 /// let mut vec = vec![1, 2, 3, 4];
1300 /// vec.resize_default(2);
1301 /// assert_eq!(vec, [1, 2]);
1304 /// [`resize`]: #method.resize
1305 #[unstable(feature = "vec_resize_default", issue = "41758")]
1306 pub fn resize_default(&mut self, new_len: usize) {
1307 let len = self.len();
1310 self.extend_with(new_len - len, ExtendDefault);
1312 self.truncate(new_len);
1317 // This code generalises `extend_with_{element,default}`.
1318 trait ExtendWith<T> {
1319 fn next(&self) -> T;
1323 struct ExtendElement<T>(T);
1324 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1325 fn next(&self) -> T { self.0.clone() }
1326 fn last(self) -> T { self.0 }
1329 struct ExtendDefault;
1330 impl<T: Default> ExtendWith<T> for ExtendDefault {
1331 fn next(&self) -> T { Default::default() }
1332 fn last(self) -> T { Default::default() }
1335 /// Extend the vector by `n` values, using the given generator.
1336 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, value: E) {
1340 let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
1341 // Use SetLenOnDrop to work around bug where compiler
1342 // may not realize the store through `ptr` through self.set_len()
1344 let mut local_len = SetLenOnDrop::new(&mut self.len);
1346 // Write all elements except the last one
1348 ptr::write(ptr, value.next());
1349 ptr = ptr.offset(1);
1350 // Increment the length in every step in case next() panics
1351 local_len.increment_len(1);
1355 // We can write the last element directly without cloning needlessly
1356 ptr::write(ptr, value.last());
1357 local_len.increment_len(1);
1360 // len set by scope guard
1365 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1367 // The idea is: The length field in SetLenOnDrop is a local variable
1368 // that the optimizer will see does not alias with any stores through the Vec's data
1369 // pointer. This is a workaround for alias analysis issue #32155
1370 struct SetLenOnDrop<'a> {
1375 impl<'a> SetLenOnDrop<'a> {
1377 fn new(len: &'a mut usize) -> Self {
1378 SetLenOnDrop { local_len: *len, len: len }
1382 fn increment_len(&mut self, increment: usize) {
1383 self.local_len += increment;
1387 impl<'a> Drop for SetLenOnDrop<'a> {
1389 fn drop(&mut self) {
1390 *self.len = self.local_len;
1394 impl<T: PartialEq> Vec<T> {
1395 /// Removes consecutive repeated elements in the vector.
1397 /// If the vector is sorted, this removes all duplicates.
1402 /// let mut vec = vec![1, 2, 2, 3, 2];
1406 /// assert_eq!(vec, [1, 2, 3, 2]);
1408 #[stable(feature = "rust1", since = "1.0.0")]
1410 pub fn dedup(&mut self) {
1411 self.dedup_by(|a, b| a == b)
1414 /// Removes the first instance of `item` from the vector if the item exists.
1419 /// # #![feature(vec_remove_item)]
1420 /// let mut vec = vec![1, 2, 3, 1];
1422 /// vec.remove_item(&1);
1424 /// assert_eq!(vec, vec![2, 3, 1]);
1426 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1427 pub fn remove_item(&mut self, item: &T) -> Option<T> {
1428 let pos = match self.iter().position(|x| *x == *item) {
1430 None => return None,
1432 Some(self.remove(pos))
1436 ////////////////////////////////////////////////////////////////////////////////
1437 // Internal methods and functions
1438 ////////////////////////////////////////////////////////////////////////////////
1441 #[stable(feature = "rust1", since = "1.0.0")]
1442 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1443 <T as SpecFromElem>::from_elem(elem, n)
1446 // Specialization trait used for Vec::from_elem
1447 trait SpecFromElem: Sized {
1448 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1451 impl<T: Clone> SpecFromElem for T {
1452 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1453 let mut v = Vec::with_capacity(n);
1454 v.extend_with(n, ExtendElement(elem));
1459 impl SpecFromElem for u8 {
1461 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1464 buf: RawVec::with_capacity_zeroed(n),
1469 let mut v = Vec::with_capacity(n);
1470 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1477 macro_rules! impl_spec_from_elem {
1478 ($t: ty, $is_zero: expr) => {
1479 impl SpecFromElem for $t {
1481 fn from_elem(elem: $t, n: usize) -> Vec<$t> {
1484 buf: RawVec::with_capacity_zeroed(n),
1488 let mut v = Vec::with_capacity(n);
1489 v.extend_with(n, ExtendElement(elem));
1496 impl_spec_from_elem!(i8, |x| x == 0);
1497 impl_spec_from_elem!(i16, |x| x == 0);
1498 impl_spec_from_elem!(i32, |x| x == 0);
1499 impl_spec_from_elem!(i64, |x| x == 0);
1500 impl_spec_from_elem!(i128, |x| x == 0);
1501 impl_spec_from_elem!(isize, |x| x == 0);
1503 impl_spec_from_elem!(u16, |x| x == 0);
1504 impl_spec_from_elem!(u32, |x| x == 0);
1505 impl_spec_from_elem!(u64, |x| x == 0);
1506 impl_spec_from_elem!(u128, |x| x == 0);
1507 impl_spec_from_elem!(usize, |x| x == 0);
1509 impl_spec_from_elem!(f32, |x: f32| x == 0. && x.is_sign_positive());
1510 impl_spec_from_elem!(f64, |x: f64| x == 0. && x.is_sign_positive());
1512 ////////////////////////////////////////////////////////////////////////////////
1513 // Common trait implementations for Vec
1514 ////////////////////////////////////////////////////////////////////////////////
1516 #[stable(feature = "rust1", since = "1.0.0")]
1517 impl<T: Clone> Clone for Vec<T> {
1519 fn clone(&self) -> Vec<T> {
1520 <[T]>::to_vec(&**self)
1523 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1524 // required for this method definition, is not available. Instead use the
1525 // `slice::to_vec` function which is only available with cfg(test)
1526 // NB see the slice::hack module in slice.rs for more information
1528 fn clone(&self) -> Vec<T> {
1529 ::slice::to_vec(&**self)
1532 fn clone_from(&mut self, other: &Vec<T>) {
1533 other.as_slice().clone_into(self);
1537 #[stable(feature = "rust1", since = "1.0.0")]
1538 impl<T: Hash> Hash for Vec<T> {
1540 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1541 Hash::hash(&**self, state)
1545 #[stable(feature = "rust1", since = "1.0.0")]
1546 impl<T> Index<usize> for Vec<T> {
1550 fn index(&self, index: usize) -> &T {
1551 // NB built-in indexing via `&[T]`
1556 #[stable(feature = "rust1", since = "1.0.0")]
1557 impl<T> IndexMut<usize> for Vec<T> {
1559 fn index_mut(&mut self, index: usize) -> &mut T {
1560 // NB built-in indexing via `&mut [T]`
1561 &mut (**self)[index]
1566 #[stable(feature = "rust1", since = "1.0.0")]
1567 impl<T> ops::Index<ops::Range<usize>> for Vec<T> {
1571 fn index(&self, index: ops::Range<usize>) -> &[T] {
1572 Index::index(&**self, index)
1575 #[stable(feature = "rust1", since = "1.0.0")]
1576 impl<T> ops::Index<ops::RangeTo<usize>> for Vec<T> {
1580 fn index(&self, index: ops::RangeTo<usize>) -> &[T] {
1581 Index::index(&**self, index)
1584 #[stable(feature = "rust1", since = "1.0.0")]
1585 impl<T> ops::Index<ops::RangeFrom<usize>> for Vec<T> {
1589 fn index(&self, index: ops::RangeFrom<usize>) -> &[T] {
1590 Index::index(&**self, index)
1593 #[stable(feature = "rust1", since = "1.0.0")]
1594 impl<T> ops::Index<ops::RangeFull> for Vec<T> {
1598 fn index(&self, _index: ops::RangeFull) -> &[T] {
1602 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1603 impl<T> ops::Index<ops::RangeInclusive<usize>> for Vec<T> {
1607 fn index(&self, index: ops::RangeInclusive<usize>) -> &[T] {
1608 Index::index(&**self, index)
1611 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1612 impl<T> ops::Index<ops::RangeToInclusive<usize>> for Vec<T> {
1616 fn index(&self, index: ops::RangeToInclusive<usize>) -> &[T] {
1617 Index::index(&**self, index)
1621 #[stable(feature = "rust1", since = "1.0.0")]
1622 impl<T> ops::IndexMut<ops::Range<usize>> for Vec<T> {
1624 fn index_mut(&mut self, index: ops::Range<usize>) -> &mut [T] {
1625 IndexMut::index_mut(&mut **self, index)
1628 #[stable(feature = "rust1", since = "1.0.0")]
1629 impl<T> ops::IndexMut<ops::RangeTo<usize>> for Vec<T> {
1631 fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut [T] {
1632 IndexMut::index_mut(&mut **self, index)
1635 #[stable(feature = "rust1", since = "1.0.0")]
1636 impl<T> ops::IndexMut<ops::RangeFrom<usize>> for Vec<T> {
1638 fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut [T] {
1639 IndexMut::index_mut(&mut **self, index)
1642 #[stable(feature = "rust1", since = "1.0.0")]
1643 impl<T> ops::IndexMut<ops::RangeFull> for Vec<T> {
1645 fn index_mut(&mut self, _index: ops::RangeFull) -> &mut [T] {
1649 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1650 impl<T> ops::IndexMut<ops::RangeInclusive<usize>> for Vec<T> {
1652 fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut [T] {
1653 IndexMut::index_mut(&mut **self, index)
1656 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1657 impl<T> ops::IndexMut<ops::RangeToInclusive<usize>> for Vec<T> {
1659 fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut [T] {
1660 IndexMut::index_mut(&mut **self, index)
1664 #[stable(feature = "rust1", since = "1.0.0")]
1665 impl<T> ops::Deref for Vec<T> {
1668 fn deref(&self) -> &[T] {
1670 let p = self.buf.ptr();
1671 assume(!p.is_null());
1672 slice::from_raw_parts(p, self.len)
1677 #[stable(feature = "rust1", since = "1.0.0")]
1678 impl<T> ops::DerefMut for Vec<T> {
1679 fn deref_mut(&mut self) -> &mut [T] {
1681 let ptr = self.buf.ptr();
1682 assume(!ptr.is_null());
1683 slice::from_raw_parts_mut(ptr, self.len)
1688 #[stable(feature = "rust1", since = "1.0.0")]
1689 impl<T> FromIterator<T> for Vec<T> {
1691 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1692 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1696 #[stable(feature = "rust1", since = "1.0.0")]
1697 impl<T> IntoIterator for Vec<T> {
1699 type IntoIter = IntoIter<T>;
1701 /// Creates a consuming iterator, that is, one that moves each value out of
1702 /// the vector (from start to end). The vector cannot be used after calling
1708 /// let v = vec!["a".to_string(), "b".to_string()];
1709 /// for s in v.into_iter() {
1710 /// // s has type String, not &String
1711 /// println!("{}", s);
1715 fn into_iter(mut self) -> IntoIter<T> {
1717 let begin = self.as_mut_ptr();
1718 assume(!begin.is_null());
1719 let end = if mem::size_of::<T>() == 0 {
1720 arith_offset(begin as *const i8, self.len() as isize) as *const T
1722 begin.offset(self.len() as isize) as *const T
1724 let cap = self.buf.cap();
1727 buf: Shared::new_unchecked(begin),
1736 #[stable(feature = "rust1", since = "1.0.0")]
1737 impl<'a, T> IntoIterator for &'a Vec<T> {
1739 type IntoIter = slice::Iter<'a, T>;
1741 fn into_iter(self) -> slice::Iter<'a, T> {
1746 #[stable(feature = "rust1", since = "1.0.0")]
1747 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1748 type Item = &'a mut T;
1749 type IntoIter = slice::IterMut<'a, T>;
1751 fn into_iter(self) -> slice::IterMut<'a, T> {
1756 #[stable(feature = "rust1", since = "1.0.0")]
1757 impl<T> Extend<T> for Vec<T> {
1759 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1760 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1764 // Specialization trait used for Vec::from_iter and Vec::extend
1765 trait SpecExtend<T, I> {
1766 fn from_iter(iter: I) -> Self;
1767 fn spec_extend(&mut self, iter: I);
1770 impl<T, I> SpecExtend<T, I> for Vec<T>
1771 where I: Iterator<Item=T>,
1773 default fn from_iter(mut iterator: I) -> Self {
1774 // Unroll the first iteration, as the vector is going to be
1775 // expanded on this iteration in every case when the iterable is not
1776 // empty, but the loop in extend_desugared() is not going to see the
1777 // vector being full in the few subsequent loop iterations.
1778 // So we get better branch prediction.
1779 let mut vector = match iterator.next() {
1780 None => return Vec::new(),
1782 let (lower, _) = iterator.size_hint();
1783 let mut vector = Vec::with_capacity(lower.saturating_add(1));
1785 ptr::write(vector.get_unchecked_mut(0), element);
1791 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
1795 default fn spec_extend(&mut self, iter: I) {
1796 self.extend_desugared(iter)
1800 impl<T, I> SpecExtend<T, I> for Vec<T>
1801 where I: TrustedLen<Item=T>,
1803 default fn from_iter(iterator: I) -> Self {
1804 let mut vector = Vec::new();
1805 vector.spec_extend(iterator);
1809 default fn spec_extend(&mut self, iterator: I) {
1810 // This is the case for a TrustedLen iterator.
1811 let (low, high) = iterator.size_hint();
1812 if let Some(high_value) = high {
1813 debug_assert_eq!(low, high_value,
1814 "TrustedLen iterator's size hint is not exact: {:?}",
1817 if let Some(additional) = high {
1818 self.reserve(additional);
1820 let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
1821 let mut local_len = SetLenOnDrop::new(&mut self.len);
1822 for element in iterator {
1823 ptr::write(ptr, element);
1824 ptr = ptr.offset(1);
1825 // NB can't overflow since we would have had to alloc the address space
1826 local_len.increment_len(1);
1830 self.extend_desugared(iterator)
1835 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
1836 fn from_iter(iterator: IntoIter<T>) -> Self {
1837 // A common case is passing a vector into a function which immediately
1838 // re-collects into a vector. We can short circuit this if the IntoIter
1839 // has not been advanced at all.
1840 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
1842 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
1845 mem::forget(iterator);
1849 let mut vector = Vec::new();
1850 vector.spec_extend(iterator);
1855 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
1857 self.append_elements(iterator.as_slice() as _);
1859 iterator.ptr = iterator.end;
1863 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
1864 where I: Iterator<Item=&'a T>,
1867 default fn from_iter(iterator: I) -> Self {
1868 SpecExtend::from_iter(iterator.cloned())
1871 default fn spec_extend(&mut self, iterator: I) {
1872 self.spec_extend(iterator.cloned())
1876 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
1879 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
1880 let slice = iterator.as_slice();
1881 self.reserve(slice.len());
1883 let len = self.len();
1884 self.set_len(len + slice.len());
1885 self.get_unchecked_mut(len..).copy_from_slice(slice);
1891 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
1892 // This is the case for a general iterator.
1894 // This function should be the moral equivalent of:
1896 // for item in iterator {
1899 while let Some(element) = iterator.next() {
1900 let len = self.len();
1901 if len == self.capacity() {
1902 let (lower, _) = iterator.size_hint();
1903 self.reserve(lower.saturating_add(1));
1906 ptr::write(self.get_unchecked_mut(len), element);
1907 // NB can't overflow since we would have had to alloc the address space
1908 self.set_len(len + 1);
1913 /// Creates a splicing iterator that replaces the specified range in the vector
1914 /// with the given `replace_with` iterator and yields the removed items.
1915 /// `replace_with` does not need to be the same length as `range`.
1917 /// Note 1: The element range is removed even if the iterator is not
1918 /// consumed until the end.
1920 /// Note 2: It is unspecified how many elements are removed from the vector,
1921 /// if the `Splice` value is leaked.
1923 /// Note 3: The input iterator `replace_with` is only consumed
1924 /// when the `Splice` value is dropped.
1926 /// Note 4: This is optimal if:
1928 /// * The tail (elements in the vector after `range`) is empty,
1929 /// * or `replace_with` yields fewer elements than `range`’s length
1930 /// * or the lower bound of its `size_hint()` is exact.
1932 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
1936 /// Panics if the starting point is greater than the end point or if
1937 /// the end point is greater than the length of the vector.
1942 /// let mut v = vec![1, 2, 3];
1943 /// let new = [7, 8];
1944 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
1945 /// assert_eq!(v, &[7, 8, 3]);
1946 /// assert_eq!(u, &[1, 2]);
1949 #[stable(feature = "vec_splice", since = "1.21.0")]
1950 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<I::IntoIter>
1951 where R: RangeArgument<usize>, I: IntoIterator<Item=T>
1954 drain: self.drain(range),
1955 replace_with: replace_with.into_iter(),
1959 /// Creates an iterator which uses a closure to determine if an element should be removed.
1961 /// If the closure returns true, then the element is removed and yielded.
1962 /// If the closure returns false, it will try again, and call the closure
1963 /// on the next element, seeing if it passes the test.
1965 /// Using this method is equivalent to the following code:
1968 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
1969 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
1971 /// while i != vec.len() {
1972 /// if some_predicate(&mut vec[i]) {
1973 /// let val = vec.remove(i);
1974 /// // your code here
1980 /// # assert_eq!(vec, vec![1, 4, 5]);
1983 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
1984 /// because it can backshift the elements of the array in bulk.
1986 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
1987 /// regardless of whether you choose to keep or remove it.
1992 /// Splitting an array into evens and odds, reusing the original allocation:
1995 /// #![feature(drain_filter)]
1996 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
1998 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
1999 /// let odds = numbers;
2001 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2002 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2004 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2005 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<T, F>
2006 where F: FnMut(&mut T) -> bool,
2008 let old_len = self.len();
2010 // Guard against us getting leaked (leak amplification)
2011 unsafe { self.set_len(0); }
2023 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2025 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2026 /// append the entire slice at once.
2028 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2029 #[stable(feature = "extend_ref", since = "1.2.0")]
2030 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2031 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2032 self.spec_extend(iter.into_iter())
2036 macro_rules! __impl_slice_eq1 {
2037 ($Lhs: ty, $Rhs: ty) => {
2038 __impl_slice_eq1! { $Lhs, $Rhs, Sized }
2040 ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
2041 #[stable(feature = "rust1", since = "1.0.0")]
2042 impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
2044 fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
2046 fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
2051 __impl_slice_eq1! { Vec<A>, Vec<B> }
2052 __impl_slice_eq1! { Vec<A>, &'b [B] }
2053 __impl_slice_eq1! { Vec<A>, &'b mut [B] }
2054 __impl_slice_eq1! { Cow<'a, [A]>, &'b [B], Clone }
2055 __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B], Clone }
2056 __impl_slice_eq1! { Cow<'a, [A]>, Vec<B>, Clone }
2058 macro_rules! array_impls {
2061 // NOTE: some less important impls are omitted to reduce code bloat
2062 __impl_slice_eq1! { Vec<A>, [B; $N] }
2063 __impl_slice_eq1! { Vec<A>, &'b [B; $N] }
2064 // __impl_slice_eq1! { Vec<A>, &'b mut [B; $N] }
2065 // __impl_slice_eq1! { Cow<'a, [A]>, [B; $N], Clone }
2066 // __impl_slice_eq1! { Cow<'a, [A]>, &'b [B; $N], Clone }
2067 // __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B; $N], Clone }
2074 10 11 12 13 14 15 16 17 18 19
2075 20 21 22 23 24 25 26 27 28 29
2079 /// Implements comparison of vectors, lexicographically.
2080 #[stable(feature = "rust1", since = "1.0.0")]
2081 impl<T: PartialOrd> PartialOrd for Vec<T> {
2083 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2084 PartialOrd::partial_cmp(&**self, &**other)
2088 #[stable(feature = "rust1", since = "1.0.0")]
2089 impl<T: Eq> Eq for Vec<T> {}
2091 /// Implements ordering of vectors, lexicographically.
2092 #[stable(feature = "rust1", since = "1.0.0")]
2093 impl<T: Ord> Ord for Vec<T> {
2095 fn cmp(&self, other: &Vec<T>) -> Ordering {
2096 Ord::cmp(&**self, &**other)
2100 #[stable(feature = "rust1", since = "1.0.0")]
2101 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2102 fn drop(&mut self) {
2105 ptr::drop_in_place(&mut self[..]);
2107 // RawVec handles deallocation
2111 #[stable(feature = "rust1", since = "1.0.0")]
2112 impl<T> Default for Vec<T> {
2113 /// Creates an empty `Vec<T>`.
2114 fn default() -> Vec<T> {
2119 #[stable(feature = "rust1", since = "1.0.0")]
2120 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2121 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2122 fmt::Debug::fmt(&**self, f)
2126 #[stable(feature = "rust1", since = "1.0.0")]
2127 impl<T> AsRef<Vec<T>> for Vec<T> {
2128 fn as_ref(&self) -> &Vec<T> {
2133 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2134 impl<T> AsMut<Vec<T>> for Vec<T> {
2135 fn as_mut(&mut self) -> &mut Vec<T> {
2140 #[stable(feature = "rust1", since = "1.0.0")]
2141 impl<T> AsRef<[T]> for Vec<T> {
2142 fn as_ref(&self) -> &[T] {
2147 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2148 impl<T> AsMut<[T]> for Vec<T> {
2149 fn as_mut(&mut self) -> &mut [T] {
2154 #[stable(feature = "rust1", since = "1.0.0")]
2155 impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
2157 fn from(s: &'a [T]) -> Vec<T> {
2161 fn from(s: &'a [T]) -> Vec<T> {
2166 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2167 impl<'a, T: Clone> From<&'a mut [T]> for Vec<T> {
2169 fn from(s: &'a mut [T]) -> Vec<T> {
2173 fn from(s: &'a mut [T]) -> Vec<T> {
2178 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2179 impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
2180 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2185 // note: test pulls in libstd, which causes errors here
2187 #[stable(feature = "vec_from_box", since = "1.18.0")]
2188 impl<T> From<Box<[T]>> for Vec<T> {
2189 fn from(s: Box<[T]>) -> Vec<T> {
2194 // note: test pulls in libstd, which causes errors here
2196 #[stable(feature = "box_from_vec", since = "1.20.0")]
2197 impl<T> From<Vec<T>> for Box<[T]> {
2198 fn from(v: Vec<T>) -> Box<[T]> {
2199 v.into_boxed_slice()
2203 #[stable(feature = "rust1", since = "1.0.0")]
2204 impl<'a> From<&'a str> for Vec<u8> {
2205 fn from(s: &'a str) -> Vec<u8> {
2206 From::from(s.as_bytes())
2210 ////////////////////////////////////////////////////////////////////////////////
2212 ////////////////////////////////////////////////////////////////////////////////
2214 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2215 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2216 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2221 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2222 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2223 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2228 #[stable(feature = "rust1", since = "1.0.0")]
2229 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
2230 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2231 Cow::Owned(FromIterator::from_iter(it))
2235 ////////////////////////////////////////////////////////////////////////////////
2237 ////////////////////////////////////////////////////////////////////////////////
2239 /// An iterator that moves out of a vector.
2241 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
2242 /// by the [`IntoIterator`] trait).
2244 /// [`Vec`]: struct.Vec.html
2245 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2246 #[stable(feature = "rust1", since = "1.0.0")]
2247 pub struct IntoIter<T> {
2254 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2255 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2256 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2257 f.debug_tuple("IntoIter")
2258 .field(&self.as_slice())
2263 impl<T> IntoIter<T> {
2264 /// Returns the remaining items of this iterator as a slice.
2269 /// let vec = vec!['a', 'b', 'c'];
2270 /// let mut into_iter = vec.into_iter();
2271 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2272 /// let _ = into_iter.next().unwrap();
2273 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2275 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2276 pub fn as_slice(&self) -> &[T] {
2278 slice::from_raw_parts(self.ptr, self.len())
2282 /// Returns the remaining items of this iterator as a mutable slice.
2287 /// let vec = vec!['a', 'b', 'c'];
2288 /// let mut into_iter = vec.into_iter();
2289 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2290 /// into_iter.as_mut_slice()[2] = 'z';
2291 /// assert_eq!(into_iter.next().unwrap(), 'a');
2292 /// assert_eq!(into_iter.next().unwrap(), 'b');
2293 /// assert_eq!(into_iter.next().unwrap(), 'z');
2295 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2296 pub fn as_mut_slice(&mut self) -> &mut [T] {
2298 slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
2303 #[stable(feature = "rust1", since = "1.0.0")]
2304 unsafe impl<T: Send> Send for IntoIter<T> {}
2305 #[stable(feature = "rust1", since = "1.0.0")]
2306 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2308 #[stable(feature = "rust1", since = "1.0.0")]
2309 impl<T> Iterator for IntoIter<T> {
2313 fn next(&mut self) -> Option<T> {
2315 if self.ptr as *const _ == self.end {
2318 if mem::size_of::<T>() == 0 {
2319 // purposefully don't use 'ptr.offset' because for
2320 // vectors with 0-size elements this would return the
2322 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2324 // Use a non-null pointer value
2325 // (self.ptr might be null because of wrapping)
2326 Some(ptr::read(1 as *mut T))
2329 self.ptr = self.ptr.offset(1);
2331 Some(ptr::read(old))
2338 fn size_hint(&self) -> (usize, Option<usize>) {
2339 let exact = match self.ptr.offset_to(self.end) {
2340 Some(x) => x as usize,
2341 None => (self.end as usize).wrapping_sub(self.ptr as usize),
2343 (exact, Some(exact))
2347 fn count(self) -> usize {
2352 #[stable(feature = "rust1", since = "1.0.0")]
2353 impl<T> DoubleEndedIterator for IntoIter<T> {
2355 fn next_back(&mut self) -> Option<T> {
2357 if self.end == self.ptr {
2360 if mem::size_of::<T>() == 0 {
2361 // See above for why 'ptr.offset' isn't used
2362 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2364 // Use a non-null pointer value
2365 // (self.end might be null because of wrapping)
2366 Some(ptr::read(1 as *mut T))
2368 self.end = self.end.offset(-1);
2370 Some(ptr::read(self.end))
2377 #[stable(feature = "rust1", since = "1.0.0")]
2378 impl<T> ExactSizeIterator for IntoIter<T> {
2379 fn is_empty(&self) -> bool {
2380 self.ptr == self.end
2384 #[unstable(feature = "fused", issue = "35602")]
2385 impl<T> FusedIterator for IntoIter<T> {}
2387 #[unstable(feature = "trusted_len", issue = "37572")]
2388 unsafe impl<T> TrustedLen for IntoIter<T> {}
2390 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2391 impl<T: Clone> Clone for IntoIter<T> {
2392 fn clone(&self) -> IntoIter<T> {
2393 self.as_slice().to_owned().into_iter()
2397 #[stable(feature = "rust1", since = "1.0.0")]
2398 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2399 fn drop(&mut self) {
2400 // destroy the remaining elements
2401 for _x in self.by_ref() {}
2403 // RawVec handles deallocation
2404 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2408 /// A draining iterator for `Vec<T>`.
2410 /// This `struct` is created by the [`drain`] method on [`Vec`].
2412 /// [`drain`]: struct.Vec.html#method.drain
2413 /// [`Vec`]: struct.Vec.html
2414 #[stable(feature = "drain", since = "1.6.0")]
2415 pub struct Drain<'a, T: 'a> {
2416 /// Index of tail to preserve
2420 /// Current remaining range to remove
2421 iter: slice::Iter<'a, T>,
2422 vec: Shared<Vec<T>>,
2425 #[stable(feature = "collection_debug", since = "1.17.0")]
2426 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Drain<'a, T> {
2427 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2428 f.debug_tuple("Drain")
2429 .field(&self.iter.as_slice())
2434 #[stable(feature = "drain", since = "1.6.0")]
2435 unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
2436 #[stable(feature = "drain", since = "1.6.0")]
2437 unsafe impl<'a, T: Send> Send for Drain<'a, T> {}
2439 #[stable(feature = "drain", since = "1.6.0")]
2440 impl<'a, T> Iterator for Drain<'a, T> {
2444 fn next(&mut self) -> Option<T> {
2445 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2448 fn size_hint(&self) -> (usize, Option<usize>) {
2449 self.iter.size_hint()
2453 #[stable(feature = "drain", since = "1.6.0")]
2454 impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
2456 fn next_back(&mut self) -> Option<T> {
2457 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2461 #[stable(feature = "drain", since = "1.6.0")]
2462 impl<'a, T> Drop for Drain<'a, T> {
2463 fn drop(&mut self) {
2464 // exhaust self first
2465 while let Some(_) = self.next() {}
2467 if self.tail_len > 0 {
2469 let source_vec = self.vec.as_mut();
2470 // memmove back untouched tail, update to new length
2471 let start = source_vec.len();
2472 let tail = self.tail_start;
2473 let src = source_vec.as_ptr().offset(tail as isize);
2474 let dst = source_vec.as_mut_ptr().offset(start as isize);
2475 ptr::copy(src, dst, self.tail_len);
2476 source_vec.set_len(start + self.tail_len);
2483 #[stable(feature = "drain", since = "1.6.0")]
2484 impl<'a, T> ExactSizeIterator for Drain<'a, T> {
2485 fn is_empty(&self) -> bool {
2486 self.iter.is_empty()
2490 #[unstable(feature = "fused", issue = "35602")]
2491 impl<'a, T> FusedIterator for Drain<'a, T> {}
2493 /// A place for insertion at the back of a `Vec`.
2495 /// See [`Vec::place_back`](struct.Vec.html#method.place_back) for details.
2496 #[must_use = "places do nothing unless written to with `<-` syntax"]
2497 #[unstable(feature = "collection_placement",
2498 reason = "struct name and placement protocol are subject to change",
2501 pub struct PlaceBack<'a, T: 'a> {
2502 vec: &'a mut Vec<T>,
2505 #[unstable(feature = "collection_placement",
2506 reason = "placement protocol is subject to change",
2508 impl<'a, T> Placer<T> for PlaceBack<'a, T> {
2509 type Place = PlaceBack<'a, T>;
2511 fn make_place(self) -> Self {
2512 // This will panic or abort if we would allocate > isize::MAX bytes
2513 // or if the length increment would overflow for zero-sized types.
2514 if self.vec.len == self.vec.buf.cap() {
2515 self.vec.buf.double();
2521 #[unstable(feature = "collection_placement",
2522 reason = "placement protocol is subject to change",
2524 impl<'a, T> Place<T> for PlaceBack<'a, T> {
2525 fn pointer(&mut self) -> *mut T {
2526 unsafe { self.vec.as_mut_ptr().offset(self.vec.len as isize) }
2530 #[unstable(feature = "collection_placement",
2531 reason = "placement protocol is subject to change",
2533 impl<'a, T> InPlace<T> for PlaceBack<'a, T> {
2534 type Owner = &'a mut T;
2536 unsafe fn finalize(mut self) -> &'a mut T {
2537 let ptr = self.pointer();
2544 /// A splicing iterator for `Vec`.
2546 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2547 /// documentation for more.
2549 /// [`splice()`]: struct.Vec.html#method.splice
2550 /// [`Vec`]: struct.Vec.html
2552 #[stable(feature = "vec_splice", since = "1.21.0")]
2553 pub struct Splice<'a, I: Iterator + 'a> {
2554 drain: Drain<'a, I::Item>,
2558 #[stable(feature = "vec_splice", since = "1.21.0")]
2559 impl<'a, I: Iterator> Iterator for Splice<'a, I> {
2560 type Item = I::Item;
2562 fn next(&mut self) -> Option<Self::Item> {
2566 fn size_hint(&self) -> (usize, Option<usize>) {
2567 self.drain.size_hint()
2571 #[stable(feature = "vec_splice", since = "1.21.0")]
2572 impl<'a, I: Iterator> DoubleEndedIterator for Splice<'a, I> {
2573 fn next_back(&mut self) -> Option<Self::Item> {
2574 self.drain.next_back()
2578 #[stable(feature = "vec_splice", since = "1.21.0")]
2579 impl<'a, I: Iterator> ExactSizeIterator for Splice<'a, I> {}
2582 #[stable(feature = "vec_splice", since = "1.21.0")]
2583 impl<'a, I: Iterator> Drop for Splice<'a, I> {
2584 fn drop(&mut self) {
2585 // exhaust drain first
2586 while let Some(_) = self.drain.next() {}
2590 if self.drain.tail_len == 0 {
2591 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2595 // First fill the range left by drain().
2596 if !self.drain.fill(&mut self.replace_with) {
2600 // There may be more elements. Use the lower bound as an estimate.
2601 // FIXME: Is the upper bound a better guess? Or something else?
2602 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2603 if lower_bound > 0 {
2604 self.drain.move_tail(lower_bound);
2605 if !self.drain.fill(&mut self.replace_with) {
2610 // Collect any remaining elements.
2611 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2612 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2613 // Now we have an exact count.
2614 if collected.len() > 0 {
2615 self.drain.move_tail(collected.len());
2616 let filled = self.drain.fill(&mut collected);
2617 debug_assert!(filled);
2618 debug_assert_eq!(collected.len(), 0);
2621 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2625 /// Private helper methods for `Splice::drop`
2626 impl<'a, T> Drain<'a, T> {
2627 /// The range from `self.vec.len` to `self.tail_start` contains elements
2628 /// that have been moved out.
2629 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2630 /// Return whether we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2631 unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
2632 let vec = self.vec.as_mut();
2633 let range_start = vec.len;
2634 let range_end = self.tail_start;
2635 let range_slice = slice::from_raw_parts_mut(
2636 vec.as_mut_ptr().offset(range_start as isize),
2637 range_end - range_start);
2639 for place in range_slice {
2640 if let Some(new_item) = replace_with.next() {
2641 ptr::write(place, new_item);
2650 /// Make room for inserting more elements before the tail.
2651 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2652 let vec = self.vec.as_mut();
2653 let used_capacity = self.tail_start + self.tail_len;
2654 vec.buf.reserve(used_capacity, extra_capacity);
2656 let new_tail_start = self.tail_start + extra_capacity;
2657 let src = vec.as_ptr().offset(self.tail_start as isize);
2658 let dst = vec.as_mut_ptr().offset(new_tail_start as isize);
2659 ptr::copy(src, dst, self.tail_len);
2660 self.tail_start = new_tail_start;
2664 /// An iterator produced by calling `drain_filter` on Vec.
2665 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2667 pub struct DrainFilter<'a, T: 'a, F>
2668 where F: FnMut(&mut T) -> bool,
2670 vec: &'a mut Vec<T>,
2677 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2678 impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
2679 where F: FnMut(&mut T) -> bool,
2683 fn next(&mut self) -> Option<T> {
2685 while self.idx != self.old_len {
2688 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2689 if (self.pred)(&mut v[i]) {
2691 return Some(ptr::read(&v[i]));
2692 } else if self.del > 0 {
2694 let src: *const T = &v[i];
2695 let dst: *mut T = &mut v[i - del];
2696 // This is safe because self.vec has length 0
2697 // thus its elements will not have Drop::drop
2698 // called on them in the event of a panic.
2699 ptr::copy_nonoverlapping(src, dst, 1);
2706 fn size_hint(&self) -> (usize, Option<usize>) {
2707 (0, Some(self.old_len - self.idx))
2711 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2712 impl<'a, T, F> Drop for DrainFilter<'a, T, F>
2713 where F: FnMut(&mut T) -> bool,
2715 fn drop(&mut self) {
2716 for _ in self.by_ref() { }
2719 self.vec.set_len(self.old_len - self.del);