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;
78 use core::ops::Bound::{Excluded, Included, Unbounded};
79 use core::ops::{InPlace, Index, IndexMut, Place, Placer, RangeBounds};
82 use core::ptr::NonNull;
89 use super::allocator::CollectionAllocErr;
91 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
96 /// let mut vec = Vec::new();
100 /// assert_eq!(vec.len(), 2);
101 /// assert_eq!(vec[0], 1);
103 /// assert_eq!(vec.pop(), Some(2));
104 /// assert_eq!(vec.len(), 1);
107 /// assert_eq!(vec[0], 7);
109 /// vec.extend([1, 2, 3].iter().cloned());
112 /// println!("{}", x);
114 /// assert_eq!(vec, [7, 1, 2, 3]);
117 /// The [`vec!`] macro is provided to make initialization more convenient:
120 /// let mut vec = vec![1, 2, 3];
122 /// assert_eq!(vec, [1, 2, 3, 4]);
125 /// It can also initialize each element of a `Vec<T>` with a given value:
128 /// let vec = vec![0; 5];
129 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
132 /// Use a `Vec<T>` as an efficient stack:
135 /// let mut stack = Vec::new();
141 /// while let Some(top) = stack.pop() {
142 /// // Prints 3, 2, 1
143 /// println!("{}", top);
149 /// The `Vec` type allows to access values by index, because it implements the
150 /// [`Index`] trait. An example will be more explicit:
153 /// let v = vec![0, 2, 4, 6];
154 /// println!("{}", v[1]); // it will display '2'
157 /// However be careful: if you try to access an index which isn't in the `Vec`,
158 /// your software will panic! You cannot do this:
161 /// let v = vec![0, 2, 4, 6];
162 /// println!("{}", v[6]); // it will panic!
165 /// In conclusion: always check if the index you want to get really exists
170 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
171 /// To get a slice, use `&`. Example:
174 /// fn read_slice(slice: &[usize]) {
178 /// let v = vec![0, 1];
181 /// // ... and that's all!
182 /// // you can also do it like this:
183 /// let x : &[usize] = &v;
186 /// In Rust, it's more common to pass slices as arguments rather than vectors
187 /// when you just want to provide a read access. The same goes for [`String`] and
190 /// # Capacity and reallocation
192 /// The capacity of a vector is the amount of space allocated for any future
193 /// elements that will be added onto the vector. This is not to be confused with
194 /// the *length* of a vector, which specifies the number of actual elements
195 /// within the vector. If a vector's length exceeds its capacity, its capacity
196 /// will automatically be increased, but its elements will have to be
199 /// For example, a vector with capacity 10 and length 0 would be an empty vector
200 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
201 /// vector will not change its capacity or cause reallocation to occur. However,
202 /// if the vector's length is increased to 11, it will have to reallocate, which
203 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
204 /// whenever possible to specify how big the vector is expected to get.
208 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
209 /// about its design. This ensures that it's as low-overhead as possible in
210 /// the general case, and can be correctly manipulated in primitive ways
211 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
212 /// If additional type parameters are added (e.g. to support custom allocators),
213 /// overriding their defaults may change the behavior.
215 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
216 /// triplet. No more, no less. The order of these fields is completely
217 /// unspecified, and you should use the appropriate methods to modify these.
218 /// The pointer will never be null, so this type is null-pointer-optimized.
220 /// However, the pointer may not actually point to allocated memory. In particular,
221 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
222 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
223 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
224 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
225 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
226 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
227 /// details are very subtle — if you intend to allocate memory using a `Vec`
228 /// and use it for something else (either to pass to unsafe code, or to build your
229 /// own memory-backed collection), be sure to deallocate this memory by using
230 /// `from_raw_parts` to recover the `Vec` and then dropping it.
232 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
233 /// (as defined by the allocator Rust is configured to use by default), and its
234 /// pointer points to [`len`] initialized, contiguous elements in order (what
235 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
236 /// `[`len`] logically uninitialized, contiguous elements.
238 /// `Vec` will never perform a "small optimization" where elements are actually
239 /// stored on the stack for two reasons:
241 /// * It would make it more difficult for unsafe code to correctly manipulate
242 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
243 /// only moved, and it would be more difficult to determine if a `Vec` had
244 /// actually allocated memory.
246 /// * It would penalize the general case, incurring an additional branch
249 /// `Vec` will never automatically shrink itself, even if completely empty. This
250 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
251 /// and then filling it back up to the same [`len`] should incur no calls to
252 /// the allocator. If you wish to free up unused memory, use
253 /// [`shrink_to_fit`][`shrink_to_fit`].
255 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
256 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
257 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
258 /// accurate, and can be relied on. It can even be used to manually free the memory
259 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
260 /// when not necessary.
262 /// `Vec` does not guarantee any particular growth strategy when reallocating
263 /// when full, nor when [`reserve`] is called. The current strategy is basic
264 /// and it may prove desirable to use a non-constant growth factor. Whatever
265 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
267 /// `vec![x; n]`, `vec![a, b, c, d]`, and
268 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
269 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
270 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
271 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
273 /// `Vec` will not specifically overwrite any data that is removed from it,
274 /// but also won't specifically preserve it. Its uninitialized memory is
275 /// scratch space that it may use however it wants. It will generally just do
276 /// whatever is most efficient or otherwise easy to implement. Do not rely on
277 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
278 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
279 /// first, that may not actually happen because the optimizer does not consider
280 /// this a side-effect that must be preserved. There is one case which we will
281 /// not break, however: using `unsafe` code to write to the excess capacity,
282 /// and then increasing the length to match, is always valid.
284 /// `Vec` does not currently guarantee the order in which elements are dropped.
285 /// The order has changed in the past and may change again.
287 /// [`vec!`]: ../../std/macro.vec.html
288 /// [`Index`]: ../../std/ops/trait.Index.html
289 /// [`String`]: ../../std/string/struct.String.html
290 /// [`&str`]: ../../std/primitive.str.html
291 /// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
292 /// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
293 /// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
294 /// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
295 /// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
296 /// [`len`]: ../../std/vec/struct.Vec.html#method.len
297 /// [`push`]: ../../std/vec/struct.Vec.html#method.push
298 /// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
299 /// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
300 /// [owned slice]: ../../std/boxed/struct.Box.html
301 #[stable(feature = "rust1", since = "1.0.0")]
307 ////////////////////////////////////////////////////////////////////////////////
309 ////////////////////////////////////////////////////////////////////////////////
312 /// Constructs a new, empty `Vec<T>`.
314 /// The vector will not allocate until elements are pushed onto it.
319 /// # #![allow(unused_mut)]
320 /// let mut vec: Vec<i32> = Vec::new();
323 #[stable(feature = "rust1", since = "1.0.0")]
324 pub fn new() -> Vec<T> {
331 /// Constructs a new, empty `Vec<T>` with the specified capacity.
333 /// The vector will be able to hold exactly `capacity` elements without
334 /// reallocating. If `capacity` is 0, the vector will not allocate.
336 /// It is important to note that although the returned vector has the
337 /// *capacity* specified, the vector will have a zero *length*. For an
338 /// explanation of the difference between length and capacity, see
339 /// *[Capacity and reallocation]*.
341 /// [Capacity and reallocation]: #capacity-and-reallocation
346 /// let mut vec = Vec::with_capacity(10);
348 /// // The vector contains no items, even though it has capacity for more
349 /// assert_eq!(vec.len(), 0);
351 /// // These are all done without reallocating...
356 /// // ...but this may make the vector reallocate
360 #[stable(feature = "rust1", since = "1.0.0")]
361 pub fn with_capacity(capacity: usize) -> Vec<T> {
363 buf: RawVec::with_capacity(capacity),
368 /// Creates a `Vec<T>` directly from the raw components of another vector.
372 /// This is highly unsafe, due to the number of invariants that aren't
375 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
376 /// (at least, it's highly likely to be incorrect if it wasn't).
377 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
378 /// * `length` needs to be less than or equal to `capacity`.
379 /// * `capacity` needs to be the capacity that the pointer was allocated with.
381 /// Violating these may cause problems like corrupting the allocator's
382 /// internal data structures. For example it is **not** safe
383 /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
385 /// The ownership of `ptr` is effectively transferred to the
386 /// `Vec<T>` which may then deallocate, reallocate or change the
387 /// contents of memory pointed to by the pointer at will. Ensure
388 /// that nothing else uses the pointer after calling this
391 /// [`String`]: ../../std/string/struct.String.html
400 /// let mut v = vec![1, 2, 3];
402 /// // Pull out the various important pieces of information about `v`
403 /// let p = v.as_mut_ptr();
404 /// let len = v.len();
405 /// let cap = v.capacity();
408 /// // Cast `v` into the void: no destructor run, so we are in
409 /// // complete control of the allocation to which `p` points.
412 /// // Overwrite memory with 4, 5, 6
413 /// for i in 0..len as isize {
414 /// ptr::write(p.offset(i), 4 + i);
417 /// // Put everything back together into a Vec
418 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
419 /// assert_eq!(rebuilt, [4, 5, 6]);
423 #[stable(feature = "rust1", since = "1.0.0")]
424 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
426 buf: RawVec::from_raw_parts(ptr, capacity),
431 /// Returns the number of elements the vector can hold without
437 /// let vec: Vec<i32> = Vec::with_capacity(10);
438 /// assert_eq!(vec.capacity(), 10);
441 #[stable(feature = "rust1", since = "1.0.0")]
442 pub fn capacity(&self) -> usize {
446 /// Reserves capacity for at least `additional` more elements to be inserted
447 /// in the given `Vec<T>`. The collection may reserve more space to avoid
448 /// frequent reallocations. After calling `reserve`, capacity will be
449 /// greater than or equal to `self.len() + additional`. Does nothing if
450 /// capacity is already sufficient.
454 /// Panics if the new capacity overflows `usize`.
459 /// let mut vec = vec![1];
461 /// assert!(vec.capacity() >= 11);
463 #[stable(feature = "rust1", since = "1.0.0")]
464 pub fn reserve(&mut self, additional: usize) {
465 self.buf.reserve(self.len, additional);
468 /// Reserves the minimum capacity for exactly `additional` more elements to
469 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
470 /// capacity will be greater than or equal to `self.len() + additional`.
471 /// Does nothing if the capacity is already sufficient.
473 /// Note that the allocator may give the collection more space than it
474 /// requests. Therefore capacity can not be relied upon to be precisely
475 /// minimal. Prefer `reserve` if future insertions are expected.
479 /// Panics if the new capacity overflows `usize`.
484 /// let mut vec = vec![1];
485 /// vec.reserve_exact(10);
486 /// assert!(vec.capacity() >= 11);
488 #[stable(feature = "rust1", since = "1.0.0")]
489 pub fn reserve_exact(&mut self, additional: usize) {
490 self.buf.reserve_exact(self.len, additional);
493 /// Tries to reserve capacity for at least `additional` more elements to be inserted
494 /// in the given `Vec<T>`. The collection may reserve more space to avoid
495 /// frequent reallocations. After calling `reserve`, capacity will be
496 /// greater than or equal to `self.len() + additional`. Does nothing if
497 /// capacity is already sufficient.
501 /// If the capacity overflows, or the allocator reports a failure, then an error
507 /// #![feature(try_reserve)]
508 /// use std::collections::CollectionAllocErr;
510 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
511 /// let mut output = Vec::new();
513 /// // Pre-reserve the memory, exiting if we can't
514 /// output.try_reserve(data.len())?;
516 /// // Now we know this can't OOM in the middle of our complex work
517 /// output.extend(data.iter().map(|&val| {
518 /// val * 2 + 5 // very complicated
523 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
525 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
526 pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
527 self.buf.try_reserve(self.len, additional)
530 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
531 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
532 /// capacity will be greater than or equal to `self.len() + additional`.
533 /// Does nothing if the capacity is already sufficient.
535 /// Note that the allocator may give the collection more space than it
536 /// requests. Therefore capacity can not be relied upon to be precisely
537 /// minimal. Prefer `reserve` if future insertions are expected.
541 /// If the capacity overflows, or the allocator reports a failure, then an error
547 /// #![feature(try_reserve)]
548 /// use std::collections::CollectionAllocErr;
550 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
551 /// let mut output = Vec::new();
553 /// // Pre-reserve the memory, exiting if we can't
554 /// output.try_reserve(data.len())?;
556 /// // Now we know this can't OOM in the middle of our complex work
557 /// output.extend(data.iter().map(|&val| {
558 /// val * 2 + 5 // very complicated
563 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
565 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
566 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
567 self.buf.try_reserve_exact(self.len, additional)
570 /// Shrinks the capacity of the vector as much as possible.
572 /// It will drop down as close as possible to the length but the allocator
573 /// may still inform the vector that there is space for a few more elements.
578 /// let mut vec = Vec::with_capacity(10);
579 /// vec.extend([1, 2, 3].iter().cloned());
580 /// assert_eq!(vec.capacity(), 10);
581 /// vec.shrink_to_fit();
582 /// assert!(vec.capacity() >= 3);
584 #[stable(feature = "rust1", since = "1.0.0")]
585 pub fn shrink_to_fit(&mut self) {
586 if self.capacity() != self.len {
587 self.buf.shrink_to_fit(self.len);
591 /// Shrinks the capacity of the vector with a lower bound.
593 /// The capacity will remain at least as large as both the length
594 /// and the supplied value.
596 /// Panics if the current capacity is smaller than the supplied
597 /// minimum capacity.
602 /// #![feature(shrink_to)]
603 /// let mut vec = Vec::with_capacity(10);
604 /// vec.extend([1, 2, 3].iter().cloned());
605 /// assert_eq!(vec.capacity(), 10);
606 /// vec.shrink_to(4);
607 /// assert!(vec.capacity() >= 4);
608 /// vec.shrink_to(0);
609 /// assert!(vec.capacity() >= 3);
611 #[unstable(feature = "shrink_to", reason = "new API", issue="0")]
612 pub fn shrink_to(&mut self, min_capacity: usize) {
613 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
616 /// Converts the vector into [`Box<[T]>`][owned slice].
618 /// Note that this will drop any excess capacity.
620 /// [owned slice]: ../../std/boxed/struct.Box.html
625 /// let v = vec![1, 2, 3];
627 /// let slice = v.into_boxed_slice();
630 /// Any excess capacity is removed:
633 /// let mut vec = Vec::with_capacity(10);
634 /// vec.extend([1, 2, 3].iter().cloned());
636 /// assert_eq!(vec.capacity(), 10);
637 /// let slice = vec.into_boxed_slice();
638 /// assert_eq!(slice.into_vec().capacity(), 3);
640 #[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 /// Returns a place for insertion at the back of the `Vec`.
1073 /// Using this method with placement syntax is equivalent to [`push`](#method.push),
1074 /// but may be more efficient.
1079 /// #![feature(collection_placement)]
1080 /// #![feature(placement_in_syntax)]
1082 /// let mut vec = vec![1, 2];
1083 /// vec.place_back() <- 3;
1084 /// vec.place_back() <- 4;
1085 /// assert_eq!(&vec, &[1, 2, 3, 4]);
1087 #[unstable(feature = "collection_placement",
1088 reason = "placement protocol is subject to change",
1090 pub fn place_back(&mut self) -> PlaceBack<T> {
1091 PlaceBack { vec: self }
1094 /// Removes the last element from a vector and returns it, or [`None`] if it
1097 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1102 /// let mut vec = vec![1, 2, 3];
1103 /// assert_eq!(vec.pop(), Some(3));
1104 /// assert_eq!(vec, [1, 2]);
1107 #[stable(feature = "rust1", since = "1.0.0")]
1108 pub fn pop(&mut self) -> Option<T> {
1114 Some(ptr::read(self.get_unchecked(self.len())))
1119 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1123 /// Panics if the number of elements in the vector overflows a `usize`.
1128 /// let mut vec = vec![1, 2, 3];
1129 /// let mut vec2 = vec![4, 5, 6];
1130 /// vec.append(&mut vec2);
1131 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1132 /// assert_eq!(vec2, []);
1135 #[stable(feature = "append", since = "1.4.0")]
1136 pub fn append(&mut self, other: &mut Self) {
1138 self.append_elements(other.as_slice() as _);
1143 /// Appends elements to `Self` from other buffer.
1145 unsafe fn append_elements(&mut self, other: *const [T]) {
1146 let count = (*other).len();
1147 self.reserve(count);
1148 let len = self.len();
1149 ptr::copy_nonoverlapping(other as *const T, self.get_unchecked_mut(len), count);
1153 /// Creates a draining iterator that removes the specified range in the vector
1154 /// and yields the removed items.
1156 /// Note 1: The element range is removed even if the iterator is only
1157 /// partially consumed or not consumed at all.
1159 /// Note 2: It is unspecified how many elements are removed from the vector
1160 /// if the `Drain` value is leaked.
1164 /// Panics if the starting point is greater than the end point or if
1165 /// the end point is greater than the length of the vector.
1170 /// let mut v = vec![1, 2, 3];
1171 /// let u: Vec<_> = v.drain(1..).collect();
1172 /// assert_eq!(v, &[1]);
1173 /// assert_eq!(u, &[2, 3]);
1175 /// // A full range clears the vector
1177 /// assert_eq!(v, &[]);
1179 #[stable(feature = "drain", since = "1.6.0")]
1180 pub fn drain<R>(&mut self, range: R) -> Drain<T>
1181 where R: RangeBounds<usize>
1185 // When the Drain is first created, it shortens the length of
1186 // the source vector to make sure no uninitialized or moved-from elements
1187 // are accessible at all if the Drain's destructor never gets to run.
1189 // Drain will ptr::read out the values to remove.
1190 // When finished, remaining tail of the vec is copied back to cover
1191 // the hole, and the vector length is restored to the new length.
1193 let len = self.len();
1194 let start = match range.start() {
1196 Excluded(&n) => n + 1,
1199 let end = match range.end() {
1200 Included(&n) => n + 1,
1204 assert!(start <= end);
1205 assert!(end <= len);
1208 // set self.vec length's to start, to be safe in case Drain is leaked
1209 self.set_len(start);
1210 // Use the borrow in the IterMut to indicate borrowing behavior of the
1211 // whole Drain iterator (like &mut T).
1212 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().offset(start as isize),
1216 tail_len: len - end,
1217 iter: range_slice.iter(),
1218 vec: NonNull::from(self),
1223 /// Clears the vector, removing all values.
1225 /// Note that this method has no effect on the allocated capacity
1231 /// let mut v = vec![1, 2, 3];
1235 /// assert!(v.is_empty());
1238 #[stable(feature = "rust1", since = "1.0.0")]
1239 pub fn clear(&mut self) {
1243 /// Returns the number of elements in the vector, also referred to
1244 /// as its 'length'.
1249 /// let a = vec![1, 2, 3];
1250 /// assert_eq!(a.len(), 3);
1253 #[stable(feature = "rust1", since = "1.0.0")]
1254 pub fn len(&self) -> usize {
1258 /// Returns `true` if the vector contains no elements.
1263 /// let mut v = Vec::new();
1264 /// assert!(v.is_empty());
1267 /// assert!(!v.is_empty());
1269 #[stable(feature = "rust1", since = "1.0.0")]
1270 pub fn is_empty(&self) -> bool {
1274 /// Splits the collection into two at the given index.
1276 /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
1277 /// and the returned `Self` contains elements `[at, len)`.
1279 /// Note that the capacity of `self` does not change.
1283 /// Panics if `at > len`.
1288 /// let mut vec = vec![1,2,3];
1289 /// let vec2 = vec.split_off(1);
1290 /// assert_eq!(vec, [1]);
1291 /// assert_eq!(vec2, [2, 3]);
1294 #[stable(feature = "split_off", since = "1.4.0")]
1295 pub fn split_off(&mut self, at: usize) -> Self {
1296 assert!(at <= self.len(), "`at` out of bounds");
1298 let other_len = self.len - at;
1299 let mut other = Vec::with_capacity(other_len);
1301 // Unsafely `set_len` and copy items to `other`.
1304 other.set_len(other_len);
1306 ptr::copy_nonoverlapping(self.as_ptr().offset(at as isize),
1314 impl<T: Clone> Vec<T> {
1315 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1317 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1318 /// difference, with each additional slot filled with `value`.
1319 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1321 /// This method requires [`Clone`] to be able clone the passed value. If
1322 /// you'd rather create a value with [`Default`] instead, see
1323 /// [`resize_default`].
1328 /// let mut vec = vec!["hello"];
1329 /// vec.resize(3, "world");
1330 /// assert_eq!(vec, ["hello", "world", "world"]);
1332 /// let mut vec = vec![1, 2, 3, 4];
1333 /// vec.resize(2, 0);
1334 /// assert_eq!(vec, [1, 2]);
1337 /// [`Clone`]: ../../std/clone/trait.Clone.html
1338 /// [`Default`]: ../../std/default/trait.Default.html
1339 /// [`resize_default`]: #method.resize_default
1340 #[stable(feature = "vec_resize", since = "1.5.0")]
1341 pub fn resize(&mut self, new_len: usize, value: T) {
1342 let len = self.len();
1345 self.extend_with(new_len - len, ExtendElement(value))
1347 self.truncate(new_len);
1351 /// Clones and appends all elements in a slice to the `Vec`.
1353 /// Iterates over the slice `other`, clones each element, and then appends
1354 /// it to this `Vec`. The `other` vector is traversed in-order.
1356 /// Note that this function is same as [`extend`] except that it is
1357 /// specialized to work with slices instead. If and when Rust gets
1358 /// specialization this function will likely be deprecated (but still
1364 /// let mut vec = vec![1];
1365 /// vec.extend_from_slice(&[2, 3, 4]);
1366 /// assert_eq!(vec, [1, 2, 3, 4]);
1369 /// [`extend`]: #method.extend
1370 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1371 pub fn extend_from_slice(&mut self, other: &[T]) {
1372 self.spec_extend(other.iter())
1376 impl<T: Default> Vec<T> {
1377 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1379 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1380 /// difference, with each additional slot filled with [`Default::default()`].
1381 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1383 /// This method uses [`Default`] to create new values on every push. If
1384 /// you'd rather [`Clone`] a given value, use [`resize`].
1389 /// #![feature(vec_resize_default)]
1391 /// let mut vec = vec![1, 2, 3];
1392 /// vec.resize_default(5);
1393 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1395 /// let mut vec = vec![1, 2, 3, 4];
1396 /// vec.resize_default(2);
1397 /// assert_eq!(vec, [1, 2]);
1400 /// [`resize`]: #method.resize
1401 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1402 /// [`Default`]: ../../std/default/trait.Default.html
1403 /// [`Clone`]: ../../std/clone/trait.Clone.html
1404 #[unstable(feature = "vec_resize_default", issue = "41758")]
1405 pub fn resize_default(&mut self, new_len: usize) {
1406 let len = self.len();
1409 self.extend_with(new_len - len, ExtendDefault);
1411 self.truncate(new_len);
1416 // This code generalises `extend_with_{element,default}`.
1417 trait ExtendWith<T> {
1418 fn next(&self) -> T;
1422 struct ExtendElement<T>(T);
1423 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1424 fn next(&self) -> T { self.0.clone() }
1425 fn last(self) -> T { self.0 }
1428 struct ExtendDefault;
1429 impl<T: Default> ExtendWith<T> for ExtendDefault {
1430 fn next(&self) -> T { Default::default() }
1431 fn last(self) -> T { Default::default() }
1434 /// Extend the vector by `n` values, using the given generator.
1435 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, value: E) {
1439 let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
1440 // Use SetLenOnDrop to work around bug where compiler
1441 // may not realize the store through `ptr` through self.set_len()
1443 let mut local_len = SetLenOnDrop::new(&mut self.len);
1445 // Write all elements except the last one
1447 ptr::write(ptr, value.next());
1448 ptr = ptr.offset(1);
1449 // Increment the length in every step in case next() panics
1450 local_len.increment_len(1);
1454 // We can write the last element directly without cloning needlessly
1455 ptr::write(ptr, value.last());
1456 local_len.increment_len(1);
1459 // len set by scope guard
1464 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1466 // The idea is: The length field in SetLenOnDrop is a local variable
1467 // that the optimizer will see does not alias with any stores through the Vec's data
1468 // pointer. This is a workaround for alias analysis issue #32155
1469 struct SetLenOnDrop<'a> {
1474 impl<'a> SetLenOnDrop<'a> {
1476 fn new(len: &'a mut usize) -> Self {
1477 SetLenOnDrop { local_len: *len, len: len }
1481 fn increment_len(&mut self, increment: usize) {
1482 self.local_len += increment;
1486 impl<'a> Drop for SetLenOnDrop<'a> {
1488 fn drop(&mut self) {
1489 *self.len = self.local_len;
1493 impl<T: PartialEq> Vec<T> {
1494 /// Removes consecutive repeated elements in the vector.
1496 /// If the vector is sorted, this removes all duplicates.
1501 /// let mut vec = vec![1, 2, 2, 3, 2];
1505 /// assert_eq!(vec, [1, 2, 3, 2]);
1507 #[stable(feature = "rust1", since = "1.0.0")]
1509 pub fn dedup(&mut self) {
1510 self.dedup_by(|a, b| a == b)
1513 /// Removes the first instance of `item` from the vector if the item exists.
1518 /// # #![feature(vec_remove_item)]
1519 /// let mut vec = vec![1, 2, 3, 1];
1521 /// vec.remove_item(&1);
1523 /// assert_eq!(vec, vec![2, 3, 1]);
1525 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1526 pub fn remove_item(&mut self, item: &T) -> Option<T> {
1527 let pos = self.iter().position(|x| *x == *item)?;
1528 Some(self.remove(pos))
1532 ////////////////////////////////////////////////////////////////////////////////
1533 // Internal methods and functions
1534 ////////////////////////////////////////////////////////////////////////////////
1537 #[stable(feature = "rust1", since = "1.0.0")]
1538 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1539 <T as SpecFromElem>::from_elem(elem, n)
1542 // Specialization trait used for Vec::from_elem
1543 trait SpecFromElem: Sized {
1544 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1547 impl<T: Clone> SpecFromElem for T {
1548 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1549 let mut v = Vec::with_capacity(n);
1550 v.extend_with(n, ExtendElement(elem));
1555 impl SpecFromElem for u8 {
1557 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1560 buf: RawVec::with_capacity_zeroed(n),
1565 let mut v = Vec::with_capacity(n);
1566 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1573 macro_rules! impl_spec_from_elem {
1574 ($t: ty, $is_zero: expr) => {
1575 impl SpecFromElem for $t {
1577 fn from_elem(elem: $t, n: usize) -> Vec<$t> {
1580 buf: RawVec::with_capacity_zeroed(n),
1584 let mut v = Vec::with_capacity(n);
1585 v.extend_with(n, ExtendElement(elem));
1592 impl_spec_from_elem!(i8, |x| x == 0);
1593 impl_spec_from_elem!(i16, |x| x == 0);
1594 impl_spec_from_elem!(i32, |x| x == 0);
1595 impl_spec_from_elem!(i64, |x| x == 0);
1596 impl_spec_from_elem!(i128, |x| x == 0);
1597 impl_spec_from_elem!(isize, |x| x == 0);
1599 impl_spec_from_elem!(u16, |x| x == 0);
1600 impl_spec_from_elem!(u32, |x| x == 0);
1601 impl_spec_from_elem!(u64, |x| x == 0);
1602 impl_spec_from_elem!(u128, |x| x == 0);
1603 impl_spec_from_elem!(usize, |x| x == 0);
1605 impl_spec_from_elem!(f32, |x: f32| x.to_bits() == 0);
1606 impl_spec_from_elem!(f64, |x: f64| x.to_bits() == 0);
1608 ////////////////////////////////////////////////////////////////////////////////
1609 // Common trait implementations for Vec
1610 ////////////////////////////////////////////////////////////////////////////////
1612 #[stable(feature = "rust1", since = "1.0.0")]
1613 impl<T: Clone> Clone for Vec<T> {
1615 fn clone(&self) -> Vec<T> {
1616 <[T]>::to_vec(&**self)
1619 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1620 // required for this method definition, is not available. Instead use the
1621 // `slice::to_vec` function which is only available with cfg(test)
1622 // NB see the slice::hack module in slice.rs for more information
1624 fn clone(&self) -> Vec<T> {
1625 ::slice::to_vec(&**self)
1628 fn clone_from(&mut self, other: &Vec<T>) {
1629 other.as_slice().clone_into(self);
1633 #[stable(feature = "rust1", since = "1.0.0")]
1634 impl<T: Hash> Hash for Vec<T> {
1636 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1637 Hash::hash(&**self, state)
1641 #[stable(feature = "rust1", since = "1.0.0")]
1642 #[rustc_on_unimplemented = "vector indices are of type `usize` or ranges of `usize`"]
1643 impl<T, I> Index<I> for Vec<T>
1645 I: ::core::slice::SliceIndex<[T]>,
1647 type Output = I::Output;
1650 fn index(&self, index: I) -> &Self::Output {
1651 Index::index(&**self, index)
1655 #[stable(feature = "rust1", since = "1.0.0")]
1656 #[rustc_on_unimplemented = "vector indices are of type `usize` or ranges of `usize`"]
1657 impl<T, I> IndexMut<I> for Vec<T>
1659 I: ::core::slice::SliceIndex<[T]>,
1662 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1663 IndexMut::index_mut(&mut **self, index)
1667 #[stable(feature = "rust1", since = "1.0.0")]
1668 impl<T> ops::Deref for Vec<T> {
1671 fn deref(&self) -> &[T] {
1673 let p = self.buf.ptr();
1674 assume(!p.is_null());
1675 slice::from_raw_parts(p, self.len)
1680 #[stable(feature = "rust1", since = "1.0.0")]
1681 impl<T> ops::DerefMut for Vec<T> {
1682 fn deref_mut(&mut self) -> &mut [T] {
1684 let ptr = self.buf.ptr();
1685 assume(!ptr.is_null());
1686 slice::from_raw_parts_mut(ptr, self.len)
1691 #[stable(feature = "rust1", since = "1.0.0")]
1692 impl<T> FromIterator<T> for Vec<T> {
1694 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1695 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1699 #[stable(feature = "rust1", since = "1.0.0")]
1700 impl<T> IntoIterator for Vec<T> {
1702 type IntoIter = IntoIter<T>;
1704 /// Creates a consuming iterator, that is, one that moves each value out of
1705 /// the vector (from start to end). The vector cannot be used after calling
1711 /// let v = vec!["a".to_string(), "b".to_string()];
1712 /// for s in v.into_iter() {
1713 /// // s has type String, not &String
1714 /// println!("{}", s);
1718 fn into_iter(mut self) -> IntoIter<T> {
1720 let begin = self.as_mut_ptr();
1721 assume(!begin.is_null());
1722 let end = if mem::size_of::<T>() == 0 {
1723 arith_offset(begin as *const i8, self.len() as isize) as *const T
1725 begin.offset(self.len() as isize) as *const T
1727 let cap = self.buf.cap();
1730 buf: NonNull::new_unchecked(begin),
1731 phantom: PhantomData,
1740 #[stable(feature = "rust1", since = "1.0.0")]
1741 impl<'a, T> IntoIterator for &'a Vec<T> {
1743 type IntoIter = slice::Iter<'a, T>;
1745 fn into_iter(self) -> slice::Iter<'a, T> {
1750 #[stable(feature = "rust1", since = "1.0.0")]
1751 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1752 type Item = &'a mut T;
1753 type IntoIter = slice::IterMut<'a, T>;
1755 fn into_iter(self) -> slice::IterMut<'a, T> {
1760 #[stable(feature = "rust1", since = "1.0.0")]
1761 impl<T> Extend<T> for Vec<T> {
1763 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1764 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1768 // Specialization trait used for Vec::from_iter and Vec::extend
1769 trait SpecExtend<T, I> {
1770 fn from_iter(iter: I) -> Self;
1771 fn spec_extend(&mut self, iter: I);
1774 impl<T, I> SpecExtend<T, I> for Vec<T>
1775 where I: Iterator<Item=T>,
1777 default fn from_iter(mut iterator: I) -> Self {
1778 // Unroll the first iteration, as the vector is going to be
1779 // expanded on this iteration in every case when the iterable is not
1780 // empty, but the loop in extend_desugared() is not going to see the
1781 // vector being full in the few subsequent loop iterations.
1782 // So we get better branch prediction.
1783 let mut vector = match iterator.next() {
1784 None => return Vec::new(),
1786 let (lower, _) = iterator.size_hint();
1787 let mut vector = Vec::with_capacity(lower.saturating_add(1));
1789 ptr::write(vector.get_unchecked_mut(0), element);
1795 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
1799 default fn spec_extend(&mut self, iter: I) {
1800 self.extend_desugared(iter)
1804 impl<T, I> SpecExtend<T, I> for Vec<T>
1805 where I: TrustedLen<Item=T>,
1807 default fn from_iter(iterator: I) -> Self {
1808 let mut vector = Vec::new();
1809 vector.spec_extend(iterator);
1813 default fn spec_extend(&mut self, iterator: I) {
1814 // This is the case for a TrustedLen iterator.
1815 let (low, high) = iterator.size_hint();
1816 if let Some(high_value) = high {
1817 debug_assert_eq!(low, high_value,
1818 "TrustedLen iterator's size hint is not exact: {:?}",
1821 if let Some(additional) = high {
1822 self.reserve(additional);
1824 let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
1825 let mut local_len = SetLenOnDrop::new(&mut self.len);
1826 for element in iterator {
1827 ptr::write(ptr, element);
1828 ptr = ptr.offset(1);
1829 // NB can't overflow since we would have had to alloc the address space
1830 local_len.increment_len(1);
1834 self.extend_desugared(iterator)
1839 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
1840 fn from_iter(iterator: IntoIter<T>) -> Self {
1841 // A common case is passing a vector into a function which immediately
1842 // re-collects into a vector. We can short circuit this if the IntoIter
1843 // has not been advanced at all.
1844 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
1846 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
1849 mem::forget(iterator);
1853 let mut vector = Vec::new();
1854 vector.spec_extend(iterator);
1859 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
1861 self.append_elements(iterator.as_slice() as _);
1863 iterator.ptr = iterator.end;
1867 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
1868 where I: Iterator<Item=&'a T>,
1871 default fn from_iter(iterator: I) -> Self {
1872 SpecExtend::from_iter(iterator.cloned())
1875 default fn spec_extend(&mut self, iterator: I) {
1876 self.spec_extend(iterator.cloned())
1880 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
1883 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
1884 let slice = iterator.as_slice();
1885 self.reserve(slice.len());
1887 let len = self.len();
1888 self.set_len(len + slice.len());
1889 self.get_unchecked_mut(len..).copy_from_slice(slice);
1895 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
1896 // This is the case for a general iterator.
1898 // This function should be the moral equivalent of:
1900 // for item in iterator {
1903 while let Some(element) = iterator.next() {
1904 let len = self.len();
1905 if len == self.capacity() {
1906 let (lower, _) = iterator.size_hint();
1907 self.reserve(lower.saturating_add(1));
1910 ptr::write(self.get_unchecked_mut(len), element);
1911 // NB can't overflow since we would have had to alloc the address space
1912 self.set_len(len + 1);
1917 /// Creates a splicing iterator that replaces the specified range in the vector
1918 /// with the given `replace_with` iterator and yields the removed items.
1919 /// `replace_with` does not need to be the same length as `range`.
1921 /// Note 1: The element range is removed even if the iterator is not
1922 /// consumed until the end.
1924 /// Note 2: It is unspecified how many elements are removed from the vector,
1925 /// if the `Splice` value is leaked.
1927 /// Note 3: The input iterator `replace_with` is only consumed
1928 /// when the `Splice` value is dropped.
1930 /// Note 4: This is optimal if:
1932 /// * The tail (elements in the vector after `range`) is empty,
1933 /// * or `replace_with` yields fewer elements than `range`’s length
1934 /// * or the lower bound of its `size_hint()` is exact.
1936 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
1940 /// Panics if the starting point is greater than the end point or if
1941 /// the end point is greater than the length of the vector.
1946 /// let mut v = vec![1, 2, 3];
1947 /// let new = [7, 8];
1948 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
1949 /// assert_eq!(v, &[7, 8, 3]);
1950 /// assert_eq!(u, &[1, 2]);
1953 #[stable(feature = "vec_splice", since = "1.21.0")]
1954 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<I::IntoIter>
1955 where R: RangeBounds<usize>, I: IntoIterator<Item=T>
1958 drain: self.drain(range),
1959 replace_with: replace_with.into_iter(),
1963 /// Creates an iterator which uses a closure to determine if an element should be removed.
1965 /// If the closure returns true, then the element is removed and yielded.
1966 /// If the closure returns false, the element will remain in the vector and will not be yielded
1967 /// by the iterator.
1969 /// Using this method is equivalent to the following code:
1972 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
1973 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
1975 /// while i != vec.len() {
1976 /// if some_predicate(&mut vec[i]) {
1977 /// let val = vec.remove(i);
1978 /// // your code here
1984 /// # assert_eq!(vec, vec![1, 4, 5]);
1987 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
1988 /// because it can backshift the elements of the array in bulk.
1990 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
1991 /// regardless of whether you choose to keep or remove it.
1996 /// Splitting an array into evens and odds, reusing the original allocation:
1999 /// #![feature(drain_filter)]
2000 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2002 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2003 /// let odds = numbers;
2005 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2006 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2008 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2009 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<T, F>
2010 where F: FnMut(&mut T) -> bool,
2012 let old_len = self.len();
2014 // Guard against us getting leaked (leak amplification)
2015 unsafe { self.set_len(0); }
2027 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2029 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2030 /// append the entire slice at once.
2032 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2033 #[stable(feature = "extend_ref", since = "1.2.0")]
2034 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2035 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2036 self.spec_extend(iter.into_iter())
2040 macro_rules! __impl_slice_eq1 {
2041 ($Lhs: ty, $Rhs: ty) => {
2042 __impl_slice_eq1! { $Lhs, $Rhs, Sized }
2044 ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
2045 #[stable(feature = "rust1", since = "1.0.0")]
2046 impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
2048 fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
2050 fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
2055 __impl_slice_eq1! { Vec<A>, Vec<B> }
2056 __impl_slice_eq1! { Vec<A>, &'b [B] }
2057 __impl_slice_eq1! { Vec<A>, &'b mut [B] }
2058 __impl_slice_eq1! { Cow<'a, [A]>, &'b [B], Clone }
2059 __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B], Clone }
2060 __impl_slice_eq1! { Cow<'a, [A]>, Vec<B>, Clone }
2062 macro_rules! array_impls {
2065 // NOTE: some less important impls are omitted to reduce code bloat
2066 __impl_slice_eq1! { Vec<A>, [B; $N] }
2067 __impl_slice_eq1! { Vec<A>, &'b [B; $N] }
2068 // __impl_slice_eq1! { Vec<A>, &'b mut [B; $N] }
2069 // __impl_slice_eq1! { Cow<'a, [A]>, [B; $N], Clone }
2070 // __impl_slice_eq1! { Cow<'a, [A]>, &'b [B; $N], Clone }
2071 // __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B; $N], Clone }
2078 10 11 12 13 14 15 16 17 18 19
2079 20 21 22 23 24 25 26 27 28 29
2083 /// Implements comparison of vectors, lexicographically.
2084 #[stable(feature = "rust1", since = "1.0.0")]
2085 impl<T: PartialOrd> PartialOrd for Vec<T> {
2087 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2088 PartialOrd::partial_cmp(&**self, &**other)
2092 #[stable(feature = "rust1", since = "1.0.0")]
2093 impl<T: Eq> Eq for Vec<T> {}
2095 /// Implements ordering of vectors, lexicographically.
2096 #[stable(feature = "rust1", since = "1.0.0")]
2097 impl<T: Ord> Ord for Vec<T> {
2099 fn cmp(&self, other: &Vec<T>) -> Ordering {
2100 Ord::cmp(&**self, &**other)
2104 #[stable(feature = "rust1", since = "1.0.0")]
2105 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2106 fn drop(&mut self) {
2109 ptr::drop_in_place(&mut self[..]);
2111 // RawVec handles deallocation
2115 #[stable(feature = "rust1", since = "1.0.0")]
2116 impl<T> Default for Vec<T> {
2117 /// Creates an empty `Vec<T>`.
2118 fn default() -> Vec<T> {
2123 #[stable(feature = "rust1", since = "1.0.0")]
2124 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2125 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2126 fmt::Debug::fmt(&**self, f)
2130 #[stable(feature = "rust1", since = "1.0.0")]
2131 impl<T> AsRef<Vec<T>> for Vec<T> {
2132 fn as_ref(&self) -> &Vec<T> {
2137 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2138 impl<T> AsMut<Vec<T>> for Vec<T> {
2139 fn as_mut(&mut self) -> &mut Vec<T> {
2144 #[stable(feature = "rust1", since = "1.0.0")]
2145 impl<T> AsRef<[T]> for Vec<T> {
2146 fn as_ref(&self) -> &[T] {
2151 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2152 impl<T> AsMut<[T]> for Vec<T> {
2153 fn as_mut(&mut self) -> &mut [T] {
2158 #[stable(feature = "rust1", since = "1.0.0")]
2159 impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
2161 fn from(s: &'a [T]) -> Vec<T> {
2165 fn from(s: &'a [T]) -> Vec<T> {
2170 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2171 impl<'a, T: Clone> From<&'a mut [T]> for Vec<T> {
2173 fn from(s: &'a mut [T]) -> Vec<T> {
2177 fn from(s: &'a mut [T]) -> Vec<T> {
2182 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2183 impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
2184 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2189 // note: test pulls in libstd, which causes errors here
2191 #[stable(feature = "vec_from_box", since = "1.18.0")]
2192 impl<T> From<Box<[T]>> for Vec<T> {
2193 fn from(s: Box<[T]>) -> Vec<T> {
2198 // note: test pulls in libstd, which causes errors here
2200 #[stable(feature = "box_from_vec", since = "1.20.0")]
2201 impl<T> From<Vec<T>> for Box<[T]> {
2202 fn from(v: Vec<T>) -> Box<[T]> {
2203 v.into_boxed_slice()
2207 #[stable(feature = "rust1", since = "1.0.0")]
2208 impl<'a> From<&'a str> for Vec<u8> {
2209 fn from(s: &'a str) -> Vec<u8> {
2210 From::from(s.as_bytes())
2214 ////////////////////////////////////////////////////////////////////////////////
2216 ////////////////////////////////////////////////////////////////////////////////
2218 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2219 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2220 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2225 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2226 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2227 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2232 #[stable(feature = "rust1", since = "1.0.0")]
2233 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
2234 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2235 Cow::Owned(FromIterator::from_iter(it))
2239 ////////////////////////////////////////////////////////////////////////////////
2241 ////////////////////////////////////////////////////////////////////////////////
2243 /// An iterator that moves out of a vector.
2245 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
2246 /// by the [`IntoIterator`] trait).
2248 /// [`Vec`]: struct.Vec.html
2249 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2250 #[stable(feature = "rust1", since = "1.0.0")]
2251 pub struct IntoIter<T> {
2253 phantom: PhantomData<T>,
2259 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2260 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2261 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2262 f.debug_tuple("IntoIter")
2263 .field(&self.as_slice())
2268 impl<T> IntoIter<T> {
2269 /// Returns the remaining items of this iterator as a slice.
2274 /// let vec = vec!['a', 'b', 'c'];
2275 /// let mut into_iter = vec.into_iter();
2276 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2277 /// let _ = into_iter.next().unwrap();
2278 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2280 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2281 pub fn as_slice(&self) -> &[T] {
2283 slice::from_raw_parts(self.ptr, self.len())
2287 /// Returns the remaining items of this iterator as a mutable slice.
2292 /// let vec = vec!['a', 'b', 'c'];
2293 /// let mut into_iter = vec.into_iter();
2294 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2295 /// into_iter.as_mut_slice()[2] = 'z';
2296 /// assert_eq!(into_iter.next().unwrap(), 'a');
2297 /// assert_eq!(into_iter.next().unwrap(), 'b');
2298 /// assert_eq!(into_iter.next().unwrap(), 'z');
2300 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2301 pub fn as_mut_slice(&mut self) -> &mut [T] {
2303 slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
2308 #[stable(feature = "rust1", since = "1.0.0")]
2309 unsafe impl<T: Send> Send for IntoIter<T> {}
2310 #[stable(feature = "rust1", since = "1.0.0")]
2311 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2313 #[stable(feature = "rust1", since = "1.0.0")]
2314 impl<T> Iterator for IntoIter<T> {
2318 fn next(&mut self) -> Option<T> {
2320 if self.ptr as *const _ == self.end {
2323 if mem::size_of::<T>() == 0 {
2324 // purposefully don't use 'ptr.offset' because for
2325 // vectors with 0-size elements this would return the
2327 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2329 // Use a non-null pointer value
2330 // (self.ptr might be null because of wrapping)
2331 Some(ptr::read(1 as *mut T))
2334 self.ptr = self.ptr.offset(1);
2336 Some(ptr::read(old))
2343 fn size_hint(&self) -> (usize, Option<usize>) {
2344 let exact = match self.ptr.offset_to(self.end) {
2345 Some(x) => x as usize,
2346 None => (self.end as usize).wrapping_sub(self.ptr as usize),
2348 (exact, Some(exact))
2352 fn count(self) -> usize {
2357 #[stable(feature = "rust1", since = "1.0.0")]
2358 impl<T> DoubleEndedIterator for IntoIter<T> {
2360 fn next_back(&mut self) -> Option<T> {
2362 if self.end == self.ptr {
2365 if mem::size_of::<T>() == 0 {
2366 // See above for why 'ptr.offset' isn't used
2367 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2369 // Use a non-null pointer value
2370 // (self.end might be null because of wrapping)
2371 Some(ptr::read(1 as *mut T))
2373 self.end = self.end.offset(-1);
2375 Some(ptr::read(self.end))
2382 #[stable(feature = "rust1", since = "1.0.0")]
2383 impl<T> ExactSizeIterator for IntoIter<T> {
2384 fn is_empty(&self) -> bool {
2385 self.ptr == self.end
2389 #[stable(feature = "fused", since = "1.26.0")]
2390 impl<T> FusedIterator for IntoIter<T> {}
2392 #[unstable(feature = "trusted_len", issue = "37572")]
2393 unsafe impl<T> TrustedLen for IntoIter<T> {}
2395 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2396 impl<T: Clone> Clone for IntoIter<T> {
2397 fn clone(&self) -> IntoIter<T> {
2398 self.as_slice().to_owned().into_iter()
2402 #[stable(feature = "rust1", since = "1.0.0")]
2403 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2404 fn drop(&mut self) {
2405 // destroy the remaining elements
2406 for _x in self.by_ref() {}
2408 // RawVec handles deallocation
2409 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2413 /// A draining iterator for `Vec<T>`.
2415 /// This `struct` is created by the [`drain`] method on [`Vec`].
2417 /// [`drain`]: struct.Vec.html#method.drain
2418 /// [`Vec`]: struct.Vec.html
2419 #[stable(feature = "drain", since = "1.6.0")]
2420 pub struct Drain<'a, T: 'a> {
2421 /// Index of tail to preserve
2425 /// Current remaining range to remove
2426 iter: slice::Iter<'a, T>,
2427 vec: NonNull<Vec<T>>,
2430 #[stable(feature = "collection_debug", since = "1.17.0")]
2431 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Drain<'a, T> {
2432 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2433 f.debug_tuple("Drain")
2434 .field(&self.iter.as_slice())
2439 #[stable(feature = "drain", since = "1.6.0")]
2440 unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
2441 #[stable(feature = "drain", since = "1.6.0")]
2442 unsafe impl<'a, T: Send> Send for Drain<'a, T> {}
2444 #[stable(feature = "drain", since = "1.6.0")]
2445 impl<'a, T> Iterator for Drain<'a, T> {
2449 fn next(&mut self) -> Option<T> {
2450 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2453 fn size_hint(&self) -> (usize, Option<usize>) {
2454 self.iter.size_hint()
2458 #[stable(feature = "drain", since = "1.6.0")]
2459 impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
2461 fn next_back(&mut self) -> Option<T> {
2462 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2466 #[stable(feature = "drain", since = "1.6.0")]
2467 impl<'a, T> Drop for Drain<'a, T> {
2468 fn drop(&mut self) {
2469 // exhaust self first
2470 while let Some(_) = self.next() {}
2472 if self.tail_len > 0 {
2474 let source_vec = self.vec.as_mut();
2475 // memmove back untouched tail, update to new length
2476 let start = source_vec.len();
2477 let tail = self.tail_start;
2478 let src = source_vec.as_ptr().offset(tail as isize);
2479 let dst = source_vec.as_mut_ptr().offset(start as isize);
2480 ptr::copy(src, dst, self.tail_len);
2481 source_vec.set_len(start + self.tail_len);
2488 #[stable(feature = "drain", since = "1.6.0")]
2489 impl<'a, T> ExactSizeIterator for Drain<'a, T> {
2490 fn is_empty(&self) -> bool {
2491 self.iter.is_empty()
2495 #[stable(feature = "fused", since = "1.26.0")]
2496 impl<'a, T> FusedIterator for Drain<'a, T> {}
2498 /// A place for insertion at the back of a `Vec`.
2500 /// See [`Vec::place_back`](struct.Vec.html#method.place_back) for details.
2501 #[must_use = "places do nothing unless written to with `<-` syntax"]
2502 #[unstable(feature = "collection_placement",
2503 reason = "struct name and placement protocol are subject to change",
2506 pub struct PlaceBack<'a, T: 'a> {
2507 vec: &'a mut Vec<T>,
2510 #[unstable(feature = "collection_placement",
2511 reason = "placement protocol is subject to change",
2513 impl<'a, T> Placer<T> for PlaceBack<'a, T> {
2514 type Place = PlaceBack<'a, T>;
2516 fn make_place(self) -> Self {
2517 // This will panic or abort if we would allocate > isize::MAX bytes
2518 // or if the length increment would overflow for zero-sized types.
2519 if self.vec.len == self.vec.buf.cap() {
2520 self.vec.buf.double();
2526 #[unstable(feature = "collection_placement",
2527 reason = "placement protocol is subject to change",
2529 unsafe impl<'a, T> Place<T> for PlaceBack<'a, T> {
2530 fn pointer(&mut self) -> *mut T {
2531 unsafe { self.vec.as_mut_ptr().offset(self.vec.len as isize) }
2535 #[unstable(feature = "collection_placement",
2536 reason = "placement protocol is subject to change",
2538 impl<'a, T> InPlace<T> for PlaceBack<'a, T> {
2539 type Owner = &'a mut T;
2541 unsafe fn finalize(mut self) -> &'a mut T {
2542 let ptr = self.pointer();
2549 /// A splicing iterator for `Vec`.
2551 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2552 /// documentation for more.
2554 /// [`splice()`]: struct.Vec.html#method.splice
2555 /// [`Vec`]: struct.Vec.html
2557 #[stable(feature = "vec_splice", since = "1.21.0")]
2558 pub struct Splice<'a, I: Iterator + 'a> {
2559 drain: Drain<'a, I::Item>,
2563 #[stable(feature = "vec_splice", since = "1.21.0")]
2564 impl<'a, I: Iterator> Iterator for Splice<'a, I> {
2565 type Item = I::Item;
2567 fn next(&mut self) -> Option<Self::Item> {
2571 fn size_hint(&self) -> (usize, Option<usize>) {
2572 self.drain.size_hint()
2576 #[stable(feature = "vec_splice", since = "1.21.0")]
2577 impl<'a, I: Iterator> DoubleEndedIterator for Splice<'a, I> {
2578 fn next_back(&mut self) -> Option<Self::Item> {
2579 self.drain.next_back()
2583 #[stable(feature = "vec_splice", since = "1.21.0")]
2584 impl<'a, I: Iterator> ExactSizeIterator for Splice<'a, I> {}
2587 #[stable(feature = "vec_splice", since = "1.21.0")]
2588 impl<'a, I: Iterator> Drop for Splice<'a, I> {
2589 fn drop(&mut self) {
2590 // exhaust drain first
2591 while let Some(_) = self.drain.next() {}
2595 if self.drain.tail_len == 0 {
2596 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2600 // First fill the range left by drain().
2601 if !self.drain.fill(&mut self.replace_with) {
2605 // There may be more elements. Use the lower bound as an estimate.
2606 // FIXME: Is the upper bound a better guess? Or something else?
2607 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2608 if lower_bound > 0 {
2609 self.drain.move_tail(lower_bound);
2610 if !self.drain.fill(&mut self.replace_with) {
2615 // Collect any remaining elements.
2616 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2617 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2618 // Now we have an exact count.
2619 if collected.len() > 0 {
2620 self.drain.move_tail(collected.len());
2621 let filled = self.drain.fill(&mut collected);
2622 debug_assert!(filled);
2623 debug_assert_eq!(collected.len(), 0);
2626 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2630 /// Private helper methods for `Splice::drop`
2631 impl<'a, T> Drain<'a, T> {
2632 /// The range from `self.vec.len` to `self.tail_start` contains elements
2633 /// that have been moved out.
2634 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2635 /// Return whether we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2636 unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
2637 let vec = self.vec.as_mut();
2638 let range_start = vec.len;
2639 let range_end = self.tail_start;
2640 let range_slice = slice::from_raw_parts_mut(
2641 vec.as_mut_ptr().offset(range_start as isize),
2642 range_end - range_start);
2644 for place in range_slice {
2645 if let Some(new_item) = replace_with.next() {
2646 ptr::write(place, new_item);
2655 /// Make room for inserting more elements before the tail.
2656 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2657 let vec = self.vec.as_mut();
2658 let used_capacity = self.tail_start + self.tail_len;
2659 vec.buf.reserve(used_capacity, extra_capacity);
2661 let new_tail_start = self.tail_start + extra_capacity;
2662 let src = vec.as_ptr().offset(self.tail_start as isize);
2663 let dst = vec.as_mut_ptr().offset(new_tail_start as isize);
2664 ptr::copy(src, dst, self.tail_len);
2665 self.tail_start = new_tail_start;
2669 /// An iterator produced by calling `drain_filter` on Vec.
2670 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2672 pub struct DrainFilter<'a, T: 'a, F>
2673 where F: FnMut(&mut T) -> bool,
2675 vec: &'a mut Vec<T>,
2682 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2683 impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
2684 where F: FnMut(&mut T) -> bool,
2688 fn next(&mut self) -> Option<T> {
2690 while self.idx != self.old_len {
2693 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2694 if (self.pred)(&mut v[i]) {
2696 return Some(ptr::read(&v[i]));
2697 } else if self.del > 0 {
2699 let src: *const T = &v[i];
2700 let dst: *mut T = &mut v[i - del];
2701 // This is safe because self.vec has length 0
2702 // thus its elements will not have Drop::drop
2703 // called on them in the event of a panic.
2704 ptr::copy_nonoverlapping(src, dst, 1);
2711 fn size_hint(&self) -> (usize, Option<usize>) {
2712 (0, Some(self.old_len - self.idx))
2716 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2717 impl<'a, T, F> Drop for DrainFilter<'a, T, F>
2718 where F: FnMut(&mut T) -> bool,
2720 fn drop(&mut self) {
2721 for _ in self.by_ref() { }
2724 self.vec.set_len(self.old_len - self.del);