1 //! A contiguous growable array type with heap-allocated contents, written
4 //! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
5 //! `O(1)` pop (from the end).
7 //! Vectors ensure they never allocate more than `isize::MAX` bytes.
11 //! You can explicitly create a [`Vec<T>`] with [`new`]:
14 //! let v: Vec<i32> = Vec::new();
17 //! ...or by using the [`vec!`] macro:
20 //! let v: Vec<i32> = vec![];
22 //! let v = vec![1, 2, 3, 4, 5];
24 //! let v = vec![0; 10]; // ten zeroes
27 //! You can [`push`] values onto the end of a vector (which will grow the vector
31 //! let mut v = vec![1, 2];
36 //! Popping values works in much the same way:
39 //! let mut v = vec![1, 2];
41 //! let two = v.pop();
44 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
47 //! let mut v = vec![1, 2, 3];
52 //! [`Vec<T>`]: ../../std/vec/struct.Vec.html
53 //! [`new`]: ../../std/vec/struct.Vec.html#method.new
54 //! [`push`]: ../../std/vec/struct.Vec.html#method.push
55 //! [`Index`]: ../../std/ops/trait.Index.html
56 //! [`IndexMut`]: ../../std/ops/trait.IndexMut.html
57 //! [`vec!`]: ../../std/macro.vec.html
59 #![stable(feature = "rust1", since = "1.0.0")]
61 use core::array::LengthAtMost32;
62 use core::cmp::{self, Ordering};
64 use core::hash::{self, Hash};
65 use core::intrinsics::{arith_offset, assume};
66 use core::iter::{FromIterator, FusedIterator, TrustedLen};
67 use core::marker::PhantomData;
69 use core::ops::Bound::{Excluded, Included, Unbounded};
70 use core::ops::{self, Index, IndexMut, RangeBounds};
71 use core::ptr::{self, NonNull};
72 use core::slice::{self, SliceIndex};
74 use crate::borrow::{Cow, ToOwned};
75 use crate::boxed::Box;
76 use crate::collections::TryReserveError;
77 use crate::raw_vec::RawVec;
79 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
84 /// let mut vec = Vec::new();
88 /// assert_eq!(vec.len(), 2);
89 /// assert_eq!(vec[0], 1);
91 /// assert_eq!(vec.pop(), Some(2));
92 /// assert_eq!(vec.len(), 1);
95 /// assert_eq!(vec[0], 7);
97 /// vec.extend([1, 2, 3].iter().copied());
100 /// println!("{}", x);
102 /// assert_eq!(vec, [7, 1, 2, 3]);
105 /// The [`vec!`] macro is provided to make initialization more convenient:
108 /// let mut vec = vec![1, 2, 3];
110 /// assert_eq!(vec, [1, 2, 3, 4]);
113 /// It can also initialize each element of a `Vec<T>` with a given value.
114 /// This may be more efficient than performing allocation and initialization
115 /// in separate steps, especially when initializing a vector of zeros:
118 /// let vec = vec![0; 5];
119 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
121 /// // The following is equivalent, but potentially slower:
122 /// let mut vec1 = Vec::with_capacity(5);
123 /// vec1.resize(5, 0);
126 /// Use a `Vec<T>` as an efficient stack:
129 /// let mut stack = Vec::new();
135 /// while let Some(top) = stack.pop() {
136 /// // Prints 3, 2, 1
137 /// println!("{}", top);
143 /// The `Vec` type allows to access values by index, because it implements the
144 /// [`Index`] trait. An example will be more explicit:
147 /// let v = vec![0, 2, 4, 6];
148 /// println!("{}", v[1]); // it will display '2'
151 /// However be careful: if you try to access an index which isn't in the `Vec`,
152 /// your software will panic! You cannot do this:
155 /// let v = vec![0, 2, 4, 6];
156 /// println!("{}", v[6]); // it will panic!
159 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
164 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
165 /// To get a slice, use `&`. Example:
168 /// fn read_slice(slice: &[usize]) {
172 /// let v = vec![0, 1];
175 /// // ... and that's all!
176 /// // you can also do it like this:
177 /// let x : &[usize] = &v;
180 /// In Rust, it's more common to pass slices as arguments rather than vectors
181 /// when you just want to provide read access. The same goes for [`String`] and
184 /// # Capacity and reallocation
186 /// The capacity of a vector is the amount of space allocated for any future
187 /// elements that will be added onto the vector. This is not to be confused with
188 /// the *length* of a vector, which specifies the number of actual elements
189 /// within the vector. If a vector's length exceeds its capacity, its capacity
190 /// will automatically be increased, but its elements will have to be
193 /// For example, a vector with capacity 10 and length 0 would be an empty vector
194 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
195 /// vector will not change its capacity or cause reallocation to occur. However,
196 /// if the vector's length is increased to 11, it will have to reallocate, which
197 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
198 /// whenever possible to specify how big the vector is expected to get.
202 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
203 /// about its design. This ensures that it's as low-overhead as possible in
204 /// the general case, and can be correctly manipulated in primitive ways
205 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
206 /// If additional type parameters are added (e.g., to support custom allocators),
207 /// overriding their defaults may change the behavior.
209 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
210 /// triplet. No more, no less. The order of these fields is completely
211 /// unspecified, and you should use the appropriate methods to modify these.
212 /// The pointer will never be null, so this type is null-pointer-optimized.
214 /// However, the pointer may not actually point to allocated memory. In particular,
215 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
216 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
217 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
218 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
219 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
220 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
221 /// details are very subtle — if you intend to allocate memory using a `Vec`
222 /// and use it for something else (either to pass to unsafe code, or to build your
223 /// own memory-backed collection), be sure to deallocate this memory by using
224 /// `from_raw_parts` to recover the `Vec` and then dropping it.
226 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
227 /// (as defined by the allocator Rust is configured to use by default), and its
228 /// pointer points to [`len`] initialized, contiguous elements in order (what
229 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
230 /// `[`len`] logically uninitialized, contiguous elements.
232 /// `Vec` will never perform a "small optimization" where elements are actually
233 /// stored on the stack for two reasons:
235 /// * It would make it more difficult for unsafe code to correctly manipulate
236 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
237 /// only moved, and it would be more difficult to determine if a `Vec` had
238 /// actually allocated memory.
240 /// * It would penalize the general case, incurring an additional branch
243 /// `Vec` will never automatically shrink itself, even if completely empty. This
244 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
245 /// and then filling it back up to the same [`len`] should incur no calls to
246 /// the allocator. If you wish to free up unused memory, use
247 /// [`shrink_to_fit`].
249 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
250 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
251 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
252 /// accurate, and can be relied on. It can even be used to manually free the memory
253 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
254 /// when not necessary.
256 /// `Vec` does not guarantee any particular growth strategy when reallocating
257 /// when full, nor when [`reserve`] is called. The current strategy is basic
258 /// and it may prove desirable to use a non-constant growth factor. Whatever
259 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
261 /// `vec![x; n]`, `vec![a, b, c, d]`, and
262 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
263 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
264 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
265 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
267 /// `Vec` will not specifically overwrite any data that is removed from it,
268 /// but also won't specifically preserve it. Its uninitialized memory is
269 /// scratch space that it may use however it wants. It will generally just do
270 /// whatever is most efficient or otherwise easy to implement. Do not rely on
271 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
272 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
273 /// first, that may not actually happen because the optimizer does not consider
274 /// this a side-effect that must be preserved. There is one case which we will
275 /// not break, however: using `unsafe` code to write to the excess capacity,
276 /// and then increasing the length to match, is always valid.
278 /// `Vec` does not currently guarantee the order in which elements are dropped.
279 /// The order has changed in the past and may change again.
281 /// [`vec!`]: ../../std/macro.vec.html
282 /// [`get`]: ../../std/vec/struct.Vec.html#method.get
283 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
284 /// [`Index`]: ../../std/ops/trait.Index.html
285 /// [`String`]: ../../std/string/struct.String.html
286 /// [`&str`]: ../../std/primitive.str.html
287 /// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
288 /// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
289 /// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
290 /// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
291 /// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
292 /// [`len`]: ../../std/vec/struct.Vec.html#method.len
293 /// [`push`]: ../../std/vec/struct.Vec.html#method.push
294 /// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
295 /// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
296 /// [owned slice]: ../../std/boxed/struct.Box.html
297 #[stable(feature = "rust1", since = "1.0.0")]
298 #[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")]
304 ////////////////////////////////////////////////////////////////////////////////
306 ////////////////////////////////////////////////////////////////////////////////
309 /// Constructs a new, empty `Vec<T>`.
311 /// The vector will not allocate until elements are pushed onto it.
316 /// # #![allow(unused_mut)]
317 /// let mut vec: Vec<i32> = Vec::new();
320 #[rustc_const_stable(feature = "const_vec_new", since = "1.32.0")]
321 #[stable(feature = "rust1", since = "1.0.0")]
322 pub const fn new() -> Vec<T> {
323 Vec { buf: RawVec::NEW, len: 0 }
326 /// Constructs a new, empty `Vec<T>` with the specified capacity.
328 /// The vector will be able to hold exactly `capacity` elements without
329 /// reallocating. If `capacity` is 0, the vector will not allocate.
331 /// It is important to note that although the returned vector has the
332 /// *capacity* specified, the vector will have a zero *length*. For an
333 /// explanation of the difference between length and capacity, see
334 /// *[Capacity and reallocation]*.
336 /// [Capacity and reallocation]: #capacity-and-reallocation
341 /// let mut vec = Vec::with_capacity(10);
343 /// // The vector contains no items, even though it has capacity for more
344 /// assert_eq!(vec.len(), 0);
346 /// // These are all done without reallocating...
351 /// // ...but this may make the vector reallocate
355 #[stable(feature = "rust1", since = "1.0.0")]
356 pub fn with_capacity(capacity: usize) -> Vec<T> {
357 Vec { buf: RawVec::with_capacity(capacity), len: 0 }
360 /// Decomposes a `Vec<T>` into its raw components.
362 /// Returns the raw pointer to the underlying data, the length of
363 /// the vector (in elements), and the allocated capacity of the
364 /// data (in elements). These are the same arguments in the same
365 /// order as the arguments to [`from_raw_parts`].
367 /// After calling this function, the caller is responsible for the
368 /// memory previously managed by the `Vec`. The only way to do
369 /// this is to convert the raw pointer, length, and capacity back
370 /// into a `Vec` with the [`from_raw_parts`] function, allowing
371 /// the destructor to perform the cleanup.
373 /// [`from_raw_parts`]: #method.from_raw_parts
378 /// #![feature(vec_into_raw_parts)]
379 /// let v: Vec<i32> = vec![-1, 0, 1];
381 /// let (ptr, len, cap) = v.into_raw_parts();
383 /// let rebuilt = unsafe {
384 /// // We can now make changes to the components, such as
385 /// // transmuting the raw pointer to a compatible type.
386 /// let ptr = ptr as *mut u32;
388 /// Vec::from_raw_parts(ptr, len, cap)
390 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
392 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
393 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
394 let mut me = mem::ManuallyDrop::new(self);
395 (me.as_mut_ptr(), me.len(), me.capacity())
398 /// Creates a `Vec<T>` directly from the raw components of another vector.
402 /// This is highly unsafe, due to the number of invariants that aren't
405 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
406 /// (at least, it's highly likely to be incorrect if it wasn't).
407 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
408 /// * `length` needs to be less than or equal to `capacity`.
409 /// * `capacity` needs to be the capacity that the pointer was allocated with.
411 /// Violating these may cause problems like corrupting the allocator's
412 /// internal data structures. For example it is **not** safe
413 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
414 /// It's also not safe to build one from a `Vec<u16>` and its length, because
415 /// the allocator cares about the alignment, and these two types have different
416 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
417 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
419 /// The ownership of `ptr` is effectively transferred to the
420 /// `Vec<T>` which may then deallocate, reallocate or change the
421 /// contents of memory pointed to by the pointer at will. Ensure
422 /// that nothing else uses the pointer after calling this
425 /// [`String`]: ../../std/string/struct.String.html
433 /// let v = vec![1, 2, 3];
435 // FIXME Update this when vec_into_raw_parts is stabilized
436 /// // Prevent running `v`'s destructor so we are in complete control
437 /// // of the allocation.
438 /// let mut v = mem::ManuallyDrop::new(v);
440 /// // Pull out the various important pieces of information about `v`
441 /// let p = v.as_mut_ptr();
442 /// let len = v.len();
443 /// let cap = v.capacity();
446 /// // Overwrite memory with 4, 5, 6
447 /// for i in 0..len as isize {
448 /// ptr::write(p.offset(i), 4 + i);
451 /// // Put everything back together into a Vec
452 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
453 /// assert_eq!(rebuilt, [4, 5, 6]);
456 #[stable(feature = "rust1", since = "1.0.0")]
457 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
458 Vec { buf: RawVec::from_raw_parts(ptr, capacity), len: length }
461 /// Returns the number of elements the vector can hold without
467 /// let vec: Vec<i32> = Vec::with_capacity(10);
468 /// assert_eq!(vec.capacity(), 10);
471 #[stable(feature = "rust1", since = "1.0.0")]
472 pub fn capacity(&self) -> usize {
476 /// Reserves capacity for at least `additional` more elements to be inserted
477 /// in the given `Vec<T>`. The collection may reserve more space to avoid
478 /// frequent reallocations. After calling `reserve`, capacity will be
479 /// greater than or equal to `self.len() + additional`. Does nothing if
480 /// capacity is already sufficient.
484 /// Panics if the new capacity overflows `usize`.
489 /// let mut vec = vec![1];
491 /// assert!(vec.capacity() >= 11);
493 #[stable(feature = "rust1", since = "1.0.0")]
494 pub fn reserve(&mut self, additional: usize) {
495 self.buf.reserve(self.len, additional);
498 /// Reserves the minimum capacity for exactly `additional` more elements to
499 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
500 /// capacity will be greater than or equal to `self.len() + additional`.
501 /// Does nothing if the capacity is already sufficient.
503 /// Note that the allocator may give the collection more space than it
504 /// requests. Therefore, capacity can not be relied upon to be precisely
505 /// minimal. Prefer `reserve` if future insertions are expected.
509 /// Panics if the new capacity overflows `usize`.
514 /// let mut vec = vec![1];
515 /// vec.reserve_exact(10);
516 /// assert!(vec.capacity() >= 11);
518 #[stable(feature = "rust1", since = "1.0.0")]
519 pub fn reserve_exact(&mut self, additional: usize) {
520 self.buf.reserve_exact(self.len, additional);
523 /// Tries to reserve capacity for at least `additional` more elements to be inserted
524 /// in the given `Vec<T>`. The collection may reserve more space to avoid
525 /// frequent reallocations. After calling `reserve`, capacity will be
526 /// greater than or equal to `self.len() + additional`. Does nothing if
527 /// capacity is already sufficient.
531 /// If the capacity overflows, or the allocator reports a failure, then an error
537 /// #![feature(try_reserve)]
538 /// use std::collections::TryReserveError;
540 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
541 /// let mut output = Vec::new();
543 /// // Pre-reserve the memory, exiting if we can't
544 /// output.try_reserve(data.len())?;
546 /// // Now we know this can't OOM in the middle of our complex work
547 /// output.extend(data.iter().map(|&val| {
548 /// val * 2 + 5 // very complicated
553 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
555 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
556 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
557 self.buf.try_reserve(self.len, additional)
560 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
561 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
562 /// capacity will be greater than or equal to `self.len() + additional`.
563 /// Does nothing if the capacity is already sufficient.
565 /// Note that the allocator may give the collection more space than it
566 /// requests. Therefore, capacity can not be relied upon to be precisely
567 /// minimal. Prefer `reserve` if future insertions are expected.
571 /// If the capacity overflows, or the allocator reports a failure, then an error
577 /// #![feature(try_reserve)]
578 /// use std::collections::TryReserveError;
580 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
581 /// let mut output = Vec::new();
583 /// // Pre-reserve the memory, exiting if we can't
584 /// output.try_reserve(data.len())?;
586 /// // Now we know this can't OOM in the middle of our complex work
587 /// output.extend(data.iter().map(|&val| {
588 /// val * 2 + 5 // very complicated
593 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
595 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
596 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
597 self.buf.try_reserve_exact(self.len, additional)
600 /// Shrinks the capacity of the vector as much as possible.
602 /// It will drop down as close as possible to the length but the allocator
603 /// may still inform the vector that there is space for a few more elements.
608 /// let mut vec = Vec::with_capacity(10);
609 /// vec.extend([1, 2, 3].iter().cloned());
610 /// assert_eq!(vec.capacity(), 10);
611 /// vec.shrink_to_fit();
612 /// assert!(vec.capacity() >= 3);
614 #[stable(feature = "rust1", since = "1.0.0")]
615 pub fn shrink_to_fit(&mut self) {
616 if self.capacity() != self.len {
617 self.buf.shrink_to_fit(self.len);
621 /// Shrinks the capacity of the vector with a lower bound.
623 /// The capacity will remain at least as large as both the length
624 /// and the supplied value.
628 /// Panics if the current capacity is smaller than the supplied
629 /// minimum capacity.
634 /// #![feature(shrink_to)]
635 /// let mut vec = Vec::with_capacity(10);
636 /// vec.extend([1, 2, 3].iter().cloned());
637 /// assert_eq!(vec.capacity(), 10);
638 /// vec.shrink_to(4);
639 /// assert!(vec.capacity() >= 4);
640 /// vec.shrink_to(0);
641 /// assert!(vec.capacity() >= 3);
643 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
644 pub fn shrink_to(&mut self, min_capacity: usize) {
645 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
648 /// Converts the vector into [`Box<[T]>`][owned slice].
650 /// Note that this will drop any excess capacity.
652 /// [owned slice]: ../../std/boxed/struct.Box.html
657 /// let v = vec![1, 2, 3];
659 /// let slice = v.into_boxed_slice();
662 /// Any excess capacity is removed:
665 /// let mut vec = Vec::with_capacity(10);
666 /// vec.extend([1, 2, 3].iter().cloned());
668 /// assert_eq!(vec.capacity(), 10);
669 /// let slice = vec.into_boxed_slice();
670 /// assert_eq!(slice.into_vec().capacity(), 3);
672 #[stable(feature = "rust1", since = "1.0.0")]
673 pub fn into_boxed_slice(mut self) -> Box<[T]> {
675 self.shrink_to_fit();
676 let buf = ptr::read(&self.buf);
682 /// Shortens the vector, keeping the first `len` elements and dropping
685 /// If `len` is greater than the vector's current length, this has no
688 /// The [`drain`] method can emulate `truncate`, but causes the excess
689 /// elements to be returned instead of dropped.
691 /// Note that this method has no effect on the allocated capacity
696 /// Truncating a five element vector to two elements:
699 /// let mut vec = vec![1, 2, 3, 4, 5];
701 /// assert_eq!(vec, [1, 2]);
704 /// No truncation occurs when `len` is greater than the vector's current
708 /// let mut vec = vec![1, 2, 3];
710 /// assert_eq!(vec, [1, 2, 3]);
713 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
717 /// let mut vec = vec![1, 2, 3];
719 /// assert_eq!(vec, []);
722 /// [`clear`]: #method.clear
723 /// [`drain`]: #method.drain
724 #[stable(feature = "rust1", since = "1.0.0")]
725 pub fn truncate(&mut self, len: usize) {
726 // This is safe because:
728 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
729 // case avoids creating an invalid slice, and
730 // * the `len` of the vector is shrunk before calling `drop_in_place`,
731 // such that no value will be dropped twice in case `drop_in_place`
732 // were to panic once (if it panics twice, the program aborts).
737 let s = self.get_unchecked_mut(len..) as *mut _;
739 ptr::drop_in_place(s);
743 /// Extracts a slice containing the entire vector.
745 /// Equivalent to `&s[..]`.
750 /// use std::io::{self, Write};
751 /// let buffer = vec![1, 2, 3, 5, 8];
752 /// io::sink().write(buffer.as_slice()).unwrap();
755 #[stable(feature = "vec_as_slice", since = "1.7.0")]
756 pub fn as_slice(&self) -> &[T] {
760 /// Extracts a mutable slice of the entire vector.
762 /// Equivalent to `&mut s[..]`.
767 /// use std::io::{self, Read};
768 /// let mut buffer = vec![0; 3];
769 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
772 #[stable(feature = "vec_as_slice", since = "1.7.0")]
773 pub fn as_mut_slice(&mut self) -> &mut [T] {
777 /// Returns a raw pointer to the vector's buffer.
779 /// The caller must ensure that the vector outlives the pointer this
780 /// function returns, or else it will end up pointing to garbage.
781 /// Modifying the vector may cause its buffer to be reallocated,
782 /// which would also make any pointers to it invalid.
784 /// The caller must also ensure that the memory the pointer (non-transitively) points to
785 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
786 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
791 /// let x = vec![1, 2, 4];
792 /// let x_ptr = x.as_ptr();
795 /// for i in 0..x.len() {
796 /// assert_eq!(*x_ptr.add(i), 1 << i);
801 /// [`as_mut_ptr`]: #method.as_mut_ptr
802 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
804 pub fn as_ptr(&self) -> *const T {
805 // We shadow the slice method of the same name to avoid going through
806 // `deref`, which creates an intermediate reference.
807 let ptr = self.buf.ptr();
809 assume(!ptr.is_null());
814 /// Returns an unsafe mutable pointer to the vector's buffer.
816 /// The caller must ensure that the vector outlives the pointer this
817 /// function returns, or else it will end up pointing to garbage.
818 /// Modifying the vector may cause its buffer to be reallocated,
819 /// which would also make any pointers to it invalid.
824 /// // Allocate vector big enough for 4 elements.
826 /// let mut x: Vec<i32> = Vec::with_capacity(size);
827 /// let x_ptr = x.as_mut_ptr();
829 /// // Initialize elements via raw pointer writes, then set length.
831 /// for i in 0..size {
832 /// *x_ptr.add(i) = i as i32;
836 /// assert_eq!(&*x, &[0,1,2,3]);
838 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
840 pub fn as_mut_ptr(&mut self) -> *mut T {
841 // We shadow the slice method of the same name to avoid going through
842 // `deref_mut`, which creates an intermediate reference.
843 let ptr = self.buf.ptr();
845 assume(!ptr.is_null());
850 /// Forces the length of the vector to `new_len`.
852 /// This is a low-level operation that maintains none of the normal
853 /// invariants of the type. Normally changing the length of a vector
854 /// is done using one of the safe operations instead, such as
855 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
857 /// [`truncate`]: #method.truncate
858 /// [`resize`]: #method.resize
859 /// [`extend`]: ../../std/iter/trait.Extend.html#tymethod.extend
860 /// [`clear`]: #method.clear
864 /// - `new_len` must be less than or equal to [`capacity()`].
865 /// - The elements at `old_len..new_len` must be initialized.
867 /// [`capacity()`]: #method.capacity
871 /// This method can be useful for situations in which the vector
872 /// is serving as a buffer for other code, particularly over FFI:
875 /// # #![allow(dead_code)]
876 /// # // This is just a minimal skeleton for the doc example;
877 /// # // don't use this as a starting point for a real library.
878 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
879 /// # const Z_OK: i32 = 0;
881 /// # fn deflateGetDictionary(
882 /// # strm: *mut std::ffi::c_void,
883 /// # dictionary: *mut u8,
884 /// # dictLength: *mut usize,
887 /// # impl StreamWrapper {
888 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
889 /// // Per the FFI method's docs, "32768 bytes is always enough".
890 /// let mut dict = Vec::with_capacity(32_768);
891 /// let mut dict_length = 0;
892 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
893 /// // 1. `dict_length` elements were initialized.
894 /// // 2. `dict_length` <= the capacity (32_768)
895 /// // which makes `set_len` safe to call.
897 /// // Make the FFI call...
898 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
900 /// // ...and update the length to what was initialized.
901 /// dict.set_len(dict_length);
911 /// While the following example is sound, there is a memory leak since
912 /// the inner vectors were not freed prior to the `set_len` call:
915 /// let mut vec = vec![vec![1, 0, 0],
919 /// // 1. `old_len..0` is empty so no elements need to be initialized.
920 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
926 /// Normally, here, one would use [`clear`] instead to correctly drop
927 /// the contents and thus not leak memory.
929 #[stable(feature = "rust1", since = "1.0.0")]
930 pub unsafe fn set_len(&mut self, new_len: usize) {
931 debug_assert!(new_len <= self.capacity());
936 /// Removes an element from the vector and returns it.
938 /// The removed element is replaced by the last element of the vector.
940 /// This does not preserve ordering, but is O(1).
944 /// Panics if `index` is out of bounds.
949 /// let mut v = vec!["foo", "bar", "baz", "qux"];
951 /// assert_eq!(v.swap_remove(1), "bar");
952 /// assert_eq!(v, ["foo", "qux", "baz"]);
954 /// assert_eq!(v.swap_remove(0), "foo");
955 /// assert_eq!(v, ["baz", "qux"]);
958 #[stable(feature = "rust1", since = "1.0.0")]
959 pub fn swap_remove(&mut self, index: usize) -> T {
961 // We replace self[index] with the last element. Note that if the
962 // bounds check on hole succeeds there must be a last element (which
963 // can be self[index] itself).
964 let hole: *mut T = &mut self[index];
965 let last = ptr::read(self.get_unchecked(self.len - 1));
967 ptr::replace(hole, last)
971 /// Inserts an element at position `index` within the vector, shifting all
972 /// elements after it to the right.
976 /// Panics if `index > len`.
981 /// let mut vec = vec![1, 2, 3];
982 /// vec.insert(1, 4);
983 /// assert_eq!(vec, [1, 4, 2, 3]);
984 /// vec.insert(4, 5);
985 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
987 #[stable(feature = "rust1", since = "1.0.0")]
988 pub fn insert(&mut self, index: usize, element: T) {
989 let len = self.len();
990 assert!(index <= len);
992 // space for the new element
993 if len == self.buf.capacity() {
999 // The spot to put the new value
1001 let p = self.as_mut_ptr().add(index);
1002 // Shift everything over to make space. (Duplicating the
1003 // `index`th element into two consecutive places.)
1004 ptr::copy(p, p.offset(1), len - index);
1005 // Write it in, overwriting the first copy of the `index`th
1007 ptr::write(p, element);
1009 self.set_len(len + 1);
1013 /// Removes and returns the element at position `index` within the vector,
1014 /// shifting all elements after it to the left.
1018 /// Panics if `index` is out of bounds.
1023 /// let mut v = vec![1, 2, 3];
1024 /// assert_eq!(v.remove(1), 2);
1025 /// assert_eq!(v, [1, 3]);
1027 #[stable(feature = "rust1", since = "1.0.0")]
1028 pub fn remove(&mut self, index: usize) -> T {
1029 let len = self.len();
1030 assert!(index < len);
1035 // the place we are taking from.
1036 let ptr = self.as_mut_ptr().add(index);
1037 // copy it out, unsafely having a copy of the value on
1038 // the stack and in the vector at the same time.
1039 ret = ptr::read(ptr);
1041 // Shift everything down to fill in that spot.
1042 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1044 self.set_len(len - 1);
1049 /// Retains only the elements specified by the predicate.
1051 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1052 /// This method operates in place, visiting each element exactly once in the
1053 /// original order, and preserves the order of the retained elements.
1058 /// let mut vec = vec![1, 2, 3, 4];
1059 /// vec.retain(|&x| x % 2 == 0);
1060 /// assert_eq!(vec, [2, 4]);
1063 /// The exact order may be useful for tracking external state, like an index.
1066 /// let mut vec = vec![1, 2, 3, 4, 5];
1067 /// let keep = [false, true, true, false, true];
1069 /// vec.retain(|_| (keep[i], i += 1).0);
1070 /// assert_eq!(vec, [2, 3, 5]);
1072 #[stable(feature = "rust1", since = "1.0.0")]
1073 pub fn retain<F>(&mut self, mut f: F)
1075 F: FnMut(&T) -> bool,
1077 let len = self.len();
1080 let v = &mut **self;
1091 self.truncate(len - del);
1095 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1098 /// If the vector is sorted, this removes all duplicates.
1103 /// let mut vec = vec![10, 20, 21, 30, 20];
1105 /// vec.dedup_by_key(|i| *i / 10);
1107 /// assert_eq!(vec, [10, 20, 30, 20]);
1109 #[stable(feature = "dedup_by", since = "1.16.0")]
1111 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1113 F: FnMut(&mut T) -> K,
1116 self.dedup_by(|a, b| key(a) == key(b))
1119 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1122 /// The `same_bucket` function is passed references to two elements from the vector and
1123 /// must determine if the elements compare equal. The elements are passed in opposite order
1124 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1126 /// If the vector is sorted, this removes all duplicates.
1131 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1133 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1135 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1137 #[stable(feature = "dedup_by", since = "1.16.0")]
1138 pub fn dedup_by<F>(&mut self, same_bucket: F)
1140 F: FnMut(&mut T, &mut T) -> bool,
1143 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
1149 /// Appends an element to the back of a collection.
1153 /// Panics if the number of elements in the vector overflows a `usize`.
1158 /// let mut vec = vec![1, 2];
1160 /// assert_eq!(vec, [1, 2, 3]);
1163 #[stable(feature = "rust1", since = "1.0.0")]
1164 pub fn push(&mut self, value: T) {
1165 // This will panic or abort if we would allocate > isize::MAX bytes
1166 // or if the length increment would overflow for zero-sized types.
1167 if self.len == self.buf.capacity() {
1171 let end = self.as_mut_ptr().add(self.len);
1172 ptr::write(end, value);
1177 /// Removes the last element from a vector and returns it, or [`None`] if it
1180 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1185 /// let mut vec = vec![1, 2, 3];
1186 /// assert_eq!(vec.pop(), Some(3));
1187 /// assert_eq!(vec, [1, 2]);
1190 #[stable(feature = "rust1", since = "1.0.0")]
1191 pub fn pop(&mut self) -> Option<T> {
1197 Some(ptr::read(self.get_unchecked(self.len())))
1202 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1206 /// Panics if the number of elements in the vector overflows a `usize`.
1211 /// let mut vec = vec![1, 2, 3];
1212 /// let mut vec2 = vec![4, 5, 6];
1213 /// vec.append(&mut vec2);
1214 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1215 /// assert_eq!(vec2, []);
1218 #[stable(feature = "append", since = "1.4.0")]
1219 pub fn append(&mut self, other: &mut Self) {
1221 self.append_elements(other.as_slice() as _);
1226 /// Appends elements to `Self` from other buffer.
1228 unsafe fn append_elements(&mut self, other: *const [T]) {
1229 let count = (*other).len();
1230 self.reserve(count);
1231 let len = self.len();
1232 ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count);
1236 /// Creates a draining iterator that removes the specified range in the vector
1237 /// and yields the removed items.
1239 /// Note 1: The element range is removed even if the iterator is only
1240 /// partially consumed or not consumed at all.
1242 /// Note 2: It is unspecified how many elements are removed from the vector
1243 /// if the `Drain` value is leaked.
1247 /// Panics if the starting point is greater than the end point or if
1248 /// the end point is greater than the length of the vector.
1253 /// let mut v = vec![1, 2, 3];
1254 /// let u: Vec<_> = v.drain(1..).collect();
1255 /// assert_eq!(v, &[1]);
1256 /// assert_eq!(u, &[2, 3]);
1258 /// // A full range clears the vector
1260 /// assert_eq!(v, &[]);
1262 #[stable(feature = "drain", since = "1.6.0")]
1263 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1265 R: RangeBounds<usize>,
1269 // When the Drain is first created, it shortens the length of
1270 // the source vector to make sure no uninitialized or moved-from elements
1271 // are accessible at all if the Drain's destructor never gets to run.
1273 // Drain will ptr::read out the values to remove.
1274 // When finished, remaining tail of the vec is copied back to cover
1275 // the hole, and the vector length is restored to the new length.
1277 let len = self.len();
1278 let start = match range.start_bound() {
1280 Excluded(&n) => n + 1,
1283 let end = match range.end_bound() {
1284 Included(&n) => n + 1,
1288 assert!(start <= end);
1289 assert!(end <= len);
1292 // set self.vec length's to start, to be safe in case Drain is leaked
1293 self.set_len(start);
1294 // Use the borrow in the IterMut to indicate borrowing behavior of the
1295 // whole Drain iterator (like &mut T).
1296 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1299 tail_len: len - end,
1300 iter: range_slice.iter(),
1301 vec: NonNull::from(self),
1306 /// Clears the vector, removing all values.
1308 /// Note that this method has no effect on the allocated capacity
1314 /// let mut v = vec![1, 2, 3];
1318 /// assert!(v.is_empty());
1321 #[stable(feature = "rust1", since = "1.0.0")]
1322 pub fn clear(&mut self) {
1326 /// Returns the number of elements in the vector, also referred to
1327 /// as its 'length'.
1332 /// let a = vec![1, 2, 3];
1333 /// assert_eq!(a.len(), 3);
1336 #[stable(feature = "rust1", since = "1.0.0")]
1337 pub fn len(&self) -> usize {
1341 /// Returns `true` if the vector contains no elements.
1346 /// let mut v = Vec::new();
1347 /// assert!(v.is_empty());
1350 /// assert!(!v.is_empty());
1352 #[stable(feature = "rust1", since = "1.0.0")]
1353 pub fn is_empty(&self) -> bool {
1357 /// Splits the collection into two at the given index.
1359 /// Returns a newly allocated vector containing the elements in the range
1360 /// `[at, len)`. After the call, the original vector will be left containing
1361 /// the elements `[0, at)` with its previous capacity unchanged.
1365 /// Panics if `at > len`.
1370 /// let mut vec = vec![1,2,3];
1371 /// let vec2 = vec.split_off(1);
1372 /// assert_eq!(vec, [1]);
1373 /// assert_eq!(vec2, [2, 3]);
1376 #[stable(feature = "split_off", since = "1.4.0")]
1377 pub fn split_off(&mut self, at: usize) -> Self {
1378 assert!(at <= self.len(), "`at` out of bounds");
1380 let other_len = self.len - at;
1381 let mut other = Vec::with_capacity(other_len);
1383 // Unsafely `set_len` and copy items to `other`.
1386 other.set_len(other_len);
1388 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1393 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1395 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1396 /// difference, with each additional slot filled with the result of
1397 /// calling the closure `f`. The return values from `f` will end up
1398 /// in the `Vec` in the order they have been generated.
1400 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1402 /// This method uses a closure to create new values on every push. If
1403 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1404 /// to use the [`Default`] trait to generate values, you can pass
1405 /// [`Default::default()`] as the second argument.
1410 /// let mut vec = vec![1, 2, 3];
1411 /// vec.resize_with(5, Default::default);
1412 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1414 /// let mut vec = vec![];
1416 /// vec.resize_with(4, || { p *= 2; p });
1417 /// assert_eq!(vec, [2, 4, 8, 16]);
1420 /// [`resize`]: #method.resize
1421 /// [`Clone`]: ../../std/clone/trait.Clone.html
1422 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1423 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1427 let len = self.len();
1429 self.extend_with(new_len - len, ExtendFunc(f));
1431 self.truncate(new_len);
1435 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1436 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1437 /// `'a`. If the type has only static references, or none at all, then this
1438 /// may be chosen to be `'static`.
1440 /// This function is similar to the `leak` function on `Box`.
1442 /// This function is mainly useful for data that lives for the remainder of
1443 /// the program's life. Dropping the returned reference will cause a memory
1451 /// #![feature(vec_leak)]
1453 /// let x = vec![1, 2, 3];
1454 /// let static_ref: &'static mut [usize] = Vec::leak(x);
1455 /// static_ref[0] += 1;
1456 /// assert_eq!(static_ref, &[2, 2, 3]);
1458 #[unstable(feature = "vec_leak", issue = "62195")]
1460 pub fn leak<'a>(vec: Vec<T>) -> &'a mut [T]
1462 T: 'a, // Technically not needed, but kept to be explicit.
1464 Box::leak(vec.into_boxed_slice())
1468 impl<T: Clone> Vec<T> {
1469 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1471 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1472 /// difference, with each additional slot filled with `value`.
1473 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1475 /// This method requires [`Clone`] to be able clone the passed value. If
1476 /// you need more flexibility (or want to rely on [`Default`] instead of
1477 /// [`Clone`]), use [`resize_with`].
1482 /// let mut vec = vec!["hello"];
1483 /// vec.resize(3, "world");
1484 /// assert_eq!(vec, ["hello", "world", "world"]);
1486 /// let mut vec = vec![1, 2, 3, 4];
1487 /// vec.resize(2, 0);
1488 /// assert_eq!(vec, [1, 2]);
1491 /// [`Clone`]: ../../std/clone/trait.Clone.html
1492 /// [`Default`]: ../../std/default/trait.Default.html
1493 /// [`resize_with`]: #method.resize_with
1494 #[stable(feature = "vec_resize", since = "1.5.0")]
1495 pub fn resize(&mut self, new_len: usize, value: T) {
1496 let len = self.len();
1499 self.extend_with(new_len - len, ExtendElement(value))
1501 self.truncate(new_len);
1505 /// Clones and appends all elements in a slice to the `Vec`.
1507 /// Iterates over the slice `other`, clones each element, and then appends
1508 /// it to this `Vec`. The `other` vector is traversed in-order.
1510 /// Note that this function is same as [`extend`] except that it is
1511 /// specialized to work with slices instead. If and when Rust gets
1512 /// specialization this function will likely be deprecated (but still
1518 /// let mut vec = vec![1];
1519 /// vec.extend_from_slice(&[2, 3, 4]);
1520 /// assert_eq!(vec, [1, 2, 3, 4]);
1523 /// [`extend`]: #method.extend
1524 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1525 pub fn extend_from_slice(&mut self, other: &[T]) {
1526 self.spec_extend(other.iter())
1530 impl<T: Default> Vec<T> {
1531 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1533 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1534 /// difference, with each additional slot filled with [`Default::default()`].
1535 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1537 /// This method uses [`Default`] to create new values on every push. If
1538 /// you'd rather [`Clone`] a given value, use [`resize`].
1543 /// # #![allow(deprecated)]
1544 /// #![feature(vec_resize_default)]
1546 /// let mut vec = vec![1, 2, 3];
1547 /// vec.resize_default(5);
1548 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1550 /// let mut vec = vec![1, 2, 3, 4];
1551 /// vec.resize_default(2);
1552 /// assert_eq!(vec, [1, 2]);
1555 /// [`resize`]: #method.resize
1556 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1557 /// [`Default`]: ../../std/default/trait.Default.html
1558 /// [`Clone`]: ../../std/clone/trait.Clone.html
1559 #[unstable(feature = "vec_resize_default", issue = "41758")]
1561 reason = "This is moving towards being removed in favor \
1562 of `.resize_with(Default::default)`. If you disagree, please comment \
1563 in the tracking issue.",
1566 pub fn resize_default(&mut self, new_len: usize) {
1567 let len = self.len();
1570 self.extend_with(new_len - len, ExtendDefault);
1572 self.truncate(new_len);
1577 // This code generalises `extend_with_{element,default}`.
1578 trait ExtendWith<T> {
1579 fn next(&mut self) -> T;
1583 struct ExtendElement<T>(T);
1584 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1585 fn next(&mut self) -> T {
1588 fn last(self) -> T {
1593 struct ExtendDefault;
1594 impl<T: Default> ExtendWith<T> for ExtendDefault {
1595 fn next(&mut self) -> T {
1598 fn last(self) -> T {
1603 struct ExtendFunc<F>(F);
1604 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1605 fn next(&mut self) -> T {
1608 fn last(mut self) -> T {
1614 /// Extend the vector by `n` values, using the given generator.
1615 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1619 let mut ptr = self.as_mut_ptr().add(self.len());
1620 // Use SetLenOnDrop to work around bug where compiler
1621 // may not realize the store through `ptr` through self.set_len()
1623 let mut local_len = SetLenOnDrop::new(&mut self.len);
1625 // Write all elements except the last one
1627 ptr::write(ptr, value.next());
1628 ptr = ptr.offset(1);
1629 // Increment the length in every step in case next() panics
1630 local_len.increment_len(1);
1634 // We can write the last element directly without cloning needlessly
1635 ptr::write(ptr, value.last());
1636 local_len.increment_len(1);
1639 // len set by scope guard
1644 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1646 // The idea is: The length field in SetLenOnDrop is a local variable
1647 // that the optimizer will see does not alias with any stores through the Vec's data
1648 // pointer. This is a workaround for alias analysis issue #32155
1649 struct SetLenOnDrop<'a> {
1654 impl<'a> SetLenOnDrop<'a> {
1656 fn new(len: &'a mut usize) -> Self {
1657 SetLenOnDrop { local_len: *len, len: len }
1661 fn increment_len(&mut self, increment: usize) {
1662 self.local_len += increment;
1666 impl Drop for SetLenOnDrop<'_> {
1668 fn drop(&mut self) {
1669 *self.len = self.local_len;
1673 impl<T: PartialEq> Vec<T> {
1674 /// Removes consecutive repeated elements in the vector according to the
1675 /// [`PartialEq`] trait implementation.
1677 /// If the vector is sorted, this removes all duplicates.
1682 /// let mut vec = vec![1, 2, 2, 3, 2];
1686 /// assert_eq!(vec, [1, 2, 3, 2]);
1688 #[stable(feature = "rust1", since = "1.0.0")]
1690 pub fn dedup(&mut self) {
1691 self.dedup_by(|a, b| a == b)
1696 /// Removes the first instance of `item` from the vector if the item exists.
1701 /// # #![feature(vec_remove_item)]
1702 /// let mut vec = vec![1, 2, 3, 1];
1704 /// vec.remove_item(&1);
1706 /// assert_eq!(vec, vec![2, 3, 1]);
1708 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1709 pub fn remove_item<V>(&mut self, item: &V) -> Option<T>
1713 let pos = self.iter().position(|x| *x == *item)?;
1714 Some(self.remove(pos))
1718 ////////////////////////////////////////////////////////////////////////////////
1719 // Internal methods and functions
1720 ////////////////////////////////////////////////////////////////////////////////
1723 #[stable(feature = "rust1", since = "1.0.0")]
1724 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1725 <T as SpecFromElem>::from_elem(elem, n)
1728 // Specialization trait used for Vec::from_elem
1729 trait SpecFromElem: Sized {
1730 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1733 impl<T: Clone> SpecFromElem for T {
1734 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1735 let mut v = Vec::with_capacity(n);
1736 v.extend_with(n, ExtendElement(elem));
1741 impl SpecFromElem for u8 {
1743 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1745 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1748 let mut v = Vec::with_capacity(n);
1749 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1756 impl<T: Clone + IsZero> SpecFromElem for T {
1758 fn from_elem(elem: T, n: usize) -> Vec<T> {
1760 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1762 let mut v = Vec::with_capacity(n);
1763 v.extend_with(n, ExtendElement(elem));
1768 unsafe trait IsZero {
1769 /// Whether this value is zero
1770 fn is_zero(&self) -> bool;
1773 macro_rules! impl_is_zero {
1774 ($t: ty, $is_zero: expr) => {
1775 unsafe impl IsZero for $t {
1777 fn is_zero(&self) -> bool {
1784 impl_is_zero!(i8, |x| x == 0);
1785 impl_is_zero!(i16, |x| x == 0);
1786 impl_is_zero!(i32, |x| x == 0);
1787 impl_is_zero!(i64, |x| x == 0);
1788 impl_is_zero!(i128, |x| x == 0);
1789 impl_is_zero!(isize, |x| x == 0);
1791 impl_is_zero!(u16, |x| x == 0);
1792 impl_is_zero!(u32, |x| x == 0);
1793 impl_is_zero!(u64, |x| x == 0);
1794 impl_is_zero!(u128, |x| x == 0);
1795 impl_is_zero!(usize, |x| x == 0);
1797 impl_is_zero!(bool, |x| x == false);
1798 impl_is_zero!(char, |x| x == '\0');
1800 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1801 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1803 unsafe impl<T> IsZero for *const T {
1805 fn is_zero(&self) -> bool {
1810 unsafe impl<T> IsZero for *mut T {
1812 fn is_zero(&self) -> bool {
1817 // `Option<&T>`, `Option<&mut T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
1818 // For fat pointers, the bytes that would be the pointer metadata in the `Some` variant
1819 // are padding in the `None` variant, so ignoring them and zero-initializing instead is ok.
1821 unsafe impl<T: ?Sized> IsZero for Option<&T> {
1823 fn is_zero(&self) -> bool {
1828 unsafe impl<T: ?Sized> IsZero for Option<&mut T> {
1830 fn is_zero(&self) -> bool {
1835 unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
1837 fn is_zero(&self) -> bool {
1842 ////////////////////////////////////////////////////////////////////////////////
1843 // Common trait implementations for Vec
1844 ////////////////////////////////////////////////////////////////////////////////
1846 #[stable(feature = "rust1", since = "1.0.0")]
1847 impl<T: Clone> Clone for Vec<T> {
1849 fn clone(&self) -> Vec<T> {
1850 <[T]>::to_vec(&**self)
1853 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1854 // required for this method definition, is not available. Instead use the
1855 // `slice::to_vec` function which is only available with cfg(test)
1856 // NB see the slice::hack module in slice.rs for more information
1858 fn clone(&self) -> Vec<T> {
1859 crate::slice::to_vec(&**self)
1862 fn clone_from(&mut self, other: &Vec<T>) {
1863 other.as_slice().clone_into(self);
1867 #[stable(feature = "rust1", since = "1.0.0")]
1868 impl<T: Hash> Hash for Vec<T> {
1870 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1871 Hash::hash(&**self, state)
1875 #[stable(feature = "rust1", since = "1.0.0")]
1876 #[rustc_on_unimplemented(
1877 message = "vector indices are of type `usize` or ranges of `usize`",
1878 label = "vector indices are of type `usize` or ranges of `usize`"
1880 impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> {
1881 type Output = I::Output;
1884 fn index(&self, index: I) -> &Self::Output {
1885 Index::index(&**self, index)
1889 #[stable(feature = "rust1", since = "1.0.0")]
1890 #[rustc_on_unimplemented(
1891 message = "vector indices are of type `usize` or ranges of `usize`",
1892 label = "vector indices are of type `usize` or ranges of `usize`"
1894 impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
1896 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1897 IndexMut::index_mut(&mut **self, index)
1901 #[stable(feature = "rust1", since = "1.0.0")]
1902 impl<T> ops::Deref for Vec<T> {
1905 fn deref(&self) -> &[T] {
1906 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
1910 #[stable(feature = "rust1", since = "1.0.0")]
1911 impl<T> ops::DerefMut for Vec<T> {
1912 fn deref_mut(&mut self) -> &mut [T] {
1913 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
1917 #[stable(feature = "rust1", since = "1.0.0")]
1918 impl<T> FromIterator<T> for Vec<T> {
1920 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1921 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1925 #[stable(feature = "rust1", since = "1.0.0")]
1926 impl<T> IntoIterator for Vec<T> {
1928 type IntoIter = IntoIter<T>;
1930 /// Creates a consuming iterator, that is, one that moves each value out of
1931 /// the vector (from start to end). The vector cannot be used after calling
1937 /// let v = vec!["a".to_string(), "b".to_string()];
1938 /// for s in v.into_iter() {
1939 /// // s has type String, not &String
1940 /// println!("{}", s);
1944 fn into_iter(mut self) -> IntoIter<T> {
1946 let begin = self.as_mut_ptr();
1947 let end = if mem::size_of::<T>() == 0 {
1948 arith_offset(begin as *const i8, self.len() as isize) as *const T
1950 begin.add(self.len()) as *const T
1952 let cap = self.buf.capacity();
1955 buf: NonNull::new_unchecked(begin),
1956 phantom: PhantomData,
1965 #[stable(feature = "rust1", since = "1.0.0")]
1966 impl<'a, T> IntoIterator for &'a Vec<T> {
1968 type IntoIter = slice::Iter<'a, T>;
1970 fn into_iter(self) -> slice::Iter<'a, T> {
1975 #[stable(feature = "rust1", since = "1.0.0")]
1976 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1977 type Item = &'a mut T;
1978 type IntoIter = slice::IterMut<'a, T>;
1980 fn into_iter(self) -> slice::IterMut<'a, T> {
1985 #[stable(feature = "rust1", since = "1.0.0")]
1986 impl<T> Extend<T> for Vec<T> {
1988 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1989 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1993 // Specialization trait used for Vec::from_iter and Vec::extend
1994 trait SpecExtend<T, I> {
1995 fn from_iter(iter: I) -> Self;
1996 fn spec_extend(&mut self, iter: I);
1999 impl<T, I> SpecExtend<T, I> for Vec<T>
2001 I: Iterator<Item = T>,
2003 default fn from_iter(mut iterator: I) -> Self {
2004 // Unroll the first iteration, as the vector is going to be
2005 // expanded on this iteration in every case when the iterable is not
2006 // empty, but the loop in extend_desugared() is not going to see the
2007 // vector being full in the few subsequent loop iterations.
2008 // So we get better branch prediction.
2009 let mut vector = match iterator.next() {
2010 None => return Vec::new(),
2012 let (lower, _) = iterator.size_hint();
2013 let mut vector = Vec::with_capacity(lower.saturating_add(1));
2015 ptr::write(vector.get_unchecked_mut(0), element);
2021 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
2025 default fn spec_extend(&mut self, iter: I) {
2026 self.extend_desugared(iter)
2030 impl<T, I> SpecExtend<T, I> for Vec<T>
2032 I: TrustedLen<Item = T>,
2034 default fn from_iter(iterator: I) -> Self {
2035 let mut vector = Vec::new();
2036 vector.spec_extend(iterator);
2040 default fn spec_extend(&mut self, iterator: I) {
2041 // This is the case for a TrustedLen iterator.
2042 let (low, high) = iterator.size_hint();
2043 if let Some(high_value) = high {
2047 "TrustedLen iterator's size hint is not exact: {:?}",
2051 if let Some(additional) = high {
2052 self.reserve(additional);
2054 let mut ptr = self.as_mut_ptr().add(self.len());
2055 let mut local_len = SetLenOnDrop::new(&mut self.len);
2056 iterator.for_each(move |element| {
2057 ptr::write(ptr, element);
2058 ptr = ptr.offset(1);
2059 // NB can't overflow since we would have had to alloc the address space
2060 local_len.increment_len(1);
2064 self.extend_desugared(iterator)
2069 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
2070 fn from_iter(iterator: IntoIter<T>) -> Self {
2071 // A common case is passing a vector into a function which immediately
2072 // re-collects into a vector. We can short circuit this if the IntoIter
2073 // has not been advanced at all.
2074 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
2076 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(), iterator.len(), iterator.cap);
2077 mem::forget(iterator);
2081 let mut vector = Vec::new();
2082 vector.spec_extend(iterator);
2087 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
2089 self.append_elements(iterator.as_slice() as _);
2091 iterator.ptr = iterator.end;
2095 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
2097 I: Iterator<Item = &'a T>,
2100 default fn from_iter(iterator: I) -> Self {
2101 SpecExtend::from_iter(iterator.cloned())
2104 default fn spec_extend(&mut self, iterator: I) {
2105 self.spec_extend(iterator.cloned())
2109 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
2113 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
2114 let slice = iterator.as_slice();
2115 self.reserve(slice.len());
2117 let len = self.len();
2118 self.set_len(len + slice.len());
2119 self.get_unchecked_mut(len..).copy_from_slice(slice);
2125 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2126 // This is the case for a general iterator.
2128 // This function should be the moral equivalent of:
2130 // for item in iterator {
2133 while let Some(element) = iterator.next() {
2134 let len = self.len();
2135 if len == self.capacity() {
2136 let (lower, _) = iterator.size_hint();
2137 self.reserve(lower.saturating_add(1));
2140 ptr::write(self.get_unchecked_mut(len), element);
2141 // NB can't overflow since we would have had to alloc the address space
2142 self.set_len(len + 1);
2147 /// Creates a splicing iterator that replaces the specified range in the vector
2148 /// with the given `replace_with` iterator and yields the removed items.
2149 /// `replace_with` does not need to be the same length as `range`.
2151 /// The element range is removed even if the iterator is not consumed until the end.
2153 /// It is unspecified how many elements are removed from the vector
2154 /// if the `Splice` value is leaked.
2156 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2158 /// This is optimal if:
2160 /// * The tail (elements in the vector after `range`) is empty,
2161 /// * or `replace_with` yields fewer elements than `range`’s length
2162 /// * or the lower bound of its `size_hint()` is exact.
2164 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2168 /// Panics if the starting point is greater than the end point or if
2169 /// the end point is greater than the length of the vector.
2174 /// let mut v = vec![1, 2, 3];
2175 /// let new = [7, 8];
2176 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2177 /// assert_eq!(v, &[7, 8, 3]);
2178 /// assert_eq!(u, &[1, 2]);
2181 #[stable(feature = "vec_splice", since = "1.21.0")]
2182 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
2184 R: RangeBounds<usize>,
2185 I: IntoIterator<Item = T>,
2187 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2190 /// Creates an iterator which uses a closure to determine if an element should be removed.
2192 /// If the closure returns true, then the element is removed and yielded.
2193 /// If the closure returns false, the element will remain in the vector and will not be yielded
2194 /// by the iterator.
2196 /// Using this method is equivalent to the following code:
2199 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2200 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2202 /// while i != vec.len() {
2203 /// if some_predicate(&mut vec[i]) {
2204 /// let val = vec.remove(i);
2205 /// // your code here
2211 /// # assert_eq!(vec, vec![1, 4, 5]);
2214 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2215 /// because it can backshift the elements of the array in bulk.
2217 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2218 /// regardless of whether you choose to keep or remove it.
2223 /// Splitting an array into evens and odds, reusing the original allocation:
2226 /// #![feature(drain_filter)]
2227 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2229 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2230 /// let odds = numbers;
2232 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2233 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2235 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2236 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
2238 F: FnMut(&mut T) -> bool,
2240 let old_len = self.len();
2242 // Guard against us getting leaked (leak amplification)
2247 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2251 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2253 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2254 /// append the entire slice at once.
2256 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2257 #[stable(feature = "extend_ref", since = "1.2.0")]
2258 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2259 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2260 self.spec_extend(iter.into_iter())
2264 macro_rules! __impl_slice_eq1 {
2265 ([$($vars:tt)*] $lhs:ty, $rhs:ty, $($constraints:tt)*) => {
2266 #[stable(feature = "rust1", since = "1.0.0")]
2267 impl<A, B, $($vars)*> PartialEq<$rhs> for $lhs
2273 fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
2275 fn ne(&self, other: &$rhs) -> bool { self[..] != other[..] }
2280 __impl_slice_eq1! { [] Vec<A>, Vec<B>, }
2281 __impl_slice_eq1! { [] Vec<A>, &[B], }
2282 __impl_slice_eq1! { [] Vec<A>, &mut [B], }
2283 __impl_slice_eq1! { [] Cow<'_, [A]>, &[B], A: Clone }
2284 __impl_slice_eq1! { [] Cow<'_, [A]>, &mut [B], A: Clone }
2285 __impl_slice_eq1! { [] Cow<'_, [A]>, Vec<B>, A: Clone }
2286 __impl_slice_eq1! { [const N: usize] Vec<A>, [B; N], [B; N]: LengthAtMost32 }
2287 __impl_slice_eq1! { [const N: usize] Vec<A>, &[B; N], [B; N]: LengthAtMost32 }
2289 // NOTE: some less important impls are omitted to reduce code bloat
2290 // FIXME(Centril): Reconsider this?
2291 //__impl_slice_eq1! { [const N: usize] Vec<A>, &mut [B; N], [B; N]: LengthAtMost32 }
2292 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, [B; N], [B; N]: LengthAtMost32 }
2293 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &[B; N], [B; N]: LengthAtMost32 }
2294 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &mut [B; N], [B; N]: LengthAtMost32 }
2296 /// Implements comparison of vectors, lexicographically.
2297 #[stable(feature = "rust1", since = "1.0.0")]
2298 impl<T: PartialOrd> PartialOrd for Vec<T> {
2300 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2301 PartialOrd::partial_cmp(&**self, &**other)
2305 #[stable(feature = "rust1", since = "1.0.0")]
2306 impl<T: Eq> Eq for Vec<T> {}
2308 /// Implements ordering of vectors, lexicographically.
2309 #[stable(feature = "rust1", since = "1.0.0")]
2310 impl<T: Ord> Ord for Vec<T> {
2312 fn cmp(&self, other: &Vec<T>) -> Ordering {
2313 Ord::cmp(&**self, &**other)
2317 #[stable(feature = "rust1", since = "1.0.0")]
2318 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2319 fn drop(&mut self) {
2322 ptr::drop_in_place(&mut self[..]);
2324 // RawVec handles deallocation
2328 #[stable(feature = "rust1", since = "1.0.0")]
2329 impl<T> Default for Vec<T> {
2330 /// Creates an empty `Vec<T>`.
2331 fn default() -> Vec<T> {
2336 #[stable(feature = "rust1", since = "1.0.0")]
2337 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2338 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2339 fmt::Debug::fmt(&**self, f)
2343 #[stable(feature = "rust1", since = "1.0.0")]
2344 impl<T> AsRef<Vec<T>> for Vec<T> {
2345 fn as_ref(&self) -> &Vec<T> {
2350 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2351 impl<T> AsMut<Vec<T>> for Vec<T> {
2352 fn as_mut(&mut self) -> &mut Vec<T> {
2357 #[stable(feature = "rust1", since = "1.0.0")]
2358 impl<T> AsRef<[T]> for Vec<T> {
2359 fn as_ref(&self) -> &[T] {
2364 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2365 impl<T> AsMut<[T]> for Vec<T> {
2366 fn as_mut(&mut self) -> &mut [T] {
2371 #[stable(feature = "rust1", since = "1.0.0")]
2372 impl<T: Clone> From<&[T]> for Vec<T> {
2374 fn from(s: &[T]) -> Vec<T> {
2378 fn from(s: &[T]) -> Vec<T> {
2379 crate::slice::to_vec(s)
2383 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2384 impl<T: Clone> From<&mut [T]> for Vec<T> {
2386 fn from(s: &mut [T]) -> Vec<T> {
2390 fn from(s: &mut [T]) -> Vec<T> {
2391 crate::slice::to_vec(s)
2395 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2396 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2398 [T]: ToOwned<Owned = Vec<T>>,
2400 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2405 // note: test pulls in libstd, which causes errors here
2407 #[stable(feature = "vec_from_box", since = "1.18.0")]
2408 impl<T> From<Box<[T]>> for Vec<T> {
2409 fn from(s: Box<[T]>) -> Vec<T> {
2414 // note: test pulls in libstd, which causes errors here
2416 #[stable(feature = "box_from_vec", since = "1.20.0")]
2417 impl<T> From<Vec<T>> for Box<[T]> {
2418 fn from(v: Vec<T>) -> Box<[T]> {
2419 v.into_boxed_slice()
2423 #[stable(feature = "rust1", since = "1.0.0")]
2424 impl From<&str> for Vec<u8> {
2425 fn from(s: &str) -> Vec<u8> {
2426 From::from(s.as_bytes())
2430 ////////////////////////////////////////////////////////////////////////////////
2432 ////////////////////////////////////////////////////////////////////////////////
2434 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2435 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2436 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2441 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2442 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2443 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2448 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2449 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2450 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2451 Cow::Borrowed(v.as_slice())
2455 #[stable(feature = "rust1", since = "1.0.0")]
2456 impl<'a, T> FromIterator<T> for Cow<'a, [T]>
2460 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2461 Cow::Owned(FromIterator::from_iter(it))
2465 ////////////////////////////////////////////////////////////////////////////////
2467 ////////////////////////////////////////////////////////////////////////////////
2469 /// An iterator that moves out of a vector.
2471 /// This `struct` is created by the `into_iter` method on [`Vec`] (provided
2472 /// by the [`IntoIterator`] trait).
2474 /// [`Vec`]: struct.Vec.html
2475 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2476 #[stable(feature = "rust1", since = "1.0.0")]
2477 pub struct IntoIter<T> {
2479 phantom: PhantomData<T>,
2485 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2486 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2487 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2488 f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
2492 impl<T> IntoIter<T> {
2493 /// Returns the remaining items of this iterator as a slice.
2498 /// let vec = vec!['a', 'b', 'c'];
2499 /// let mut into_iter = vec.into_iter();
2500 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2501 /// let _ = into_iter.next().unwrap();
2502 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2504 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2505 pub fn as_slice(&self) -> &[T] {
2506 unsafe { slice::from_raw_parts(self.ptr, self.len()) }
2509 /// Returns the remaining items of this iterator as a mutable slice.
2514 /// let vec = vec!['a', 'b', 'c'];
2515 /// let mut into_iter = vec.into_iter();
2516 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2517 /// into_iter.as_mut_slice()[2] = 'z';
2518 /// assert_eq!(into_iter.next().unwrap(), 'a');
2519 /// assert_eq!(into_iter.next().unwrap(), 'b');
2520 /// assert_eq!(into_iter.next().unwrap(), 'z');
2522 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2523 pub fn as_mut_slice(&mut self) -> &mut [T] {
2524 unsafe { slice::from_raw_parts_mut(self.ptr as *mut T, self.len()) }
2528 #[stable(feature = "rust1", since = "1.0.0")]
2529 unsafe impl<T: Send> Send for IntoIter<T> {}
2530 #[stable(feature = "rust1", since = "1.0.0")]
2531 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2533 #[stable(feature = "rust1", since = "1.0.0")]
2534 impl<T> Iterator for IntoIter<T> {
2538 fn next(&mut self) -> Option<T> {
2540 if self.ptr as *const _ == self.end {
2543 if mem::size_of::<T>() == 0 {
2544 // purposefully don't use 'ptr.offset' because for
2545 // vectors with 0-size elements this would return the
2547 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2549 // Make up a value of this ZST.
2553 self.ptr = self.ptr.offset(1);
2555 Some(ptr::read(old))
2562 fn size_hint(&self) -> (usize, Option<usize>) {
2563 let exact = if mem::size_of::<T>() == 0 {
2564 (self.end as usize).wrapping_sub(self.ptr as usize)
2566 unsafe { self.end.offset_from(self.ptr) as usize }
2568 (exact, Some(exact))
2572 fn count(self) -> usize {
2577 #[stable(feature = "rust1", since = "1.0.0")]
2578 impl<T> DoubleEndedIterator for IntoIter<T> {
2580 fn next_back(&mut self) -> Option<T> {
2582 if self.end == self.ptr {
2585 if mem::size_of::<T>() == 0 {
2586 // See above for why 'ptr.offset' isn't used
2587 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2589 // Make up a value of this ZST.
2592 self.end = self.end.offset(-1);
2594 Some(ptr::read(self.end))
2601 #[stable(feature = "rust1", since = "1.0.0")]
2602 impl<T> ExactSizeIterator for IntoIter<T> {
2603 fn is_empty(&self) -> bool {
2604 self.ptr == self.end
2608 #[stable(feature = "fused", since = "1.26.0")]
2609 impl<T> FusedIterator for IntoIter<T> {}
2611 #[unstable(feature = "trusted_len", issue = "37572")]
2612 unsafe impl<T> TrustedLen for IntoIter<T> {}
2614 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2615 impl<T: Clone> Clone for IntoIter<T> {
2616 fn clone(&self) -> IntoIter<T> {
2617 self.as_slice().to_owned().into_iter()
2621 #[stable(feature = "rust1", since = "1.0.0")]
2622 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2623 fn drop(&mut self) {
2624 // destroy the remaining elements
2625 for _x in self.by_ref() {}
2627 // RawVec handles deallocation
2628 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2632 /// A draining iterator for `Vec<T>`.
2634 /// This `struct` is created by the [`drain`] method on [`Vec`].
2636 /// [`drain`]: struct.Vec.html#method.drain
2637 /// [`Vec`]: struct.Vec.html
2638 #[stable(feature = "drain", since = "1.6.0")]
2639 pub struct Drain<'a, T: 'a> {
2640 /// Index of tail to preserve
2644 /// Current remaining range to remove
2645 iter: slice::Iter<'a, T>,
2646 vec: NonNull<Vec<T>>,
2649 #[stable(feature = "collection_debug", since = "1.17.0")]
2650 impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
2651 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2652 f.debug_tuple("Drain").field(&self.iter.as_slice()).finish()
2656 impl<'a, T> Drain<'a, T> {
2657 /// Returns the remaining items of this iterator as a slice.
2662 /// # #![feature(vec_drain_as_slice)]
2663 /// let mut vec = vec!['a', 'b', 'c'];
2664 /// let mut drain = vec.drain(..);
2665 /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']);
2666 /// let _ = drain.next().unwrap();
2667 /// assert_eq!(drain.as_slice(), &['b', 'c']);
2669 #[unstable(feature = "vec_drain_as_slice", reason = "recently added", issue = "58957")]
2670 pub fn as_slice(&self) -> &[T] {
2671 self.iter.as_slice()
2675 #[stable(feature = "drain", since = "1.6.0")]
2676 unsafe impl<T: Sync> Sync for Drain<'_, T> {}
2677 #[stable(feature = "drain", since = "1.6.0")]
2678 unsafe impl<T: Send> Send for Drain<'_, T> {}
2680 #[stable(feature = "drain", since = "1.6.0")]
2681 impl<T> Iterator for Drain<'_, T> {
2685 fn next(&mut self) -> Option<T> {
2686 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2689 fn size_hint(&self) -> (usize, Option<usize>) {
2690 self.iter.size_hint()
2694 #[stable(feature = "drain", since = "1.6.0")]
2695 impl<T> DoubleEndedIterator for Drain<'_, T> {
2697 fn next_back(&mut self) -> Option<T> {
2698 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2702 #[stable(feature = "drain", since = "1.6.0")]
2703 impl<T> Drop for Drain<'_, T> {
2704 fn drop(&mut self) {
2705 // exhaust self first
2706 self.for_each(drop);
2708 if self.tail_len > 0 {
2710 let source_vec = self.vec.as_mut();
2711 // memmove back untouched tail, update to new length
2712 let start = source_vec.len();
2713 let tail = self.tail_start;
2715 let src = source_vec.as_ptr().add(tail);
2716 let dst = source_vec.as_mut_ptr().add(start);
2717 ptr::copy(src, dst, self.tail_len);
2719 source_vec.set_len(start + self.tail_len);
2725 #[stable(feature = "drain", since = "1.6.0")]
2726 impl<T> ExactSizeIterator for Drain<'_, T> {
2727 fn is_empty(&self) -> bool {
2728 self.iter.is_empty()
2732 #[unstable(feature = "trusted_len", issue = "37572")]
2733 unsafe impl<T> TrustedLen for Drain<'_, T> {}
2735 #[stable(feature = "fused", since = "1.26.0")]
2736 impl<T> FusedIterator for Drain<'_, T> {}
2738 /// A splicing iterator for `Vec`.
2740 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2741 /// documentation for more.
2743 /// [`splice()`]: struct.Vec.html#method.splice
2744 /// [`Vec`]: struct.Vec.html
2746 #[stable(feature = "vec_splice", since = "1.21.0")]
2747 pub struct Splice<'a, I: Iterator + 'a> {
2748 drain: Drain<'a, I::Item>,
2752 #[stable(feature = "vec_splice", since = "1.21.0")]
2753 impl<I: Iterator> Iterator for Splice<'_, I> {
2754 type Item = I::Item;
2756 fn next(&mut self) -> Option<Self::Item> {
2760 fn size_hint(&self) -> (usize, Option<usize>) {
2761 self.drain.size_hint()
2765 #[stable(feature = "vec_splice", since = "1.21.0")]
2766 impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
2767 fn next_back(&mut self) -> Option<Self::Item> {
2768 self.drain.next_back()
2772 #[stable(feature = "vec_splice", since = "1.21.0")]
2773 impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}
2775 #[stable(feature = "vec_splice", since = "1.21.0")]
2776 impl<I: Iterator> Drop for Splice<'_, I> {
2777 fn drop(&mut self) {
2778 self.drain.by_ref().for_each(drop);
2781 if self.drain.tail_len == 0 {
2782 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2786 // First fill the range left by drain().
2787 if !self.drain.fill(&mut self.replace_with) {
2791 // There may be more elements. Use the lower bound as an estimate.
2792 // FIXME: Is the upper bound a better guess? Or something else?
2793 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2794 if lower_bound > 0 {
2795 self.drain.move_tail(lower_bound);
2796 if !self.drain.fill(&mut self.replace_with) {
2801 // Collect any remaining elements.
2802 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2803 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2804 // Now we have an exact count.
2805 if collected.len() > 0 {
2806 self.drain.move_tail(collected.len());
2807 let filled = self.drain.fill(&mut collected);
2808 debug_assert!(filled);
2809 debug_assert_eq!(collected.len(), 0);
2812 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2816 /// Private helper methods for `Splice::drop`
2817 impl<T> Drain<'_, T> {
2818 /// The range from `self.vec.len` to `self.tail_start` contains elements
2819 /// that have been moved out.
2820 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2821 /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2822 unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool {
2823 let vec = self.vec.as_mut();
2824 let range_start = vec.len;
2825 let range_end = self.tail_start;
2827 slice::from_raw_parts_mut(vec.as_mut_ptr().add(range_start), range_end - range_start);
2829 for place in range_slice {
2830 if let Some(new_item) = replace_with.next() {
2831 ptr::write(place, new_item);
2840 /// Makes room for inserting more elements before the tail.
2841 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2842 let vec = self.vec.as_mut();
2843 let used_capacity = self.tail_start + self.tail_len;
2844 vec.buf.reserve(used_capacity, extra_capacity);
2846 let new_tail_start = self.tail_start + extra_capacity;
2847 let src = vec.as_ptr().add(self.tail_start);
2848 let dst = vec.as_mut_ptr().add(new_tail_start);
2849 ptr::copy(src, dst, self.tail_len);
2850 self.tail_start = new_tail_start;
2854 /// An iterator produced by calling `drain_filter` on Vec.
2855 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2857 pub struct DrainFilter<'a, T, F>
2859 F: FnMut(&mut T) -> bool,
2861 vec: &'a mut Vec<T>,
2862 /// The index of the item that will be inspected by the next call to `next`.
2864 /// The number of items that have been drained (removed) thus far.
2866 /// The original length of `vec` prior to draining.
2868 /// The filter test predicate.
2870 /// A flag that indicates a panic has occurred in the filter test prodicate.
2871 /// This is used as a hint in the drop implmentation to prevent consumption
2872 /// of the remainder of the `DrainFilter`. Any unprocessed items will be
2873 /// backshifted in the `vec`, but no further items will be dropped or
2874 /// tested by the filter predicate.
2878 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2879 impl<T, F> Iterator for DrainFilter<'_, T, F>
2881 F: FnMut(&mut T) -> bool,
2885 fn next(&mut self) -> Option<T> {
2887 while self.idx < self.old_len {
2889 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2890 self.panic_flag = true;
2891 let drained = (self.pred)(&mut v[i]);
2892 self.panic_flag = false;
2893 // Update the index *after* the predicate is called. If the index
2894 // is updated prior and the predicate panics, the element at this
2895 // index would be leaked.
2899 return Some(ptr::read(&v[i]));
2900 } else if self.del > 0 {
2902 let src: *const T = &v[i];
2903 let dst: *mut T = &mut v[i - del];
2904 ptr::copy_nonoverlapping(src, dst, 1);
2911 fn size_hint(&self) -> (usize, Option<usize>) {
2912 (0, Some(self.old_len - self.idx))
2916 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2917 impl<T, F> Drop for DrainFilter<'_, T, F>
2919 F: FnMut(&mut T) -> bool,
2921 fn drop(&mut self) {
2922 struct BackshiftOnDrop<'a, 'b, T, F>
2924 F: FnMut(&mut T) -> bool,
2926 drain: &'b mut DrainFilter<'a, T, F>,
2929 impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F>
2931 F: FnMut(&mut T) -> bool,
2933 fn drop(&mut self) {
2935 if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
2936 // This is a pretty messed up state, and there isn't really an
2937 // obviously right thing to do. We don't want to keep trying
2938 // to execute `pred`, so we just backshift all the unprocessed
2939 // elements and tell the vec that they still exist. The backshift
2940 // is required to prevent a double-drop of the last successfully
2941 // drained item prior to a panic in the predicate.
2942 let ptr = self.drain.vec.as_mut_ptr();
2943 let src = ptr.add(self.drain.idx);
2944 let dst = src.sub(self.drain.del);
2945 let tail_len = self.drain.old_len - self.drain.idx;
2946 src.copy_to(dst, tail_len);
2948 self.drain.vec.set_len(self.drain.old_len - self.drain.del);
2953 let backshift = BackshiftOnDrop { drain: self };
2955 // Attempt to consume any remaining elements if the filter predicate
2956 // has not yet panicked. We'll backshift any remaining elements
2957 // whether we've already panicked or if the consumption here panics.
2958 if !backshift.drain.panic_flag {
2959 backshift.drain.for_each(drop);