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::{self, Ordering};
71 use core::hash::{self, Hash};
72 use core::intrinsics::{arith_offset, assume};
73 use core::iter::{FromIterator, FusedIterator, TrustedLen};
74 use core::marker::PhantomData;
79 use core::ops::Bound::{Excluded, Included, Unbounded};
80 use core::ops::{Index, IndexMut, RangeBounds};
83 use core::ptr::NonNull;
86 use alloc::CollectionAllocErr;
92 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
97 /// let mut vec = Vec::new();
101 /// assert_eq!(vec.len(), 2);
102 /// assert_eq!(vec[0], 1);
104 /// assert_eq!(vec.pop(), Some(2));
105 /// assert_eq!(vec.len(), 1);
108 /// assert_eq!(vec[0], 7);
110 /// vec.extend([1, 2, 3].iter().cloned());
113 /// println!("{}", x);
115 /// assert_eq!(vec, [7, 1, 2, 3]);
118 /// The [`vec!`] macro is provided to make initialization more convenient:
121 /// let mut vec = vec![1, 2, 3];
123 /// assert_eq!(vec, [1, 2, 3, 4]);
126 /// It can also initialize each element of a `Vec<T>` with a given value:
129 /// let vec = vec![0; 5];
130 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
133 /// Use a `Vec<T>` as an efficient stack:
136 /// let mut stack = Vec::new();
142 /// while let Some(top) = stack.pop() {
143 /// // Prints 3, 2, 1
144 /// println!("{}", top);
150 /// The `Vec` type allows to access values by index, because it implements the
151 /// [`Index`] trait. An example will be more explicit:
154 /// let v = vec![0, 2, 4, 6];
155 /// println!("{}", v[1]); // it will display '2'
158 /// However be careful: if you try to access an index which isn't in the `Vec`,
159 /// your software will panic! You cannot do this:
162 /// let v = vec![0, 2, 4, 6];
163 /// println!("{}", v[6]); // it will panic!
166 /// In conclusion: always check if the index you want to get really exists
171 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
172 /// To get a slice, use `&`. Example:
175 /// fn read_slice(slice: &[usize]) {
179 /// let v = vec![0, 1];
182 /// // ... and that's all!
183 /// // you can also do it like this:
184 /// let x : &[usize] = &v;
187 /// In Rust, it's more common to pass slices as arguments rather than vectors
188 /// when you just want to provide a read access. The same goes for [`String`] and
191 /// # Capacity and reallocation
193 /// The capacity of a vector is the amount of space allocated for any future
194 /// elements that will be added onto the vector. This is not to be confused with
195 /// the *length* of a vector, which specifies the number of actual elements
196 /// within the vector. If a vector's length exceeds its capacity, its capacity
197 /// will automatically be increased, but its elements will have to be
200 /// For example, a vector with capacity 10 and length 0 would be an empty vector
201 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
202 /// vector will not change its capacity or cause reallocation to occur. However,
203 /// if the vector's length is increased to 11, it will have to reallocate, which
204 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
205 /// whenever possible to specify how big the vector is expected to get.
209 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
210 /// about its design. This ensures that it's as low-overhead as possible in
211 /// the general case, and can be correctly manipulated in primitive ways
212 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
213 /// If additional type parameters are added (e.g. to support custom allocators),
214 /// overriding their defaults may change the behavior.
216 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
217 /// triplet. No more, no less. The order of these fields is completely
218 /// unspecified, and you should use the appropriate methods to modify these.
219 /// The pointer will never be null, so this type is null-pointer-optimized.
221 /// However, the pointer may not actually point to allocated memory. In particular,
222 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
223 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
224 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
225 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
226 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
227 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
228 /// details are very subtle — if you intend to allocate memory using a `Vec`
229 /// and use it for something else (either to pass to unsafe code, or to build your
230 /// own memory-backed collection), be sure to deallocate this memory by using
231 /// `from_raw_parts` to recover the `Vec` and then dropping it.
233 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
234 /// (as defined by the allocator Rust is configured to use by default), and its
235 /// pointer points to [`len`] initialized, contiguous elements in order (what
236 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
237 /// `[`len`] logically uninitialized, contiguous elements.
239 /// `Vec` will never perform a "small optimization" where elements are actually
240 /// stored on the stack for two reasons:
242 /// * It would make it more difficult for unsafe code to correctly manipulate
243 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
244 /// only moved, and it would be more difficult to determine if a `Vec` had
245 /// actually allocated memory.
247 /// * It would penalize the general case, incurring an additional branch
250 /// `Vec` will never automatically shrink itself, even if completely empty. This
251 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
252 /// and then filling it back up to the same [`len`] should incur no calls to
253 /// the allocator. If you wish to free up unused memory, use
254 /// [`shrink_to_fit`][`shrink_to_fit`].
256 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
257 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
258 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
259 /// accurate, and can be relied on. It can even be used to manually free the memory
260 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
261 /// when not necessary.
263 /// `Vec` does not guarantee any particular growth strategy when reallocating
264 /// when full, nor when [`reserve`] is called. The current strategy is basic
265 /// and it may prove desirable to use a non-constant growth factor. Whatever
266 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
268 /// `vec![x; n]`, `vec![a, b, c, d]`, and
269 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
270 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
271 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
272 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
274 /// `Vec` will not specifically overwrite any data that is removed from it,
275 /// but also won't specifically preserve it. Its uninitialized memory is
276 /// scratch space that it may use however it wants. It will generally just do
277 /// whatever is most efficient or otherwise easy to implement. Do not rely on
278 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
279 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
280 /// first, that may not actually happen because the optimizer does not consider
281 /// this a side-effect that must be preserved. There is one case which we will
282 /// not break, however: using `unsafe` code to write to the excess capacity,
283 /// and then increasing the length to match, is always valid.
285 /// `Vec` does not currently guarantee the order in which elements are dropped.
286 /// The order has changed in the past and may change again.
288 /// [`vec!`]: ../../std/macro.vec.html
289 /// [`Index`]: ../../std/ops/trait.Index.html
290 /// [`String`]: ../../std/string/struct.String.html
291 /// [`&str`]: ../../std/primitive.str.html
292 /// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
293 /// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
294 /// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
295 /// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
296 /// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
297 /// [`len`]: ../../std/vec/struct.Vec.html#method.len
298 /// [`push`]: ../../std/vec/struct.Vec.html#method.push
299 /// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
300 /// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
301 /// [owned slice]: ../../std/boxed/struct.Box.html
302 #[stable(feature = "rust1", since = "1.0.0")]
308 ////////////////////////////////////////////////////////////////////////////////
310 ////////////////////////////////////////////////////////////////////////////////
313 /// Constructs a new, empty `Vec<T>`.
315 /// The vector will not allocate until elements are pushed onto it.
320 /// # #![allow(unused_mut)]
321 /// let mut vec: Vec<i32> = Vec::new();
324 #[stable(feature = "rust1", since = "1.0.0")]
325 pub fn new() -> Vec<T> {
332 /// Constructs a new, empty `Vec<T>` with the specified capacity.
334 /// The vector will be able to hold exactly `capacity` elements without
335 /// reallocating. If `capacity` is 0, the vector will not allocate.
337 /// It is important to note that although the returned vector has the
338 /// *capacity* specified, the vector will have a zero *length*. For an
339 /// explanation of the difference between length and capacity, see
340 /// *[Capacity and reallocation]*.
342 /// [Capacity and reallocation]: #capacity-and-reallocation
347 /// let mut vec = Vec::with_capacity(10);
349 /// // The vector contains no items, even though it has capacity for more
350 /// assert_eq!(vec.len(), 0);
352 /// // These are all done without reallocating...
357 /// // ...but this may make the vector reallocate
361 #[stable(feature = "rust1", since = "1.0.0")]
362 pub fn with_capacity(capacity: usize) -> Vec<T> {
364 buf: RawVec::with_capacity(capacity),
369 /// Creates a `Vec<T>` directly from the raw components of another vector.
373 /// This is highly unsafe, due to the number of invariants that aren't
376 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
377 /// (at least, it's highly likely to be incorrect if it wasn't).
378 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
379 /// * `length` needs to be less than or equal to `capacity`.
380 /// * `capacity` needs to be the capacity that the pointer was allocated with.
382 /// Violating these may cause problems like corrupting the allocator's
383 /// internal data structures. For example it is **not** safe
384 /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
386 /// The ownership of `ptr` is effectively transferred to the
387 /// `Vec<T>` which may then deallocate, reallocate or change the
388 /// contents of memory pointed to by the pointer at will. Ensure
389 /// that nothing else uses the pointer after calling this
392 /// [`String`]: ../../std/string/struct.String.html
401 /// let mut v = vec![1, 2, 3];
403 /// // Pull out the various important pieces of information about `v`
404 /// let p = v.as_mut_ptr();
405 /// let len = v.len();
406 /// let cap = v.capacity();
409 /// // Cast `v` into the void: no destructor run, so we are in
410 /// // complete control of the allocation to which `p` points.
413 /// // Overwrite memory with 4, 5, 6
414 /// for i in 0..len as isize {
415 /// ptr::write(p.offset(i), 4 + i);
418 /// // Put everything back together into a Vec
419 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
420 /// assert_eq!(rebuilt, [4, 5, 6]);
424 #[stable(feature = "rust1", since = "1.0.0")]
425 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
427 buf: RawVec::from_raw_parts(ptr, capacity),
432 /// Returns the number of elements the vector can hold without
438 /// let vec: Vec<i32> = Vec::with_capacity(10);
439 /// assert_eq!(vec.capacity(), 10);
442 #[stable(feature = "rust1", since = "1.0.0")]
443 pub fn capacity(&self) -> usize {
447 /// Reserves capacity for at least `additional` more elements to be inserted
448 /// in the given `Vec<T>`. The collection may reserve more space to avoid
449 /// frequent reallocations. After calling `reserve`, capacity will be
450 /// greater than or equal to `self.len() + additional`. Does nothing if
451 /// capacity is already sufficient.
455 /// Panics if the new capacity overflows `usize`.
460 /// let mut vec = vec![1];
462 /// assert!(vec.capacity() >= 11);
464 #[stable(feature = "rust1", since = "1.0.0")]
465 pub fn reserve(&mut self, additional: usize) {
466 self.buf.reserve(self.len, additional);
469 /// Reserves the minimum capacity for exactly `additional` more elements to
470 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
471 /// capacity will be greater than or equal to `self.len() + additional`.
472 /// Does nothing if the capacity is already sufficient.
474 /// Note that the allocator may give the collection more space than it
475 /// requests. Therefore capacity can not be relied upon to be precisely
476 /// minimal. Prefer `reserve` if future insertions are expected.
480 /// Panics if the new capacity overflows `usize`.
485 /// let mut vec = vec![1];
486 /// vec.reserve_exact(10);
487 /// assert!(vec.capacity() >= 11);
489 #[stable(feature = "rust1", since = "1.0.0")]
490 pub fn reserve_exact(&mut self, additional: usize) {
491 self.buf.reserve_exact(self.len, additional);
494 /// Tries to reserve capacity for at least `additional` more elements to be inserted
495 /// in the given `Vec<T>`. The collection may reserve more space to avoid
496 /// frequent reallocations. After calling `reserve`, capacity will be
497 /// greater than or equal to `self.len() + additional`. Does nothing if
498 /// capacity is already sufficient.
502 /// If the capacity overflows, or the allocator reports a failure, then an error
508 /// #![feature(try_reserve)]
509 /// use std::collections::CollectionAllocErr;
511 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
512 /// let mut output = Vec::new();
514 /// // Pre-reserve the memory, exiting if we can't
515 /// output.try_reserve(data.len())?;
517 /// // Now we know this can't OOM in the middle of our complex work
518 /// output.extend(data.iter().map(|&val| {
519 /// val * 2 + 5 // very complicated
524 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
526 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
527 pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
528 self.buf.try_reserve(self.len, additional)
531 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
532 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
533 /// capacity will be greater than or equal to `self.len() + additional`.
534 /// Does nothing if the capacity is already sufficient.
536 /// Note that the allocator may give the collection more space than it
537 /// requests. Therefore capacity can not be relied upon to be precisely
538 /// minimal. Prefer `reserve` if future insertions are expected.
542 /// If the capacity overflows, or the allocator reports a failure, then an error
548 /// #![feature(try_reserve)]
549 /// use std::collections::CollectionAllocErr;
551 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
552 /// let mut output = Vec::new();
554 /// // Pre-reserve the memory, exiting if we can't
555 /// output.try_reserve(data.len())?;
557 /// // Now we know this can't OOM in the middle of our complex work
558 /// output.extend(data.iter().map(|&val| {
559 /// val * 2 + 5 // very complicated
564 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
566 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
567 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
568 self.buf.try_reserve_exact(self.len, additional)
571 /// Shrinks the capacity of the vector as much as possible.
573 /// It will drop down as close as possible to the length but the allocator
574 /// may still inform the vector that there is space for a few more elements.
579 /// let mut vec = Vec::with_capacity(10);
580 /// vec.extend([1, 2, 3].iter().cloned());
581 /// assert_eq!(vec.capacity(), 10);
582 /// vec.shrink_to_fit();
583 /// assert!(vec.capacity() >= 3);
585 #[stable(feature = "rust1", since = "1.0.0")]
586 pub fn shrink_to_fit(&mut self) {
587 if self.capacity() != self.len {
588 self.buf.shrink_to_fit(self.len);
592 /// Shrinks the capacity of the vector with a lower bound.
594 /// The capacity will remain at least as large as both the length
595 /// and the supplied value.
597 /// Panics if the current capacity is smaller than the supplied
598 /// minimum capacity.
603 /// #![feature(shrink_to)]
604 /// let mut vec = Vec::with_capacity(10);
605 /// vec.extend([1, 2, 3].iter().cloned());
606 /// assert_eq!(vec.capacity(), 10);
607 /// vec.shrink_to(4);
608 /// assert!(vec.capacity() >= 4);
609 /// vec.shrink_to(0);
610 /// assert!(vec.capacity() >= 3);
612 #[unstable(feature = "shrink_to", reason = "new API", issue="0")]
613 pub fn shrink_to(&mut self, min_capacity: usize) {
614 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
617 /// Converts the vector into [`Box<[T]>`][owned slice].
619 /// Note that this will drop any excess capacity.
621 /// [owned slice]: ../../std/boxed/struct.Box.html
626 /// let v = vec![1, 2, 3];
628 /// let slice = v.into_boxed_slice();
631 /// Any excess capacity is removed:
634 /// let mut vec = Vec::with_capacity(10);
635 /// vec.extend([1, 2, 3].iter().cloned());
637 /// assert_eq!(vec.capacity(), 10);
638 /// let slice = vec.into_boxed_slice();
639 /// assert_eq!(slice.into_vec().capacity(), 3);
641 #[stable(feature = "rust1", since = "1.0.0")]
642 pub fn into_boxed_slice(mut self) -> Box<[T]> {
644 self.shrink_to_fit();
645 let buf = ptr::read(&self.buf);
651 /// Shortens the vector, keeping the first `len` elements and dropping
654 /// If `len` is greater than the vector's current length, this has no
657 /// The [`drain`] method can emulate `truncate`, but causes the excess
658 /// elements to be returned instead of dropped.
660 /// Note that this method has no effect on the allocated capacity
665 /// Truncating a five element vector to two elements:
668 /// let mut vec = vec![1, 2, 3, 4, 5];
670 /// assert_eq!(vec, [1, 2]);
673 /// No truncation occurs when `len` is greater than the vector's current
677 /// let mut vec = vec![1, 2, 3];
679 /// assert_eq!(vec, [1, 2, 3]);
682 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
686 /// let mut vec = vec![1, 2, 3];
688 /// assert_eq!(vec, []);
691 /// [`clear`]: #method.clear
692 /// [`drain`]: #method.drain
693 #[stable(feature = "rust1", since = "1.0.0")]
694 pub fn truncate(&mut self, len: usize) {
696 // drop any extra elements
697 while len < self.len {
698 // decrement len before the drop_in_place(), so a panic on Drop
699 // doesn't re-drop the just-failed value.
702 ptr::drop_in_place(self.get_unchecked_mut(len));
707 /// Extracts a slice containing the entire vector.
709 /// Equivalent to `&s[..]`.
714 /// use std::io::{self, Write};
715 /// let buffer = vec![1, 2, 3, 5, 8];
716 /// io::sink().write(buffer.as_slice()).unwrap();
719 #[stable(feature = "vec_as_slice", since = "1.7.0")]
720 pub fn as_slice(&self) -> &[T] {
724 /// Extracts a mutable slice of the entire vector.
726 /// Equivalent to `&mut s[..]`.
731 /// use std::io::{self, Read};
732 /// let mut buffer = vec![0; 3];
733 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
736 #[stable(feature = "vec_as_slice", since = "1.7.0")]
737 pub fn as_mut_slice(&mut self) -> &mut [T] {
741 /// Sets the length of a vector.
743 /// This will explicitly set the size of the vector, without actually
744 /// modifying its buffers, so it is up to the caller to ensure that the
745 /// vector is actually the specified size.
752 /// let mut vec = vec!['r', 'u', 's', 't'];
755 /// ptr::drop_in_place(&mut vec[3]);
758 /// assert_eq!(vec, ['r', 'u', 's']);
761 /// In this example, there is a memory leak since the memory locations
762 /// owned by the inner vectors were not freed prior to the `set_len` call:
765 /// let mut vec = vec![vec![1, 0, 0],
773 /// In this example, the vector gets expanded from zero to four items
774 /// without any memory allocations occurring, resulting in vector
775 /// values of unallocated memory:
778 /// let mut vec: Vec<char> = Vec::new();
785 #[stable(feature = "rust1", since = "1.0.0")]
786 pub unsafe fn set_len(&mut self, len: usize) {
790 /// Removes an element from the vector and returns it.
792 /// The removed element is replaced by the last element of the vector.
794 /// This does not preserve ordering, but is O(1).
798 /// Panics if `index` is out of bounds.
803 /// let mut v = vec!["foo", "bar", "baz", "qux"];
805 /// assert_eq!(v.swap_remove(1), "bar");
806 /// assert_eq!(v, ["foo", "qux", "baz"]);
808 /// assert_eq!(v.swap_remove(0), "foo");
809 /// assert_eq!(v, ["baz", "qux"]);
812 #[stable(feature = "rust1", since = "1.0.0")]
813 pub fn swap_remove(&mut self, index: usize) -> T {
814 let length = self.len();
815 self.swap(index, length - 1);
819 /// Inserts an element at position `index` within the vector, shifting all
820 /// elements after it to the right.
824 /// Panics if `index > len`.
829 /// let mut vec = vec![1, 2, 3];
830 /// vec.insert(1, 4);
831 /// assert_eq!(vec, [1, 4, 2, 3]);
832 /// vec.insert(4, 5);
833 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
835 #[stable(feature = "rust1", since = "1.0.0")]
836 pub fn insert(&mut self, index: usize, element: T) {
837 let len = self.len();
838 assert!(index <= len);
840 // space for the new element
841 if len == self.buf.cap() {
847 // The spot to put the new value
849 let p = self.as_mut_ptr().offset(index as isize);
850 // Shift everything over to make space. (Duplicating the
851 // `index`th element into two consecutive places.)
852 ptr::copy(p, p.offset(1), len - index);
853 // Write it in, overwriting the first copy of the `index`th
855 ptr::write(p, element);
857 self.set_len(len + 1);
861 /// Removes and returns the element at position `index` within the vector,
862 /// shifting all elements after it to the left.
866 /// Panics if `index` is out of bounds.
871 /// let mut v = vec![1, 2, 3];
872 /// assert_eq!(v.remove(1), 2);
873 /// assert_eq!(v, [1, 3]);
875 #[stable(feature = "rust1", since = "1.0.0")]
876 pub fn remove(&mut self, index: usize) -> T {
877 let len = self.len();
878 assert!(index < len);
883 // the place we are taking from.
884 let ptr = self.as_mut_ptr().offset(index as isize);
885 // copy it out, unsafely having a copy of the value on
886 // the stack and in the vector at the same time.
887 ret = ptr::read(ptr);
889 // Shift everything down to fill in that spot.
890 ptr::copy(ptr.offset(1), ptr, len - index - 1);
892 self.set_len(len - 1);
897 /// Retains only the elements specified by the predicate.
899 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
900 /// This method operates in place and preserves the order of the retained
906 /// let mut vec = vec![1, 2, 3, 4];
907 /// vec.retain(|&x| x%2 == 0);
908 /// assert_eq!(vec, [2, 4]);
910 #[stable(feature = "rust1", since = "1.0.0")]
911 pub fn retain<F>(&mut self, mut f: F)
912 where F: FnMut(&T) -> bool
914 self.drain_filter(|x| !f(x));
917 /// Removes all but the first of consecutive elements in the vector that resolve to the same
920 /// If the vector is sorted, this removes all duplicates.
925 /// let mut vec = vec![10, 20, 21, 30, 20];
927 /// vec.dedup_by_key(|i| *i / 10);
929 /// assert_eq!(vec, [10, 20, 30, 20]);
931 #[stable(feature = "dedup_by", since = "1.16.0")]
933 pub fn dedup_by_key<F, K>(&mut self, mut key: F) where F: FnMut(&mut T) -> K, K: PartialEq {
934 self.dedup_by(|a, b| key(a) == key(b))
937 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
940 /// The `same_bucket` function is passed references to two elements from the vector, and
941 /// returns `true` if the elements compare equal, or `false` if they do not. The elements are
942 /// passed in opposite order from their order in the vector, so if `same_bucket(a, b)` returns
943 /// `true`, `a` is removed.
945 /// If the vector is sorted, this removes all duplicates.
950 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
952 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
954 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
956 #[stable(feature = "dedup_by", since = "1.16.0")]
957 pub fn dedup_by<F>(&mut self, mut same_bucket: F) where F: FnMut(&mut T, &mut T) -> bool {
959 // Although we have a mutable reference to `self`, we cannot make
960 // *arbitrary* changes. The `same_bucket` calls could panic, so we
961 // must ensure that the vector is in a valid state at all time.
963 // The way that we handle this is by using swaps; we iterate
964 // over all the elements, swapping as we go so that at the end
965 // the elements we wish to keep are in the front, and those we
966 // wish to reject are at the back. We can then truncate the
967 // vector. This operation is still O(n).
969 // Example: We start in this state, where `r` represents "next
970 // read" and `w` represents "next_write`.
973 // +---+---+---+---+---+---+
974 // | 0 | 1 | 1 | 2 | 3 | 3 |
975 // +---+---+---+---+---+---+
978 // Comparing self[r] against self[w-1], this is not a duplicate, so
979 // we swap self[r] and self[w] (no effect as r==w) and then increment both
980 // r and w, leaving us with:
983 // +---+---+---+---+---+---+
984 // | 0 | 1 | 1 | 2 | 3 | 3 |
985 // +---+---+---+---+---+---+
988 // Comparing self[r] against self[w-1], this value is a duplicate,
989 // so we increment `r` but leave everything else unchanged:
992 // +---+---+---+---+---+---+
993 // | 0 | 1 | 1 | 2 | 3 | 3 |
994 // +---+---+---+---+---+---+
997 // Comparing self[r] against self[w-1], this is not a duplicate,
998 // so swap self[r] and self[w] and advance r and w:
1001 // +---+---+---+---+---+---+
1002 // | 0 | 1 | 2 | 1 | 3 | 3 |
1003 // +---+---+---+---+---+---+
1006 // Not a duplicate, repeat:
1009 // +---+---+---+---+---+---+
1010 // | 0 | 1 | 2 | 3 | 1 | 3 |
1011 // +---+---+---+---+---+---+
1014 // Duplicate, advance r. End of vec. Truncate to w.
1016 let ln = self.len();
1021 // Avoid bounds checks by using raw pointers.
1022 let p = self.as_mut_ptr();
1023 let mut r: usize = 1;
1024 let mut w: usize = 1;
1027 let p_r = p.offset(r as isize);
1028 let p_wm1 = p.offset((w - 1) as isize);
1029 if !same_bucket(&mut *p_r, &mut *p_wm1) {
1031 let p_w = p_wm1.offset(1);
1032 mem::swap(&mut *p_r, &mut *p_w);
1043 /// Appends an element to the back of a collection.
1047 /// Panics if the number of elements in the vector overflows a `usize`.
1052 /// let mut vec = vec![1, 2];
1054 /// assert_eq!(vec, [1, 2, 3]);
1057 #[stable(feature = "rust1", since = "1.0.0")]
1058 pub fn push(&mut self, value: T) {
1059 // This will panic or abort if we would allocate > isize::MAX bytes
1060 // or if the length increment would overflow for zero-sized types.
1061 if self.len == self.buf.cap() {
1065 let end = self.as_mut_ptr().offset(self.len as isize);
1066 ptr::write(end, value);
1071 /// Removes the last element from a vector and returns it, or [`None`] if it
1074 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1079 /// let mut vec = vec![1, 2, 3];
1080 /// assert_eq!(vec.pop(), Some(3));
1081 /// assert_eq!(vec, [1, 2]);
1084 #[stable(feature = "rust1", since = "1.0.0")]
1085 pub fn pop(&mut self) -> Option<T> {
1091 Some(ptr::read(self.get_unchecked(self.len())))
1096 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1100 /// Panics if the number of elements in the vector overflows a `usize`.
1105 /// let mut vec = vec![1, 2, 3];
1106 /// let mut vec2 = vec![4, 5, 6];
1107 /// vec.append(&mut vec2);
1108 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1109 /// assert_eq!(vec2, []);
1112 #[stable(feature = "append", since = "1.4.0")]
1113 pub fn append(&mut self, other: &mut Self) {
1115 self.append_elements(other.as_slice() as _);
1120 /// Appends elements to `Self` from other buffer.
1122 unsafe fn append_elements(&mut self, other: *const [T]) {
1123 let count = (*other).len();
1124 self.reserve(count);
1125 let len = self.len();
1126 ptr::copy_nonoverlapping(other as *const T, self.get_unchecked_mut(len), count);
1130 /// Creates a draining iterator that removes the specified range in the vector
1131 /// and yields the removed items.
1133 /// Note 1: The element range is removed even if the iterator is only
1134 /// partially consumed or not consumed at all.
1136 /// Note 2: It is unspecified how many elements are removed from the vector
1137 /// if the `Drain` value is leaked.
1141 /// Panics if the starting point is greater than the end point or if
1142 /// the end point is greater than the length of the vector.
1147 /// let mut v = vec![1, 2, 3];
1148 /// let u: Vec<_> = v.drain(1..).collect();
1149 /// assert_eq!(v, &[1]);
1150 /// assert_eq!(u, &[2, 3]);
1152 /// // A full range clears the vector
1154 /// assert_eq!(v, &[]);
1156 #[stable(feature = "drain", since = "1.6.0")]
1157 pub fn drain<R>(&mut self, range: R) -> Drain<T>
1158 where R: RangeBounds<usize>
1162 // When the Drain is first created, it shortens the length of
1163 // the source vector to make sure no uninitialized or moved-from elements
1164 // are accessible at all if the Drain's destructor never gets to run.
1166 // Drain will ptr::read out the values to remove.
1167 // When finished, remaining tail of the vec is copied back to cover
1168 // the hole, and the vector length is restored to the new length.
1170 let len = self.len();
1171 let start = match range.start() {
1173 Excluded(&n) => n + 1,
1176 let end = match range.end() {
1177 Included(&n) => n + 1,
1181 assert!(start <= end);
1182 assert!(end <= len);
1185 // set self.vec length's to start, to be safe in case Drain is leaked
1186 self.set_len(start);
1187 // Use the borrow in the IterMut to indicate borrowing behavior of the
1188 // whole Drain iterator (like &mut T).
1189 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().offset(start as isize),
1193 tail_len: len - end,
1194 iter: range_slice.iter(),
1195 vec: NonNull::from(self),
1200 /// Clears the vector, removing all values.
1202 /// Note that this method has no effect on the allocated capacity
1208 /// let mut v = vec![1, 2, 3];
1212 /// assert!(v.is_empty());
1215 #[stable(feature = "rust1", since = "1.0.0")]
1216 pub fn clear(&mut self) {
1220 /// Returns the number of elements in the vector, also referred to
1221 /// as its 'length'.
1226 /// let a = vec![1, 2, 3];
1227 /// assert_eq!(a.len(), 3);
1230 #[stable(feature = "rust1", since = "1.0.0")]
1231 pub fn len(&self) -> usize {
1235 /// Returns `true` if the vector contains no elements.
1240 /// let mut v = Vec::new();
1241 /// assert!(v.is_empty());
1244 /// assert!(!v.is_empty());
1246 #[stable(feature = "rust1", since = "1.0.0")]
1247 pub fn is_empty(&self) -> bool {
1251 /// Splits the collection into two at the given index.
1253 /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
1254 /// and the returned `Self` contains elements `[at, len)`.
1256 /// Note that the capacity of `self` does not change.
1260 /// Panics if `at > len`.
1265 /// let mut vec = vec![1,2,3];
1266 /// let vec2 = vec.split_off(1);
1267 /// assert_eq!(vec, [1]);
1268 /// assert_eq!(vec2, [2, 3]);
1271 #[stable(feature = "split_off", since = "1.4.0")]
1272 pub fn split_off(&mut self, at: usize) -> Self {
1273 assert!(at <= self.len(), "`at` out of bounds");
1275 let other_len = self.len - at;
1276 let mut other = Vec::with_capacity(other_len);
1278 // Unsafely `set_len` and copy items to `other`.
1281 other.set_len(other_len);
1283 ptr::copy_nonoverlapping(self.as_ptr().offset(at as isize),
1290 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1292 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1293 /// difference, with each additional slot filled with the result of
1294 /// calling the closure `f`. The return values from `f` will end up
1295 /// in the `Vec` in the order they have been generated.
1297 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1299 /// This method uses a closure to create new values on every push. If
1300 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1301 /// to use the [`Default`] trait to generate values, you can pass
1302 /// [`Default::default()`] as the second argument..
1307 /// #![feature(vec_resize_with)]
1309 /// let mut vec = vec![1, 2, 3];
1310 /// vec.resize_with(5, Default::default);
1311 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1313 /// let mut vec = vec![];
1315 /// vec.resize_with(4, || { p *= 2; p });
1316 /// assert_eq!(vec, [2, 4, 8, 16]);
1319 /// [`resize`]: #method.resize
1320 /// [`Clone`]: ../../std/clone/trait.Clone.html
1321 #[unstable(feature = "vec_resize_with", issue = "41758")]
1322 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1323 where F: FnMut() -> T
1325 let len = self.len();
1327 self.extend_with(new_len - len, ExtendFunc(f));
1329 self.truncate(new_len);
1334 impl<T: Clone> Vec<T> {
1335 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1337 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1338 /// difference, with each additional slot filled with `value`.
1339 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1341 /// This method requires [`Clone`] to be able clone the passed value. If
1342 /// you need more flexibility (or want to rely on [`Default`] instead of
1343 /// [`Clone`]), use [`resize_with`].
1348 /// let mut vec = vec!["hello"];
1349 /// vec.resize(3, "world");
1350 /// assert_eq!(vec, ["hello", "world", "world"]);
1352 /// let mut vec = vec![1, 2, 3, 4];
1353 /// vec.resize(2, 0);
1354 /// assert_eq!(vec, [1, 2]);
1357 /// [`Clone`]: ../../std/clone/trait.Clone.html
1358 /// [`Default`]: ../../std/default/trait.Default.html
1359 /// [`resize_with`]: #method.resize_with
1360 #[stable(feature = "vec_resize", since = "1.5.0")]
1361 pub fn resize(&mut self, new_len: usize, value: T) {
1362 let len = self.len();
1365 self.extend_with(new_len - len, ExtendElement(value))
1367 self.truncate(new_len);
1371 /// Clones and appends all elements in a slice to the `Vec`.
1373 /// Iterates over the slice `other`, clones each element, and then appends
1374 /// it to this `Vec`. The `other` vector is traversed in-order.
1376 /// Note that this function is same as [`extend`] except that it is
1377 /// specialized to work with slices instead. If and when Rust gets
1378 /// specialization this function will likely be deprecated (but still
1384 /// let mut vec = vec![1];
1385 /// vec.extend_from_slice(&[2, 3, 4]);
1386 /// assert_eq!(vec, [1, 2, 3, 4]);
1389 /// [`extend`]: #method.extend
1390 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1391 pub fn extend_from_slice(&mut self, other: &[T]) {
1392 self.spec_extend(other.iter())
1396 impl<T: Default> Vec<T> {
1397 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1399 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1400 /// difference, with each additional slot filled with [`Default::default()`].
1401 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1403 /// This method uses [`Default`] to create new values on every push. If
1404 /// you'd rather [`Clone`] a given value, use [`resize`].
1409 /// #![feature(vec_resize_default)]
1411 /// let mut vec = vec![1, 2, 3];
1412 /// vec.resize_default(5);
1413 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1415 /// let mut vec = vec![1, 2, 3, 4];
1416 /// vec.resize_default(2);
1417 /// assert_eq!(vec, [1, 2]);
1420 /// [`resize`]: #method.resize
1421 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1422 /// [`Default`]: ../../std/default/trait.Default.html
1423 /// [`Clone`]: ../../std/clone/trait.Clone.html
1424 #[unstable(feature = "vec_resize_default", issue = "41758")]
1425 pub fn resize_default(&mut self, new_len: usize) {
1426 let len = self.len();
1429 self.extend_with(new_len - len, ExtendDefault);
1431 self.truncate(new_len);
1436 // This code generalises `extend_with_{element,default}`.
1437 trait ExtendWith<T> {
1438 fn next(&mut self) -> T;
1442 struct ExtendElement<T>(T);
1443 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1444 fn next(&mut self) -> T { self.0.clone() }
1445 fn last(self) -> T { self.0 }
1448 struct ExtendDefault;
1449 impl<T: Default> ExtendWith<T> for ExtendDefault {
1450 fn next(&mut self) -> T { Default::default() }
1451 fn last(self) -> T { Default::default() }
1454 struct ExtendFunc<F>(F);
1455 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1456 fn next(&mut self) -> T { (self.0)() }
1457 fn last(mut self) -> T { (self.0)() }
1461 /// Extend the vector by `n` values, using the given generator.
1462 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1466 let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
1467 // Use SetLenOnDrop to work around bug where compiler
1468 // may not realize the store through `ptr` through self.set_len()
1470 let mut local_len = SetLenOnDrop::new(&mut self.len);
1472 // Write all elements except the last one
1474 ptr::write(ptr, value.next());
1475 ptr = ptr.offset(1);
1476 // Increment the length in every step in case next() panics
1477 local_len.increment_len(1);
1481 // We can write the last element directly without cloning needlessly
1482 ptr::write(ptr, value.last());
1483 local_len.increment_len(1);
1486 // len set by scope guard
1491 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1493 // The idea is: The length field in SetLenOnDrop is a local variable
1494 // that the optimizer will see does not alias with any stores through the Vec's data
1495 // pointer. This is a workaround for alias analysis issue #32155
1496 struct SetLenOnDrop<'a> {
1501 impl<'a> SetLenOnDrop<'a> {
1503 fn new(len: &'a mut usize) -> Self {
1504 SetLenOnDrop { local_len: *len, len: len }
1508 fn increment_len(&mut self, increment: usize) {
1509 self.local_len += increment;
1513 impl<'a> Drop for SetLenOnDrop<'a> {
1515 fn drop(&mut self) {
1516 *self.len = self.local_len;
1520 impl<T: PartialEq> Vec<T> {
1521 /// Removes consecutive repeated elements in the vector.
1523 /// If the vector is sorted, this removes all duplicates.
1528 /// let mut vec = vec![1, 2, 2, 3, 2];
1532 /// assert_eq!(vec, [1, 2, 3, 2]);
1534 #[stable(feature = "rust1", since = "1.0.0")]
1536 pub fn dedup(&mut self) {
1537 self.dedup_by(|a, b| a == b)
1540 /// Removes the first instance of `item` from the vector if the item exists.
1545 /// # #![feature(vec_remove_item)]
1546 /// let mut vec = vec![1, 2, 3, 1];
1548 /// vec.remove_item(&1);
1550 /// assert_eq!(vec, vec![2, 3, 1]);
1552 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1553 pub fn remove_item(&mut self, item: &T) -> Option<T> {
1554 let pos = self.iter().position(|x| *x == *item)?;
1555 Some(self.remove(pos))
1559 ////////////////////////////////////////////////////////////////////////////////
1560 // Internal methods and functions
1561 ////////////////////////////////////////////////////////////////////////////////
1564 #[stable(feature = "rust1", since = "1.0.0")]
1565 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1566 <T as SpecFromElem>::from_elem(elem, n)
1569 // Specialization trait used for Vec::from_elem
1570 trait SpecFromElem: Sized {
1571 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1574 impl<T: Clone> SpecFromElem for T {
1575 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1576 let mut v = Vec::with_capacity(n);
1577 v.extend_with(n, ExtendElement(elem));
1582 impl SpecFromElem for u8 {
1584 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1587 buf: RawVec::with_capacity_zeroed(n),
1592 let mut v = Vec::with_capacity(n);
1593 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1600 impl<T: Clone + IsZero> SpecFromElem for T {
1602 fn from_elem(elem: T, n: usize) -> Vec<T> {
1605 buf: RawVec::with_capacity_zeroed(n),
1609 let mut v = Vec::with_capacity(n);
1610 v.extend_with(n, ExtendElement(elem));
1615 unsafe trait IsZero {
1616 /// Whether this value is zero
1617 fn is_zero(&self) -> bool;
1620 macro_rules! impl_is_zero {
1621 ($t: ty, $is_zero: expr) => {
1622 unsafe impl IsZero for $t {
1624 fn is_zero(&self) -> bool {
1631 impl_is_zero!(i8, |x| x == 0);
1632 impl_is_zero!(i16, |x| x == 0);
1633 impl_is_zero!(i32, |x| x == 0);
1634 impl_is_zero!(i64, |x| x == 0);
1635 impl_is_zero!(i128, |x| x == 0);
1636 impl_is_zero!(isize, |x| x == 0);
1638 impl_is_zero!(u16, |x| x == 0);
1639 impl_is_zero!(u32, |x| x == 0);
1640 impl_is_zero!(u64, |x| x == 0);
1641 impl_is_zero!(u128, |x| x == 0);
1642 impl_is_zero!(usize, |x| x == 0);
1644 impl_is_zero!(char, |x| x == '\0');
1646 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1647 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1649 unsafe impl<T: ?Sized> IsZero for *const T {
1651 fn is_zero(&self) -> bool {
1656 unsafe impl<T: ?Sized> IsZero for *mut T {
1658 fn is_zero(&self) -> bool {
1664 ////////////////////////////////////////////////////////////////////////////////
1665 // Common trait implementations for Vec
1666 ////////////////////////////////////////////////////////////////////////////////
1668 #[stable(feature = "rust1", since = "1.0.0")]
1669 impl<T: Clone> Clone for Vec<T> {
1671 fn clone(&self) -> Vec<T> {
1672 <[T]>::to_vec(&**self)
1675 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1676 // required for this method definition, is not available. Instead use the
1677 // `slice::to_vec` function which is only available with cfg(test)
1678 // NB see the slice::hack module in slice.rs for more information
1680 fn clone(&self) -> Vec<T> {
1681 ::slice::to_vec(&**self)
1684 fn clone_from(&mut self, other: &Vec<T>) {
1685 other.as_slice().clone_into(self);
1689 #[stable(feature = "rust1", since = "1.0.0")]
1690 impl<T: Hash> Hash for Vec<T> {
1692 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1693 Hash::hash(&**self, state)
1697 #[stable(feature = "rust1", since = "1.0.0")]
1698 #[rustc_on_unimplemented = "vector indices are of type `usize` or ranges of `usize`"]
1699 impl<T, I> Index<I> for Vec<T>
1701 I: ::core::slice::SliceIndex<[T]>,
1703 type Output = I::Output;
1706 fn index(&self, index: I) -> &Self::Output {
1707 Index::index(&**self, index)
1711 #[stable(feature = "rust1", since = "1.0.0")]
1712 #[rustc_on_unimplemented = "vector indices are of type `usize` or ranges of `usize`"]
1713 impl<T, I> IndexMut<I> for Vec<T>
1715 I: ::core::slice::SliceIndex<[T]>,
1718 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1719 IndexMut::index_mut(&mut **self, index)
1723 #[stable(feature = "rust1", since = "1.0.0")]
1724 impl<T> ops::Deref for Vec<T> {
1727 fn deref(&self) -> &[T] {
1729 let p = self.buf.ptr();
1730 assume(!p.is_null());
1731 slice::from_raw_parts(p, self.len)
1736 #[stable(feature = "rust1", since = "1.0.0")]
1737 impl<T> ops::DerefMut for Vec<T> {
1738 fn deref_mut(&mut self) -> &mut [T] {
1740 let ptr = self.buf.ptr();
1741 assume(!ptr.is_null());
1742 slice::from_raw_parts_mut(ptr, self.len)
1747 #[stable(feature = "rust1", since = "1.0.0")]
1748 impl<T> FromIterator<T> for Vec<T> {
1750 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1751 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1755 #[stable(feature = "rust1", since = "1.0.0")]
1756 impl<T> IntoIterator for Vec<T> {
1758 type IntoIter = IntoIter<T>;
1760 /// Creates a consuming iterator, that is, one that moves each value out of
1761 /// the vector (from start to end). The vector cannot be used after calling
1767 /// let v = vec!["a".to_string(), "b".to_string()];
1768 /// for s in v.into_iter() {
1769 /// // s has type String, not &String
1770 /// println!("{}", s);
1774 fn into_iter(mut self) -> IntoIter<T> {
1776 let begin = self.as_mut_ptr();
1777 assume(!begin.is_null());
1778 let end = if mem::size_of::<T>() == 0 {
1779 arith_offset(begin as *const i8, self.len() as isize) as *const T
1781 begin.offset(self.len() as isize) as *const T
1783 let cap = self.buf.cap();
1786 buf: NonNull::new_unchecked(begin),
1787 phantom: PhantomData,
1796 #[stable(feature = "rust1", since = "1.0.0")]
1797 impl<'a, T> IntoIterator for &'a Vec<T> {
1799 type IntoIter = slice::Iter<'a, T>;
1801 fn into_iter(self) -> slice::Iter<'a, T> {
1806 #[stable(feature = "rust1", since = "1.0.0")]
1807 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1808 type Item = &'a mut T;
1809 type IntoIter = slice::IterMut<'a, T>;
1811 fn into_iter(self) -> slice::IterMut<'a, T> {
1816 #[stable(feature = "rust1", since = "1.0.0")]
1817 impl<T> Extend<T> for Vec<T> {
1819 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1820 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1824 // Specialization trait used for Vec::from_iter and Vec::extend
1825 trait SpecExtend<T, I> {
1826 fn from_iter(iter: I) -> Self;
1827 fn spec_extend(&mut self, iter: I);
1830 impl<T, I> SpecExtend<T, I> for Vec<T>
1831 where I: Iterator<Item=T>,
1833 default fn from_iter(mut iterator: I) -> Self {
1834 // Unroll the first iteration, as the vector is going to be
1835 // expanded on this iteration in every case when the iterable is not
1836 // empty, but the loop in extend_desugared() is not going to see the
1837 // vector being full in the few subsequent loop iterations.
1838 // So we get better branch prediction.
1839 let mut vector = match iterator.next() {
1840 None => return Vec::new(),
1842 let (lower, _) = iterator.size_hint();
1843 let mut vector = Vec::with_capacity(lower.saturating_add(1));
1845 ptr::write(vector.get_unchecked_mut(0), element);
1851 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
1855 default fn spec_extend(&mut self, iter: I) {
1856 self.extend_desugared(iter)
1860 impl<T, I> SpecExtend<T, I> for Vec<T>
1861 where I: TrustedLen<Item=T>,
1863 default fn from_iter(iterator: I) -> Self {
1864 let mut vector = Vec::new();
1865 vector.spec_extend(iterator);
1869 default fn spec_extend(&mut self, iterator: I) {
1870 // This is the case for a TrustedLen iterator.
1871 let (low, high) = iterator.size_hint();
1872 if let Some(high_value) = high {
1873 debug_assert_eq!(low, high_value,
1874 "TrustedLen iterator's size hint is not exact: {:?}",
1877 if let Some(additional) = high {
1878 self.reserve(additional);
1880 let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
1881 let mut local_len = SetLenOnDrop::new(&mut self.len);
1882 for element in iterator {
1883 ptr::write(ptr, element);
1884 ptr = ptr.offset(1);
1885 // NB can't overflow since we would have had to alloc the address space
1886 local_len.increment_len(1);
1890 self.extend_desugared(iterator)
1895 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
1896 fn from_iter(iterator: IntoIter<T>) -> Self {
1897 // A common case is passing a vector into a function which immediately
1898 // re-collects into a vector. We can short circuit this if the IntoIter
1899 // has not been advanced at all.
1900 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
1902 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
1905 mem::forget(iterator);
1909 let mut vector = Vec::new();
1910 vector.spec_extend(iterator);
1915 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
1917 self.append_elements(iterator.as_slice() as _);
1919 iterator.ptr = iterator.end;
1923 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
1924 where I: Iterator<Item=&'a T>,
1927 default fn from_iter(iterator: I) -> Self {
1928 SpecExtend::from_iter(iterator.cloned())
1931 default fn spec_extend(&mut self, iterator: I) {
1932 self.spec_extend(iterator.cloned())
1936 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
1939 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
1940 let slice = iterator.as_slice();
1941 self.reserve(slice.len());
1943 let len = self.len();
1944 self.set_len(len + slice.len());
1945 self.get_unchecked_mut(len..).copy_from_slice(slice);
1951 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
1952 // This is the case for a general iterator.
1954 // This function should be the moral equivalent of:
1956 // for item in iterator {
1959 while let Some(element) = iterator.next() {
1960 let len = self.len();
1961 if len == self.capacity() {
1962 let (lower, _) = iterator.size_hint();
1963 self.reserve(lower.saturating_add(1));
1966 ptr::write(self.get_unchecked_mut(len), element);
1967 // NB can't overflow since we would have had to alloc the address space
1968 self.set_len(len + 1);
1973 /// Creates a splicing iterator that replaces the specified range in the vector
1974 /// with the given `replace_with` iterator and yields the removed items.
1975 /// `replace_with` does not need to be the same length as `range`.
1977 /// Note 1: The element range is removed even if the iterator is not
1978 /// consumed until the end.
1980 /// Note 2: It is unspecified how many elements are removed from the vector,
1981 /// if the `Splice` value is leaked.
1983 /// Note 3: The input iterator `replace_with` is only consumed
1984 /// when the `Splice` value is dropped.
1986 /// Note 4: This is optimal if:
1988 /// * The tail (elements in the vector after `range`) is empty,
1989 /// * or `replace_with` yields fewer elements than `range`’s length
1990 /// * or the lower bound of its `size_hint()` is exact.
1992 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
1996 /// Panics if the starting point is greater than the end point or if
1997 /// the end point is greater than the length of the vector.
2002 /// let mut v = vec![1, 2, 3];
2003 /// let new = [7, 8];
2004 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2005 /// assert_eq!(v, &[7, 8, 3]);
2006 /// assert_eq!(u, &[1, 2]);
2009 #[stable(feature = "vec_splice", since = "1.21.0")]
2010 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<I::IntoIter>
2011 where R: RangeBounds<usize>, I: IntoIterator<Item=T>
2014 drain: self.drain(range),
2015 replace_with: replace_with.into_iter(),
2019 /// Creates an iterator which uses a closure to determine if an element should be removed.
2021 /// If the closure returns true, then the element is removed and yielded.
2022 /// If the closure returns false, the element will remain in the vector and will not be yielded
2023 /// by the iterator.
2025 /// Using this method is equivalent to the following code:
2028 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2029 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2031 /// while i != vec.len() {
2032 /// if some_predicate(&mut vec[i]) {
2033 /// let val = vec.remove(i);
2034 /// // your code here
2040 /// # assert_eq!(vec, vec![1, 4, 5]);
2043 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2044 /// because it can backshift the elements of the array in bulk.
2046 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2047 /// regardless of whether you choose to keep or remove it.
2052 /// Splitting an array into evens and odds, reusing the original allocation:
2055 /// #![feature(drain_filter)]
2056 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2058 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2059 /// let odds = numbers;
2061 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2062 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2064 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2065 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<T, F>
2066 where F: FnMut(&mut T) -> bool,
2068 let old_len = self.len();
2070 // Guard against us getting leaked (leak amplification)
2071 unsafe { self.set_len(0); }
2083 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2085 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2086 /// append the entire slice at once.
2088 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2089 #[stable(feature = "extend_ref", since = "1.2.0")]
2090 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2091 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2092 self.spec_extend(iter.into_iter())
2096 macro_rules! __impl_slice_eq1 {
2097 ($Lhs: ty, $Rhs: ty) => {
2098 __impl_slice_eq1! { $Lhs, $Rhs, Sized }
2100 ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
2101 #[stable(feature = "rust1", since = "1.0.0")]
2102 impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
2104 fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
2106 fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
2111 __impl_slice_eq1! { Vec<A>, Vec<B> }
2112 __impl_slice_eq1! { Vec<A>, &'b [B] }
2113 __impl_slice_eq1! { Vec<A>, &'b mut [B] }
2114 __impl_slice_eq1! { Cow<'a, [A]>, &'b [B], Clone }
2115 __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B], Clone }
2116 __impl_slice_eq1! { Cow<'a, [A]>, Vec<B>, Clone }
2118 macro_rules! array_impls {
2121 // NOTE: some less important impls are omitted to reduce code bloat
2122 __impl_slice_eq1! { Vec<A>, [B; $N] }
2123 __impl_slice_eq1! { Vec<A>, &'b [B; $N] }
2124 // __impl_slice_eq1! { Vec<A>, &'b mut [B; $N] }
2125 // __impl_slice_eq1! { Cow<'a, [A]>, [B; $N], Clone }
2126 // __impl_slice_eq1! { Cow<'a, [A]>, &'b [B; $N], Clone }
2127 // __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B; $N], Clone }
2134 10 11 12 13 14 15 16 17 18 19
2135 20 21 22 23 24 25 26 27 28 29
2139 /// Implements comparison of vectors, lexicographically.
2140 #[stable(feature = "rust1", since = "1.0.0")]
2141 impl<T: PartialOrd> PartialOrd for Vec<T> {
2143 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2144 PartialOrd::partial_cmp(&**self, &**other)
2148 #[stable(feature = "rust1", since = "1.0.0")]
2149 impl<T: Eq> Eq for Vec<T> {}
2151 /// Implements ordering of vectors, lexicographically.
2152 #[stable(feature = "rust1", since = "1.0.0")]
2153 impl<T: Ord> Ord for Vec<T> {
2155 fn cmp(&self, other: &Vec<T>) -> Ordering {
2156 Ord::cmp(&**self, &**other)
2160 #[stable(feature = "rust1", since = "1.0.0")]
2161 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2162 fn drop(&mut self) {
2165 ptr::drop_in_place(&mut self[..]);
2167 // RawVec handles deallocation
2171 #[stable(feature = "rust1", since = "1.0.0")]
2172 impl<T> Default for Vec<T> {
2173 /// Creates an empty `Vec<T>`.
2174 fn default() -> Vec<T> {
2179 #[stable(feature = "rust1", since = "1.0.0")]
2180 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2181 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2182 fmt::Debug::fmt(&**self, f)
2186 #[stable(feature = "rust1", since = "1.0.0")]
2187 impl<T> AsRef<Vec<T>> for Vec<T> {
2188 fn as_ref(&self) -> &Vec<T> {
2193 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2194 impl<T> AsMut<Vec<T>> for Vec<T> {
2195 fn as_mut(&mut self) -> &mut Vec<T> {
2200 #[stable(feature = "rust1", since = "1.0.0")]
2201 impl<T> AsRef<[T]> for Vec<T> {
2202 fn as_ref(&self) -> &[T] {
2207 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2208 impl<T> AsMut<[T]> for Vec<T> {
2209 fn as_mut(&mut self) -> &mut [T] {
2214 #[stable(feature = "rust1", since = "1.0.0")]
2215 impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
2217 fn from(s: &'a [T]) -> Vec<T> {
2221 fn from(s: &'a [T]) -> Vec<T> {
2226 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2227 impl<'a, T: Clone> From<&'a mut [T]> for Vec<T> {
2229 fn from(s: &'a mut [T]) -> Vec<T> {
2233 fn from(s: &'a mut [T]) -> Vec<T> {
2238 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2239 impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
2240 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2245 // note: test pulls in libstd, which causes errors here
2247 #[stable(feature = "vec_from_box", since = "1.18.0")]
2248 impl<T> From<Box<[T]>> for Vec<T> {
2249 fn from(s: Box<[T]>) -> Vec<T> {
2254 // note: test pulls in libstd, which causes errors here
2256 #[stable(feature = "box_from_vec", since = "1.20.0")]
2257 impl<T> From<Vec<T>> for Box<[T]> {
2258 fn from(v: Vec<T>) -> Box<[T]> {
2259 v.into_boxed_slice()
2263 #[stable(feature = "rust1", since = "1.0.0")]
2264 impl<'a> From<&'a str> for Vec<u8> {
2265 fn from(s: &'a str) -> Vec<u8> {
2266 From::from(s.as_bytes())
2270 ////////////////////////////////////////////////////////////////////////////////
2272 ////////////////////////////////////////////////////////////////////////////////
2274 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2275 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2276 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2281 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2282 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2283 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2288 #[stable(feature = "rust1", since = "1.0.0")]
2289 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
2290 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2291 Cow::Owned(FromIterator::from_iter(it))
2295 ////////////////////////////////////////////////////////////////////////////////
2297 ////////////////////////////////////////////////////////////////////////////////
2299 /// An iterator that moves out of a vector.
2301 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
2302 /// by the [`IntoIterator`] trait).
2304 /// [`Vec`]: struct.Vec.html
2305 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2306 #[stable(feature = "rust1", since = "1.0.0")]
2307 pub struct IntoIter<T> {
2309 phantom: PhantomData<T>,
2315 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2316 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2317 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2318 f.debug_tuple("IntoIter")
2319 .field(&self.as_slice())
2324 impl<T> IntoIter<T> {
2325 /// Returns the remaining items of this iterator as a slice.
2330 /// let vec = vec!['a', 'b', 'c'];
2331 /// let mut into_iter = vec.into_iter();
2332 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2333 /// let _ = into_iter.next().unwrap();
2334 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2336 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2337 pub fn as_slice(&self) -> &[T] {
2339 slice::from_raw_parts(self.ptr, self.len())
2343 /// Returns the remaining items of this iterator as a mutable slice.
2348 /// let vec = vec!['a', 'b', 'c'];
2349 /// let mut into_iter = vec.into_iter();
2350 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2351 /// into_iter.as_mut_slice()[2] = 'z';
2352 /// assert_eq!(into_iter.next().unwrap(), 'a');
2353 /// assert_eq!(into_iter.next().unwrap(), 'b');
2354 /// assert_eq!(into_iter.next().unwrap(), 'z');
2356 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2357 pub fn as_mut_slice(&mut self) -> &mut [T] {
2359 slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
2364 #[stable(feature = "rust1", since = "1.0.0")]
2365 unsafe impl<T: Send> Send for IntoIter<T> {}
2366 #[stable(feature = "rust1", since = "1.0.0")]
2367 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2369 #[stable(feature = "rust1", since = "1.0.0")]
2370 impl<T> Iterator for IntoIter<T> {
2374 fn next(&mut self) -> Option<T> {
2376 if self.ptr as *const _ == self.end {
2379 if mem::size_of::<T>() == 0 {
2380 // purposefully don't use 'ptr.offset' because for
2381 // vectors with 0-size elements this would return the
2383 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2385 // Use a non-null pointer value
2386 // (self.ptr might be null because of wrapping)
2387 Some(ptr::read(1 as *mut T))
2390 self.ptr = self.ptr.offset(1);
2392 Some(ptr::read(old))
2399 fn size_hint(&self) -> (usize, Option<usize>) {
2400 let exact = if mem::size_of::<T>() == 0 {
2401 (self.end as usize).wrapping_sub(self.ptr as usize)
2403 unsafe { self.end.offset_from(self.ptr) as usize }
2405 (exact, Some(exact))
2409 fn count(self) -> usize {
2414 #[stable(feature = "rust1", since = "1.0.0")]
2415 impl<T> DoubleEndedIterator for IntoIter<T> {
2417 fn next_back(&mut self) -> Option<T> {
2419 if self.end == self.ptr {
2422 if mem::size_of::<T>() == 0 {
2423 // See above for why 'ptr.offset' isn't used
2424 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2426 // Use a non-null pointer value
2427 // (self.end might be null because of wrapping)
2428 Some(ptr::read(1 as *mut T))
2430 self.end = self.end.offset(-1);
2432 Some(ptr::read(self.end))
2439 #[stable(feature = "rust1", since = "1.0.0")]
2440 impl<T> ExactSizeIterator for IntoIter<T> {
2441 fn is_empty(&self) -> bool {
2442 self.ptr == self.end
2446 #[stable(feature = "fused", since = "1.26.0")]
2447 impl<T> FusedIterator for IntoIter<T> {}
2449 #[unstable(feature = "trusted_len", issue = "37572")]
2450 unsafe impl<T> TrustedLen for IntoIter<T> {}
2452 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2453 impl<T: Clone> Clone for IntoIter<T> {
2454 fn clone(&self) -> IntoIter<T> {
2455 self.as_slice().to_owned().into_iter()
2459 #[stable(feature = "rust1", since = "1.0.0")]
2460 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2461 fn drop(&mut self) {
2462 // destroy the remaining elements
2463 for _x in self.by_ref() {}
2465 // RawVec handles deallocation
2466 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2470 /// A draining iterator for `Vec<T>`.
2472 /// This `struct` is created by the [`drain`] method on [`Vec`].
2474 /// [`drain`]: struct.Vec.html#method.drain
2475 /// [`Vec`]: struct.Vec.html
2476 #[stable(feature = "drain", since = "1.6.0")]
2477 pub struct Drain<'a, T: 'a> {
2478 /// Index of tail to preserve
2482 /// Current remaining range to remove
2483 iter: slice::Iter<'a, T>,
2484 vec: NonNull<Vec<T>>,
2487 #[stable(feature = "collection_debug", since = "1.17.0")]
2488 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Drain<'a, T> {
2489 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2490 f.debug_tuple("Drain")
2491 .field(&self.iter.as_slice())
2496 #[stable(feature = "drain", since = "1.6.0")]
2497 unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
2498 #[stable(feature = "drain", since = "1.6.0")]
2499 unsafe impl<'a, T: Send> Send for Drain<'a, T> {}
2501 #[stable(feature = "drain", since = "1.6.0")]
2502 impl<'a, T> Iterator for Drain<'a, T> {
2506 fn next(&mut self) -> Option<T> {
2507 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2510 fn size_hint(&self) -> (usize, Option<usize>) {
2511 self.iter.size_hint()
2515 #[stable(feature = "drain", since = "1.6.0")]
2516 impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
2518 fn next_back(&mut self) -> Option<T> {
2519 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2523 #[stable(feature = "drain", since = "1.6.0")]
2524 impl<'a, T> Drop for Drain<'a, T> {
2525 fn drop(&mut self) {
2526 // exhaust self first
2527 self.for_each(drop);
2529 if self.tail_len > 0 {
2531 let source_vec = self.vec.as_mut();
2532 // memmove back untouched tail, update to new length
2533 let start = source_vec.len();
2534 let tail = self.tail_start;
2535 let src = source_vec.as_ptr().offset(tail as isize);
2536 let dst = source_vec.as_mut_ptr().offset(start as isize);
2537 ptr::copy(src, dst, self.tail_len);
2538 source_vec.set_len(start + self.tail_len);
2545 #[stable(feature = "drain", since = "1.6.0")]
2546 impl<'a, T> ExactSizeIterator for Drain<'a, T> {
2547 fn is_empty(&self) -> bool {
2548 self.iter.is_empty()
2552 #[stable(feature = "fused", since = "1.26.0")]
2553 impl<'a, T> FusedIterator for Drain<'a, T> {}
2555 /// A splicing iterator for `Vec`.
2557 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2558 /// documentation for more.
2560 /// [`splice()`]: struct.Vec.html#method.splice
2561 /// [`Vec`]: struct.Vec.html
2563 #[stable(feature = "vec_splice", since = "1.21.0")]
2564 pub struct Splice<'a, I: Iterator + 'a> {
2565 drain: Drain<'a, I::Item>,
2569 #[stable(feature = "vec_splice", since = "1.21.0")]
2570 impl<'a, I: Iterator> Iterator for Splice<'a, I> {
2571 type Item = I::Item;
2573 fn next(&mut self) -> Option<Self::Item> {
2577 fn size_hint(&self) -> (usize, Option<usize>) {
2578 self.drain.size_hint()
2582 #[stable(feature = "vec_splice", since = "1.21.0")]
2583 impl<'a, I: Iterator> DoubleEndedIterator for Splice<'a, I> {
2584 fn next_back(&mut self) -> Option<Self::Item> {
2585 self.drain.next_back()
2589 #[stable(feature = "vec_splice", since = "1.21.0")]
2590 impl<'a, I: Iterator> ExactSizeIterator for Splice<'a, I> {}
2593 #[stable(feature = "vec_splice", since = "1.21.0")]
2594 impl<'a, I: Iterator> Drop for Splice<'a, I> {
2595 fn drop(&mut self) {
2596 self.drain.by_ref().for_each(drop);
2599 if self.drain.tail_len == 0 {
2600 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2604 // First fill the range left by drain().
2605 if !self.drain.fill(&mut self.replace_with) {
2609 // There may be more elements. Use the lower bound as an estimate.
2610 // FIXME: Is the upper bound a better guess? Or something else?
2611 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2612 if lower_bound > 0 {
2613 self.drain.move_tail(lower_bound);
2614 if !self.drain.fill(&mut self.replace_with) {
2619 // Collect any remaining elements.
2620 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2621 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2622 // Now we have an exact count.
2623 if collected.len() > 0 {
2624 self.drain.move_tail(collected.len());
2625 let filled = self.drain.fill(&mut collected);
2626 debug_assert!(filled);
2627 debug_assert_eq!(collected.len(), 0);
2630 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2634 /// Private helper methods for `Splice::drop`
2635 impl<'a, T> Drain<'a, T> {
2636 /// The range from `self.vec.len` to `self.tail_start` contains elements
2637 /// that have been moved out.
2638 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2639 /// Return whether we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2640 unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
2641 let vec = self.vec.as_mut();
2642 let range_start = vec.len;
2643 let range_end = self.tail_start;
2644 let range_slice = slice::from_raw_parts_mut(
2645 vec.as_mut_ptr().offset(range_start as isize),
2646 range_end - range_start);
2648 for place in range_slice {
2649 if let Some(new_item) = replace_with.next() {
2650 ptr::write(place, new_item);
2659 /// Make room for inserting more elements before the tail.
2660 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2661 let vec = self.vec.as_mut();
2662 let used_capacity = self.tail_start + self.tail_len;
2663 vec.buf.reserve(used_capacity, extra_capacity);
2665 let new_tail_start = self.tail_start + extra_capacity;
2666 let src = vec.as_ptr().offset(self.tail_start as isize);
2667 let dst = vec.as_mut_ptr().offset(new_tail_start as isize);
2668 ptr::copy(src, dst, self.tail_len);
2669 self.tail_start = new_tail_start;
2673 /// An iterator produced by calling `drain_filter` on Vec.
2674 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2676 pub struct DrainFilter<'a, T: 'a, F>
2677 where F: FnMut(&mut T) -> bool,
2679 vec: &'a mut Vec<T>,
2686 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2687 impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
2688 where F: FnMut(&mut T) -> bool,
2692 fn next(&mut self) -> Option<T> {
2694 while self.idx != self.old_len {
2697 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2698 if (self.pred)(&mut v[i]) {
2700 return Some(ptr::read(&v[i]));
2701 } else if self.del > 0 {
2703 let src: *const T = &v[i];
2704 let dst: *mut T = &mut v[i - del];
2705 // This is safe because self.vec has length 0
2706 // thus its elements will not have Drop::drop
2707 // called on them in the event of a panic.
2708 ptr::copy_nonoverlapping(src, dst, 1);
2715 fn size_hint(&self) -> (usize, Option<usize>) {
2716 (0, Some(self.old_len - self.idx))
2720 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2721 impl<'a, T, F> Drop for DrainFilter<'a, T, F>
2722 where F: FnMut(&mut T) -> bool,
2724 fn drop(&mut self) {
2725 self.for_each(drop);
2727 self.vec.set_len(self.old_len - self.del);