1 // ignore-tidy-filelength
2 //! A contiguous growable array type with heap-allocated contents, written
5 //! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
6 //! `O(1)` pop (from the end).
8 //! Vectors ensure they never allocate more than `isize::MAX` bytes.
12 //! You can explicitly create a [`Vec<T>`] with [`new`]:
15 //! let v: Vec<i32> = Vec::new();
18 //! ...or by using the [`vec!`] macro:
21 //! let v: Vec<i32> = vec![];
23 //! let v = vec![1, 2, 3, 4, 5];
25 //! let v = vec![0; 10]; // ten zeroes
28 //! You can [`push`] values onto the end of a vector (which will grow the vector
32 //! let mut v = vec![1, 2];
37 //! Popping values works in much the same way:
40 //! let mut v = vec![1, 2];
42 //! let two = v.pop();
45 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
48 //! let mut v = vec![1, 2, 3];
53 //! [`Vec<T>`]: ../../std/vec/struct.Vec.html
54 //! [`new`]: ../../std/vec/struct.Vec.html#method.new
55 //! [`push`]: ../../std/vec/struct.Vec.html#method.push
56 //! [`Index`]: ../../std/ops/trait.Index.html
57 //! [`IndexMut`]: ../../std/ops/trait.IndexMut.html
58 //! [`vec!`]: ../../std/macro.vec.html
60 #![stable(feature = "rust1", since = "1.0.0")]
62 use core::cmp::{self, Ordering};
64 use core::hash::{Hash, Hasher};
65 use core::intrinsics::{arith_offset, assume};
66 use core::iter::{FromIterator, FusedIterator, TrustedLen};
67 use core::marker::PhantomData;
68 use core::mem::{self, ManuallyDrop, MaybeUninit};
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 = "1.39.0")]
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);
345 /// assert_eq!(vec.capacity(), 10);
347 /// // These are all done without reallocating...
351 /// assert_eq!(vec.len(), 10);
352 /// assert_eq!(vec.capacity(), 10);
354 /// // ...but this may make the vector reallocate
356 /// assert_eq!(vec.len(), 11);
357 /// assert!(vec.capacity() >= 11);
360 #[stable(feature = "rust1", since = "1.0.0")]
361 pub fn with_capacity(capacity: usize) -> Vec<T> {
362 Vec { buf: RawVec::with_capacity(capacity), len: 0 }
365 /// Decomposes a `Vec<T>` into its raw components.
367 /// Returns the raw pointer to the underlying data, the length of
368 /// the vector (in elements), and the allocated capacity of the
369 /// data (in elements). These are the same arguments in the same
370 /// order as the arguments to [`from_raw_parts`].
372 /// After calling this function, the caller is responsible for the
373 /// memory previously managed by the `Vec`. The only way to do
374 /// this is to convert the raw pointer, length, and capacity back
375 /// into a `Vec` with the [`from_raw_parts`] function, allowing
376 /// the destructor to perform the cleanup.
378 /// [`from_raw_parts`]: #method.from_raw_parts
383 /// #![feature(vec_into_raw_parts)]
384 /// let v: Vec<i32> = vec![-1, 0, 1];
386 /// let (ptr, len, cap) = v.into_raw_parts();
388 /// let rebuilt = unsafe {
389 /// // We can now make changes to the components, such as
390 /// // transmuting the raw pointer to a compatible type.
391 /// let ptr = ptr as *mut u32;
393 /// Vec::from_raw_parts(ptr, len, cap)
395 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
397 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
398 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
399 let mut me = ManuallyDrop::new(self);
400 (me.as_mut_ptr(), me.len(), me.capacity())
403 /// Creates a `Vec<T>` directly from the raw components of another vector.
407 /// This is highly unsafe, due to the number of invariants that aren't
410 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
411 /// (at least, it's highly likely to be incorrect if it wasn't).
412 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
413 /// (`T` having a less strict alignment is not sufficient, the alignment really
414 /// needs to be equal to satsify the [`dealloc`] requirement that memory must be
415 /// allocated and deallocated with the same layout.)
416 /// * `length` needs to be less than or equal to `capacity`.
417 /// * `capacity` needs to be the capacity that the pointer was allocated with.
419 /// Violating these may cause problems like corrupting the allocator's
420 /// internal data structures. For example it is **not** safe
421 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
422 /// It's also not safe to build one from a `Vec<u16>` and its length, because
423 /// the allocator cares about the alignment, and these two types have different
424 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
425 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
427 /// The ownership of `ptr` is effectively transferred to the
428 /// `Vec<T>` which may then deallocate, reallocate or change the
429 /// contents of memory pointed to by the pointer at will. Ensure
430 /// that nothing else uses the pointer after calling this
433 /// [`String`]: ../../std/string/struct.String.html
434 /// [`dealloc`]: ../../alloc/alloc/trait.GlobalAlloc.html#tymethod.dealloc
442 /// let v = vec![1, 2, 3];
444 // FIXME Update this when vec_into_raw_parts is stabilized
445 /// // Prevent running `v`'s destructor so we are in complete control
446 /// // of the allocation.
447 /// let mut v = mem::ManuallyDrop::new(v);
449 /// // Pull out the various important pieces of information about `v`
450 /// let p = v.as_mut_ptr();
451 /// let len = v.len();
452 /// let cap = v.capacity();
455 /// // Overwrite memory with 4, 5, 6
456 /// for i in 0..len as isize {
457 /// ptr::write(p.offset(i), 4 + i);
460 /// // Put everything back together into a Vec
461 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
462 /// assert_eq!(rebuilt, [4, 5, 6]);
465 #[stable(feature = "rust1", since = "1.0.0")]
466 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
467 unsafe { Vec { buf: RawVec::from_raw_parts(ptr, capacity), len: length } }
470 /// Returns the number of elements the vector can hold without
476 /// let vec: Vec<i32> = Vec::with_capacity(10);
477 /// assert_eq!(vec.capacity(), 10);
480 #[stable(feature = "rust1", since = "1.0.0")]
481 pub fn capacity(&self) -> usize {
485 /// Reserves capacity for at least `additional` more elements to be inserted
486 /// in the given `Vec<T>`. The collection may reserve more space to avoid
487 /// frequent reallocations. After calling `reserve`, capacity will be
488 /// greater than or equal to `self.len() + additional`. Does nothing if
489 /// capacity is already sufficient.
493 /// Panics if the new capacity exceeds `isize::MAX` bytes.
498 /// let mut vec = vec![1];
500 /// assert!(vec.capacity() >= 11);
502 #[stable(feature = "rust1", since = "1.0.0")]
503 pub fn reserve(&mut self, additional: usize) {
504 self.buf.reserve(self.len, additional);
507 /// Reserves the minimum capacity for exactly `additional` more elements to
508 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
509 /// capacity will be greater than or equal to `self.len() + additional`.
510 /// Does nothing if the capacity is already sufficient.
512 /// Note that the allocator may give the collection more space than it
513 /// requests. Therefore, capacity can not be relied upon to be precisely
514 /// minimal. Prefer `reserve` if future insertions are expected.
518 /// Panics if the new capacity overflows `usize`.
523 /// let mut vec = vec![1];
524 /// vec.reserve_exact(10);
525 /// assert!(vec.capacity() >= 11);
527 #[stable(feature = "rust1", since = "1.0.0")]
528 pub fn reserve_exact(&mut self, additional: usize) {
529 self.buf.reserve_exact(self.len, additional);
532 /// Tries to reserve capacity for at least `additional` more elements to be inserted
533 /// in the given `Vec<T>`. The collection may reserve more space to avoid
534 /// frequent reallocations. After calling `reserve`, capacity will be
535 /// greater than or equal to `self.len() + additional`. Does nothing if
536 /// capacity is already sufficient.
540 /// If the capacity overflows, or the allocator reports a failure, then an error
546 /// #![feature(try_reserve)]
547 /// use std::collections::TryReserveError;
549 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
550 /// let mut output = Vec::new();
552 /// // Pre-reserve the memory, exiting if we can't
553 /// output.try_reserve(data.len())?;
555 /// // Now we know this can't OOM in the middle of our complex work
556 /// output.extend(data.iter().map(|&val| {
557 /// val * 2 + 5 // very complicated
562 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
564 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
565 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
566 self.buf.try_reserve(self.len, additional)
569 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
570 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
571 /// capacity will be greater than or equal to `self.len() + additional`.
572 /// Does nothing if the capacity is already sufficient.
574 /// Note that the allocator may give the collection more space than it
575 /// requests. Therefore, capacity can not be relied upon to be precisely
576 /// minimal. Prefer `reserve` if future insertions are expected.
580 /// If the capacity overflows, or the allocator reports a failure, then an error
586 /// #![feature(try_reserve)]
587 /// use std::collections::TryReserveError;
589 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
590 /// let mut output = Vec::new();
592 /// // Pre-reserve the memory, exiting if we can't
593 /// output.try_reserve(data.len())?;
595 /// // Now we know this can't OOM in the middle of our complex work
596 /// output.extend(data.iter().map(|&val| {
597 /// val * 2 + 5 // very complicated
602 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
604 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
605 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
606 self.buf.try_reserve_exact(self.len, additional)
609 /// Shrinks the capacity of the vector as much as possible.
611 /// It will drop down as close as possible to the length but the allocator
612 /// may still inform the vector that there is space for a few more elements.
617 /// let mut vec = Vec::with_capacity(10);
618 /// vec.extend([1, 2, 3].iter().cloned());
619 /// assert_eq!(vec.capacity(), 10);
620 /// vec.shrink_to_fit();
621 /// assert!(vec.capacity() >= 3);
623 #[stable(feature = "rust1", since = "1.0.0")]
624 pub fn shrink_to_fit(&mut self) {
625 // The capacity is never less than the length, and there's nothing to do when
626 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
627 // by only calling it with a greater capacity.
628 if self.capacity() > self.len {
629 self.buf.shrink_to_fit(self.len);
633 /// Shrinks the capacity of the vector with a lower bound.
635 /// The capacity will remain at least as large as both the length
636 /// and the supplied value.
640 /// Panics if the current capacity is smaller than the supplied
641 /// minimum capacity.
646 /// #![feature(shrink_to)]
647 /// let mut vec = Vec::with_capacity(10);
648 /// vec.extend([1, 2, 3].iter().cloned());
649 /// assert_eq!(vec.capacity(), 10);
650 /// vec.shrink_to(4);
651 /// assert!(vec.capacity() >= 4);
652 /// vec.shrink_to(0);
653 /// assert!(vec.capacity() >= 3);
655 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
656 pub fn shrink_to(&mut self, min_capacity: usize) {
657 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
660 /// Converts the vector into [`Box<[T]>`][owned slice].
662 /// Note that this will drop any excess capacity.
664 /// [owned slice]: ../../std/boxed/struct.Box.html
669 /// let v = vec![1, 2, 3];
671 /// let slice = v.into_boxed_slice();
674 /// Any excess capacity is removed:
677 /// let mut vec = Vec::with_capacity(10);
678 /// vec.extend([1, 2, 3].iter().cloned());
680 /// assert_eq!(vec.capacity(), 10);
681 /// let slice = vec.into_boxed_slice();
682 /// assert_eq!(slice.into_vec().capacity(), 3);
684 #[stable(feature = "rust1", since = "1.0.0")]
685 pub fn into_boxed_slice(mut self) -> Box<[T]> {
687 self.shrink_to_fit();
688 let me = ManuallyDrop::new(self);
689 let buf = ptr::read(&me.buf);
691 buf.into_box(len).assume_init()
695 /// Shortens the vector, keeping the first `len` elements and dropping
698 /// If `len` is greater than the vector's current length, this has no
701 /// The [`drain`] method can emulate `truncate`, but causes the excess
702 /// elements to be returned instead of dropped.
704 /// Note that this method has no effect on the allocated capacity
709 /// Truncating a five element vector to two elements:
712 /// let mut vec = vec![1, 2, 3, 4, 5];
714 /// assert_eq!(vec, [1, 2]);
717 /// No truncation occurs when `len` is greater than the vector's current
721 /// let mut vec = vec![1, 2, 3];
723 /// assert_eq!(vec, [1, 2, 3]);
726 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
730 /// let mut vec = vec![1, 2, 3];
732 /// assert_eq!(vec, []);
735 /// [`clear`]: #method.clear
736 /// [`drain`]: #method.drain
737 #[stable(feature = "rust1", since = "1.0.0")]
738 pub fn truncate(&mut self, len: usize) {
739 // This is safe because:
741 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
742 // case avoids creating an invalid slice, and
743 // * the `len` of the vector is shrunk before calling `drop_in_place`,
744 // such that no value will be dropped twice in case `drop_in_place`
745 // were to panic once (if it panics twice, the program aborts).
750 let remaining_len = self.len - len;
751 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
753 ptr::drop_in_place(s);
757 /// Extracts a slice containing the entire vector.
759 /// Equivalent to `&s[..]`.
764 /// use std::io::{self, Write};
765 /// let buffer = vec![1, 2, 3, 5, 8];
766 /// io::sink().write(buffer.as_slice()).unwrap();
769 #[stable(feature = "vec_as_slice", since = "1.7.0")]
770 pub fn as_slice(&self) -> &[T] {
774 /// Extracts a mutable slice of the entire vector.
776 /// Equivalent to `&mut s[..]`.
781 /// use std::io::{self, Read};
782 /// let mut buffer = vec![0; 3];
783 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
786 #[stable(feature = "vec_as_slice", since = "1.7.0")]
787 pub fn as_mut_slice(&mut self) -> &mut [T] {
791 /// Returns a raw pointer to the vector's buffer.
793 /// The caller must ensure that the vector outlives the pointer this
794 /// function returns, or else it will end up pointing to garbage.
795 /// Modifying the vector may cause its buffer to be reallocated,
796 /// which would also make any pointers to it invalid.
798 /// The caller must also ensure that the memory the pointer (non-transitively) points to
799 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
800 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
805 /// let x = vec![1, 2, 4];
806 /// let x_ptr = x.as_ptr();
809 /// for i in 0..x.len() {
810 /// assert_eq!(*x_ptr.add(i), 1 << i);
815 /// [`as_mut_ptr`]: #method.as_mut_ptr
816 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
818 pub fn as_ptr(&self) -> *const T {
819 // We shadow the slice method of the same name to avoid going through
820 // `deref`, which creates an intermediate reference.
821 let ptr = self.buf.ptr();
823 assume(!ptr.is_null());
828 /// Returns an unsafe mutable pointer to the vector's buffer.
830 /// The caller must ensure that the vector outlives the pointer this
831 /// function returns, or else it will end up pointing to garbage.
832 /// Modifying the vector may cause its buffer to be reallocated,
833 /// which would also make any pointers to it invalid.
838 /// // Allocate vector big enough for 4 elements.
840 /// let mut x: Vec<i32> = Vec::with_capacity(size);
841 /// let x_ptr = x.as_mut_ptr();
843 /// // Initialize elements via raw pointer writes, then set length.
845 /// for i in 0..size {
846 /// *x_ptr.add(i) = i as i32;
850 /// assert_eq!(&*x, &[0,1,2,3]);
852 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
854 pub fn as_mut_ptr(&mut self) -> *mut T {
855 // We shadow the slice method of the same name to avoid going through
856 // `deref_mut`, which creates an intermediate reference.
857 let ptr = self.buf.ptr();
859 assume(!ptr.is_null());
864 /// Forces the length of the vector to `new_len`.
866 /// This is a low-level operation that maintains none of the normal
867 /// invariants of the type. Normally changing the length of a vector
868 /// is done using one of the safe operations instead, such as
869 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
871 /// [`truncate`]: #method.truncate
872 /// [`resize`]: #method.resize
873 /// [`extend`]: ../../std/iter/trait.Extend.html#tymethod.extend
874 /// [`clear`]: #method.clear
878 /// - `new_len` must be less than or equal to [`capacity()`].
879 /// - The elements at `old_len..new_len` must be initialized.
881 /// [`capacity()`]: #method.capacity
885 /// This method can be useful for situations in which the vector
886 /// is serving as a buffer for other code, particularly over FFI:
889 /// # #![allow(dead_code)]
890 /// # // This is just a minimal skeleton for the doc example;
891 /// # // don't use this as a starting point for a real library.
892 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
893 /// # const Z_OK: i32 = 0;
895 /// # fn deflateGetDictionary(
896 /// # strm: *mut std::ffi::c_void,
897 /// # dictionary: *mut u8,
898 /// # dictLength: *mut usize,
901 /// # impl StreamWrapper {
902 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
903 /// // Per the FFI method's docs, "32768 bytes is always enough".
904 /// let mut dict = Vec::with_capacity(32_768);
905 /// let mut dict_length = 0;
906 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
907 /// // 1. `dict_length` elements were initialized.
908 /// // 2. `dict_length` <= the capacity (32_768)
909 /// // which makes `set_len` safe to call.
911 /// // Make the FFI call...
912 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
914 /// // ...and update the length to what was initialized.
915 /// dict.set_len(dict_length);
925 /// While the following example is sound, there is a memory leak since
926 /// the inner vectors were not freed prior to the `set_len` call:
929 /// let mut vec = vec![vec![1, 0, 0],
933 /// // 1. `old_len..0` is empty so no elements need to be initialized.
934 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
940 /// Normally, here, one would use [`clear`] instead to correctly drop
941 /// the contents and thus not leak memory.
943 #[stable(feature = "rust1", since = "1.0.0")]
944 pub unsafe fn set_len(&mut self, new_len: usize) {
945 debug_assert!(new_len <= self.capacity());
950 /// Removes an element from the vector and returns it.
952 /// The removed element is replaced by the last element of the vector.
954 /// This does not preserve ordering, but is O(1).
958 /// Panics if `index` is out of bounds.
963 /// let mut v = vec!["foo", "bar", "baz", "qux"];
965 /// assert_eq!(v.swap_remove(1), "bar");
966 /// assert_eq!(v, ["foo", "qux", "baz"]);
968 /// assert_eq!(v.swap_remove(0), "foo");
969 /// assert_eq!(v, ["baz", "qux"]);
972 #[stable(feature = "rust1", since = "1.0.0")]
973 pub fn swap_remove(&mut self, index: usize) -> T {
976 fn assert_failed(index: usize, len: usize) -> ! {
977 panic!("swap_remove index (is {}) should be < len (is {})", index, len);
980 let len = self.len();
982 assert_failed(index, len);
985 // We replace self[index] with the last element. Note that if the
986 // bounds check above succeeds there must be a last element (which
987 // can be self[index] itself).
988 let last = ptr::read(self.as_ptr().add(len - 1));
989 let hole = self.as_mut_ptr().add(index);
990 self.set_len(len - 1);
991 ptr::replace(hole, last)
995 /// Inserts an element at position `index` within the vector, shifting all
996 /// elements after it to the right.
1000 /// Panics if `index > len`.
1005 /// let mut vec = vec![1, 2, 3];
1006 /// vec.insert(1, 4);
1007 /// assert_eq!(vec, [1, 4, 2, 3]);
1008 /// vec.insert(4, 5);
1009 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1011 #[stable(feature = "rust1", since = "1.0.0")]
1012 pub fn insert(&mut self, index: usize, element: T) {
1015 fn assert_failed(index: usize, len: usize) -> ! {
1016 panic!("insertion index (is {}) should be <= len (is {})", index, len);
1019 let len = self.len();
1021 assert_failed(index, len);
1024 // space for the new element
1025 if len == self.buf.capacity() {
1031 // The spot to put the new value
1033 let p = self.as_mut_ptr().add(index);
1034 // Shift everything over to make space. (Duplicating the
1035 // `index`th element into two consecutive places.)
1036 ptr::copy(p, p.offset(1), len - index);
1037 // Write it in, overwriting the first copy of the `index`th
1039 ptr::write(p, element);
1041 self.set_len(len + 1);
1045 /// Removes and returns the element at position `index` within the vector,
1046 /// shifting all elements after it to the left.
1050 /// Panics if `index` is out of bounds.
1055 /// let mut v = vec![1, 2, 3];
1056 /// assert_eq!(v.remove(1), 2);
1057 /// assert_eq!(v, [1, 3]);
1059 #[stable(feature = "rust1", since = "1.0.0")]
1060 pub fn remove(&mut self, index: usize) -> T {
1063 fn assert_failed(index: usize, len: usize) -> ! {
1064 panic!("removal index (is {}) should be < len (is {})", index, len);
1067 let len = self.len();
1069 assert_failed(index, len);
1075 // the place we are taking from.
1076 let ptr = self.as_mut_ptr().add(index);
1077 // copy it out, unsafely having a copy of the value on
1078 // the stack and in the vector at the same time.
1079 ret = ptr::read(ptr);
1081 // Shift everything down to fill in that spot.
1082 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1084 self.set_len(len - 1);
1089 /// Retains only the elements specified by the predicate.
1091 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1092 /// This method operates in place, visiting each element exactly once in the
1093 /// original order, and preserves the order of the retained elements.
1098 /// let mut vec = vec![1, 2, 3, 4];
1099 /// vec.retain(|&x| x % 2 == 0);
1100 /// assert_eq!(vec, [2, 4]);
1103 /// The exact order may be useful for tracking external state, like an index.
1106 /// let mut vec = vec![1, 2, 3, 4, 5];
1107 /// let keep = [false, true, true, false, true];
1109 /// vec.retain(|_| (keep[i], i += 1).0);
1110 /// assert_eq!(vec, [2, 3, 5]);
1112 #[stable(feature = "rust1", since = "1.0.0")]
1113 pub fn retain<F>(&mut self, mut f: F)
1115 F: FnMut(&T) -> bool,
1117 let len = self.len();
1120 let v = &mut **self;
1131 self.truncate(len - del);
1135 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1138 /// If the vector is sorted, this removes all duplicates.
1143 /// let mut vec = vec![10, 20, 21, 30, 20];
1145 /// vec.dedup_by_key(|i| *i / 10);
1147 /// assert_eq!(vec, [10, 20, 30, 20]);
1149 #[stable(feature = "dedup_by", since = "1.16.0")]
1151 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1153 F: FnMut(&mut T) -> K,
1156 self.dedup_by(|a, b| key(a) == key(b))
1159 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1162 /// The `same_bucket` function is passed references to two elements from the vector and
1163 /// must determine if the elements compare equal. The elements are passed in opposite order
1164 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1166 /// If the vector is sorted, this removes all duplicates.
1171 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1173 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1175 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1177 #[stable(feature = "dedup_by", since = "1.16.0")]
1178 pub fn dedup_by<F>(&mut self, same_bucket: F)
1180 F: FnMut(&mut T, &mut T) -> bool,
1183 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
1189 /// Appends an element to the back of a collection.
1193 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1198 /// let mut vec = vec![1, 2];
1200 /// assert_eq!(vec, [1, 2, 3]);
1203 #[stable(feature = "rust1", since = "1.0.0")]
1204 pub fn push(&mut self, value: T) {
1205 // This will panic or abort if we would allocate > isize::MAX bytes
1206 // or if the length increment would overflow for zero-sized types.
1207 if self.len == self.buf.capacity() {
1211 let end = self.as_mut_ptr().add(self.len);
1212 ptr::write(end, value);
1217 /// Removes the last element from a vector and returns it, or [`None`] if it
1220 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1225 /// let mut vec = vec![1, 2, 3];
1226 /// assert_eq!(vec.pop(), Some(3));
1227 /// assert_eq!(vec, [1, 2]);
1230 #[stable(feature = "rust1", since = "1.0.0")]
1231 pub fn pop(&mut self) -> Option<T> {
1237 Some(ptr::read(self.as_ptr().add(self.len())))
1242 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1246 /// Panics if the number of elements in the vector overflows a `usize`.
1251 /// let mut vec = vec![1, 2, 3];
1252 /// let mut vec2 = vec![4, 5, 6];
1253 /// vec.append(&mut vec2);
1254 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1255 /// assert_eq!(vec2, []);
1258 #[stable(feature = "append", since = "1.4.0")]
1259 pub fn append(&mut self, other: &mut Self) {
1261 self.append_elements(other.as_slice() as _);
1266 /// Appends elements to `Self` from other buffer.
1268 unsafe fn append_elements(&mut self, other: *const [T]) {
1269 let count = unsafe { (*other).len() };
1270 self.reserve(count);
1271 let len = self.len();
1272 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1276 /// Creates a draining iterator that removes the specified range in the vector
1277 /// and yields the removed items.
1279 /// When the iterator **is** dropped, all elements in the range are removed
1280 /// from the vector, even if the iterator was not fully consumed. If the
1281 /// iterator **is not** dropped (with [`mem::forget`] for example), it is
1282 /// unspecified how many elements are removed.
1286 /// Panics if the starting point is greater than the end point or if
1287 /// the end point is greater than the length of the vector.
1292 /// let mut v = vec![1, 2, 3];
1293 /// let u: Vec<_> = v.drain(1..).collect();
1294 /// assert_eq!(v, &[1]);
1295 /// assert_eq!(u, &[2, 3]);
1297 /// // A full range clears the vector
1299 /// assert_eq!(v, &[]);
1301 #[stable(feature = "drain", since = "1.6.0")]
1302 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1304 R: RangeBounds<usize>,
1308 // When the Drain is first created, it shortens the length of
1309 // the source vector to make sure no uninitialized or moved-from elements
1310 // are accessible at all if the Drain's destructor never gets to run.
1312 // Drain will ptr::read out the values to remove.
1313 // When finished, remaining tail of the vec is copied back to cover
1314 // the hole, and the vector length is restored to the new length.
1316 let len = self.len();
1317 let start = match range.start_bound() {
1319 Excluded(&n) => n + 1,
1322 let end = match range.end_bound() {
1323 Included(&n) => n + 1,
1330 fn start_assert_failed(start: usize, end: usize) -> ! {
1331 panic!("start drain index (is {}) should be <= end drain index (is {})", start, end);
1336 fn end_assert_failed(end: usize, len: usize) -> ! {
1337 panic!("end drain index (is {}) should be <= len (is {})", end, len);
1341 start_assert_failed(start, end);
1344 end_assert_failed(end, len);
1348 // set self.vec length's to start, to be safe in case Drain is leaked
1349 self.set_len(start);
1350 // Use the borrow in the IterMut to indicate borrowing behavior of the
1351 // whole Drain iterator (like &mut T).
1352 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1355 tail_len: len - end,
1356 iter: range_slice.iter(),
1357 vec: NonNull::from(self),
1362 /// Clears the vector, removing all values.
1364 /// Note that this method has no effect on the allocated capacity
1370 /// let mut v = vec![1, 2, 3];
1374 /// assert!(v.is_empty());
1377 #[stable(feature = "rust1", since = "1.0.0")]
1378 pub fn clear(&mut self) {
1382 /// Returns the number of elements in the vector, also referred to
1383 /// as its 'length'.
1388 /// let a = vec![1, 2, 3];
1389 /// assert_eq!(a.len(), 3);
1392 #[stable(feature = "rust1", since = "1.0.0")]
1393 pub fn len(&self) -> usize {
1397 /// Returns `true` if the vector contains no elements.
1402 /// let mut v = Vec::new();
1403 /// assert!(v.is_empty());
1406 /// assert!(!v.is_empty());
1408 #[stable(feature = "rust1", since = "1.0.0")]
1409 pub fn is_empty(&self) -> bool {
1413 /// Splits the collection into two at the given index.
1415 /// Returns a newly allocated vector containing the elements in the range
1416 /// `[at, len)`. After the call, the original vector will be left containing
1417 /// the elements `[0, at)` with its previous capacity unchanged.
1421 /// Panics if `at > len`.
1426 /// let mut vec = vec![1,2,3];
1427 /// let vec2 = vec.split_off(1);
1428 /// assert_eq!(vec, [1]);
1429 /// assert_eq!(vec2, [2, 3]);
1432 #[must_use = "use `.truncate()` if you don't need the other half"]
1433 #[stable(feature = "split_off", since = "1.4.0")]
1434 pub fn split_off(&mut self, at: usize) -> Self {
1437 fn assert_failed(at: usize, len: usize) -> ! {
1438 panic!("`at` split index (is {}) should be <= len (is {})", at, len);
1441 if at > self.len() {
1442 assert_failed(at, self.len());
1445 let other_len = self.len - at;
1446 let mut other = Vec::with_capacity(other_len);
1448 // Unsafely `set_len` and copy items to `other`.
1451 other.set_len(other_len);
1453 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1458 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1460 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1461 /// difference, with each additional slot filled with the result of
1462 /// calling the closure `f`. The return values from `f` will end up
1463 /// in the `Vec` in the order they have been generated.
1465 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1467 /// This method uses a closure to create new values on every push. If
1468 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1469 /// to use the [`Default`] trait to generate values, you can pass
1470 /// [`Default::default()`] as the second argument.
1475 /// let mut vec = vec![1, 2, 3];
1476 /// vec.resize_with(5, Default::default);
1477 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1479 /// let mut vec = vec![];
1481 /// vec.resize_with(4, || { p *= 2; p });
1482 /// assert_eq!(vec, [2, 4, 8, 16]);
1485 /// [`resize`]: #method.resize
1486 /// [`Clone`]: ../../std/clone/trait.Clone.html
1487 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1488 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1492 let len = self.len();
1494 self.extend_with(new_len - len, ExtendFunc(f));
1496 self.truncate(new_len);
1500 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1501 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1502 /// `'a`. If the type has only static references, or none at all, then this
1503 /// may be chosen to be `'static`.
1505 /// This function is similar to the `leak` function on `Box`.
1507 /// This function is mainly useful for data that lives for the remainder of
1508 /// the program's life. Dropping the returned reference will cause a memory
1516 /// let x = vec![1, 2, 3];
1517 /// let static_ref: &'static mut [usize] = x.leak();
1518 /// static_ref[0] += 1;
1519 /// assert_eq!(static_ref, &[2, 2, 3]);
1521 #[stable(feature = "vec_leak", since = "1.47.0")]
1523 pub fn leak<'a>(self) -> &'a mut [T]
1525 T: 'a, // Technically not needed, but kept to be explicit.
1527 Box::leak(self.into_boxed_slice())
1530 /// Returns the remaining spare capacity of the vector as a slice of
1531 /// `MaybeUninit<T>`.
1533 /// The returned slice can be used to fill the vector with data (e.g. by
1534 /// reading from a file) before marking the data as initialized using the
1535 /// [`set_len`] method.
1537 /// [`set_len`]: #method.set_len
1542 /// #![feature(vec_spare_capacity, maybe_uninit_extra)]
1544 /// // Allocate vector big enough for 10 elements.
1545 /// let mut v = Vec::with_capacity(10);
1547 /// // Fill in the first 3 elements.
1548 /// let uninit = v.spare_capacity_mut();
1549 /// uninit[0].write(0);
1550 /// uninit[1].write(1);
1551 /// uninit[2].write(2);
1553 /// // Mark the first 3 elements of the vector as being initialized.
1558 /// assert_eq!(&v, &[0, 1, 2]);
1560 #[unstable(feature = "vec_spare_capacity", issue = "75017")]
1562 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
1564 slice::from_raw_parts_mut(
1565 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
1566 self.buf.capacity() - self.len,
1572 impl<T: Clone> Vec<T> {
1573 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1575 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1576 /// difference, with each additional slot filled with `value`.
1577 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1579 /// This method requires `T` to implement [`Clone`],
1580 /// in order to be able to clone the passed value.
1581 /// If you need more flexibility (or want to rely on [`Default`] instead of
1582 /// [`Clone`]), use [`resize_with`].
1587 /// let mut vec = vec!["hello"];
1588 /// vec.resize(3, "world");
1589 /// assert_eq!(vec, ["hello", "world", "world"]);
1591 /// let mut vec = vec![1, 2, 3, 4];
1592 /// vec.resize(2, 0);
1593 /// assert_eq!(vec, [1, 2]);
1596 /// [`Clone`]: ../../std/clone/trait.Clone.html
1597 /// [`Default`]: ../../std/default/trait.Default.html
1598 /// [`resize_with`]: #method.resize_with
1599 #[stable(feature = "vec_resize", since = "1.5.0")]
1600 pub fn resize(&mut self, new_len: usize, value: T) {
1601 let len = self.len();
1604 self.extend_with(new_len - len, ExtendElement(value))
1606 self.truncate(new_len);
1610 /// Clones and appends all elements in a slice to the `Vec`.
1612 /// Iterates over the slice `other`, clones each element, and then appends
1613 /// it to this `Vec`. The `other` vector is traversed in-order.
1615 /// Note that this function is same as [`extend`] except that it is
1616 /// specialized to work with slices instead. If and when Rust gets
1617 /// specialization this function will likely be deprecated (but still
1623 /// let mut vec = vec![1];
1624 /// vec.extend_from_slice(&[2, 3, 4]);
1625 /// assert_eq!(vec, [1, 2, 3, 4]);
1628 /// [`extend`]: #method.extend
1629 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1630 pub fn extend_from_slice(&mut self, other: &[T]) {
1631 self.spec_extend(other.iter())
1635 impl<T: Default> Vec<T> {
1636 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1638 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1639 /// difference, with each additional slot filled with [`Default::default()`].
1640 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1642 /// This method uses [`Default`] to create new values on every push. If
1643 /// you'd rather [`Clone`] a given value, use [`resize`].
1648 /// # #![allow(deprecated)]
1649 /// #![feature(vec_resize_default)]
1651 /// let mut vec = vec![1, 2, 3];
1652 /// vec.resize_default(5);
1653 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1655 /// let mut vec = vec![1, 2, 3, 4];
1656 /// vec.resize_default(2);
1657 /// assert_eq!(vec, [1, 2]);
1660 /// [`resize`]: #method.resize
1661 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1662 /// [`Default`]: ../../std/default/trait.Default.html
1663 /// [`Clone`]: ../../std/clone/trait.Clone.html
1664 #[unstable(feature = "vec_resize_default", issue = "41758")]
1666 reason = "This is moving towards being removed in favor \
1667 of `.resize_with(Default::default)`. If you disagree, please comment \
1668 in the tracking issue.",
1671 pub fn resize_default(&mut self, new_len: usize) {
1672 let len = self.len();
1675 self.extend_with(new_len - len, ExtendDefault);
1677 self.truncate(new_len);
1682 // This code generalizes `extend_with_{element,default}`.
1683 trait ExtendWith<T> {
1684 fn next(&mut self) -> T;
1688 struct ExtendElement<T>(T);
1689 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1690 fn next(&mut self) -> T {
1693 fn last(self) -> T {
1698 struct ExtendDefault;
1699 impl<T: Default> ExtendWith<T> for ExtendDefault {
1700 fn next(&mut self) -> T {
1703 fn last(self) -> T {
1708 struct ExtendFunc<F>(F);
1709 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1710 fn next(&mut self) -> T {
1713 fn last(mut self) -> T {
1719 /// Extend the vector by `n` values, using the given generator.
1720 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1724 let mut ptr = self.as_mut_ptr().add(self.len());
1725 // Use SetLenOnDrop to work around bug where compiler
1726 // may not realize the store through `ptr` through self.set_len()
1728 let mut local_len = SetLenOnDrop::new(&mut self.len);
1730 // Write all elements except the last one
1732 ptr::write(ptr, value.next());
1733 ptr = ptr.offset(1);
1734 // Increment the length in every step in case next() panics
1735 local_len.increment_len(1);
1739 // We can write the last element directly without cloning needlessly
1740 ptr::write(ptr, value.last());
1741 local_len.increment_len(1);
1744 // len set by scope guard
1749 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1751 // The idea is: The length field in SetLenOnDrop is a local variable
1752 // that the optimizer will see does not alias with any stores through the Vec's data
1753 // pointer. This is a workaround for alias analysis issue #32155
1754 struct SetLenOnDrop<'a> {
1759 impl<'a> SetLenOnDrop<'a> {
1761 fn new(len: &'a mut usize) -> Self {
1762 SetLenOnDrop { local_len: *len, len }
1766 fn increment_len(&mut self, increment: usize) {
1767 self.local_len += increment;
1771 impl Drop for SetLenOnDrop<'_> {
1773 fn drop(&mut self) {
1774 *self.len = self.local_len;
1778 impl<T: PartialEq> Vec<T> {
1779 /// Removes consecutive repeated elements in the vector according to the
1780 /// [`PartialEq`] trait implementation.
1782 /// If the vector is sorted, this removes all duplicates.
1787 /// let mut vec = vec![1, 2, 2, 3, 2];
1791 /// assert_eq!(vec, [1, 2, 3, 2]);
1793 #[stable(feature = "rust1", since = "1.0.0")]
1795 pub fn dedup(&mut self) {
1796 self.dedup_by(|a, b| a == b)
1801 /// Removes the first instance of `item` from the vector if the item exists.
1803 /// This method will be removed soon.
1804 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1806 reason = "Removing the first item equal to a needle is already easily possible \
1807 with iterators and the current Vec methods. Furthermore, having a method for \
1808 one particular case of removal (linear search, only the first item, no swap remove) \
1809 but not for others is inconsistent. This method will be removed soon.",
1812 pub fn remove_item<V>(&mut self, item: &V) -> Option<T>
1816 let pos = self.iter().position(|x| *x == *item)?;
1817 Some(self.remove(pos))
1821 ////////////////////////////////////////////////////////////////////////////////
1822 // Internal methods and functions
1823 ////////////////////////////////////////////////////////////////////////////////
1826 #[stable(feature = "rust1", since = "1.0.0")]
1827 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1828 <T as SpecFromElem>::from_elem(elem, n)
1831 // Specialization trait used for Vec::from_elem
1832 trait SpecFromElem: Sized {
1833 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1836 impl<T: Clone> SpecFromElem for T {
1837 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1838 let mut v = Vec::with_capacity(n);
1839 v.extend_with(n, ExtendElement(elem));
1844 impl SpecFromElem for i8 {
1846 fn from_elem(elem: i8, n: usize) -> Vec<i8> {
1848 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1851 let mut v = Vec::with_capacity(n);
1852 ptr::write_bytes(v.as_mut_ptr(), elem as u8, n);
1859 impl SpecFromElem for u8 {
1861 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1863 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1866 let mut v = Vec::with_capacity(n);
1867 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1874 impl<T: Clone + IsZero> SpecFromElem for T {
1876 fn from_elem(elem: T, n: usize) -> Vec<T> {
1878 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1880 let mut v = Vec::with_capacity(n);
1881 v.extend_with(n, ExtendElement(elem));
1886 #[rustc_specialization_trait]
1887 unsafe trait IsZero {
1888 /// Whether this value is zero
1889 fn is_zero(&self) -> bool;
1892 macro_rules! impl_is_zero {
1893 ($t:ty, $is_zero:expr) => {
1894 unsafe impl IsZero for $t {
1896 fn is_zero(&self) -> bool {
1903 impl_is_zero!(i16, |x| x == 0);
1904 impl_is_zero!(i32, |x| x == 0);
1905 impl_is_zero!(i64, |x| x == 0);
1906 impl_is_zero!(i128, |x| x == 0);
1907 impl_is_zero!(isize, |x| x == 0);
1909 impl_is_zero!(u16, |x| x == 0);
1910 impl_is_zero!(u32, |x| x == 0);
1911 impl_is_zero!(u64, |x| x == 0);
1912 impl_is_zero!(u128, |x| x == 0);
1913 impl_is_zero!(usize, |x| x == 0);
1915 impl_is_zero!(bool, |x| x == false);
1916 impl_is_zero!(char, |x| x == '\0');
1918 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1919 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1921 unsafe impl<T> IsZero for *const T {
1923 fn is_zero(&self) -> bool {
1928 unsafe impl<T> IsZero for *mut T {
1930 fn is_zero(&self) -> bool {
1935 // `Option<&T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
1936 // For fat pointers, the bytes that would be the pointer metadata in the `Some`
1937 // variant are padding in the `None` variant, so ignoring them and
1938 // zero-initializing instead is ok.
1939 // `Option<&mut T>` never implements `Clone`, so there's no need for an impl of
1942 unsafe impl<T: ?Sized> IsZero for Option<&T> {
1944 fn is_zero(&self) -> bool {
1949 unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
1951 fn is_zero(&self) -> bool {
1956 ////////////////////////////////////////////////////////////////////////////////
1957 // Common trait implementations for Vec
1958 ////////////////////////////////////////////////////////////////////////////////
1960 #[stable(feature = "rust1", since = "1.0.0")]
1961 impl<T> ops::Deref for Vec<T> {
1964 fn deref(&self) -> &[T] {
1965 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
1969 #[stable(feature = "rust1", since = "1.0.0")]
1970 impl<T> ops::DerefMut for Vec<T> {
1971 fn deref_mut(&mut self) -> &mut [T] {
1972 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
1976 #[stable(feature = "rust1", since = "1.0.0")]
1977 impl<T: Clone> Clone for Vec<T> {
1979 fn clone(&self) -> Vec<T> {
1980 <[T]>::to_vec(&**self)
1983 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1984 // required for this method definition, is not available. Instead use the
1985 // `slice::to_vec` function which is only available with cfg(test)
1986 // NB see the slice::hack module in slice.rs for more information
1988 fn clone(&self) -> Vec<T> {
1989 crate::slice::to_vec(&**self)
1992 fn clone_from(&mut self, other: &Vec<T>) {
1993 other.as_slice().clone_into(self);
1997 #[stable(feature = "rust1", since = "1.0.0")]
1998 impl<T: Hash> Hash for Vec<T> {
2000 fn hash<H: Hasher>(&self, state: &mut H) {
2001 Hash::hash(&**self, state)
2005 #[stable(feature = "rust1", since = "1.0.0")]
2006 #[rustc_on_unimplemented(
2007 message = "vector indices are of type `usize` or ranges of `usize`",
2008 label = "vector indices are of type `usize` or ranges of `usize`"
2010 impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> {
2011 type Output = I::Output;
2014 fn index(&self, index: I) -> &Self::Output {
2015 Index::index(&**self, index)
2019 #[stable(feature = "rust1", since = "1.0.0")]
2020 #[rustc_on_unimplemented(
2021 message = "vector indices are of type `usize` or ranges of `usize`",
2022 label = "vector indices are of type `usize` or ranges of `usize`"
2024 impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
2026 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2027 IndexMut::index_mut(&mut **self, index)
2031 #[stable(feature = "rust1", since = "1.0.0")]
2032 impl<T> FromIterator<T> for Vec<T> {
2034 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2035 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
2039 #[stable(feature = "rust1", since = "1.0.0")]
2040 impl<T> IntoIterator for Vec<T> {
2042 type IntoIter = IntoIter<T>;
2044 /// Creates a consuming iterator, that is, one that moves each value out of
2045 /// the vector (from start to end). The vector cannot be used after calling
2051 /// let v = vec!["a".to_string(), "b".to_string()];
2052 /// for s in v.into_iter() {
2053 /// // s has type String, not &String
2054 /// println!("{}", s);
2058 fn into_iter(self) -> IntoIter<T> {
2060 let mut me = ManuallyDrop::new(self);
2061 let begin = me.as_mut_ptr();
2062 let end = if mem::size_of::<T>() == 0 {
2063 arith_offset(begin as *const i8, me.len() as isize) as *const T
2065 begin.add(me.len()) as *const T
2067 let cap = me.buf.capacity();
2069 buf: NonNull::new_unchecked(begin),
2070 phantom: PhantomData,
2079 #[stable(feature = "rust1", since = "1.0.0")]
2080 impl<'a, T> IntoIterator for &'a Vec<T> {
2082 type IntoIter = slice::Iter<'a, T>;
2084 fn into_iter(self) -> slice::Iter<'a, T> {
2089 #[stable(feature = "rust1", since = "1.0.0")]
2090 impl<'a, T> IntoIterator for &'a mut Vec<T> {
2091 type Item = &'a mut T;
2092 type IntoIter = slice::IterMut<'a, T>;
2094 fn into_iter(self) -> slice::IterMut<'a, T> {
2099 #[stable(feature = "rust1", since = "1.0.0")]
2100 impl<T> Extend<T> for Vec<T> {
2102 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2103 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2107 fn extend_one(&mut self, item: T) {
2112 fn extend_reserve(&mut self, additional: usize) {
2113 self.reserve(additional);
2117 // Specialization trait used for Vec::from_iter and Vec::extend
2118 trait SpecExtend<T, I> {
2119 fn from_iter(iter: I) -> Self;
2120 fn spec_extend(&mut self, iter: I);
2123 impl<T, I> SpecExtend<T, I> for Vec<T>
2125 I: Iterator<Item = T>,
2127 default fn from_iter(mut iterator: I) -> Self {
2128 // Unroll the first iteration, as the vector is going to be
2129 // expanded on this iteration in every case when the iterable is not
2130 // empty, but the loop in extend_desugared() is not going to see the
2131 // vector being full in the few subsequent loop iterations.
2132 // So we get better branch prediction.
2133 let mut vector = match iterator.next() {
2134 None => return Vec::new(),
2136 let (lower, _) = iterator.size_hint();
2137 let mut vector = Vec::with_capacity(lower.saturating_add(1));
2139 ptr::write(vector.as_mut_ptr(), element);
2145 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
2149 default fn spec_extend(&mut self, iter: I) {
2150 self.extend_desugared(iter)
2154 impl<T, I> SpecExtend<T, I> for Vec<T>
2156 I: TrustedLen<Item = T>,
2158 default fn from_iter(iterator: I) -> Self {
2159 let mut vector = Vec::new();
2160 vector.spec_extend(iterator);
2164 default fn spec_extend(&mut self, iterator: I) {
2165 // This is the case for a TrustedLen iterator.
2166 let (low, high) = iterator.size_hint();
2167 if let Some(high_value) = high {
2171 "TrustedLen iterator's size hint is not exact: {:?}",
2175 if let Some(additional) = high {
2176 self.reserve(additional);
2178 let mut ptr = self.as_mut_ptr().add(self.len());
2179 let mut local_len = SetLenOnDrop::new(&mut self.len);
2180 iterator.for_each(move |element| {
2181 ptr::write(ptr, element);
2182 ptr = ptr.offset(1);
2183 // NB can't overflow since we would have had to alloc the address space
2184 local_len.increment_len(1);
2188 self.extend_desugared(iterator)
2193 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
2194 fn from_iter(iterator: IntoIter<T>) -> Self {
2195 // A common case is passing a vector into a function which immediately
2196 // re-collects into a vector. We can short circuit this if the IntoIter
2197 // has not been advanced at all.
2198 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
2200 let it = ManuallyDrop::new(iterator);
2201 Vec::from_raw_parts(it.buf.as_ptr(), it.len(), it.cap)
2204 let mut vector = Vec::new();
2205 vector.spec_extend(iterator);
2210 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
2212 self.append_elements(iterator.as_slice() as _);
2214 iterator.ptr = iterator.end;
2218 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
2220 I: Iterator<Item = &'a T>,
2223 default fn from_iter(iterator: I) -> Self {
2224 SpecExtend::from_iter(iterator.cloned())
2227 default fn spec_extend(&mut self, iterator: I) {
2228 self.spec_extend(iterator.cloned())
2232 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
2236 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
2237 let slice = iterator.as_slice();
2238 self.reserve(slice.len());
2240 let len = self.len();
2241 let dst_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(len), slice.len());
2242 dst_slice.copy_from_slice(slice);
2243 self.set_len(len + slice.len());
2249 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2250 // This is the case for a general iterator.
2252 // This function should be the moral equivalent of:
2254 // for item in iterator {
2257 while let Some(element) = iterator.next() {
2258 let len = self.len();
2259 if len == self.capacity() {
2260 let (lower, _) = iterator.size_hint();
2261 self.reserve(lower.saturating_add(1));
2264 ptr::write(self.as_mut_ptr().add(len), element);
2265 // NB can't overflow since we would have had to alloc the address space
2266 self.set_len(len + 1);
2271 /// Creates a splicing iterator that replaces the specified range in the vector
2272 /// with the given `replace_with` iterator and yields the removed items.
2273 /// `replace_with` does not need to be the same length as `range`.
2275 /// `range` is removed even if the iterator is not consumed until the end.
2277 /// It is unspecified how many elements are removed from the vector
2278 /// if the `Splice` value is leaked.
2280 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2282 /// This is optimal if:
2284 /// * The tail (elements in the vector after `range`) is empty,
2285 /// * or `replace_with` yields fewer elements than `range`’s length
2286 /// * or the lower bound of its `size_hint()` is exact.
2288 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2292 /// Panics if the starting point is greater than the end point or if
2293 /// the end point is greater than the length of the vector.
2298 /// let mut v = vec![1, 2, 3];
2299 /// let new = [7, 8];
2300 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2301 /// assert_eq!(v, &[7, 8, 3]);
2302 /// assert_eq!(u, &[1, 2]);
2305 #[stable(feature = "vec_splice", since = "1.21.0")]
2306 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
2308 R: RangeBounds<usize>,
2309 I: IntoIterator<Item = T>,
2311 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2314 /// Creates an iterator which uses a closure to determine if an element should be removed.
2316 /// If the closure returns true, then the element is removed and yielded.
2317 /// If the closure returns false, the element will remain in the vector and will not be yielded
2318 /// by the iterator.
2320 /// Using this method is equivalent to the following code:
2323 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2324 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2326 /// while i != vec.len() {
2327 /// if some_predicate(&mut vec[i]) {
2328 /// let val = vec.remove(i);
2329 /// // your code here
2335 /// # assert_eq!(vec, vec![1, 4, 5]);
2338 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2339 /// because it can backshift the elements of the array in bulk.
2341 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2342 /// regardless of whether you choose to keep or remove it.
2347 /// Splitting an array into evens and odds, reusing the original allocation:
2350 /// #![feature(drain_filter)]
2351 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2353 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2354 /// let odds = numbers;
2356 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2357 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2359 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2360 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
2362 F: FnMut(&mut T) -> bool,
2364 let old_len = self.len();
2366 // Guard against us getting leaked (leak amplification)
2371 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2375 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2377 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2378 /// append the entire slice at once.
2380 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2381 #[stable(feature = "extend_ref", since = "1.2.0")]
2382 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2383 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2384 self.spec_extend(iter.into_iter())
2388 fn extend_one(&mut self, &item: &'a T) {
2393 fn extend_reserve(&mut self, additional: usize) {
2394 self.reserve(additional);
2398 macro_rules! __impl_slice_eq1 {
2399 ([$($vars:tt)*] $lhs:ty, $rhs:ty $(where $ty:ty: $bound:ident)?, #[$stability:meta]) => {
2401 impl<A, B, $($vars)*> PartialEq<$rhs> for $lhs
2407 fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
2409 fn ne(&self, other: &$rhs) -> bool { self[..] != other[..] }
2414 __impl_slice_eq1! { [] Vec<A>, Vec<B>, #[stable(feature = "rust1", since = "1.0.0")] }
2415 __impl_slice_eq1! { [] Vec<A>, &[B], #[stable(feature = "rust1", since = "1.0.0")] }
2416 __impl_slice_eq1! { [] Vec<A>, &mut [B], #[stable(feature = "rust1", since = "1.0.0")] }
2417 __impl_slice_eq1! { [] &[A], Vec<B>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] }
2418 __impl_slice_eq1! { [] &mut [A], Vec<B>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] }
2419 __impl_slice_eq1! { [] Cow<'_, [A]>, Vec<B> where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
2420 __impl_slice_eq1! { [] Cow<'_, [A]>, &[B] where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
2421 __impl_slice_eq1! { [] Cow<'_, [A]>, &mut [B] where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
2422 __impl_slice_eq1! { [const N: usize] Vec<A>, [B; N], #[stable(feature = "rust1", since = "1.0.0")] }
2423 __impl_slice_eq1! { [const N: usize] Vec<A>, &[B; N], #[stable(feature = "rust1", since = "1.0.0")] }
2425 // NOTE: some less important impls are omitted to reduce code bloat
2426 // FIXME(Centril): Reconsider this?
2427 //__impl_slice_eq1! { [const N: usize] Vec<A>, &mut [B; N], }
2428 //__impl_slice_eq1! { [const N: usize] [A; N], Vec<B>, }
2429 //__impl_slice_eq1! { [const N: usize] &[A; N], Vec<B>, }
2430 //__impl_slice_eq1! { [const N: usize] &mut [A; N], Vec<B>, }
2431 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, [B; N], }
2432 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &[B; N], }
2433 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &mut [B; N], }
2435 /// Implements comparison of vectors, lexicographically.
2436 #[stable(feature = "rust1", since = "1.0.0")]
2437 impl<T: PartialOrd> PartialOrd for Vec<T> {
2439 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2440 PartialOrd::partial_cmp(&**self, &**other)
2444 #[stable(feature = "rust1", since = "1.0.0")]
2445 impl<T: Eq> Eq for Vec<T> {}
2447 /// Implements ordering of vectors, lexicographically.
2448 #[stable(feature = "rust1", since = "1.0.0")]
2449 impl<T: Ord> Ord for Vec<T> {
2451 fn cmp(&self, other: &Vec<T>) -> Ordering {
2452 Ord::cmp(&**self, &**other)
2456 #[stable(feature = "rust1", since = "1.0.0")]
2457 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2458 fn drop(&mut self) {
2461 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2462 // could avoid questions of validity in certain cases
2463 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
2465 // RawVec handles deallocation
2469 #[stable(feature = "rust1", since = "1.0.0")]
2470 impl<T> Default for Vec<T> {
2471 /// Creates an empty `Vec<T>`.
2472 fn default() -> Vec<T> {
2477 #[stable(feature = "rust1", since = "1.0.0")]
2478 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2479 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2480 fmt::Debug::fmt(&**self, f)
2484 #[stable(feature = "rust1", since = "1.0.0")]
2485 impl<T> AsRef<Vec<T>> for Vec<T> {
2486 fn as_ref(&self) -> &Vec<T> {
2491 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2492 impl<T> AsMut<Vec<T>> for Vec<T> {
2493 fn as_mut(&mut self) -> &mut Vec<T> {
2498 #[stable(feature = "rust1", since = "1.0.0")]
2499 impl<T> AsRef<[T]> for Vec<T> {
2500 fn as_ref(&self) -> &[T] {
2505 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2506 impl<T> AsMut<[T]> for Vec<T> {
2507 fn as_mut(&mut self) -> &mut [T] {
2512 #[stable(feature = "rust1", since = "1.0.0")]
2513 impl<T: Clone> From<&[T]> for Vec<T> {
2515 fn from(s: &[T]) -> Vec<T> {
2519 fn from(s: &[T]) -> Vec<T> {
2520 crate::slice::to_vec(s)
2524 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2525 impl<T: Clone> From<&mut [T]> for Vec<T> {
2527 fn from(s: &mut [T]) -> Vec<T> {
2531 fn from(s: &mut [T]) -> Vec<T> {
2532 crate::slice::to_vec(s)
2536 #[stable(feature = "vec_from_array", since = "1.44.0")]
2537 impl<T, const N: usize> From<[T; N]> for Vec<T> {
2539 fn from(s: [T; N]) -> Vec<T> {
2540 <[T]>::into_vec(box s)
2543 fn from(s: [T; N]) -> Vec<T> {
2544 crate::slice::into_vec(box s)
2548 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2549 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2551 [T]: ToOwned<Owned = Vec<T>>,
2553 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2558 // note: test pulls in libstd, which causes errors here
2560 #[stable(feature = "vec_from_box", since = "1.18.0")]
2561 impl<T> From<Box<[T]>> for Vec<T> {
2562 fn from(s: Box<[T]>) -> Vec<T> {
2567 // note: test pulls in libstd, which causes errors here
2569 #[stable(feature = "box_from_vec", since = "1.20.0")]
2570 impl<T> From<Vec<T>> for Box<[T]> {
2571 fn from(v: Vec<T>) -> Box<[T]> {
2572 v.into_boxed_slice()
2576 #[stable(feature = "rust1", since = "1.0.0")]
2577 impl From<&str> for Vec<u8> {
2578 fn from(s: &str) -> Vec<u8> {
2579 From::from(s.as_bytes())
2583 ////////////////////////////////////////////////////////////////////////////////
2585 ////////////////////////////////////////////////////////////////////////////////
2587 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2588 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2589 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2594 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2595 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2596 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2601 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2602 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2603 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2604 Cow::Borrowed(v.as_slice())
2608 #[stable(feature = "rust1", since = "1.0.0")]
2609 impl<'a, T> FromIterator<T> for Cow<'a, [T]>
2613 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2614 Cow::Owned(FromIterator::from_iter(it))
2618 ////////////////////////////////////////////////////////////////////////////////
2620 ////////////////////////////////////////////////////////////////////////////////
2622 /// An iterator that moves out of a vector.
2624 /// This `struct` is created by the `into_iter` method on [`Vec`] (provided
2625 /// by the [`IntoIterator`] trait).
2626 #[stable(feature = "rust1", since = "1.0.0")]
2627 pub struct IntoIter<T> {
2629 phantom: PhantomData<T>,
2635 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2636 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2637 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2638 f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
2642 impl<T> IntoIter<T> {
2643 /// Returns the remaining items of this iterator as a slice.
2648 /// let vec = vec!['a', 'b', 'c'];
2649 /// let mut into_iter = vec.into_iter();
2650 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2651 /// let _ = into_iter.next().unwrap();
2652 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2654 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2655 pub fn as_slice(&self) -> &[T] {
2656 unsafe { slice::from_raw_parts(self.ptr, self.len()) }
2659 /// Returns the remaining items of this iterator as a mutable slice.
2664 /// let vec = vec!['a', 'b', 'c'];
2665 /// let mut into_iter = vec.into_iter();
2666 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2667 /// into_iter.as_mut_slice()[2] = 'z';
2668 /// assert_eq!(into_iter.next().unwrap(), 'a');
2669 /// assert_eq!(into_iter.next().unwrap(), 'b');
2670 /// assert_eq!(into_iter.next().unwrap(), 'z');
2672 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2673 pub fn as_mut_slice(&mut self) -> &mut [T] {
2674 unsafe { &mut *self.as_raw_mut_slice() }
2677 fn as_raw_mut_slice(&mut self) -> *mut [T] {
2678 ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len())
2682 #[stable(feature = "vec_intoiter_as_ref", since = "1.46.0")]
2683 impl<T> AsRef<[T]> for IntoIter<T> {
2684 fn as_ref(&self) -> &[T] {
2689 #[stable(feature = "rust1", since = "1.0.0")]
2690 unsafe impl<T: Send> Send for IntoIter<T> {}
2691 #[stable(feature = "rust1", since = "1.0.0")]
2692 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2694 #[stable(feature = "rust1", since = "1.0.0")]
2695 impl<T> Iterator for IntoIter<T> {
2699 fn next(&mut self) -> Option<T> {
2701 if self.ptr as *const _ == self.end {
2704 if mem::size_of::<T>() == 0 {
2705 // purposefully don't use 'ptr.offset' because for
2706 // vectors with 0-size elements this would return the
2708 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2710 // Make up a value of this ZST.
2714 self.ptr = self.ptr.offset(1);
2716 Some(ptr::read(old))
2723 fn size_hint(&self) -> (usize, Option<usize>) {
2724 let exact = if mem::size_of::<T>() == 0 {
2725 (self.end as usize).wrapping_sub(self.ptr as usize)
2727 unsafe { self.end.offset_from(self.ptr) as usize }
2729 (exact, Some(exact))
2733 fn count(self) -> usize {
2738 #[stable(feature = "rust1", since = "1.0.0")]
2739 impl<T> DoubleEndedIterator for IntoIter<T> {
2741 fn next_back(&mut self) -> Option<T> {
2743 if self.end == self.ptr {
2746 if mem::size_of::<T>() == 0 {
2747 // See above for why 'ptr.offset' isn't used
2748 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2750 // Make up a value of this ZST.
2753 self.end = self.end.offset(-1);
2755 Some(ptr::read(self.end))
2762 #[stable(feature = "rust1", since = "1.0.0")]
2763 impl<T> ExactSizeIterator for IntoIter<T> {
2764 fn is_empty(&self) -> bool {
2765 self.ptr == self.end
2769 #[stable(feature = "fused", since = "1.26.0")]
2770 impl<T> FusedIterator for IntoIter<T> {}
2772 #[unstable(feature = "trusted_len", issue = "37572")]
2773 unsafe impl<T> TrustedLen for IntoIter<T> {}
2775 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2776 impl<T: Clone> Clone for IntoIter<T> {
2777 fn clone(&self) -> IntoIter<T> {
2778 self.as_slice().to_owned().into_iter()
2782 #[stable(feature = "rust1", since = "1.0.0")]
2783 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2784 fn drop(&mut self) {
2785 struct DropGuard<'a, T>(&'a mut IntoIter<T>);
2787 impl<T> Drop for DropGuard<'_, T> {
2788 fn drop(&mut self) {
2789 // RawVec handles deallocation
2790 let _ = unsafe { RawVec::from_raw_parts(self.0.buf.as_ptr(), self.0.cap) };
2794 let guard = DropGuard(self);
2795 // destroy the remaining elements
2797 ptr::drop_in_place(guard.0.as_raw_mut_slice());
2799 // now `guard` will be dropped and do the rest
2803 /// A draining iterator for `Vec<T>`.
2805 /// This `struct` is created by [`Vec::drain`].
2806 #[stable(feature = "drain", since = "1.6.0")]
2807 pub struct Drain<'a, T: 'a> {
2808 /// Index of tail to preserve
2812 /// Current remaining range to remove
2813 iter: slice::Iter<'a, T>,
2814 vec: NonNull<Vec<T>>,
2817 #[stable(feature = "collection_debug", since = "1.17.0")]
2818 impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
2819 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2820 f.debug_tuple("Drain").field(&self.iter.as_slice()).finish()
2824 impl<'a, T> Drain<'a, T> {
2825 /// Returns the remaining items of this iterator as a slice.
2830 /// let mut vec = vec!['a', 'b', 'c'];
2831 /// let mut drain = vec.drain(..);
2832 /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']);
2833 /// let _ = drain.next().unwrap();
2834 /// assert_eq!(drain.as_slice(), &['b', 'c']);
2836 #[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
2837 pub fn as_slice(&self) -> &[T] {
2838 self.iter.as_slice()
2842 #[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
2843 impl<'a, T> AsRef<[T]> for Drain<'a, T> {
2844 fn as_ref(&self) -> &[T] {
2849 #[stable(feature = "drain", since = "1.6.0")]
2850 unsafe impl<T: Sync> Sync for Drain<'_, T> {}
2851 #[stable(feature = "drain", since = "1.6.0")]
2852 unsafe impl<T: Send> Send for Drain<'_, T> {}
2854 #[stable(feature = "drain", since = "1.6.0")]
2855 impl<T> Iterator for Drain<'_, T> {
2859 fn next(&mut self) -> Option<T> {
2860 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2863 fn size_hint(&self) -> (usize, Option<usize>) {
2864 self.iter.size_hint()
2868 #[stable(feature = "drain", since = "1.6.0")]
2869 impl<T> DoubleEndedIterator for Drain<'_, T> {
2871 fn next_back(&mut self) -> Option<T> {
2872 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2876 #[stable(feature = "drain", since = "1.6.0")]
2877 impl<T> Drop for Drain<'_, T> {
2878 fn drop(&mut self) {
2879 /// Continues dropping the remaining elements in the `Drain`, then moves back the
2880 /// un-`Drain`ed elements to restore the original `Vec`.
2881 struct DropGuard<'r, 'a, T>(&'r mut Drain<'a, T>);
2883 impl<'r, 'a, T> Drop for DropGuard<'r, 'a, T> {
2884 fn drop(&mut self) {
2885 // Continue the same loop we have below. If the loop already finished, this does
2887 self.0.for_each(drop);
2889 if self.0.tail_len > 0 {
2891 let source_vec = self.0.vec.as_mut();
2892 // memmove back untouched tail, update to new length
2893 let start = source_vec.len();
2894 let tail = self.0.tail_start;
2896 let src = source_vec.as_ptr().add(tail);
2897 let dst = source_vec.as_mut_ptr().add(start);
2898 ptr::copy(src, dst, self.0.tail_len);
2900 source_vec.set_len(start + self.0.tail_len);
2906 // exhaust self first
2907 while let Some(item) = self.next() {
2908 let guard = DropGuard(self);
2913 // Drop a `DropGuard` to move back the non-drained tail of `self`.
2918 #[stable(feature = "drain", since = "1.6.0")]
2919 impl<T> ExactSizeIterator for Drain<'_, T> {
2920 fn is_empty(&self) -> bool {
2921 self.iter.is_empty()
2925 #[unstable(feature = "trusted_len", issue = "37572")]
2926 unsafe impl<T> TrustedLen for Drain<'_, T> {}
2928 #[stable(feature = "fused", since = "1.26.0")]
2929 impl<T> FusedIterator for Drain<'_, T> {}
2931 /// A splicing iterator for `Vec`.
2933 /// This struct is created by [`Vec::splice()`].
2934 /// See its documentation for more.
2936 #[stable(feature = "vec_splice", since = "1.21.0")]
2937 pub struct Splice<'a, I: Iterator + 'a> {
2938 drain: Drain<'a, I::Item>,
2942 #[stable(feature = "vec_splice", since = "1.21.0")]
2943 impl<I: Iterator> Iterator for Splice<'_, I> {
2944 type Item = I::Item;
2946 fn next(&mut self) -> Option<Self::Item> {
2950 fn size_hint(&self) -> (usize, Option<usize>) {
2951 self.drain.size_hint()
2955 #[stable(feature = "vec_splice", since = "1.21.0")]
2956 impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
2957 fn next_back(&mut self) -> Option<Self::Item> {
2958 self.drain.next_back()
2962 #[stable(feature = "vec_splice", since = "1.21.0")]
2963 impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}
2965 #[stable(feature = "vec_splice", since = "1.21.0")]
2966 impl<I: Iterator> Drop for Splice<'_, I> {
2967 fn drop(&mut self) {
2968 self.drain.by_ref().for_each(drop);
2971 if self.drain.tail_len == 0 {
2972 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2976 // First fill the range left by drain().
2977 if !self.drain.fill(&mut self.replace_with) {
2981 // There may be more elements. Use the lower bound as an estimate.
2982 // FIXME: Is the upper bound a better guess? Or something else?
2983 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2984 if lower_bound > 0 {
2985 self.drain.move_tail(lower_bound);
2986 if !self.drain.fill(&mut self.replace_with) {
2991 // Collect any remaining elements.
2992 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2993 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2994 // Now we have an exact count.
2995 if collected.len() > 0 {
2996 self.drain.move_tail(collected.len());
2997 let filled = self.drain.fill(&mut collected);
2998 debug_assert!(filled);
2999 debug_assert_eq!(collected.len(), 0);
3002 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
3006 /// Private helper methods for `Splice::drop`
3007 impl<T> Drain<'_, T> {
3008 /// The range from `self.vec.len` to `self.tail_start` contains elements
3009 /// that have been moved out.
3010 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
3011 /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
3012 unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool {
3013 let vec = unsafe { self.vec.as_mut() };
3014 let range_start = vec.len;
3015 let range_end = self.tail_start;
3016 let range_slice = unsafe {
3017 slice::from_raw_parts_mut(vec.as_mut_ptr().add(range_start), range_end - range_start)
3020 for place in range_slice {
3021 if let Some(new_item) = replace_with.next() {
3022 unsafe { ptr::write(place, new_item) };
3031 /// Makes room for inserting more elements before the tail.
3032 unsafe fn move_tail(&mut self, additional: usize) {
3033 let vec = unsafe { self.vec.as_mut() };
3034 let len = self.tail_start + self.tail_len;
3035 vec.buf.reserve(len, additional);
3037 let new_tail_start = self.tail_start + additional;
3039 let src = vec.as_ptr().add(self.tail_start);
3040 let dst = vec.as_mut_ptr().add(new_tail_start);
3041 ptr::copy(src, dst, self.tail_len);
3043 self.tail_start = new_tail_start;
3047 /// An iterator produced by calling `drain_filter` on Vec.
3048 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
3050 pub struct DrainFilter<'a, T, F>
3052 F: FnMut(&mut T) -> bool,
3054 vec: &'a mut Vec<T>,
3055 /// The index of the item that will be inspected by the next call to `next`.
3057 /// The number of items that have been drained (removed) thus far.
3059 /// The original length of `vec` prior to draining.
3061 /// The filter test predicate.
3063 /// A flag that indicates a panic has occurred in the filter test prodicate.
3064 /// This is used as a hint in the drop implementation to prevent consumption
3065 /// of the remainder of the `DrainFilter`. Any unprocessed items will be
3066 /// backshifted in the `vec`, but no further items will be dropped or
3067 /// tested by the filter predicate.
3071 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
3072 impl<T, F> Iterator for DrainFilter<'_, T, F>
3074 F: FnMut(&mut T) -> bool,
3078 fn next(&mut self) -> Option<T> {
3080 while self.idx < self.old_len {
3082 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
3083 self.panic_flag = true;
3084 let drained = (self.pred)(&mut v[i]);
3085 self.panic_flag = false;
3086 // Update the index *after* the predicate is called. If the index
3087 // is updated prior and the predicate panics, the element at this
3088 // index would be leaked.
3092 return Some(ptr::read(&v[i]));
3093 } else if self.del > 0 {
3095 let src: *const T = &v[i];
3096 let dst: *mut T = &mut v[i - del];
3097 ptr::copy_nonoverlapping(src, dst, 1);
3104 fn size_hint(&self) -> (usize, Option<usize>) {
3105 (0, Some(self.old_len - self.idx))
3109 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
3110 impl<T, F> Drop for DrainFilter<'_, T, F>
3112 F: FnMut(&mut T) -> bool,
3114 fn drop(&mut self) {
3115 struct BackshiftOnDrop<'a, 'b, T, F>
3117 F: FnMut(&mut T) -> bool,
3119 drain: &'b mut DrainFilter<'a, T, F>,
3122 impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F>
3124 F: FnMut(&mut T) -> bool,
3126 fn drop(&mut self) {
3128 if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
3129 // This is a pretty messed up state, and there isn't really an
3130 // obviously right thing to do. We don't want to keep trying
3131 // to execute `pred`, so we just backshift all the unprocessed
3132 // elements and tell the vec that they still exist. The backshift
3133 // is required to prevent a double-drop of the last successfully
3134 // drained item prior to a panic in the predicate.
3135 let ptr = self.drain.vec.as_mut_ptr();
3136 let src = ptr.add(self.drain.idx);
3137 let dst = src.sub(self.drain.del);
3138 let tail_len = self.drain.old_len - self.drain.idx;
3139 src.copy_to(dst, tail_len);
3141 self.drain.vec.set_len(self.drain.old_len - self.drain.del);
3146 let backshift = BackshiftOnDrop { drain: self };
3148 // Attempt to consume any remaining elements if the filter predicate
3149 // has not yet panicked. We'll backshift any remaining elements
3150 // whether we've already panicked or if the consumption here panics.
3151 if !backshift.drain.panic_flag {
3152 backshift.drain.for_each(drop);