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`] with [`Vec::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 //! [`push`]: Vec::push
55 #![stable(feature = "rust1", since = "1.0.0")]
57 use core::cmp::{self, Ordering};
59 use core::hash::{Hash, Hasher};
60 use core::intrinsics::{arith_offset, assume};
61 use core::iter::{FromIterator, FusedIterator, TrustedLen};
62 use core::marker::PhantomData;
63 use core::mem::{self, ManuallyDrop, MaybeUninit};
64 use core::ops::Bound::{Excluded, Included, Unbounded};
65 use core::ops::{self, Index, IndexMut, RangeBounds};
66 use core::ptr::{self, NonNull};
67 use core::slice::{self, SliceIndex};
69 use crate::borrow::{Cow, ToOwned};
70 use crate::boxed::Box;
71 use crate::collections::TryReserveError;
72 use crate::raw_vec::RawVec;
74 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
79 /// let mut vec = Vec::new();
83 /// assert_eq!(vec.len(), 2);
84 /// assert_eq!(vec[0], 1);
86 /// assert_eq!(vec.pop(), Some(2));
87 /// assert_eq!(vec.len(), 1);
90 /// assert_eq!(vec[0], 7);
92 /// vec.extend([1, 2, 3].iter().copied());
95 /// println!("{}", x);
97 /// assert_eq!(vec, [7, 1, 2, 3]);
100 /// The [`vec!`] macro is provided to make initialization more convenient:
103 /// let mut vec = vec![1, 2, 3];
105 /// assert_eq!(vec, [1, 2, 3, 4]);
108 /// It can also initialize each element of a `Vec<T>` with a given value.
109 /// This may be more efficient than performing allocation and initialization
110 /// in separate steps, especially when initializing a vector of zeros:
113 /// let vec = vec![0; 5];
114 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
116 /// // The following is equivalent, but potentially slower:
117 /// let mut vec1 = Vec::with_capacity(5);
118 /// vec1.resize(5, 0);
121 /// Use a `Vec<T>` as an efficient stack:
124 /// let mut stack = Vec::new();
130 /// while let Some(top) = stack.pop() {
131 /// // Prints 3, 2, 1
132 /// println!("{}", top);
138 /// The `Vec` type allows to access values by index, because it implements the
139 /// [`Index`] trait. An example will be more explicit:
142 /// let v = vec![0, 2, 4, 6];
143 /// println!("{}", v[1]); // it will display '2'
146 /// However be careful: if you try to access an index which isn't in the `Vec`,
147 /// your software will panic! You cannot do this:
150 /// let v = vec![0, 2, 4, 6];
151 /// println!("{}", v[6]); // it will panic!
154 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
159 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
160 /// To get a slice, use `&`. Example:
163 /// fn read_slice(slice: &[usize]) {
167 /// let v = vec![0, 1];
170 /// // ... and that's all!
171 /// // you can also do it like this:
172 /// let x : &[usize] = &v;
175 /// In Rust, it's more common to pass slices as arguments rather than vectors
176 /// when you just want to provide read access. The same goes for [`String`] and
179 /// # Capacity and reallocation
181 /// The capacity of a vector is the amount of space allocated for any future
182 /// elements that will be added onto the vector. This is not to be confused with
183 /// the *length* of a vector, which specifies the number of actual elements
184 /// within the vector. If a vector's length exceeds its capacity, its capacity
185 /// will automatically be increased, but its elements will have to be
188 /// For example, a vector with capacity 10 and length 0 would be an empty vector
189 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
190 /// vector will not change its capacity or cause reallocation to occur. However,
191 /// if the vector's length is increased to 11, it will have to reallocate, which
192 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
193 /// whenever possible to specify how big the vector is expected to get.
197 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
198 /// about its design. This ensures that it's as low-overhead as possible in
199 /// the general case, and can be correctly manipulated in primitive ways
200 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
201 /// If additional type parameters are added (e.g., to support custom allocators),
202 /// overriding their defaults may change the behavior.
204 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
205 /// triplet. No more, no less. The order of these fields is completely
206 /// unspecified, and you should use the appropriate methods to modify these.
207 /// The pointer will never be null, so this type is null-pointer-optimized.
209 /// However, the pointer may not actually point to allocated memory. In particular,
210 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
211 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
212 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
213 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
214 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
215 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
216 /// details are very subtle — if you intend to allocate memory using a `Vec`
217 /// and use it for something else (either to pass to unsafe code, or to build your
218 /// own memory-backed collection), be sure to deallocate this memory by using
219 /// `from_raw_parts` to recover the `Vec` and then dropping it.
221 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
222 /// (as defined by the allocator Rust is configured to use by default), and its
223 /// pointer points to [`len`] initialized, contiguous elements in order (what
224 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
225 /// `[`len`] logically uninitialized, contiguous elements.
227 /// `Vec` will never perform a "small optimization" where elements are actually
228 /// stored on the stack for two reasons:
230 /// * It would make it more difficult for unsafe code to correctly manipulate
231 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
232 /// only moved, and it would be more difficult to determine if a `Vec` had
233 /// actually allocated memory.
235 /// * It would penalize the general case, incurring an additional branch
238 /// `Vec` will never automatically shrink itself, even if completely empty. This
239 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
240 /// and then filling it back up to the same [`len`] should incur no calls to
241 /// the allocator. If you wish to free up unused memory, use
242 /// [`shrink_to_fit`].
244 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
245 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
246 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
247 /// accurate, and can be relied on. It can even be used to manually free the memory
248 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
249 /// when not necessary.
251 /// `Vec` does not guarantee any particular growth strategy when reallocating
252 /// when full, nor when [`reserve`] is called. The current strategy is basic
253 /// and it may prove desirable to use a non-constant growth factor. Whatever
254 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
256 /// `vec![x; n]`, `vec![a, b, c, d]`, and
257 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
258 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
259 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
260 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
262 /// `Vec` will not specifically overwrite any data that is removed from it,
263 /// but also won't specifically preserve it. Its uninitialized memory is
264 /// scratch space that it may use however it wants. It will generally just do
265 /// whatever is most efficient or otherwise easy to implement. Do not rely on
266 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
267 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
268 /// first, that may not actually happen because the optimizer does not consider
269 /// this a side-effect that must be preserved. There is one case which we will
270 /// not break, however: using `unsafe` code to write to the excess capacity,
271 /// and then increasing the length to match, is always valid.
273 /// `Vec` does not currently guarantee the order in which elements are dropped.
274 /// The order has changed in the past and may change again.
276 /// [`get`]: ../../std/vec/struct.Vec.html#method.get
277 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
278 /// [`String`]: crate::string::String
279 /// [`&str`]: type@str
280 /// [`shrink_to_fit`]: Vec::shrink_to_fit
281 /// [`capacity`]: Vec::capacity
282 /// [`mem::size_of::<T>`]: core::mem::size_of
283 /// [`len`]: Vec::len
284 /// [`push`]: Vec::push
285 /// [`insert`]: Vec::insert
286 /// [`reserve`]: Vec::reserve
287 /// [owned slice]: Box
288 #[stable(feature = "rust1", since = "1.0.0")]
289 #[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")]
295 ////////////////////////////////////////////////////////////////////////////////
297 ////////////////////////////////////////////////////////////////////////////////
300 /// Constructs a new, empty `Vec<T>`.
302 /// The vector will not allocate until elements are pushed onto it.
307 /// # #![allow(unused_mut)]
308 /// let mut vec: Vec<i32> = Vec::new();
311 #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
312 #[stable(feature = "rust1", since = "1.0.0")]
313 pub const fn new() -> Vec<T> {
314 Vec { buf: RawVec::NEW, len: 0 }
317 /// Constructs a new, empty `Vec<T>` with the specified capacity.
319 /// The vector will be able to hold exactly `capacity` elements without
320 /// reallocating. If `capacity` is 0, the vector will not allocate.
322 /// It is important to note that although the returned vector has the
323 /// *capacity* specified, the vector will have a zero *length*. For an
324 /// explanation of the difference between length and capacity, see
325 /// *[Capacity and reallocation]*.
327 /// [Capacity and reallocation]: #capacity-and-reallocation
332 /// let mut vec = Vec::with_capacity(10);
334 /// // The vector contains no items, even though it has capacity for more
335 /// assert_eq!(vec.len(), 0);
336 /// assert_eq!(vec.capacity(), 10);
338 /// // These are all done without reallocating...
342 /// assert_eq!(vec.len(), 10);
343 /// assert_eq!(vec.capacity(), 10);
345 /// // ...but this may make the vector reallocate
347 /// assert_eq!(vec.len(), 11);
348 /// assert!(vec.capacity() >= 11);
351 #[stable(feature = "rust1", since = "1.0.0")]
352 pub fn with_capacity(capacity: usize) -> Vec<T> {
353 Vec { buf: RawVec::with_capacity(capacity), len: 0 }
356 /// Decomposes a `Vec<T>` into its raw components.
358 /// Returns the raw pointer to the underlying data, the length of
359 /// the vector (in elements), and the allocated capacity of the
360 /// data (in elements). These are the same arguments in the same
361 /// order as the arguments to [`from_raw_parts`].
363 /// After calling this function, the caller is responsible for the
364 /// memory previously managed by the `Vec`. The only way to do
365 /// this is to convert the raw pointer, length, and capacity back
366 /// into a `Vec` with the [`from_raw_parts`] function, allowing
367 /// the destructor to perform the cleanup.
369 /// [`from_raw_parts`]: Vec::from_raw_parts
374 /// #![feature(vec_into_raw_parts)]
375 /// let v: Vec<i32> = vec![-1, 0, 1];
377 /// let (ptr, len, cap) = v.into_raw_parts();
379 /// let rebuilt = unsafe {
380 /// // We can now make changes to the components, such as
381 /// // transmuting the raw pointer to a compatible type.
382 /// let ptr = ptr as *mut u32;
384 /// Vec::from_raw_parts(ptr, len, cap)
386 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
388 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
389 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
390 let mut me = ManuallyDrop::new(self);
391 (me.as_mut_ptr(), me.len(), me.capacity())
394 /// Creates a `Vec<T>` directly from the raw components of another vector.
398 /// This is highly unsafe, due to the number of invariants that aren't
401 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
402 /// (at least, it's highly likely to be incorrect if it wasn't).
403 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
404 /// (`T` having a less strict alignment is not sufficient, the alignment really
405 /// needs to be equal to satsify the [`dealloc`] requirement that memory must be
406 /// allocated and deallocated with the same layout.)
407 /// * `length` needs to be less than or equal to `capacity`.
408 /// * `capacity` needs to be the capacity that the pointer was allocated with.
410 /// Violating these may cause problems like corrupting the allocator's
411 /// internal data structures. For example it is **not** safe
412 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
413 /// It's also not safe to build one from a `Vec<u16>` and its length, because
414 /// the allocator cares about the alignment, and these two types have different
415 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
416 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
418 /// The ownership of `ptr` is effectively transferred to the
419 /// `Vec<T>` which may then deallocate, reallocate or change the
420 /// contents of memory pointed to by the pointer at will. Ensure
421 /// that nothing else uses the pointer after calling this
424 /// [`String`]: crate::string::String
425 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
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 unsafe { 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 exceeds `isize::MAX` bytes.
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 // The capacity is never less than the length, and there's nothing to do when
617 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
618 // by only calling it with a greater capacity.
619 if self.capacity() > self.len {
620 self.buf.shrink_to_fit(self.len);
624 /// Shrinks the capacity of the vector with a lower bound.
626 /// The capacity will remain at least as large as both the length
627 /// and the supplied value.
631 /// Panics if the current capacity is smaller than the supplied
632 /// minimum capacity.
637 /// #![feature(shrink_to)]
638 /// let mut vec = Vec::with_capacity(10);
639 /// vec.extend([1, 2, 3].iter().cloned());
640 /// assert_eq!(vec.capacity(), 10);
641 /// vec.shrink_to(4);
642 /// assert!(vec.capacity() >= 4);
643 /// vec.shrink_to(0);
644 /// assert!(vec.capacity() >= 3);
646 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
647 pub fn shrink_to(&mut self, min_capacity: usize) {
648 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
651 /// Converts the vector into [`Box<[T]>`][owned slice].
653 /// Note that this will drop any excess capacity.
655 /// [owned slice]: Box
660 /// let v = vec![1, 2, 3];
662 /// let slice = v.into_boxed_slice();
665 /// Any excess capacity is removed:
668 /// let mut vec = Vec::with_capacity(10);
669 /// vec.extend([1, 2, 3].iter().cloned());
671 /// assert_eq!(vec.capacity(), 10);
672 /// let slice = vec.into_boxed_slice();
673 /// assert_eq!(slice.into_vec().capacity(), 3);
675 #[stable(feature = "rust1", since = "1.0.0")]
676 pub fn into_boxed_slice(mut self) -> Box<[T]> {
678 self.shrink_to_fit();
679 let me = ManuallyDrop::new(self);
680 let buf = ptr::read(&me.buf);
682 buf.into_box(len).assume_init()
686 /// Shortens the vector, keeping the first `len` elements and dropping
689 /// If `len` is greater than the vector's current length, this has no
692 /// The [`drain`] method can emulate `truncate`, but causes the excess
693 /// elements to be returned instead of dropped.
695 /// Note that this method has no effect on the allocated capacity
700 /// Truncating a five element vector to two elements:
703 /// let mut vec = vec![1, 2, 3, 4, 5];
705 /// assert_eq!(vec, [1, 2]);
708 /// No truncation occurs when `len` is greater than the vector's current
712 /// let mut vec = vec![1, 2, 3];
714 /// assert_eq!(vec, [1, 2, 3]);
717 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
721 /// let mut vec = vec![1, 2, 3];
723 /// assert_eq!(vec, []);
726 /// [`clear`]: Vec::clear
727 /// [`drain`]: Vec::drain
728 #[stable(feature = "rust1", since = "1.0.0")]
729 pub fn truncate(&mut self, len: usize) {
730 // This is safe because:
732 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
733 // case avoids creating an invalid slice, and
734 // * the `len` of the vector is shrunk before calling `drop_in_place`,
735 // such that no value will be dropped twice in case `drop_in_place`
736 // were to panic once (if it panics twice, the program aborts).
741 let remaining_len = self.len - len;
742 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
744 ptr::drop_in_place(s);
748 /// Extracts a slice containing the entire vector.
750 /// Equivalent to `&s[..]`.
755 /// use std::io::{self, Write};
756 /// let buffer = vec![1, 2, 3, 5, 8];
757 /// io::sink().write(buffer.as_slice()).unwrap();
760 #[stable(feature = "vec_as_slice", since = "1.7.0")]
761 pub fn as_slice(&self) -> &[T] {
765 /// Extracts a mutable slice of the entire vector.
767 /// Equivalent to `&mut s[..]`.
772 /// use std::io::{self, Read};
773 /// let mut buffer = vec![0; 3];
774 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
777 #[stable(feature = "vec_as_slice", since = "1.7.0")]
778 pub fn as_mut_slice(&mut self) -> &mut [T] {
782 /// Returns a raw pointer to the vector's buffer.
784 /// The caller must ensure that the vector outlives the pointer this
785 /// function returns, or else it will end up pointing to garbage.
786 /// Modifying the vector may cause its buffer to be reallocated,
787 /// which would also make any pointers to it invalid.
789 /// The caller must also ensure that the memory the pointer (non-transitively) points to
790 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
791 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
796 /// let x = vec![1, 2, 4];
797 /// let x_ptr = x.as_ptr();
800 /// for i in 0..x.len() {
801 /// assert_eq!(*x_ptr.add(i), 1 << i);
806 /// [`as_mut_ptr`]: Vec::as_mut_ptr
807 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
809 pub fn as_ptr(&self) -> *const T {
810 // We shadow the slice method of the same name to avoid going through
811 // `deref`, which creates an intermediate reference.
812 let ptr = self.buf.ptr();
814 assume(!ptr.is_null());
819 /// Returns an unsafe mutable pointer to the vector's buffer.
821 /// The caller must ensure that the vector outlives the pointer this
822 /// function returns, or else it will end up pointing to garbage.
823 /// Modifying the vector may cause its buffer to be reallocated,
824 /// which would also make any pointers to it invalid.
829 /// // Allocate vector big enough for 4 elements.
831 /// let mut x: Vec<i32> = Vec::with_capacity(size);
832 /// let x_ptr = x.as_mut_ptr();
834 /// // Initialize elements via raw pointer writes, then set length.
836 /// for i in 0..size {
837 /// *x_ptr.add(i) = i as i32;
841 /// assert_eq!(&*x, &[0,1,2,3]);
843 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
845 pub fn as_mut_ptr(&mut self) -> *mut T {
846 // We shadow the slice method of the same name to avoid going through
847 // `deref_mut`, which creates an intermediate reference.
848 let ptr = self.buf.ptr();
850 assume(!ptr.is_null());
855 /// Forces the length of the vector to `new_len`.
857 /// This is a low-level operation that maintains none of the normal
858 /// invariants of the type. Normally changing the length of a vector
859 /// is done using one of the safe operations instead, such as
860 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
862 /// [`truncate`]: Vec::truncate
863 /// [`resize`]: Vec::resize
864 /// [`extend`]: Extend::extend
865 /// [`clear`]: Vec::clear
869 /// - `new_len` must be less than or equal to [`capacity()`].
870 /// - The elements at `old_len..new_len` must be initialized.
872 /// [`capacity()`]: Vec::capacity
876 /// This method can be useful for situations in which the vector
877 /// is serving as a buffer for other code, particularly over FFI:
880 /// # #![allow(dead_code)]
881 /// # // This is just a minimal skeleton for the doc example;
882 /// # // don't use this as a starting point for a real library.
883 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
884 /// # const Z_OK: i32 = 0;
886 /// # fn deflateGetDictionary(
887 /// # strm: *mut std::ffi::c_void,
888 /// # dictionary: *mut u8,
889 /// # dictLength: *mut usize,
892 /// # impl StreamWrapper {
893 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
894 /// // Per the FFI method's docs, "32768 bytes is always enough".
895 /// let mut dict = Vec::with_capacity(32_768);
896 /// let mut dict_length = 0;
897 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
898 /// // 1. `dict_length` elements were initialized.
899 /// // 2. `dict_length` <= the capacity (32_768)
900 /// // which makes `set_len` safe to call.
902 /// // Make the FFI call...
903 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
905 /// // ...and update the length to what was initialized.
906 /// dict.set_len(dict_length);
916 /// While the following example is sound, there is a memory leak since
917 /// the inner vectors were not freed prior to the `set_len` call:
920 /// let mut vec = vec![vec![1, 0, 0],
924 /// // 1. `old_len..0` is empty so no elements need to be initialized.
925 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
931 /// Normally, here, one would use [`clear`] instead to correctly drop
932 /// the contents and thus not leak memory.
934 #[stable(feature = "rust1", since = "1.0.0")]
935 pub unsafe fn set_len(&mut self, new_len: usize) {
936 debug_assert!(new_len <= self.capacity());
941 /// Removes an element from the vector and returns it.
943 /// The removed element is replaced by the last element of the vector.
945 /// This does not preserve ordering, but is O(1).
949 /// Panics if `index` is out of bounds.
954 /// let mut v = vec!["foo", "bar", "baz", "qux"];
956 /// assert_eq!(v.swap_remove(1), "bar");
957 /// assert_eq!(v, ["foo", "qux", "baz"]);
959 /// assert_eq!(v.swap_remove(0), "foo");
960 /// assert_eq!(v, ["baz", "qux"]);
963 #[stable(feature = "rust1", since = "1.0.0")]
964 pub fn swap_remove(&mut self, index: usize) -> T {
967 fn assert_failed(index: usize, len: usize) -> ! {
968 panic!("swap_remove index (is {}) should be < len (is {})", index, len);
971 let len = self.len();
973 assert_failed(index, len);
976 // We replace self[index] with the last element. Note that if the
977 // bounds check above succeeds there must be a last element (which
978 // can be self[index] itself).
979 let last = ptr::read(self.as_ptr().add(len - 1));
980 let hole = self.as_mut_ptr().add(index);
981 self.set_len(len - 1);
982 ptr::replace(hole, last)
986 /// Inserts an element at position `index` within the vector, shifting all
987 /// elements after it to the right.
991 /// Panics if `index > len`.
996 /// let mut vec = vec![1, 2, 3];
997 /// vec.insert(1, 4);
998 /// assert_eq!(vec, [1, 4, 2, 3]);
999 /// vec.insert(4, 5);
1000 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1002 #[stable(feature = "rust1", since = "1.0.0")]
1003 pub fn insert(&mut self, index: usize, element: T) {
1006 fn assert_failed(index: usize, len: usize) -> ! {
1007 panic!("insertion index (is {}) should be <= len (is {})", index, len);
1010 let len = self.len();
1012 assert_failed(index, len);
1015 // space for the new element
1016 if len == self.buf.capacity() {
1022 // The spot to put the new value
1024 let p = self.as_mut_ptr().add(index);
1025 // Shift everything over to make space. (Duplicating the
1026 // `index`th element into two consecutive places.)
1027 ptr::copy(p, p.offset(1), len - index);
1028 // Write it in, overwriting the first copy of the `index`th
1030 ptr::write(p, element);
1032 self.set_len(len + 1);
1036 /// Removes and returns the element at position `index` within the vector,
1037 /// shifting all elements after it to the left.
1041 /// Panics if `index` is out of bounds.
1046 /// let mut v = vec![1, 2, 3];
1047 /// assert_eq!(v.remove(1), 2);
1048 /// assert_eq!(v, [1, 3]);
1050 #[stable(feature = "rust1", since = "1.0.0")]
1051 pub fn remove(&mut self, index: usize) -> T {
1054 fn assert_failed(index: usize, len: usize) -> ! {
1055 panic!("removal index (is {}) should be < len (is {})", index, len);
1058 let len = self.len();
1060 assert_failed(index, len);
1066 // the place we are taking from.
1067 let ptr = self.as_mut_ptr().add(index);
1068 // copy it out, unsafely having a copy of the value on
1069 // the stack and in the vector at the same time.
1070 ret = ptr::read(ptr);
1072 // Shift everything down to fill in that spot.
1073 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1075 self.set_len(len - 1);
1080 /// Retains only the elements specified by the predicate.
1082 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1083 /// This method operates in place, visiting each element exactly once in the
1084 /// original order, and preserves the order of the retained elements.
1089 /// let mut vec = vec![1, 2, 3, 4];
1090 /// vec.retain(|&x| x % 2 == 0);
1091 /// assert_eq!(vec, [2, 4]);
1094 /// The exact order may be useful for tracking external state, like an index.
1097 /// let mut vec = vec![1, 2, 3, 4, 5];
1098 /// let keep = [false, true, true, false, true];
1100 /// vec.retain(|_| (keep[i], i += 1).0);
1101 /// assert_eq!(vec, [2, 3, 5]);
1103 #[stable(feature = "rust1", since = "1.0.0")]
1104 pub fn retain<F>(&mut self, mut f: F)
1106 F: FnMut(&T) -> bool,
1108 let len = self.len();
1111 let v = &mut **self;
1122 self.truncate(len - del);
1126 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1129 /// If the vector is sorted, this removes all duplicates.
1134 /// let mut vec = vec![10, 20, 21, 30, 20];
1136 /// vec.dedup_by_key(|i| *i / 10);
1138 /// assert_eq!(vec, [10, 20, 30, 20]);
1140 #[stable(feature = "dedup_by", since = "1.16.0")]
1142 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1144 F: FnMut(&mut T) -> K,
1147 self.dedup_by(|a, b| key(a) == key(b))
1150 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1153 /// The `same_bucket` function is passed references to two elements from the vector and
1154 /// must determine if the elements compare equal. The elements are passed in opposite order
1155 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1157 /// If the vector is sorted, this removes all duplicates.
1162 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1164 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1166 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1168 #[stable(feature = "dedup_by", since = "1.16.0")]
1169 pub fn dedup_by<F>(&mut self, same_bucket: F)
1171 F: FnMut(&mut T, &mut T) -> bool,
1174 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
1180 /// Appends an element to the back of a collection.
1184 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1189 /// let mut vec = vec![1, 2];
1191 /// assert_eq!(vec, [1, 2, 3]);
1194 #[stable(feature = "rust1", since = "1.0.0")]
1195 pub fn push(&mut self, value: T) {
1196 // This will panic or abort if we would allocate > isize::MAX bytes
1197 // or if the length increment would overflow for zero-sized types.
1198 if self.len == self.buf.capacity() {
1202 let end = self.as_mut_ptr().add(self.len);
1203 ptr::write(end, value);
1208 /// Removes the last element from a vector and returns it, or [`None`] if it
1214 /// let mut vec = vec![1, 2, 3];
1215 /// assert_eq!(vec.pop(), Some(3));
1216 /// assert_eq!(vec, [1, 2]);
1219 #[stable(feature = "rust1", since = "1.0.0")]
1220 pub fn pop(&mut self) -> Option<T> {
1226 Some(ptr::read(self.as_ptr().add(self.len())))
1231 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1235 /// Panics if the number of elements in the vector overflows a `usize`.
1240 /// let mut vec = vec![1, 2, 3];
1241 /// let mut vec2 = vec![4, 5, 6];
1242 /// vec.append(&mut vec2);
1243 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1244 /// assert_eq!(vec2, []);
1247 #[stable(feature = "append", since = "1.4.0")]
1248 pub fn append(&mut self, other: &mut Self) {
1250 self.append_elements(other.as_slice() as _);
1255 /// Appends elements to `Self` from other buffer.
1257 unsafe fn append_elements(&mut self, other: *const [T]) {
1258 let count = unsafe { (*other).len() };
1259 self.reserve(count);
1260 let len = self.len();
1261 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1265 /// Creates a draining iterator that removes the specified range in the vector
1266 /// and yields the removed items.
1268 /// When the iterator **is** dropped, all elements in the range are removed
1269 /// from the vector, even if the iterator was not fully consumed. If the
1270 /// iterator **is not** dropped (with [`mem::forget`] for example), it is
1271 /// unspecified how many elements are removed.
1275 /// Panics if the starting point is greater than the end point or if
1276 /// the end point is greater than the length of the vector.
1281 /// let mut v = vec![1, 2, 3];
1282 /// let u: Vec<_> = v.drain(1..).collect();
1283 /// assert_eq!(v, &[1]);
1284 /// assert_eq!(u, &[2, 3]);
1286 /// // A full range clears the vector
1288 /// assert_eq!(v, &[]);
1290 #[stable(feature = "drain", since = "1.6.0")]
1291 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1293 R: RangeBounds<usize>,
1297 // When the Drain is first created, it shortens the length of
1298 // the source vector to make sure no uninitialized or moved-from elements
1299 // are accessible at all if the Drain's destructor never gets to run.
1301 // Drain will ptr::read out the values to remove.
1302 // When finished, remaining tail of the vec is copied back to cover
1303 // the hole, and the vector length is restored to the new length.
1305 let len = self.len();
1306 let start = match range.start_bound() {
1308 Excluded(&n) => n + 1,
1311 let end = match range.end_bound() {
1312 Included(&n) => n + 1,
1319 fn start_assert_failed(start: usize, end: usize) -> ! {
1320 panic!("start drain index (is {}) should be <= end drain index (is {})", start, end);
1325 fn end_assert_failed(end: usize, len: usize) -> ! {
1326 panic!("end drain index (is {}) should be <= len (is {})", end, len);
1330 start_assert_failed(start, end);
1333 end_assert_failed(end, len);
1337 // set self.vec length's to start, to be safe in case Drain is leaked
1338 self.set_len(start);
1339 // Use the borrow in the IterMut to indicate borrowing behavior of the
1340 // whole Drain iterator (like &mut T).
1341 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1344 tail_len: len - end,
1345 iter: range_slice.iter(),
1346 vec: NonNull::from(self),
1351 /// Clears the vector, removing all values.
1353 /// Note that this method has no effect on the allocated capacity
1359 /// let mut v = vec![1, 2, 3];
1363 /// assert!(v.is_empty());
1366 #[stable(feature = "rust1", since = "1.0.0")]
1367 pub fn clear(&mut self) {
1371 /// Returns the number of elements in the vector, also referred to
1372 /// as its 'length'.
1377 /// let a = vec![1, 2, 3];
1378 /// assert_eq!(a.len(), 3);
1381 #[stable(feature = "rust1", since = "1.0.0")]
1382 pub fn len(&self) -> usize {
1386 /// Returns `true` if the vector contains no elements.
1391 /// let mut v = Vec::new();
1392 /// assert!(v.is_empty());
1395 /// assert!(!v.is_empty());
1397 #[stable(feature = "rust1", since = "1.0.0")]
1398 pub fn is_empty(&self) -> bool {
1402 /// Splits the collection into two at the given index.
1404 /// Returns a newly allocated vector containing the elements in the range
1405 /// `[at, len)`. After the call, the original vector will be left containing
1406 /// the elements `[0, at)` with its previous capacity unchanged.
1410 /// Panics if `at > len`.
1415 /// let mut vec = vec![1,2,3];
1416 /// let vec2 = vec.split_off(1);
1417 /// assert_eq!(vec, [1]);
1418 /// assert_eq!(vec2, [2, 3]);
1421 #[must_use = "use `.truncate()` if you don't need the other half"]
1422 #[stable(feature = "split_off", since = "1.4.0")]
1423 pub fn split_off(&mut self, at: usize) -> Self {
1426 fn assert_failed(at: usize, len: usize) -> ! {
1427 panic!("`at` split index (is {}) should be <= len (is {})", at, len);
1430 if at > self.len() {
1431 assert_failed(at, self.len());
1434 let other_len = self.len - at;
1435 let mut other = Vec::with_capacity(other_len);
1437 // Unsafely `set_len` and copy items to `other`.
1440 other.set_len(other_len);
1442 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1447 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1449 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1450 /// difference, with each additional slot filled with the result of
1451 /// calling the closure `f`. The return values from `f` will end up
1452 /// in the `Vec` in the order they have been generated.
1454 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1456 /// This method uses a closure to create new values on every push. If
1457 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
1458 /// want to use the [`Default`] trait to generate values, you can
1459 /// pass [`Default::default`] as the second argument.
1464 /// let mut vec = vec![1, 2, 3];
1465 /// vec.resize_with(5, Default::default);
1466 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1468 /// let mut vec = vec![];
1470 /// vec.resize_with(4, || { p *= 2; p });
1471 /// assert_eq!(vec, [2, 4, 8, 16]);
1473 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1474 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1478 let len = self.len();
1480 self.extend_with(new_len - len, ExtendFunc(f));
1482 self.truncate(new_len);
1486 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1487 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1488 /// `'a`. If the type has only static references, or none at all, then this
1489 /// may be chosen to be `'static`.
1491 /// This function is similar to the `leak` function on `Box`.
1493 /// This function is mainly useful for data that lives for the remainder of
1494 /// the program's life. Dropping the returned reference will cause a memory
1502 /// let x = vec![1, 2, 3];
1503 /// let static_ref: &'static mut [usize] = x.leak();
1504 /// static_ref[0] += 1;
1505 /// assert_eq!(static_ref, &[2, 2, 3]);
1507 #[stable(feature = "vec_leak", since = "1.47.0")]
1509 pub fn leak<'a>(self) -> &'a mut [T]
1511 T: 'a, // Technically not needed, but kept to be explicit.
1513 Box::leak(self.into_boxed_slice())
1516 /// Returns the remaining spare capacity of the vector as a slice of
1517 /// `MaybeUninit<T>`.
1519 /// The returned slice can be used to fill the vector with data (e.g. by
1520 /// reading from a file) before marking the data as initialized using the
1521 /// [`set_len`] method.
1523 /// [`set_len`]: Vec::set_len
1528 /// #![feature(vec_spare_capacity, maybe_uninit_extra)]
1530 /// // Allocate vector big enough for 10 elements.
1531 /// let mut v = Vec::with_capacity(10);
1533 /// // Fill in the first 3 elements.
1534 /// let uninit = v.spare_capacity_mut();
1535 /// uninit[0].write(0);
1536 /// uninit[1].write(1);
1537 /// uninit[2].write(2);
1539 /// // Mark the first 3 elements of the vector as being initialized.
1544 /// assert_eq!(&v, &[0, 1, 2]);
1546 #[unstable(feature = "vec_spare_capacity", issue = "75017")]
1548 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
1550 slice::from_raw_parts_mut(
1551 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
1552 self.buf.capacity() - self.len,
1558 impl<T: Clone> Vec<T> {
1559 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1561 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1562 /// difference, with each additional slot filled with `value`.
1563 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1565 /// This method requires `T` to implement [`Clone`],
1566 /// in order to be able to clone the passed value.
1567 /// If you need more flexibility (or want to rely on [`Default`] instead of
1568 /// [`Clone`]), use [`resize_with`].
1573 /// let mut vec = vec!["hello"];
1574 /// vec.resize(3, "world");
1575 /// assert_eq!(vec, ["hello", "world", "world"]);
1577 /// let mut vec = vec![1, 2, 3, 4];
1578 /// vec.resize(2, 0);
1579 /// assert_eq!(vec, [1, 2]);
1582 /// [`resize_with`]: Vec::resize_with
1583 #[stable(feature = "vec_resize", since = "1.5.0")]
1584 pub fn resize(&mut self, new_len: usize, value: T) {
1585 let len = self.len();
1588 self.extend_with(new_len - len, ExtendElement(value))
1590 self.truncate(new_len);
1594 /// Clones and appends all elements in a slice to the `Vec`.
1596 /// Iterates over the slice `other`, clones each element, and then appends
1597 /// it to this `Vec`. The `other` vector is traversed in-order.
1599 /// Note that this function is same as [`extend`] except that it is
1600 /// specialized to work with slices instead. If and when Rust gets
1601 /// specialization this function will likely be deprecated (but still
1607 /// let mut vec = vec![1];
1608 /// vec.extend_from_slice(&[2, 3, 4]);
1609 /// assert_eq!(vec, [1, 2, 3, 4]);
1612 /// [`extend`]: #method.extend
1613 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1614 pub fn extend_from_slice(&mut self, other: &[T]) {
1615 self.spec_extend(other.iter())
1619 impl<T: Default> Vec<T> {
1620 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1622 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1623 /// difference, with each additional slot filled with [`Default::default()`].
1624 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1626 /// This method uses [`Default`] to create new values on every push. If
1627 /// you'd rather [`Clone`] a given value, use [`resize`].
1632 /// # #![allow(deprecated)]
1633 /// #![feature(vec_resize_default)]
1635 /// let mut vec = vec![1, 2, 3];
1636 /// vec.resize_default(5);
1637 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1639 /// let mut vec = vec![1, 2, 3, 4];
1640 /// vec.resize_default(2);
1641 /// assert_eq!(vec, [1, 2]);
1644 /// [`resize`]: Vec::resize
1645 #[unstable(feature = "vec_resize_default", issue = "41758")]
1647 reason = "This is moving towards being removed in favor \
1648 of `.resize_with(Default::default)`. If you disagree, please comment \
1649 in the tracking issue.",
1652 pub fn resize_default(&mut self, new_len: usize) {
1653 let len = self.len();
1656 self.extend_with(new_len - len, ExtendDefault);
1658 self.truncate(new_len);
1663 // This code generalizes `extend_with_{element,default}`.
1664 trait ExtendWith<T> {
1665 fn next(&mut self) -> T;
1669 struct ExtendElement<T>(T);
1670 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1671 fn next(&mut self) -> T {
1674 fn last(self) -> T {
1679 struct ExtendDefault;
1680 impl<T: Default> ExtendWith<T> for ExtendDefault {
1681 fn next(&mut self) -> T {
1684 fn last(self) -> T {
1689 struct ExtendFunc<F>(F);
1690 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1691 fn next(&mut self) -> T {
1694 fn last(mut self) -> T {
1700 /// Extend the vector by `n` values, using the given generator.
1701 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1705 let mut ptr = self.as_mut_ptr().add(self.len());
1706 // Use SetLenOnDrop to work around bug where compiler
1707 // may not realize the store through `ptr` through self.set_len()
1709 let mut local_len = SetLenOnDrop::new(&mut self.len);
1711 // Write all elements except the last one
1713 ptr::write(ptr, value.next());
1714 ptr = ptr.offset(1);
1715 // Increment the length in every step in case next() panics
1716 local_len.increment_len(1);
1720 // We can write the last element directly without cloning needlessly
1721 ptr::write(ptr, value.last());
1722 local_len.increment_len(1);
1725 // len set by scope guard
1730 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1732 // The idea is: The length field in SetLenOnDrop is a local variable
1733 // that the optimizer will see does not alias with any stores through the Vec's data
1734 // pointer. This is a workaround for alias analysis issue #32155
1735 struct SetLenOnDrop<'a> {
1740 impl<'a> SetLenOnDrop<'a> {
1742 fn new(len: &'a mut usize) -> Self {
1743 SetLenOnDrop { local_len: *len, len }
1747 fn increment_len(&mut self, increment: usize) {
1748 self.local_len += increment;
1752 impl Drop for SetLenOnDrop<'_> {
1754 fn drop(&mut self) {
1755 *self.len = self.local_len;
1759 impl<T: PartialEq> Vec<T> {
1760 /// Removes consecutive repeated elements in the vector according to the
1761 /// [`PartialEq`] trait implementation.
1763 /// If the vector is sorted, this removes all duplicates.
1768 /// let mut vec = vec![1, 2, 2, 3, 2];
1772 /// assert_eq!(vec, [1, 2, 3, 2]);
1774 #[stable(feature = "rust1", since = "1.0.0")]
1776 pub fn dedup(&mut self) {
1777 self.dedup_by(|a, b| a == b)
1782 /// Removes the first instance of `item` from the vector if the item exists.
1784 /// This method will be removed soon.
1785 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1787 reason = "Removing the first item equal to a needle is already easily possible \
1788 with iterators and the current Vec methods. Furthermore, having a method for \
1789 one particular case of removal (linear search, only the first item, no swap remove) \
1790 but not for others is inconsistent. This method will be removed soon.",
1793 pub fn remove_item<V>(&mut self, item: &V) -> Option<T>
1797 let pos = self.iter().position(|x| *x == *item)?;
1798 Some(self.remove(pos))
1802 ////////////////////////////////////////////////////////////////////////////////
1803 // Internal methods and functions
1804 ////////////////////////////////////////////////////////////////////////////////
1807 #[stable(feature = "rust1", since = "1.0.0")]
1808 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1809 <T as SpecFromElem>::from_elem(elem, n)
1812 // Specialization trait used for Vec::from_elem
1813 trait SpecFromElem: Sized {
1814 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1817 impl<T: Clone> SpecFromElem for T {
1818 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1819 let mut v = Vec::with_capacity(n);
1820 v.extend_with(n, ExtendElement(elem));
1825 impl SpecFromElem for i8 {
1827 fn from_elem(elem: i8, n: usize) -> Vec<i8> {
1829 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1832 let mut v = Vec::with_capacity(n);
1833 ptr::write_bytes(v.as_mut_ptr(), elem as u8, n);
1840 impl SpecFromElem for u8 {
1842 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1844 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1847 let mut v = Vec::with_capacity(n);
1848 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1855 impl<T: Clone + IsZero> SpecFromElem for T {
1857 fn from_elem(elem: T, n: usize) -> Vec<T> {
1859 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1861 let mut v = Vec::with_capacity(n);
1862 v.extend_with(n, ExtendElement(elem));
1867 #[rustc_specialization_trait]
1868 unsafe trait IsZero {
1869 /// Whether this value is zero
1870 fn is_zero(&self) -> bool;
1873 macro_rules! impl_is_zero {
1874 ($t:ty, $is_zero:expr) => {
1875 unsafe impl IsZero for $t {
1877 fn is_zero(&self) -> bool {
1884 impl_is_zero!(i16, |x| x == 0);
1885 impl_is_zero!(i32, |x| x == 0);
1886 impl_is_zero!(i64, |x| x == 0);
1887 impl_is_zero!(i128, |x| x == 0);
1888 impl_is_zero!(isize, |x| x == 0);
1890 impl_is_zero!(u16, |x| x == 0);
1891 impl_is_zero!(u32, |x| x == 0);
1892 impl_is_zero!(u64, |x| x == 0);
1893 impl_is_zero!(u128, |x| x == 0);
1894 impl_is_zero!(usize, |x| x == 0);
1896 impl_is_zero!(bool, |x| x == false);
1897 impl_is_zero!(char, |x| x == '\0');
1899 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1900 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1902 unsafe impl<T> IsZero for *const T {
1904 fn is_zero(&self) -> bool {
1909 unsafe impl<T> IsZero for *mut T {
1911 fn is_zero(&self) -> bool {
1916 // `Option<&T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
1917 // For fat pointers, the bytes that would be the pointer metadata in the `Some`
1918 // variant are padding in the `None` variant, so ignoring them and
1919 // zero-initializing instead is ok.
1920 // `Option<&mut T>` never implements `Clone`, so there's no need for an impl of
1923 unsafe impl<T: ?Sized> IsZero for Option<&T> {
1925 fn is_zero(&self) -> bool {
1930 unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
1932 fn is_zero(&self) -> bool {
1937 ////////////////////////////////////////////////////////////////////////////////
1938 // Common trait implementations for Vec
1939 ////////////////////////////////////////////////////////////////////////////////
1941 #[stable(feature = "rust1", since = "1.0.0")]
1942 impl<T> ops::Deref for Vec<T> {
1945 fn deref(&self) -> &[T] {
1946 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
1950 #[stable(feature = "rust1", since = "1.0.0")]
1951 impl<T> ops::DerefMut for Vec<T> {
1952 fn deref_mut(&mut self) -> &mut [T] {
1953 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
1957 #[stable(feature = "rust1", since = "1.0.0")]
1958 impl<T: Clone> Clone for Vec<T> {
1960 fn clone(&self) -> Vec<T> {
1961 <[T]>::to_vec(&**self)
1964 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1965 // required for this method definition, is not available. Instead use the
1966 // `slice::to_vec` function which is only available with cfg(test)
1967 // NB see the slice::hack module in slice.rs for more information
1969 fn clone(&self) -> Vec<T> {
1970 crate::slice::to_vec(&**self)
1973 fn clone_from(&mut self, other: &Vec<T>) {
1974 other.as_slice().clone_into(self);
1978 #[stable(feature = "rust1", since = "1.0.0")]
1979 impl<T: Hash> Hash for Vec<T> {
1981 fn hash<H: Hasher>(&self, state: &mut H) {
1982 Hash::hash(&**self, state)
1986 #[stable(feature = "rust1", since = "1.0.0")]
1987 #[rustc_on_unimplemented(
1988 message = "vector indices are of type `usize` or ranges of `usize`",
1989 label = "vector indices are of type `usize` or ranges of `usize`"
1991 impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> {
1992 type Output = I::Output;
1995 fn index(&self, index: I) -> &Self::Output {
1996 Index::index(&**self, index)
2000 #[stable(feature = "rust1", since = "1.0.0")]
2001 #[rustc_on_unimplemented(
2002 message = "vector indices are of type `usize` or ranges of `usize`",
2003 label = "vector indices are of type `usize` or ranges of `usize`"
2005 impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
2007 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2008 IndexMut::index_mut(&mut **self, index)
2012 #[stable(feature = "rust1", since = "1.0.0")]
2013 impl<T> FromIterator<T> for Vec<T> {
2015 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2016 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
2020 #[stable(feature = "rust1", since = "1.0.0")]
2021 impl<T> IntoIterator for Vec<T> {
2023 type IntoIter = IntoIter<T>;
2025 /// Creates a consuming iterator, that is, one that moves each value out of
2026 /// the vector (from start to end). The vector cannot be used after calling
2032 /// let v = vec!["a".to_string(), "b".to_string()];
2033 /// for s in v.into_iter() {
2034 /// // s has type String, not &String
2035 /// println!("{}", s);
2039 fn into_iter(self) -> IntoIter<T> {
2041 let mut me = ManuallyDrop::new(self);
2042 let begin = me.as_mut_ptr();
2043 let end = if mem::size_of::<T>() == 0 {
2044 arith_offset(begin as *const i8, me.len() as isize) as *const T
2046 begin.add(me.len()) as *const T
2048 let cap = me.buf.capacity();
2050 buf: NonNull::new_unchecked(begin),
2051 phantom: PhantomData,
2060 #[stable(feature = "rust1", since = "1.0.0")]
2061 impl<'a, T> IntoIterator for &'a Vec<T> {
2063 type IntoIter = slice::Iter<'a, T>;
2065 fn into_iter(self) -> slice::Iter<'a, T> {
2070 #[stable(feature = "rust1", since = "1.0.0")]
2071 impl<'a, T> IntoIterator for &'a mut Vec<T> {
2072 type Item = &'a mut T;
2073 type IntoIter = slice::IterMut<'a, T>;
2075 fn into_iter(self) -> slice::IterMut<'a, T> {
2080 #[stable(feature = "rust1", since = "1.0.0")]
2081 impl<T> Extend<T> for Vec<T> {
2083 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2084 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2088 fn extend_one(&mut self, item: T) {
2093 fn extend_reserve(&mut self, additional: usize) {
2094 self.reserve(additional);
2098 // Specialization trait used for Vec::from_iter and Vec::extend
2099 trait SpecExtend<T, I> {
2100 fn from_iter(iter: I) -> Self;
2101 fn spec_extend(&mut self, iter: I);
2104 impl<T, I> SpecExtend<T, I> for Vec<T>
2106 I: Iterator<Item = T>,
2108 default fn from_iter(mut iterator: I) -> Self {
2109 // Unroll the first iteration, as the vector is going to be
2110 // expanded on this iteration in every case when the iterable is not
2111 // empty, but the loop in extend_desugared() is not going to see the
2112 // vector being full in the few subsequent loop iterations.
2113 // So we get better branch prediction.
2114 let mut vector = match iterator.next() {
2115 None => return Vec::new(),
2117 let (lower, _) = iterator.size_hint();
2118 let mut vector = Vec::with_capacity(lower.saturating_add(1));
2120 ptr::write(vector.as_mut_ptr(), element);
2126 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
2130 default fn spec_extend(&mut self, iter: I) {
2131 self.extend_desugared(iter)
2135 impl<T, I> SpecExtend<T, I> for Vec<T>
2137 I: TrustedLen<Item = T>,
2139 default fn from_iter(iterator: I) -> Self {
2140 let mut vector = Vec::new();
2141 vector.spec_extend(iterator);
2145 default fn spec_extend(&mut self, iterator: I) {
2146 // This is the case for a TrustedLen iterator.
2147 let (low, high) = iterator.size_hint();
2148 if let Some(high_value) = high {
2152 "TrustedLen iterator's size hint is not exact: {:?}",
2156 if let Some(additional) = high {
2157 self.reserve(additional);
2159 let mut ptr = self.as_mut_ptr().add(self.len());
2160 let mut local_len = SetLenOnDrop::new(&mut self.len);
2161 iterator.for_each(move |element| {
2162 ptr::write(ptr, element);
2163 ptr = ptr.offset(1);
2164 // NB can't overflow since we would have had to alloc the address space
2165 local_len.increment_len(1);
2169 self.extend_desugared(iterator)
2174 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
2175 fn from_iter(iterator: IntoIter<T>) -> Self {
2176 // A common case is passing a vector into a function which immediately
2177 // re-collects into a vector. We can short circuit this if the IntoIter
2178 // has not been advanced at all.
2179 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
2181 let it = ManuallyDrop::new(iterator);
2182 Vec::from_raw_parts(it.buf.as_ptr(), it.len(), it.cap)
2185 let mut vector = Vec::new();
2186 vector.spec_extend(iterator);
2191 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
2193 self.append_elements(iterator.as_slice() as _);
2195 iterator.ptr = iterator.end;
2199 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
2201 I: Iterator<Item = &'a T>,
2204 default fn from_iter(iterator: I) -> Self {
2205 SpecExtend::from_iter(iterator.cloned())
2208 default fn spec_extend(&mut self, iterator: I) {
2209 self.spec_extend(iterator.cloned())
2213 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
2217 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
2218 let slice = iterator.as_slice();
2219 self.reserve(slice.len());
2221 let len = self.len();
2222 let dst_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(len), slice.len());
2223 dst_slice.copy_from_slice(slice);
2224 self.set_len(len + slice.len());
2230 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2231 // This is the case for a general iterator.
2233 // This function should be the moral equivalent of:
2235 // for item in iterator {
2238 while let Some(element) = iterator.next() {
2239 let len = self.len();
2240 if len == self.capacity() {
2241 let (lower, _) = iterator.size_hint();
2242 self.reserve(lower.saturating_add(1));
2245 ptr::write(self.as_mut_ptr().add(len), element);
2246 // NB can't overflow since we would have had to alloc the address space
2247 self.set_len(len + 1);
2252 /// Creates a splicing iterator that replaces the specified range in the vector
2253 /// with the given `replace_with` iterator and yields the removed items.
2254 /// `replace_with` does not need to be the same length as `range`.
2256 /// `range` is removed even if the iterator is not consumed until the end.
2258 /// It is unspecified how many elements are removed from the vector
2259 /// if the `Splice` value is leaked.
2261 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2263 /// This is optimal if:
2265 /// * The tail (elements in the vector after `range`) is empty,
2266 /// * or `replace_with` yields fewer elements than `range`’s length
2267 /// * or the lower bound of its `size_hint()` is exact.
2269 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2273 /// Panics if the starting point is greater than the end point or if
2274 /// the end point is greater than the length of the vector.
2279 /// let mut v = vec![1, 2, 3];
2280 /// let new = [7, 8];
2281 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2282 /// assert_eq!(v, &[7, 8, 3]);
2283 /// assert_eq!(u, &[1, 2]);
2286 #[stable(feature = "vec_splice", since = "1.21.0")]
2287 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
2289 R: RangeBounds<usize>,
2290 I: IntoIterator<Item = T>,
2292 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2295 /// Creates an iterator which uses a closure to determine if an element should be removed.
2297 /// If the closure returns true, then the element is removed and yielded.
2298 /// If the closure returns false, the element will remain in the vector and will not be yielded
2299 /// by the iterator.
2301 /// Using this method is equivalent to the following code:
2304 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2305 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2307 /// while i != vec.len() {
2308 /// if some_predicate(&mut vec[i]) {
2309 /// let val = vec.remove(i);
2310 /// // your code here
2316 /// # assert_eq!(vec, vec![1, 4, 5]);
2319 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2320 /// because it can backshift the elements of the array in bulk.
2322 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2323 /// regardless of whether you choose to keep or remove it.
2327 /// Splitting an array into evens and odds, reusing the original allocation:
2330 /// #![feature(drain_filter)]
2331 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2333 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2334 /// let odds = numbers;
2336 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2337 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2339 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2340 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
2342 F: FnMut(&mut T) -> bool,
2344 let old_len = self.len();
2346 // Guard against us getting leaked (leak amplification)
2351 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2355 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2357 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2358 /// append the entire slice at once.
2360 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2361 #[stable(feature = "extend_ref", since = "1.2.0")]
2362 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2363 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2364 self.spec_extend(iter.into_iter())
2368 fn extend_one(&mut self, &item: &'a T) {
2373 fn extend_reserve(&mut self, additional: usize) {
2374 self.reserve(additional);
2378 macro_rules! __impl_slice_eq1 {
2379 ([$($vars:tt)*] $lhs:ty, $rhs:ty $(where $ty:ty: $bound:ident)?, #[$stability:meta]) => {
2381 impl<A, B, $($vars)*> PartialEq<$rhs> for $lhs
2387 fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
2389 fn ne(&self, other: &$rhs) -> bool { self[..] != other[..] }
2394 __impl_slice_eq1! { [] Vec<A>, Vec<B>, #[stable(feature = "rust1", since = "1.0.0")] }
2395 __impl_slice_eq1! { [] Vec<A>, &[B], #[stable(feature = "rust1", since = "1.0.0")] }
2396 __impl_slice_eq1! { [] Vec<A>, &mut [B], #[stable(feature = "rust1", since = "1.0.0")] }
2397 __impl_slice_eq1! { [] &[A], Vec<B>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] }
2398 __impl_slice_eq1! { [] &mut [A], Vec<B>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] }
2399 __impl_slice_eq1! { [] Cow<'_, [A]>, Vec<B> where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
2400 __impl_slice_eq1! { [] Cow<'_, [A]>, &[B] where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
2401 __impl_slice_eq1! { [] Cow<'_, [A]>, &mut [B] where A: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
2402 __impl_slice_eq1! { [const N: usize] Vec<A>, [B; N], #[stable(feature = "rust1", since = "1.0.0")] }
2403 __impl_slice_eq1! { [const N: usize] Vec<A>, &[B; N], #[stable(feature = "rust1", since = "1.0.0")] }
2405 // NOTE: some less important impls are omitted to reduce code bloat
2406 // FIXME(Centril): Reconsider this?
2407 //__impl_slice_eq1! { [const N: usize] Vec<A>, &mut [B; N], }
2408 //__impl_slice_eq1! { [const N: usize] [A; N], Vec<B>, }
2409 //__impl_slice_eq1! { [const N: usize] &[A; N], Vec<B>, }
2410 //__impl_slice_eq1! { [const N: usize] &mut [A; N], Vec<B>, }
2411 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, [B; N], }
2412 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &[B; N], }
2413 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &mut [B; N], }
2415 /// Implements comparison of vectors, lexicographically.
2416 #[stable(feature = "rust1", since = "1.0.0")]
2417 impl<T: PartialOrd> PartialOrd for Vec<T> {
2419 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2420 PartialOrd::partial_cmp(&**self, &**other)
2424 #[stable(feature = "rust1", since = "1.0.0")]
2425 impl<T: Eq> Eq for Vec<T> {}
2427 /// Implements ordering of vectors, lexicographically.
2428 #[stable(feature = "rust1", since = "1.0.0")]
2429 impl<T: Ord> Ord for Vec<T> {
2431 fn cmp(&self, other: &Vec<T>) -> Ordering {
2432 Ord::cmp(&**self, &**other)
2436 #[stable(feature = "rust1", since = "1.0.0")]
2437 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2438 fn drop(&mut self) {
2441 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2442 // could avoid questions of validity in certain cases
2443 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
2445 // RawVec handles deallocation
2449 #[stable(feature = "rust1", since = "1.0.0")]
2450 impl<T> Default for Vec<T> {
2451 /// Creates an empty `Vec<T>`.
2452 fn default() -> Vec<T> {
2457 #[stable(feature = "rust1", since = "1.0.0")]
2458 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2459 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2460 fmt::Debug::fmt(&**self, f)
2464 #[stable(feature = "rust1", since = "1.0.0")]
2465 impl<T> AsRef<Vec<T>> for Vec<T> {
2466 fn as_ref(&self) -> &Vec<T> {
2471 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2472 impl<T> AsMut<Vec<T>> for Vec<T> {
2473 fn as_mut(&mut self) -> &mut Vec<T> {
2478 #[stable(feature = "rust1", since = "1.0.0")]
2479 impl<T> AsRef<[T]> for Vec<T> {
2480 fn as_ref(&self) -> &[T] {
2485 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2486 impl<T> AsMut<[T]> for Vec<T> {
2487 fn as_mut(&mut self) -> &mut [T] {
2492 #[stable(feature = "rust1", since = "1.0.0")]
2493 impl<T: Clone> From<&[T]> for Vec<T> {
2495 fn from(s: &[T]) -> Vec<T> {
2499 fn from(s: &[T]) -> Vec<T> {
2500 crate::slice::to_vec(s)
2504 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2505 impl<T: Clone> From<&mut [T]> for Vec<T> {
2507 fn from(s: &mut [T]) -> Vec<T> {
2511 fn from(s: &mut [T]) -> Vec<T> {
2512 crate::slice::to_vec(s)
2516 #[stable(feature = "vec_from_array", since = "1.44.0")]
2517 impl<T, const N: usize> From<[T; N]> for Vec<T> {
2519 fn from(s: [T; N]) -> Vec<T> {
2520 <[T]>::into_vec(box s)
2523 fn from(s: [T; N]) -> Vec<T> {
2524 crate::slice::into_vec(box s)
2528 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2529 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2531 [T]: ToOwned<Owned = Vec<T>>,
2533 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2538 // note: test pulls in libstd, which causes errors here
2540 #[stable(feature = "vec_from_box", since = "1.18.0")]
2541 impl<T> From<Box<[T]>> for Vec<T> {
2542 fn from(s: Box<[T]>) -> Vec<T> {
2547 // note: test pulls in libstd, which causes errors here
2549 #[stable(feature = "box_from_vec", since = "1.20.0")]
2550 impl<T> From<Vec<T>> for Box<[T]> {
2551 fn from(v: Vec<T>) -> Box<[T]> {
2552 v.into_boxed_slice()
2556 #[stable(feature = "rust1", since = "1.0.0")]
2557 impl From<&str> for Vec<u8> {
2558 fn from(s: &str) -> Vec<u8> {
2559 From::from(s.as_bytes())
2563 ////////////////////////////////////////////////////////////////////////////////
2565 ////////////////////////////////////////////////////////////////////////////////
2567 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2568 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2569 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2574 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2575 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2576 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2581 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2582 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2583 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2584 Cow::Borrowed(v.as_slice())
2588 #[stable(feature = "rust1", since = "1.0.0")]
2589 impl<'a, T> FromIterator<T> for Cow<'a, [T]>
2593 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2594 Cow::Owned(FromIterator::from_iter(it))
2598 ////////////////////////////////////////////////////////////////////////////////
2600 ////////////////////////////////////////////////////////////////////////////////
2602 /// An iterator that moves out of a vector.
2604 /// This `struct` is created by the `into_iter` method on [`Vec`] (provided
2605 /// by the [`IntoIterator`] trait).
2606 #[stable(feature = "rust1", since = "1.0.0")]
2607 pub struct IntoIter<T> {
2609 phantom: PhantomData<T>,
2615 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2616 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2617 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2618 f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
2622 impl<T> IntoIter<T> {
2623 /// Returns the remaining items of this iterator as a slice.
2628 /// let vec = vec!['a', 'b', 'c'];
2629 /// let mut into_iter = vec.into_iter();
2630 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2631 /// let _ = into_iter.next().unwrap();
2632 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2634 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2635 pub fn as_slice(&self) -> &[T] {
2636 unsafe { slice::from_raw_parts(self.ptr, self.len()) }
2639 /// Returns the remaining items of this iterator as a mutable slice.
2644 /// let vec = vec!['a', 'b', 'c'];
2645 /// let mut into_iter = vec.into_iter();
2646 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2647 /// into_iter.as_mut_slice()[2] = 'z';
2648 /// assert_eq!(into_iter.next().unwrap(), 'a');
2649 /// assert_eq!(into_iter.next().unwrap(), 'b');
2650 /// assert_eq!(into_iter.next().unwrap(), 'z');
2652 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2653 pub fn as_mut_slice(&mut self) -> &mut [T] {
2654 unsafe { &mut *self.as_raw_mut_slice() }
2657 fn as_raw_mut_slice(&mut self) -> *mut [T] {
2658 ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len())
2662 #[stable(feature = "vec_intoiter_as_ref", since = "1.46.0")]
2663 impl<T> AsRef<[T]> for IntoIter<T> {
2664 fn as_ref(&self) -> &[T] {
2669 #[stable(feature = "rust1", since = "1.0.0")]
2670 unsafe impl<T: Send> Send for IntoIter<T> {}
2671 #[stable(feature = "rust1", since = "1.0.0")]
2672 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2674 #[stable(feature = "rust1", since = "1.0.0")]
2675 impl<T> Iterator for IntoIter<T> {
2679 fn next(&mut self) -> Option<T> {
2681 if self.ptr as *const _ == self.end {
2684 if mem::size_of::<T>() == 0 {
2685 // purposefully don't use 'ptr.offset' because for
2686 // vectors with 0-size elements this would return the
2688 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2690 // Make up a value of this ZST.
2694 self.ptr = self.ptr.offset(1);
2696 Some(ptr::read(old))
2703 fn size_hint(&self) -> (usize, Option<usize>) {
2704 let exact = if mem::size_of::<T>() == 0 {
2705 (self.end as usize).wrapping_sub(self.ptr as usize)
2707 unsafe { self.end.offset_from(self.ptr) as usize }
2709 (exact, Some(exact))
2713 fn count(self) -> usize {
2718 #[stable(feature = "rust1", since = "1.0.0")]
2719 impl<T> DoubleEndedIterator for IntoIter<T> {
2721 fn next_back(&mut self) -> Option<T> {
2723 if self.end == self.ptr {
2726 if mem::size_of::<T>() == 0 {
2727 // See above for why 'ptr.offset' isn't used
2728 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2730 // Make up a value of this ZST.
2733 self.end = self.end.offset(-1);
2735 Some(ptr::read(self.end))
2742 #[stable(feature = "rust1", since = "1.0.0")]
2743 impl<T> ExactSizeIterator for IntoIter<T> {
2744 fn is_empty(&self) -> bool {
2745 self.ptr == self.end
2749 #[stable(feature = "fused", since = "1.26.0")]
2750 impl<T> FusedIterator for IntoIter<T> {}
2752 #[unstable(feature = "trusted_len", issue = "37572")]
2753 unsafe impl<T> TrustedLen for IntoIter<T> {}
2755 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2756 impl<T: Clone> Clone for IntoIter<T> {
2757 fn clone(&self) -> IntoIter<T> {
2758 self.as_slice().to_owned().into_iter()
2762 #[stable(feature = "rust1", since = "1.0.0")]
2763 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2764 fn drop(&mut self) {
2765 struct DropGuard<'a, T>(&'a mut IntoIter<T>);
2767 impl<T> Drop for DropGuard<'_, T> {
2768 fn drop(&mut self) {
2769 // RawVec handles deallocation
2770 let _ = unsafe { RawVec::from_raw_parts(self.0.buf.as_ptr(), self.0.cap) };
2774 let guard = DropGuard(self);
2775 // destroy the remaining elements
2777 ptr::drop_in_place(guard.0.as_raw_mut_slice());
2779 // now `guard` will be dropped and do the rest
2783 /// A draining iterator for `Vec<T>`.
2785 /// This `struct` is created by [`Vec::drain`].
2786 #[stable(feature = "drain", since = "1.6.0")]
2787 pub struct Drain<'a, T: 'a> {
2788 /// Index of tail to preserve
2792 /// Current remaining range to remove
2793 iter: slice::Iter<'a, T>,
2794 vec: NonNull<Vec<T>>,
2797 #[stable(feature = "collection_debug", since = "1.17.0")]
2798 impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
2799 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2800 f.debug_tuple("Drain").field(&self.iter.as_slice()).finish()
2804 impl<'a, T> Drain<'a, T> {
2805 /// Returns the remaining items of this iterator as a slice.
2810 /// let mut vec = vec!['a', 'b', 'c'];
2811 /// let mut drain = vec.drain(..);
2812 /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']);
2813 /// let _ = drain.next().unwrap();
2814 /// assert_eq!(drain.as_slice(), &['b', 'c']);
2816 #[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
2817 pub fn as_slice(&self) -> &[T] {
2818 self.iter.as_slice()
2822 #[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
2823 impl<'a, T> AsRef<[T]> for Drain<'a, T> {
2824 fn as_ref(&self) -> &[T] {
2829 #[stable(feature = "drain", since = "1.6.0")]
2830 unsafe impl<T: Sync> Sync for Drain<'_, T> {}
2831 #[stable(feature = "drain", since = "1.6.0")]
2832 unsafe impl<T: Send> Send for Drain<'_, T> {}
2834 #[stable(feature = "drain", since = "1.6.0")]
2835 impl<T> Iterator for Drain<'_, T> {
2839 fn next(&mut self) -> Option<T> {
2840 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2843 fn size_hint(&self) -> (usize, Option<usize>) {
2844 self.iter.size_hint()
2848 #[stable(feature = "drain", since = "1.6.0")]
2849 impl<T> DoubleEndedIterator for Drain<'_, T> {
2851 fn next_back(&mut self) -> Option<T> {
2852 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2856 #[stable(feature = "drain", since = "1.6.0")]
2857 impl<T> Drop for Drain<'_, T> {
2858 fn drop(&mut self) {
2859 /// Continues dropping the remaining elements in the `Drain`, then moves back the
2860 /// un-`Drain`ed elements to restore the original `Vec`.
2861 struct DropGuard<'r, 'a, T>(&'r mut Drain<'a, T>);
2863 impl<'r, 'a, T> Drop for DropGuard<'r, 'a, T> {
2864 fn drop(&mut self) {
2865 // Continue the same loop we have below. If the loop already finished, this does
2867 self.0.for_each(drop);
2869 if self.0.tail_len > 0 {
2871 let source_vec = self.0.vec.as_mut();
2872 // memmove back untouched tail, update to new length
2873 let start = source_vec.len();
2874 let tail = self.0.tail_start;
2876 let src = source_vec.as_ptr().add(tail);
2877 let dst = source_vec.as_mut_ptr().add(start);
2878 ptr::copy(src, dst, self.0.tail_len);
2880 source_vec.set_len(start + self.0.tail_len);
2886 // exhaust self first
2887 while let Some(item) = self.next() {
2888 let guard = DropGuard(self);
2893 // Drop a `DropGuard` to move back the non-drained tail of `self`.
2898 #[stable(feature = "drain", since = "1.6.0")]
2899 impl<T> ExactSizeIterator for Drain<'_, T> {
2900 fn is_empty(&self) -> bool {
2901 self.iter.is_empty()
2905 #[unstable(feature = "trusted_len", issue = "37572")]
2906 unsafe impl<T> TrustedLen for Drain<'_, T> {}
2908 #[stable(feature = "fused", since = "1.26.0")]
2909 impl<T> FusedIterator for Drain<'_, T> {}
2911 /// A splicing iterator for `Vec`.
2913 /// This struct is created by [`Vec::splice()`].
2914 /// See its documentation for more.
2916 #[stable(feature = "vec_splice", since = "1.21.0")]
2917 pub struct Splice<'a, I: Iterator + 'a> {
2918 drain: Drain<'a, I::Item>,
2922 #[stable(feature = "vec_splice", since = "1.21.0")]
2923 impl<I: Iterator> Iterator for Splice<'_, I> {
2924 type Item = I::Item;
2926 fn next(&mut self) -> Option<Self::Item> {
2930 fn size_hint(&self) -> (usize, Option<usize>) {
2931 self.drain.size_hint()
2935 #[stable(feature = "vec_splice", since = "1.21.0")]
2936 impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
2937 fn next_back(&mut self) -> Option<Self::Item> {
2938 self.drain.next_back()
2942 #[stable(feature = "vec_splice", since = "1.21.0")]
2943 impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}
2945 #[stable(feature = "vec_splice", since = "1.21.0")]
2946 impl<I: Iterator> Drop for Splice<'_, I> {
2947 fn drop(&mut self) {
2948 self.drain.by_ref().for_each(drop);
2951 if self.drain.tail_len == 0 {
2952 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2956 // First fill the range left by drain().
2957 if !self.drain.fill(&mut self.replace_with) {
2961 // There may be more elements. Use the lower bound as an estimate.
2962 // FIXME: Is the upper bound a better guess? Or something else?
2963 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2964 if lower_bound > 0 {
2965 self.drain.move_tail(lower_bound);
2966 if !self.drain.fill(&mut self.replace_with) {
2971 // Collect any remaining elements.
2972 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2973 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2974 // Now we have an exact count.
2975 if collected.len() > 0 {
2976 self.drain.move_tail(collected.len());
2977 let filled = self.drain.fill(&mut collected);
2978 debug_assert!(filled);
2979 debug_assert_eq!(collected.len(), 0);
2982 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2986 /// Private helper methods for `Splice::drop`
2987 impl<T> Drain<'_, T> {
2988 /// The range from `self.vec.len` to `self.tail_start` contains elements
2989 /// that have been moved out.
2990 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2991 /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2992 unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool {
2993 let vec = unsafe { self.vec.as_mut() };
2994 let range_start = vec.len;
2995 let range_end = self.tail_start;
2996 let range_slice = unsafe {
2997 slice::from_raw_parts_mut(vec.as_mut_ptr().add(range_start), range_end - range_start)
3000 for place in range_slice {
3001 if let Some(new_item) = replace_with.next() {
3002 unsafe { ptr::write(place, new_item) };
3011 /// Makes room for inserting more elements before the tail.
3012 unsafe fn move_tail(&mut self, additional: usize) {
3013 let vec = unsafe { self.vec.as_mut() };
3014 let len = self.tail_start + self.tail_len;
3015 vec.buf.reserve(len, additional);
3017 let new_tail_start = self.tail_start + additional;
3019 let src = vec.as_ptr().add(self.tail_start);
3020 let dst = vec.as_mut_ptr().add(new_tail_start);
3021 ptr::copy(src, dst, self.tail_len);
3023 self.tail_start = new_tail_start;
3027 /// An iterator produced by calling `drain_filter` on Vec.
3028 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
3030 pub struct DrainFilter<'a, T, F>
3032 F: FnMut(&mut T) -> bool,
3034 vec: &'a mut Vec<T>,
3035 /// The index of the item that will be inspected by the next call to `next`.
3037 /// The number of items that have been drained (removed) thus far.
3039 /// The original length of `vec` prior to draining.
3041 /// The filter test predicate.
3043 /// A flag that indicates a panic has occurred in the filter test prodicate.
3044 /// This is used as a hint in the drop implementation to prevent consumption
3045 /// of the remainder of the `DrainFilter`. Any unprocessed items will be
3046 /// backshifted in the `vec`, but no further items will be dropped or
3047 /// tested by the filter predicate.
3051 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
3052 impl<T, F> Iterator for DrainFilter<'_, T, F>
3054 F: FnMut(&mut T) -> bool,
3058 fn next(&mut self) -> Option<T> {
3060 while self.idx < self.old_len {
3062 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
3063 self.panic_flag = true;
3064 let drained = (self.pred)(&mut v[i]);
3065 self.panic_flag = false;
3066 // Update the index *after* the predicate is called. If the index
3067 // is updated prior and the predicate panics, the element at this
3068 // index would be leaked.
3072 return Some(ptr::read(&v[i]));
3073 } else if self.del > 0 {
3075 let src: *const T = &v[i];
3076 let dst: *mut T = &mut v[i - del];
3077 ptr::copy_nonoverlapping(src, dst, 1);
3084 fn size_hint(&self) -> (usize, Option<usize>) {
3085 (0, Some(self.old_len - self.idx))
3089 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
3090 impl<T, F> Drop for DrainFilter<'_, T, F>
3092 F: FnMut(&mut T) -> bool,
3094 fn drop(&mut self) {
3095 struct BackshiftOnDrop<'a, 'b, T, F>
3097 F: FnMut(&mut T) -> bool,
3099 drain: &'b mut DrainFilter<'a, T, F>,
3102 impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F>
3104 F: FnMut(&mut T) -> bool,
3106 fn drop(&mut self) {
3108 if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
3109 // This is a pretty messed up state, and there isn't really an
3110 // obviously right thing to do. We don't want to keep trying
3111 // to execute `pred`, so we just backshift all the unprocessed
3112 // elements and tell the vec that they still exist. The backshift
3113 // is required to prevent a double-drop of the last successfully
3114 // drained item prior to a panic in the predicate.
3115 let ptr = self.drain.vec.as_mut_ptr();
3116 let src = ptr.add(self.drain.idx);
3117 let dst = src.sub(self.drain.del);
3118 let tail_len = self.drain.old_len - self.drain.idx;
3119 src.copy_to(dst, tail_len);
3121 self.drain.vec.set_len(self.drain.old_len - self.drain.del);
3126 let backshift = BackshiftOnDrop { drain: self };
3128 // Attempt to consume any remaining elements if the filter predicate
3129 // has not yet panicked. We'll backshift any remaining elements
3130 // whether we've already panicked or if the consumption here panics.
3131 if !backshift.drain.panic_flag {
3132 backshift.drain.for_each(drop);