1 //! A contiguous growable array type with heap-allocated contents, written
4 //! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
5 //! `O(1)` pop (from the end).
9 //! You can explicitly create a [`Vec<T>`] with [`new`]:
12 //! let v: Vec<i32> = Vec::new();
15 //! ...or by using the [`vec!`] macro:
18 //! let v: Vec<i32> = vec![];
20 //! let v = vec![1, 2, 3, 4, 5];
22 //! let v = vec![0; 10]; // ten zeroes
25 //! You can [`push`] values onto the end of a vector (which will grow the vector
29 //! let mut v = vec![1, 2];
34 //! Popping values works in much the same way:
37 //! let mut v = vec![1, 2];
39 //! let two = v.pop();
42 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
45 //! let mut v = vec![1, 2, 3];
50 //! [`Vec<T>`]: ../../std/vec/struct.Vec.html
51 //! [`new`]: ../../std/vec/struct.Vec.html#method.new
52 //! [`push`]: ../../std/vec/struct.Vec.html#method.push
53 //! [`Index`]: ../../std/ops/trait.Index.html
54 //! [`IndexMut`]: ../../std/ops/trait.IndexMut.html
55 //! [`vec!`]: ../../std/macro.vec.html
57 #![stable(feature = "rust1", since = "1.0.0")]
59 use core::array::LengthAtMost32;
60 use core::cmp::{self, Ordering};
62 use core::hash::{self, Hash};
63 use core::intrinsics::{arith_offset, assume};
64 use core::iter::{FromIterator, FusedIterator, TrustedLen};
65 use core::marker::PhantomData;
67 use core::ops::Bound::{Excluded, Included, Unbounded};
68 use core::ops::{self, Index, IndexMut, RangeBounds};
69 use core::ptr::{self, NonNull};
70 use core::slice::{self, SliceIndex};
72 use crate::borrow::{Cow, ToOwned};
73 use crate::boxed::Box;
74 use crate::collections::TryReserveError;
75 use crate::raw_vec::RawVec;
77 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
82 /// let mut vec = Vec::new();
86 /// assert_eq!(vec.len(), 2);
87 /// assert_eq!(vec[0], 1);
89 /// assert_eq!(vec.pop(), Some(2));
90 /// assert_eq!(vec.len(), 1);
93 /// assert_eq!(vec[0], 7);
95 /// vec.extend([1, 2, 3].iter().copied());
98 /// println!("{}", x);
100 /// assert_eq!(vec, [7, 1, 2, 3]);
103 /// The [`vec!`] macro is provided to make initialization more convenient:
106 /// let mut vec = vec![1, 2, 3];
108 /// assert_eq!(vec, [1, 2, 3, 4]);
111 /// It can also initialize each element of a `Vec<T>` with a given value.
112 /// This may be more efficient than performing allocation and initialization
113 /// in separate steps, especially when initializing a vector of zeros:
116 /// let vec = vec![0; 5];
117 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
119 /// // The following is equivalent, but potentially slower:
120 /// let mut vec1 = Vec::with_capacity(5);
121 /// vec1.resize(5, 0);
124 /// Use a `Vec<T>` as an efficient stack:
127 /// let mut stack = Vec::new();
133 /// while let Some(top) = stack.pop() {
134 /// // Prints 3, 2, 1
135 /// println!("{}", top);
141 /// The `Vec` type allows to access values by index, because it implements the
142 /// [`Index`] trait. An example will be more explicit:
145 /// let v = vec![0, 2, 4, 6];
146 /// println!("{}", v[1]); // it will display '2'
149 /// However be careful: if you try to access an index which isn't in the `Vec`,
150 /// your software will panic! You cannot do this:
153 /// let v = vec![0, 2, 4, 6];
154 /// println!("{}", v[6]); // it will panic!
157 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
162 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
163 /// To get a slice, use `&`. Example:
166 /// fn read_slice(slice: &[usize]) {
170 /// let v = vec![0, 1];
173 /// // ... and that's all!
174 /// // you can also do it like this:
175 /// let x : &[usize] = &v;
178 /// In Rust, it's more common to pass slices as arguments rather than vectors
179 /// when you just want to provide a read access. The same goes for [`String`] and
182 /// # Capacity and reallocation
184 /// The capacity of a vector is the amount of space allocated for any future
185 /// elements that will be added onto the vector. This is not to be confused with
186 /// the *length* of a vector, which specifies the number of actual elements
187 /// within the vector. If a vector's length exceeds its capacity, its capacity
188 /// will automatically be increased, but its elements will have to be
191 /// For example, a vector with capacity 10 and length 0 would be an empty vector
192 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
193 /// vector will not change its capacity or cause reallocation to occur. However,
194 /// if the vector's length is increased to 11, it will have to reallocate, which
195 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
196 /// whenever possible to specify how big the vector is expected to get.
200 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
201 /// about its design. This ensures that it's as low-overhead as possible in
202 /// the general case, and can be correctly manipulated in primitive ways
203 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
204 /// If additional type parameters are added (e.g., to support custom allocators),
205 /// overriding their defaults may change the behavior.
207 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
208 /// triplet. No more, no less. The order of these fields is completely
209 /// unspecified, and you should use the appropriate methods to modify these.
210 /// The pointer will never be null, so this type is null-pointer-optimized.
212 /// However, the pointer may not actually point to allocated memory. In particular,
213 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
214 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
215 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
216 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
217 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
218 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
219 /// details are very subtle — if you intend to allocate memory using a `Vec`
220 /// and use it for something else (either to pass to unsafe code, or to build your
221 /// own memory-backed collection), be sure to deallocate this memory by using
222 /// `from_raw_parts` to recover the `Vec` and then dropping it.
224 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
225 /// (as defined by the allocator Rust is configured to use by default), and its
226 /// pointer points to [`len`] initialized, contiguous elements in order (what
227 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
228 /// `[`len`] logically uninitialized, contiguous elements.
230 /// `Vec` will never perform a "small optimization" where elements are actually
231 /// stored on the stack for two reasons:
233 /// * It would make it more difficult for unsafe code to correctly manipulate
234 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
235 /// only moved, and it would be more difficult to determine if a `Vec` had
236 /// actually allocated memory.
238 /// * It would penalize the general case, incurring an additional branch
241 /// `Vec` will never automatically shrink itself, even if completely empty. This
242 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
243 /// and then filling it back up to the same [`len`] should incur no calls to
244 /// the allocator. If you wish to free up unused memory, use
245 /// [`shrink_to_fit`].
247 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
248 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
249 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
250 /// accurate, and can be relied on. It can even be used to manually free the memory
251 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
252 /// when not necessary.
254 /// `Vec` does not guarantee any particular growth strategy when reallocating
255 /// when full, nor when [`reserve`] is called. The current strategy is basic
256 /// and it may prove desirable to use a non-constant growth factor. Whatever
257 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
259 /// `vec![x; n]`, `vec![a, b, c, d]`, and
260 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
261 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
262 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
263 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
265 /// `Vec` will not specifically overwrite any data that is removed from it,
266 /// but also won't specifically preserve it. Its uninitialized memory is
267 /// scratch space that it may use however it wants. It will generally just do
268 /// whatever is most efficient or otherwise easy to implement. Do not rely on
269 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
270 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
271 /// first, that may not actually happen because the optimizer does not consider
272 /// this a side-effect that must be preserved. There is one case which we will
273 /// not break, however: using `unsafe` code to write to the excess capacity,
274 /// and then increasing the length to match, is always valid.
276 /// `Vec` does not currently guarantee the order in which elements are dropped.
277 /// The order has changed in the past and may change again.
279 /// [`vec!`]: ../../std/macro.vec.html
280 /// [`get`]: ../../std/vec/struct.Vec.html#method.get
281 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
282 /// [`Index`]: ../../std/ops/trait.Index.html
283 /// [`String`]: ../../std/string/struct.String.html
284 /// [`&str`]: ../../std/primitive.str.html
285 /// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
286 /// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
287 /// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
288 /// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
289 /// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
290 /// [`len`]: ../../std/vec/struct.Vec.html#method.len
291 /// [`push`]: ../../std/vec/struct.Vec.html#method.push
292 /// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
293 /// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
294 /// [owned slice]: ../../std/boxed/struct.Box.html
295 #[stable(feature = "rust1", since = "1.0.0")]
296 #[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")]
302 ////////////////////////////////////////////////////////////////////////////////
304 ////////////////////////////////////////////////////////////////////////////////
307 /// Constructs a new, empty `Vec<T>`.
309 /// The vector will not allocate until elements are pushed onto it.
314 /// # #![allow(unused_mut)]
315 /// let mut vec: Vec<i32> = Vec::new();
318 #[rustc_const_stable(feature = "const_vec_new", since = "1.32.0")]
319 #[stable(feature = "rust1", since = "1.0.0")]
320 pub const fn new() -> Vec<T> {
321 Vec { buf: RawVec::NEW, len: 0 }
324 /// Constructs a new, empty `Vec<T>` with the specified capacity.
326 /// The vector will be able to hold exactly `capacity` elements without
327 /// reallocating. If `capacity` is 0, the vector will not allocate.
329 /// It is important to note that although the returned vector has the
330 /// *capacity* specified, the vector will have a zero *length*. For an
331 /// explanation of the difference between length and capacity, see
332 /// *[Capacity and reallocation]*.
334 /// [Capacity and reallocation]: #capacity-and-reallocation
339 /// let mut vec = Vec::with_capacity(10);
341 /// // The vector contains no items, even though it has capacity for more
342 /// assert_eq!(vec.len(), 0);
344 /// // These are all done without reallocating...
349 /// // ...but this may make the vector reallocate
353 #[stable(feature = "rust1", since = "1.0.0")]
354 pub fn with_capacity(capacity: usize) -> Vec<T> {
355 Vec { buf: RawVec::with_capacity(capacity), len: 0 }
358 /// Decomposes a `Vec<T>` into its raw components.
360 /// Returns the raw pointer to the underlying data, the length of
361 /// the vector (in elements), and the allocated capacity of the
362 /// data (in elements). These are the same arguments in the same
363 /// order as the arguments to [`from_raw_parts`].
365 /// After calling this function, the caller is responsible for the
366 /// memory previously managed by the `Vec`. The only way to do
367 /// this is to convert the raw pointer, length, and capacity back
368 /// into a `Vec` with the [`from_raw_parts`] function, allowing
369 /// the destructor to perform the cleanup.
371 /// [`from_raw_parts`]: #method.from_raw_parts
376 /// #![feature(vec_into_raw_parts)]
377 /// let v: Vec<i32> = vec![-1, 0, 1];
379 /// let (ptr, len, cap) = v.into_raw_parts();
381 /// let rebuilt = unsafe {
382 /// // We can now make changes to the components, such as
383 /// // transmuting the raw pointer to a compatible type.
384 /// let ptr = ptr as *mut u32;
386 /// Vec::from_raw_parts(ptr, len, cap)
388 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
390 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
391 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
392 let mut me = mem::ManuallyDrop::new(self);
393 (me.as_mut_ptr(), me.len(), me.capacity())
396 /// Creates a `Vec<T>` directly from the raw components of another vector.
400 /// This is highly unsafe, due to the number of invariants that aren't
403 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
404 /// (at least, it's highly likely to be incorrect if it wasn't).
405 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
406 /// * `length` needs to be less than or equal to `capacity`.
407 /// * `capacity` needs to be the capacity that the pointer was allocated with.
409 /// Violating these may cause problems like corrupting the allocator's
410 /// internal data structures. For example it is **not** safe
411 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
412 /// It's also not safe to build one from a `Vec<u16>` and its length, because
413 /// the allocator cares about the alignment, and these two types have different
414 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
415 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
417 /// The ownership of `ptr` is effectively transferred to the
418 /// `Vec<T>` which may then deallocate, reallocate or change the
419 /// contents of memory pointed to by the pointer at will. Ensure
420 /// that nothing else uses the pointer after calling this
423 /// [`String`]: ../../std/string/struct.String.html
431 /// let v = vec![1, 2, 3];
433 // FIXME Update this when vec_into_raw_parts is stabilized
434 /// // Prevent running `v`'s destructor so we are in complete control
435 /// // of the allocation.
436 /// let mut v = mem::ManuallyDrop::new(v);
438 /// // Pull out the various important pieces of information about `v`
439 /// let p = v.as_mut_ptr();
440 /// let len = v.len();
441 /// let cap = v.capacity();
444 /// // Overwrite memory with 4, 5, 6
445 /// for i in 0..len as isize {
446 /// ptr::write(p.offset(i), 4 + i);
449 /// // Put everything back together into a Vec
450 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
451 /// assert_eq!(rebuilt, [4, 5, 6]);
454 #[stable(feature = "rust1", since = "1.0.0")]
455 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
456 Vec { buf: RawVec::from_raw_parts(ptr, capacity), len: length }
459 /// Returns the number of elements the vector can hold without
465 /// let vec: Vec<i32> = Vec::with_capacity(10);
466 /// assert_eq!(vec.capacity(), 10);
469 #[stable(feature = "rust1", since = "1.0.0")]
470 pub fn capacity(&self) -> usize {
474 /// Reserves capacity for at least `additional` more elements to be inserted
475 /// in the given `Vec<T>`. The collection may reserve more space to avoid
476 /// frequent reallocations. After calling `reserve`, capacity will be
477 /// greater than or equal to `self.len() + additional`. Does nothing if
478 /// capacity is already sufficient.
482 /// Panics if the new capacity overflows `usize`.
487 /// let mut vec = vec![1];
489 /// assert!(vec.capacity() >= 11);
491 #[stable(feature = "rust1", since = "1.0.0")]
492 pub fn reserve(&mut self, additional: usize) {
493 self.buf.reserve(self.len, additional);
496 /// Reserves the minimum capacity for exactly `additional` more elements to
497 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
498 /// capacity will be greater than or equal to `self.len() + additional`.
499 /// Does nothing if the capacity is already sufficient.
501 /// Note that the allocator may give the collection more space than it
502 /// requests. Therefore, capacity can not be relied upon to be precisely
503 /// minimal. Prefer `reserve` if future insertions are expected.
507 /// Panics if the new capacity overflows `usize`.
512 /// let mut vec = vec![1];
513 /// vec.reserve_exact(10);
514 /// assert!(vec.capacity() >= 11);
516 #[stable(feature = "rust1", since = "1.0.0")]
517 pub fn reserve_exact(&mut self, additional: usize) {
518 self.buf.reserve_exact(self.len, additional);
521 /// Tries to reserve capacity for at least `additional` more elements to be inserted
522 /// in the given `Vec<T>`. The collection may reserve more space to avoid
523 /// frequent reallocations. After calling `reserve`, capacity will be
524 /// greater than or equal to `self.len() + additional`. Does nothing if
525 /// capacity is already sufficient.
529 /// If the capacity overflows, or the allocator reports a failure, then an error
535 /// #![feature(try_reserve)]
536 /// use std::collections::TryReserveError;
538 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
539 /// let mut output = Vec::new();
541 /// // Pre-reserve the memory, exiting if we can't
542 /// output.try_reserve(data.len())?;
544 /// // Now we know this can't OOM in the middle of our complex work
545 /// output.extend(data.iter().map(|&val| {
546 /// val * 2 + 5 // very complicated
551 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
553 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
554 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
555 self.buf.try_reserve(self.len, additional)
558 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
559 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
560 /// capacity will be greater than or equal to `self.len() + additional`.
561 /// Does nothing if the capacity is already sufficient.
563 /// Note that the allocator may give the collection more space than it
564 /// requests. Therefore, capacity can not be relied upon to be precisely
565 /// minimal. Prefer `reserve` if future insertions are expected.
569 /// If the capacity overflows, or the allocator reports a failure, then an error
575 /// #![feature(try_reserve)]
576 /// use std::collections::TryReserveError;
578 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
579 /// let mut output = Vec::new();
581 /// // Pre-reserve the memory, exiting if we can't
582 /// output.try_reserve(data.len())?;
584 /// // Now we know this can't OOM in the middle of our complex work
585 /// output.extend(data.iter().map(|&val| {
586 /// val * 2 + 5 // very complicated
591 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
593 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
594 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
595 self.buf.try_reserve_exact(self.len, additional)
598 /// Shrinks the capacity of the vector as much as possible.
600 /// It will drop down as close as possible to the length but the allocator
601 /// may still inform the vector that there is space for a few more elements.
606 /// let mut vec = Vec::with_capacity(10);
607 /// vec.extend([1, 2, 3].iter().cloned());
608 /// assert_eq!(vec.capacity(), 10);
609 /// vec.shrink_to_fit();
610 /// assert!(vec.capacity() >= 3);
612 #[stable(feature = "rust1", since = "1.0.0")]
613 pub fn shrink_to_fit(&mut self) {
614 if self.capacity() != self.len {
615 self.buf.shrink_to_fit(self.len);
619 /// Shrinks the capacity of the vector with a lower bound.
621 /// The capacity will remain at least as large as both the length
622 /// and the supplied value.
626 /// Panics if the current capacity is smaller than the supplied
627 /// minimum capacity.
632 /// #![feature(shrink_to)]
633 /// let mut vec = Vec::with_capacity(10);
634 /// vec.extend([1, 2, 3].iter().cloned());
635 /// assert_eq!(vec.capacity(), 10);
636 /// vec.shrink_to(4);
637 /// assert!(vec.capacity() >= 4);
638 /// vec.shrink_to(0);
639 /// assert!(vec.capacity() >= 3);
641 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
642 pub fn shrink_to(&mut self, min_capacity: usize) {
643 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
646 /// Converts the vector into [`Box<[T]>`][owned slice].
648 /// Note that this will drop any excess capacity.
650 /// [owned slice]: ../../std/boxed/struct.Box.html
655 /// let v = vec![1, 2, 3];
657 /// let slice = v.into_boxed_slice();
660 /// Any excess capacity is removed:
663 /// let mut vec = Vec::with_capacity(10);
664 /// vec.extend([1, 2, 3].iter().cloned());
666 /// assert_eq!(vec.capacity(), 10);
667 /// let slice = vec.into_boxed_slice();
668 /// assert_eq!(slice.into_vec().capacity(), 3);
670 #[stable(feature = "rust1", since = "1.0.0")]
671 pub fn into_boxed_slice(mut self) -> Box<[T]> {
673 self.shrink_to_fit();
674 let buf = ptr::read(&self.buf);
680 /// Shortens the vector, keeping the first `len` elements and dropping
683 /// If `len` is greater than the vector's current length, this has no
686 /// The [`drain`] method can emulate `truncate`, but causes the excess
687 /// elements to be returned instead of dropped.
689 /// Note that this method has no effect on the allocated capacity
694 /// Truncating a five element vector to two elements:
697 /// let mut vec = vec![1, 2, 3, 4, 5];
699 /// assert_eq!(vec, [1, 2]);
702 /// No truncation occurs when `len` is greater than the vector's current
706 /// let mut vec = vec![1, 2, 3];
708 /// assert_eq!(vec, [1, 2, 3]);
711 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
715 /// let mut vec = vec![1, 2, 3];
717 /// assert_eq!(vec, []);
720 /// [`clear`]: #method.clear
721 /// [`drain`]: #method.drain
722 #[stable(feature = "rust1", since = "1.0.0")]
723 pub fn truncate(&mut self, len: usize) {
724 // This is safe because:
726 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
727 // case avoids creating an invalid slice, and
728 // * the `len` of the vector is shrunk before calling `drop_in_place`,
729 // such that no value will be dropped twice in case `drop_in_place`
730 // were to panic once (if it panics twice, the program aborts).
735 let s = self.get_unchecked_mut(len..) as *mut _;
737 ptr::drop_in_place(s);
741 /// Extracts a slice containing the entire vector.
743 /// Equivalent to `&s[..]`.
748 /// use std::io::{self, Write};
749 /// let buffer = vec![1, 2, 3, 5, 8];
750 /// io::sink().write(buffer.as_slice()).unwrap();
753 #[stable(feature = "vec_as_slice", since = "1.7.0")]
754 pub fn as_slice(&self) -> &[T] {
758 /// Extracts a mutable slice of the entire vector.
760 /// Equivalent to `&mut s[..]`.
765 /// use std::io::{self, Read};
766 /// let mut buffer = vec![0; 3];
767 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
770 #[stable(feature = "vec_as_slice", since = "1.7.0")]
771 pub fn as_mut_slice(&mut self) -> &mut [T] {
775 /// Returns a raw pointer to the vector's buffer.
777 /// The caller must ensure that the vector outlives the pointer this
778 /// function returns, or else it will end up pointing to garbage.
779 /// Modifying the vector may cause its buffer to be reallocated,
780 /// which would also make any pointers to it invalid.
782 /// The caller must also ensure that the memory the pointer (non-transitively) points to
783 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
784 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
789 /// let x = vec![1, 2, 4];
790 /// let x_ptr = x.as_ptr();
793 /// for i in 0..x.len() {
794 /// assert_eq!(*x_ptr.add(i), 1 << i);
799 /// [`as_mut_ptr`]: #method.as_mut_ptr
800 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
802 pub fn as_ptr(&self) -> *const T {
803 // We shadow the slice method of the same name to avoid going through
804 // `deref`, which creates an intermediate reference.
805 let ptr = self.buf.ptr();
807 assume(!ptr.is_null());
812 /// Returns an unsafe mutable pointer to the vector's buffer.
814 /// The caller must ensure that the vector outlives the pointer this
815 /// function returns, or else it will end up pointing to garbage.
816 /// Modifying the vector may cause its buffer to be reallocated,
817 /// which would also make any pointers to it invalid.
822 /// // Allocate vector big enough for 4 elements.
824 /// let mut x: Vec<i32> = Vec::with_capacity(size);
825 /// let x_ptr = x.as_mut_ptr();
827 /// // Initialize elements via raw pointer writes, then set length.
829 /// for i in 0..size {
830 /// *x_ptr.add(i) = i as i32;
834 /// assert_eq!(&*x, &[0,1,2,3]);
836 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
838 pub fn as_mut_ptr(&mut self) -> *mut T {
839 // We shadow the slice method of the same name to avoid going through
840 // `deref_mut`, which creates an intermediate reference.
841 let ptr = self.buf.ptr();
843 assume(!ptr.is_null());
848 /// Forces the length of the vector to `new_len`.
850 /// This is a low-level operation that maintains none of the normal
851 /// invariants of the type. Normally changing the length of a vector
852 /// is done using one of the safe operations instead, such as
853 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
855 /// [`truncate`]: #method.truncate
856 /// [`resize`]: #method.resize
857 /// [`extend`]: ../../std/iter/trait.Extend.html#tymethod.extend
858 /// [`clear`]: #method.clear
862 /// - `new_len` must be less than or equal to [`capacity()`].
863 /// - The elements at `old_len..new_len` must be initialized.
865 /// [`capacity()`]: #method.capacity
869 /// This method can be useful for situations in which the vector
870 /// is serving as a buffer for other code, particularly over FFI:
873 /// # #![allow(dead_code)]
874 /// # // This is just a minimal skeleton for the doc example;
875 /// # // don't use this as a starting point for a real library.
876 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
877 /// # const Z_OK: i32 = 0;
879 /// # fn deflateGetDictionary(
880 /// # strm: *mut std::ffi::c_void,
881 /// # dictionary: *mut u8,
882 /// # dictLength: *mut usize,
885 /// # impl StreamWrapper {
886 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
887 /// // Per the FFI method's docs, "32768 bytes is always enough".
888 /// let mut dict = Vec::with_capacity(32_768);
889 /// let mut dict_length = 0;
890 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
891 /// // 1. `dict_length` elements were initialized.
892 /// // 2. `dict_length` <= the capacity (32_768)
893 /// // which makes `set_len` safe to call.
895 /// // Make the FFI call...
896 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
898 /// // ...and update the length to what was initialized.
899 /// dict.set_len(dict_length);
909 /// While the following example is sound, there is a memory leak since
910 /// the inner vectors were not freed prior to the `set_len` call:
913 /// let mut vec = vec![vec![1, 0, 0],
917 /// // 1. `old_len..0` is empty so no elements need to be initialized.
918 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
924 /// Normally, here, one would use [`clear`] instead to correctly drop
925 /// the contents and thus not leak memory.
927 #[stable(feature = "rust1", since = "1.0.0")]
928 pub unsafe fn set_len(&mut self, new_len: usize) {
929 debug_assert!(new_len <= self.capacity());
934 /// Removes an element from the vector and returns it.
936 /// The removed element is replaced by the last element of the vector.
938 /// This does not preserve ordering, but is O(1).
942 /// Panics if `index` is out of bounds.
947 /// let mut v = vec!["foo", "bar", "baz", "qux"];
949 /// assert_eq!(v.swap_remove(1), "bar");
950 /// assert_eq!(v, ["foo", "qux", "baz"]);
952 /// assert_eq!(v.swap_remove(0), "foo");
953 /// assert_eq!(v, ["baz", "qux"]);
956 #[stable(feature = "rust1", since = "1.0.0")]
957 pub fn swap_remove(&mut self, index: usize) -> T {
959 // We replace self[index] with the last element. Note that if the
960 // bounds check on hole succeeds there must be a last element (which
961 // can be self[index] itself).
962 let hole: *mut T = &mut self[index];
963 let last = ptr::read(self.get_unchecked(self.len - 1));
965 ptr::replace(hole, last)
969 /// Inserts an element at position `index` within the vector, shifting all
970 /// elements after it to the right.
974 /// Panics if `index > len`.
979 /// let mut vec = vec![1, 2, 3];
980 /// vec.insert(1, 4);
981 /// assert_eq!(vec, [1, 4, 2, 3]);
982 /// vec.insert(4, 5);
983 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
985 #[stable(feature = "rust1", since = "1.0.0")]
986 pub fn insert(&mut self, index: usize, element: T) {
987 let len = self.len();
988 assert!(index <= len);
990 // space for the new element
991 if len == self.buf.capacity() {
997 // The spot to put the new value
999 let p = self.as_mut_ptr().add(index);
1000 // Shift everything over to make space. (Duplicating the
1001 // `index`th element into two consecutive places.)
1002 ptr::copy(p, p.offset(1), len - index);
1003 // Write it in, overwriting the first copy of the `index`th
1005 ptr::write(p, element);
1007 self.set_len(len + 1);
1011 /// Removes and returns the element at position `index` within the vector,
1012 /// shifting all elements after it to the left.
1016 /// Panics if `index` is out of bounds.
1021 /// let mut v = vec![1, 2, 3];
1022 /// assert_eq!(v.remove(1), 2);
1023 /// assert_eq!(v, [1, 3]);
1025 #[stable(feature = "rust1", since = "1.0.0")]
1026 pub fn remove(&mut self, index: usize) -> T {
1027 let len = self.len();
1028 assert!(index < len);
1033 // the place we are taking from.
1034 let ptr = self.as_mut_ptr().add(index);
1035 // copy it out, unsafely having a copy of the value on
1036 // the stack and in the vector at the same time.
1037 ret = ptr::read(ptr);
1039 // Shift everything down to fill in that spot.
1040 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1042 self.set_len(len - 1);
1047 /// Retains only the elements specified by the predicate.
1049 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1050 /// This method operates in place, visiting each element exactly once in the
1051 /// original order, and preserves the order of the retained elements.
1056 /// let mut vec = vec![1, 2, 3, 4];
1057 /// vec.retain(|&x| x % 2 == 0);
1058 /// assert_eq!(vec, [2, 4]);
1061 /// The exact order may be useful for tracking external state, like an index.
1064 /// let mut vec = vec![1, 2, 3, 4, 5];
1065 /// let keep = [false, true, true, false, true];
1067 /// vec.retain(|_| (keep[i], i += 1).0);
1068 /// assert_eq!(vec, [2, 3, 5]);
1070 #[stable(feature = "rust1", since = "1.0.0")]
1071 pub fn retain<F>(&mut self, mut f: F)
1073 F: FnMut(&T) -> bool,
1075 let len = self.len();
1078 let v = &mut **self;
1089 self.truncate(len - del);
1093 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1096 /// If the vector is sorted, this removes all duplicates.
1101 /// let mut vec = vec![10, 20, 21, 30, 20];
1103 /// vec.dedup_by_key(|i| *i / 10);
1105 /// assert_eq!(vec, [10, 20, 30, 20]);
1107 #[stable(feature = "dedup_by", since = "1.16.0")]
1109 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1111 F: FnMut(&mut T) -> K,
1114 self.dedup_by(|a, b| key(a) == key(b))
1117 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1120 /// The `same_bucket` function is passed references to two elements from the vector and
1121 /// must determine if the elements compare equal. The elements are passed in opposite order
1122 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1124 /// If the vector is sorted, this removes all duplicates.
1129 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1131 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1133 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1135 #[stable(feature = "dedup_by", since = "1.16.0")]
1136 pub fn dedup_by<F>(&mut self, same_bucket: F)
1138 F: FnMut(&mut T, &mut T) -> bool,
1141 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
1147 /// Appends an element to the back of a collection.
1151 /// Panics if the number of elements in the vector overflows a `usize`.
1156 /// let mut vec = vec![1, 2];
1158 /// assert_eq!(vec, [1, 2, 3]);
1161 #[stable(feature = "rust1", since = "1.0.0")]
1162 pub fn push(&mut self, value: T) {
1163 // This will panic or abort if we would allocate > isize::MAX bytes
1164 // or if the length increment would overflow for zero-sized types.
1165 if self.len == self.buf.capacity() {
1169 let end = self.as_mut_ptr().add(self.len);
1170 ptr::write(end, value);
1175 /// Removes the last element from a vector and returns it, or [`None`] if it
1178 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1183 /// let mut vec = vec![1, 2, 3];
1184 /// assert_eq!(vec.pop(), Some(3));
1185 /// assert_eq!(vec, [1, 2]);
1188 #[stable(feature = "rust1", since = "1.0.0")]
1189 pub fn pop(&mut self) -> Option<T> {
1195 Some(ptr::read(self.get_unchecked(self.len())))
1200 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1204 /// Panics if the number of elements in the vector overflows a `usize`.
1209 /// let mut vec = vec![1, 2, 3];
1210 /// let mut vec2 = vec![4, 5, 6];
1211 /// vec.append(&mut vec2);
1212 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1213 /// assert_eq!(vec2, []);
1216 #[stable(feature = "append", since = "1.4.0")]
1217 pub fn append(&mut self, other: &mut Self) {
1219 self.append_elements(other.as_slice() as _);
1224 /// Appends elements to `Self` from other buffer.
1226 unsafe fn append_elements(&mut self, other: *const [T]) {
1227 let count = (*other).len();
1228 self.reserve(count);
1229 let len = self.len();
1230 ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count);
1234 /// Creates a draining iterator that removes the specified range in the vector
1235 /// and yields the removed items.
1237 /// Note 1: The element range is removed even if the iterator is only
1238 /// partially consumed or not consumed at all.
1240 /// Note 2: It is unspecified how many elements are removed from the vector
1241 /// if the `Drain` value is leaked.
1245 /// Panics if the starting point is greater than the end point or if
1246 /// the end point is greater than the length of the vector.
1251 /// let mut v = vec![1, 2, 3];
1252 /// let u: Vec<_> = v.drain(1..).collect();
1253 /// assert_eq!(v, &[1]);
1254 /// assert_eq!(u, &[2, 3]);
1256 /// // A full range clears the vector
1258 /// assert_eq!(v, &[]);
1260 #[stable(feature = "drain", since = "1.6.0")]
1261 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1263 R: RangeBounds<usize>,
1267 // When the Drain is first created, it shortens the length of
1268 // the source vector to make sure no uninitialized or moved-from elements
1269 // are accessible at all if the Drain's destructor never gets to run.
1271 // Drain will ptr::read out the values to remove.
1272 // When finished, remaining tail of the vec is copied back to cover
1273 // the hole, and the vector length is restored to the new length.
1275 let len = self.len();
1276 let start = match range.start_bound() {
1278 Excluded(&n) => n + 1,
1281 let end = match range.end_bound() {
1282 Included(&n) => n + 1,
1286 assert!(start <= end);
1287 assert!(end <= len);
1290 // set self.vec length's to start, to be safe in case Drain is leaked
1291 self.set_len(start);
1292 // Use the borrow in the IterMut to indicate borrowing behavior of the
1293 // whole Drain iterator (like &mut T).
1294 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1297 tail_len: len - end,
1298 iter: range_slice.iter(),
1299 vec: NonNull::from(self),
1304 /// Clears the vector, removing all values.
1306 /// Note that this method has no effect on the allocated capacity
1312 /// let mut v = vec![1, 2, 3];
1316 /// assert!(v.is_empty());
1319 #[stable(feature = "rust1", since = "1.0.0")]
1320 pub fn clear(&mut self) {
1324 /// Returns the number of elements in the vector, also referred to
1325 /// as its 'length'.
1330 /// let a = vec![1, 2, 3];
1331 /// assert_eq!(a.len(), 3);
1334 #[stable(feature = "rust1", since = "1.0.0")]
1335 pub fn len(&self) -> usize {
1339 /// Returns `true` if the vector contains no elements.
1344 /// let mut v = Vec::new();
1345 /// assert!(v.is_empty());
1348 /// assert!(!v.is_empty());
1350 #[stable(feature = "rust1", since = "1.0.0")]
1351 pub fn is_empty(&self) -> bool {
1355 /// Splits the collection into two at the given index.
1357 /// Returns a newly allocated vector containing the elements in the range
1358 /// `[at, len)`. After the call, the original vector will be left containing
1359 /// the elements `[0, at)` with its previous capacity unchanged.
1363 /// Panics if `at > len`.
1368 /// let mut vec = vec![1,2,3];
1369 /// let vec2 = vec.split_off(1);
1370 /// assert_eq!(vec, [1]);
1371 /// assert_eq!(vec2, [2, 3]);
1374 #[stable(feature = "split_off", since = "1.4.0")]
1375 pub fn split_off(&mut self, at: usize) -> Self {
1376 assert!(at <= self.len(), "`at` out of bounds");
1378 let other_len = self.len - at;
1379 let mut other = Vec::with_capacity(other_len);
1381 // Unsafely `set_len` and copy items to `other`.
1384 other.set_len(other_len);
1386 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1391 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1393 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1394 /// difference, with each additional slot filled with the result of
1395 /// calling the closure `f`. The return values from `f` will end up
1396 /// in the `Vec` in the order they have been generated.
1398 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1400 /// This method uses a closure to create new values on every push. If
1401 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1402 /// to use the [`Default`] trait to generate values, you can pass
1403 /// [`Default::default()`] as the second argument.
1408 /// let mut vec = vec![1, 2, 3];
1409 /// vec.resize_with(5, Default::default);
1410 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1412 /// let mut vec = vec![];
1414 /// vec.resize_with(4, || { p *= 2; p });
1415 /// assert_eq!(vec, [2, 4, 8, 16]);
1418 /// [`resize`]: #method.resize
1419 /// [`Clone`]: ../../std/clone/trait.Clone.html
1420 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1421 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1425 let len = self.len();
1427 self.extend_with(new_len - len, ExtendFunc(f));
1429 self.truncate(new_len);
1433 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1434 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1435 /// `'a`. If the type has only static references, or none at all, then this
1436 /// may be chosen to be `'static`.
1438 /// This function is similar to the `leak` function on `Box`.
1440 /// This function is mainly useful for data that lives for the remainder of
1441 /// the program's life. Dropping the returned reference will cause a memory
1449 /// #![feature(vec_leak)]
1451 /// let x = vec![1, 2, 3];
1452 /// let static_ref: &'static mut [usize] = Vec::leak(x);
1453 /// static_ref[0] += 1;
1454 /// assert_eq!(static_ref, &[2, 2, 3]);
1456 #[unstable(feature = "vec_leak", issue = "62195")]
1458 pub fn leak<'a>(vec: Vec<T>) -> &'a mut [T]
1460 T: 'a, // Technically not needed, but kept to be explicit.
1462 Box::leak(vec.into_boxed_slice())
1466 impl<T: Clone> Vec<T> {
1467 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1469 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1470 /// difference, with each additional slot filled with `value`.
1471 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1473 /// This method requires [`Clone`] to be able clone the passed value. If
1474 /// you need more flexibility (or want to rely on [`Default`] instead of
1475 /// [`Clone`]), use [`resize_with`].
1480 /// let mut vec = vec!["hello"];
1481 /// vec.resize(3, "world");
1482 /// assert_eq!(vec, ["hello", "world", "world"]);
1484 /// let mut vec = vec![1, 2, 3, 4];
1485 /// vec.resize(2, 0);
1486 /// assert_eq!(vec, [1, 2]);
1489 /// [`Clone`]: ../../std/clone/trait.Clone.html
1490 /// [`Default`]: ../../std/default/trait.Default.html
1491 /// [`resize_with`]: #method.resize_with
1492 #[stable(feature = "vec_resize", since = "1.5.0")]
1493 pub fn resize(&mut self, new_len: usize, value: T) {
1494 let len = self.len();
1497 self.extend_with(new_len - len, ExtendElement(value))
1499 self.truncate(new_len);
1503 /// Clones and appends all elements in a slice to the `Vec`.
1505 /// Iterates over the slice `other`, clones each element, and then appends
1506 /// it to this `Vec`. The `other` vector is traversed in-order.
1508 /// Note that this function is same as [`extend`] except that it is
1509 /// specialized to work with slices instead. If and when Rust gets
1510 /// specialization this function will likely be deprecated (but still
1516 /// let mut vec = vec![1];
1517 /// vec.extend_from_slice(&[2, 3, 4]);
1518 /// assert_eq!(vec, [1, 2, 3, 4]);
1521 /// [`extend`]: #method.extend
1522 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1523 pub fn extend_from_slice(&mut self, other: &[T]) {
1524 self.spec_extend(other.iter())
1528 impl<T: Default> Vec<T> {
1529 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1531 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1532 /// difference, with each additional slot filled with [`Default::default()`].
1533 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1535 /// This method uses [`Default`] to create new values on every push. If
1536 /// you'd rather [`Clone`] a given value, use [`resize`].
1541 /// # #![allow(deprecated)]
1542 /// #![feature(vec_resize_default)]
1544 /// let mut vec = vec![1, 2, 3];
1545 /// vec.resize_default(5);
1546 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1548 /// let mut vec = vec![1, 2, 3, 4];
1549 /// vec.resize_default(2);
1550 /// assert_eq!(vec, [1, 2]);
1553 /// [`resize`]: #method.resize
1554 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1555 /// [`Default`]: ../../std/default/trait.Default.html
1556 /// [`Clone`]: ../../std/clone/trait.Clone.html
1557 #[unstable(feature = "vec_resize_default", issue = "41758")]
1559 reason = "This is moving towards being removed in favor \
1560 of `.resize_with(Default::default)`. If you disagree, please comment \
1561 in the tracking issue.",
1564 pub fn resize_default(&mut self, new_len: usize) {
1565 let len = self.len();
1568 self.extend_with(new_len - len, ExtendDefault);
1570 self.truncate(new_len);
1575 // This code generalises `extend_with_{element,default}`.
1576 trait ExtendWith<T> {
1577 fn next(&mut self) -> T;
1581 struct ExtendElement<T>(T);
1582 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1583 fn next(&mut self) -> T {
1586 fn last(self) -> T {
1591 struct ExtendDefault;
1592 impl<T: Default> ExtendWith<T> for ExtendDefault {
1593 fn next(&mut self) -> T {
1596 fn last(self) -> T {
1601 struct ExtendFunc<F>(F);
1602 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1603 fn next(&mut self) -> T {
1606 fn last(mut self) -> T {
1612 /// Extend the vector by `n` values, using the given generator.
1613 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1617 let mut ptr = self.as_mut_ptr().add(self.len());
1618 // Use SetLenOnDrop to work around bug where compiler
1619 // may not realize the store through `ptr` through self.set_len()
1621 let mut local_len = SetLenOnDrop::new(&mut self.len);
1623 // Write all elements except the last one
1625 ptr::write(ptr, value.next());
1626 ptr = ptr.offset(1);
1627 // Increment the length in every step in case next() panics
1628 local_len.increment_len(1);
1632 // We can write the last element directly without cloning needlessly
1633 ptr::write(ptr, value.last());
1634 local_len.increment_len(1);
1637 // len set by scope guard
1642 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1644 // The idea is: The length field in SetLenOnDrop is a local variable
1645 // that the optimizer will see does not alias with any stores through the Vec's data
1646 // pointer. This is a workaround for alias analysis issue #32155
1647 struct SetLenOnDrop<'a> {
1652 impl<'a> SetLenOnDrop<'a> {
1654 fn new(len: &'a mut usize) -> Self {
1655 SetLenOnDrop { local_len: *len, len: len }
1659 fn increment_len(&mut self, increment: usize) {
1660 self.local_len += increment;
1664 impl Drop for SetLenOnDrop<'_> {
1666 fn drop(&mut self) {
1667 *self.len = self.local_len;
1671 impl<T: PartialEq> Vec<T> {
1672 /// Removes consecutive repeated elements in the vector according to the
1673 /// [`PartialEq`] trait implementation.
1675 /// If the vector is sorted, this removes all duplicates.
1680 /// let mut vec = vec![1, 2, 2, 3, 2];
1684 /// assert_eq!(vec, [1, 2, 3, 2]);
1686 #[stable(feature = "rust1", since = "1.0.0")]
1688 pub fn dedup(&mut self) {
1689 self.dedup_by(|a, b| a == b)
1694 /// Removes the first instance of `item` from the vector if the item exists.
1699 /// # #![feature(vec_remove_item)]
1700 /// let mut vec = vec![1, 2, 3, 1];
1702 /// vec.remove_item(&1);
1704 /// assert_eq!(vec, vec![2, 3, 1]);
1706 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1707 pub fn remove_item<V>(&mut self, item: &V) -> Option<T>
1711 let pos = self.iter().position(|x| *x == *item)?;
1712 Some(self.remove(pos))
1716 ////////////////////////////////////////////////////////////////////////////////
1717 // Internal methods and functions
1718 ////////////////////////////////////////////////////////////////////////////////
1721 #[stable(feature = "rust1", since = "1.0.0")]
1722 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1723 <T as SpecFromElem>::from_elem(elem, n)
1726 // Specialization trait used for Vec::from_elem
1727 trait SpecFromElem: Sized {
1728 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1731 impl<T: Clone> SpecFromElem for T {
1732 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1733 let mut v = Vec::with_capacity(n);
1734 v.extend_with(n, ExtendElement(elem));
1739 impl SpecFromElem for u8 {
1741 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1743 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1746 let mut v = Vec::with_capacity(n);
1747 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1754 impl<T: Clone + IsZero> SpecFromElem for T {
1756 fn from_elem(elem: T, n: usize) -> Vec<T> {
1758 return Vec { buf: RawVec::with_capacity_zeroed(n), len: n };
1760 let mut v = Vec::with_capacity(n);
1761 v.extend_with(n, ExtendElement(elem));
1766 unsafe trait IsZero {
1767 /// Whether this value is zero
1768 fn is_zero(&self) -> bool;
1771 macro_rules! impl_is_zero {
1772 ($t: ty, $is_zero: expr) => {
1773 unsafe impl IsZero for $t {
1775 fn is_zero(&self) -> bool {
1782 impl_is_zero!(i8, |x| x == 0);
1783 impl_is_zero!(i16, |x| x == 0);
1784 impl_is_zero!(i32, |x| x == 0);
1785 impl_is_zero!(i64, |x| x == 0);
1786 impl_is_zero!(i128, |x| x == 0);
1787 impl_is_zero!(isize, |x| x == 0);
1789 impl_is_zero!(u16, |x| x == 0);
1790 impl_is_zero!(u32, |x| x == 0);
1791 impl_is_zero!(u64, |x| x == 0);
1792 impl_is_zero!(u128, |x| x == 0);
1793 impl_is_zero!(usize, |x| x == 0);
1795 impl_is_zero!(bool, |x| x == false);
1796 impl_is_zero!(char, |x| x == '\0');
1798 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1799 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1801 unsafe impl<T> IsZero for *const T {
1803 fn is_zero(&self) -> bool {
1808 unsafe impl<T> IsZero for *mut T {
1810 fn is_zero(&self) -> bool {
1815 // `Option<&T>`, `Option<&mut T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
1816 // For fat pointers, the bytes that would be the pointer metadata in the `Some` variant
1817 // are padding in the `None` variant, so ignoring them and zero-initializing instead is ok.
1819 unsafe impl<T: ?Sized> IsZero for Option<&T> {
1821 fn is_zero(&self) -> bool {
1826 unsafe impl<T: ?Sized> IsZero for Option<&mut T> {
1828 fn is_zero(&self) -> bool {
1833 unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
1835 fn is_zero(&self) -> bool {
1840 ////////////////////////////////////////////////////////////////////////////////
1841 // Common trait implementations for Vec
1842 ////////////////////////////////////////////////////////////////////////////////
1844 #[stable(feature = "rust1", since = "1.0.0")]
1845 impl<T: Clone> Clone for Vec<T> {
1847 fn clone(&self) -> Vec<T> {
1848 <[T]>::to_vec(&**self)
1851 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1852 // required for this method definition, is not available. Instead use the
1853 // `slice::to_vec` function which is only available with cfg(test)
1854 // NB see the slice::hack module in slice.rs for more information
1856 fn clone(&self) -> Vec<T> {
1857 crate::slice::to_vec(&**self)
1860 fn clone_from(&mut self, other: &Vec<T>) {
1861 other.as_slice().clone_into(self);
1865 #[stable(feature = "rust1", since = "1.0.0")]
1866 impl<T: Hash> Hash for Vec<T> {
1868 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1869 Hash::hash(&**self, state)
1873 #[stable(feature = "rust1", since = "1.0.0")]
1874 #[rustc_on_unimplemented(
1875 message = "vector indices are of type `usize` or ranges of `usize`",
1876 label = "vector indices are of type `usize` or ranges of `usize`"
1878 impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> {
1879 type Output = I::Output;
1882 fn index(&self, index: I) -> &Self::Output {
1883 Index::index(&**self, index)
1887 #[stable(feature = "rust1", since = "1.0.0")]
1888 #[rustc_on_unimplemented(
1889 message = "vector indices are of type `usize` or ranges of `usize`",
1890 label = "vector indices are of type `usize` or ranges of `usize`"
1892 impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
1894 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1895 IndexMut::index_mut(&mut **self, index)
1899 #[stable(feature = "rust1", since = "1.0.0")]
1900 impl<T> ops::Deref for Vec<T> {
1903 fn deref(&self) -> &[T] {
1904 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
1908 #[stable(feature = "rust1", since = "1.0.0")]
1909 impl<T> ops::DerefMut for Vec<T> {
1910 fn deref_mut(&mut self) -> &mut [T] {
1911 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
1915 #[stable(feature = "rust1", since = "1.0.0")]
1916 impl<T> FromIterator<T> for Vec<T> {
1918 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1919 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1923 #[stable(feature = "rust1", since = "1.0.0")]
1924 impl<T> IntoIterator for Vec<T> {
1926 type IntoIter = IntoIter<T>;
1928 /// Creates a consuming iterator, that is, one that moves each value out of
1929 /// the vector (from start to end). The vector cannot be used after calling
1935 /// let v = vec!["a".to_string(), "b".to_string()];
1936 /// for s in v.into_iter() {
1937 /// // s has type String, not &String
1938 /// println!("{}", s);
1942 fn into_iter(mut self) -> IntoIter<T> {
1944 let begin = self.as_mut_ptr();
1945 let end = if mem::size_of::<T>() == 0 {
1946 arith_offset(begin as *const i8, self.len() as isize) as *const T
1948 begin.add(self.len()) as *const T
1950 let cap = self.buf.capacity();
1953 buf: NonNull::new_unchecked(begin),
1954 phantom: PhantomData,
1963 #[stable(feature = "rust1", since = "1.0.0")]
1964 impl<'a, T> IntoIterator for &'a Vec<T> {
1966 type IntoIter = slice::Iter<'a, T>;
1968 fn into_iter(self) -> slice::Iter<'a, T> {
1973 #[stable(feature = "rust1", since = "1.0.0")]
1974 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1975 type Item = &'a mut T;
1976 type IntoIter = slice::IterMut<'a, T>;
1978 fn into_iter(self) -> slice::IterMut<'a, T> {
1983 #[stable(feature = "rust1", since = "1.0.0")]
1984 impl<T> Extend<T> for Vec<T> {
1986 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1987 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1991 // Specialization trait used for Vec::from_iter and Vec::extend
1992 trait SpecExtend<T, I> {
1993 fn from_iter(iter: I) -> Self;
1994 fn spec_extend(&mut self, iter: I);
1997 impl<T, I> SpecExtend<T, I> for Vec<T>
1999 I: Iterator<Item = T>,
2001 default fn from_iter(mut iterator: I) -> Self {
2002 // Unroll the first iteration, as the vector is going to be
2003 // expanded on this iteration in every case when the iterable is not
2004 // empty, but the loop in extend_desugared() is not going to see the
2005 // vector being full in the few subsequent loop iterations.
2006 // So we get better branch prediction.
2007 let mut vector = match iterator.next() {
2008 None => return Vec::new(),
2010 let (lower, _) = iterator.size_hint();
2011 let mut vector = Vec::with_capacity(lower.saturating_add(1));
2013 ptr::write(vector.get_unchecked_mut(0), element);
2019 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
2023 default fn spec_extend(&mut self, iter: I) {
2024 self.extend_desugared(iter)
2028 impl<T, I> SpecExtend<T, I> for Vec<T>
2030 I: TrustedLen<Item = T>,
2032 default fn from_iter(iterator: I) -> Self {
2033 let mut vector = Vec::new();
2034 vector.spec_extend(iterator);
2038 default fn spec_extend(&mut self, iterator: I) {
2039 // This is the case for a TrustedLen iterator.
2040 let (low, high) = iterator.size_hint();
2041 if let Some(high_value) = high {
2045 "TrustedLen iterator's size hint is not exact: {:?}",
2049 if let Some(additional) = high {
2050 self.reserve(additional);
2052 let mut ptr = self.as_mut_ptr().add(self.len());
2053 let mut local_len = SetLenOnDrop::new(&mut self.len);
2054 iterator.for_each(move |element| {
2055 ptr::write(ptr, element);
2056 ptr = ptr.offset(1);
2057 // NB can't overflow since we would have had to alloc the address space
2058 local_len.increment_len(1);
2062 self.extend_desugared(iterator)
2067 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
2068 fn from_iter(iterator: IntoIter<T>) -> Self {
2069 // A common case is passing a vector into a function which immediately
2070 // re-collects into a vector. We can short circuit this if the IntoIter
2071 // has not been advanced at all.
2072 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
2074 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(), iterator.len(), iterator.cap);
2075 mem::forget(iterator);
2079 let mut vector = Vec::new();
2080 vector.spec_extend(iterator);
2085 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
2087 self.append_elements(iterator.as_slice() as _);
2089 iterator.ptr = iterator.end;
2093 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
2095 I: Iterator<Item = &'a T>,
2098 default fn from_iter(iterator: I) -> Self {
2099 SpecExtend::from_iter(iterator.cloned())
2102 default fn spec_extend(&mut self, iterator: I) {
2103 self.spec_extend(iterator.cloned())
2107 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
2111 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
2112 let slice = iterator.as_slice();
2113 self.reserve(slice.len());
2115 let len = self.len();
2116 self.set_len(len + slice.len());
2117 self.get_unchecked_mut(len..).copy_from_slice(slice);
2123 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2124 // This is the case for a general iterator.
2126 // This function should be the moral equivalent of:
2128 // for item in iterator {
2131 while let Some(element) = iterator.next() {
2132 let len = self.len();
2133 if len == self.capacity() {
2134 let (lower, _) = iterator.size_hint();
2135 self.reserve(lower.saturating_add(1));
2138 ptr::write(self.get_unchecked_mut(len), element);
2139 // NB can't overflow since we would have had to alloc the address space
2140 self.set_len(len + 1);
2145 /// Creates a splicing iterator that replaces the specified range in the vector
2146 /// with the given `replace_with` iterator and yields the removed items.
2147 /// `replace_with` does not need to be the same length as `range`.
2149 /// The element range is removed even if the iterator is not consumed until the end.
2151 /// It is unspecified how many elements are removed from the vector
2152 /// if the `Splice` value is leaked.
2154 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2156 /// This is optimal if:
2158 /// * The tail (elements in the vector after `range`) is empty,
2159 /// * or `replace_with` yields fewer elements than `range`’s length
2160 /// * or the lower bound of its `size_hint()` is exact.
2162 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2166 /// Panics if the starting point is greater than the end point or if
2167 /// the end point is greater than the length of the vector.
2172 /// let mut v = vec![1, 2, 3];
2173 /// let new = [7, 8];
2174 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2175 /// assert_eq!(v, &[7, 8, 3]);
2176 /// assert_eq!(u, &[1, 2]);
2179 #[stable(feature = "vec_splice", since = "1.21.0")]
2180 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
2182 R: RangeBounds<usize>,
2183 I: IntoIterator<Item = T>,
2185 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2188 /// Creates an iterator which uses a closure to determine if an element should be removed.
2190 /// If the closure returns true, then the element is removed and yielded.
2191 /// If the closure returns false, the element will remain in the vector and will not be yielded
2192 /// by the iterator.
2194 /// Using this method is equivalent to the following code:
2197 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2198 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2200 /// while i != vec.len() {
2201 /// if some_predicate(&mut vec[i]) {
2202 /// let val = vec.remove(i);
2203 /// // your code here
2209 /// # assert_eq!(vec, vec![1, 4, 5]);
2212 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2213 /// because it can backshift the elements of the array in bulk.
2215 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2216 /// regardless of whether you choose to keep or remove it.
2221 /// Splitting an array into evens and odds, reusing the original allocation:
2224 /// #![feature(drain_filter)]
2225 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2227 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2228 /// let odds = numbers;
2230 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2231 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2233 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2234 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
2236 F: FnMut(&mut T) -> bool,
2238 let old_len = self.len();
2240 // Guard against us getting leaked (leak amplification)
2245 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2249 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2251 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2252 /// append the entire slice at once.
2254 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2255 #[stable(feature = "extend_ref", since = "1.2.0")]
2256 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2257 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2258 self.spec_extend(iter.into_iter())
2262 macro_rules! __impl_slice_eq1 {
2263 ([$($vars:tt)*] $lhs:ty, $rhs:ty, $($constraints:tt)*) => {
2264 #[stable(feature = "rust1", since = "1.0.0")]
2265 impl<A, B, $($vars)*> PartialEq<$rhs> for $lhs
2271 fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
2273 fn ne(&self, other: &$rhs) -> bool { self[..] != other[..] }
2278 __impl_slice_eq1! { [] Vec<A>, Vec<B>, }
2279 __impl_slice_eq1! { [] Vec<A>, &[B], }
2280 __impl_slice_eq1! { [] Vec<A>, &mut [B], }
2281 __impl_slice_eq1! { [] Cow<'_, [A]>, &[B], A: Clone }
2282 __impl_slice_eq1! { [] Cow<'_, [A]>, &mut [B], A: Clone }
2283 __impl_slice_eq1! { [] Cow<'_, [A]>, Vec<B>, A: Clone }
2284 __impl_slice_eq1! { [const N: usize] Vec<A>, [B; N], [B; N]: LengthAtMost32 }
2285 __impl_slice_eq1! { [const N: usize] Vec<A>, &[B; N], [B; N]: LengthAtMost32 }
2287 // NOTE: some less important impls are omitted to reduce code bloat
2288 // FIXME(Centril): Reconsider this?
2289 //__impl_slice_eq1! { [const N: usize] Vec<A>, &mut [B; N], [B; N]: LengthAtMost32 }
2290 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, [B; N], [B; N]: LengthAtMost32 }
2291 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &[B; N], [B; N]: LengthAtMost32 }
2292 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &mut [B; N], [B; N]: LengthAtMost32 }
2294 /// Implements comparison of vectors, lexicographically.
2295 #[stable(feature = "rust1", since = "1.0.0")]
2296 impl<T: PartialOrd> PartialOrd for Vec<T> {
2298 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2299 PartialOrd::partial_cmp(&**self, &**other)
2303 #[stable(feature = "rust1", since = "1.0.0")]
2304 impl<T: Eq> Eq for Vec<T> {}
2306 /// Implements ordering of vectors, lexicographically.
2307 #[stable(feature = "rust1", since = "1.0.0")]
2308 impl<T: Ord> Ord for Vec<T> {
2310 fn cmp(&self, other: &Vec<T>) -> Ordering {
2311 Ord::cmp(&**self, &**other)
2315 #[stable(feature = "rust1", since = "1.0.0")]
2316 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2317 fn drop(&mut self) {
2320 ptr::drop_in_place(&mut self[..]);
2322 // RawVec handles deallocation
2326 #[stable(feature = "rust1", since = "1.0.0")]
2327 impl<T> Default for Vec<T> {
2328 /// Creates an empty `Vec<T>`.
2329 fn default() -> Vec<T> {
2334 #[stable(feature = "rust1", since = "1.0.0")]
2335 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2336 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2337 fmt::Debug::fmt(&**self, f)
2341 #[stable(feature = "rust1", since = "1.0.0")]
2342 impl<T> AsRef<Vec<T>> for Vec<T> {
2343 fn as_ref(&self) -> &Vec<T> {
2348 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2349 impl<T> AsMut<Vec<T>> for Vec<T> {
2350 fn as_mut(&mut self) -> &mut Vec<T> {
2355 #[stable(feature = "rust1", since = "1.0.0")]
2356 impl<T> AsRef<[T]> for Vec<T> {
2357 fn as_ref(&self) -> &[T] {
2362 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2363 impl<T> AsMut<[T]> for Vec<T> {
2364 fn as_mut(&mut self) -> &mut [T] {
2369 #[stable(feature = "rust1", since = "1.0.0")]
2370 impl<T: Clone> From<&[T]> for Vec<T> {
2372 fn from(s: &[T]) -> Vec<T> {
2376 fn from(s: &[T]) -> Vec<T> {
2377 crate::slice::to_vec(s)
2381 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2382 impl<T: Clone> From<&mut [T]> for Vec<T> {
2384 fn from(s: &mut [T]) -> Vec<T> {
2388 fn from(s: &mut [T]) -> Vec<T> {
2389 crate::slice::to_vec(s)
2393 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2394 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2396 [T]: ToOwned<Owned = Vec<T>>,
2398 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2403 // note: test pulls in libstd, which causes errors here
2405 #[stable(feature = "vec_from_box", since = "1.18.0")]
2406 impl<T> From<Box<[T]>> for Vec<T> {
2407 fn from(s: Box<[T]>) -> Vec<T> {
2412 // note: test pulls in libstd, which causes errors here
2414 #[stable(feature = "box_from_vec", since = "1.20.0")]
2415 impl<T> From<Vec<T>> for Box<[T]> {
2416 fn from(v: Vec<T>) -> Box<[T]> {
2417 v.into_boxed_slice()
2421 #[stable(feature = "rust1", since = "1.0.0")]
2422 impl From<&str> for Vec<u8> {
2423 fn from(s: &str) -> Vec<u8> {
2424 From::from(s.as_bytes())
2428 ////////////////////////////////////////////////////////////////////////////////
2430 ////////////////////////////////////////////////////////////////////////////////
2432 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2433 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2434 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2439 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2440 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2441 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2446 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2447 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2448 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2449 Cow::Borrowed(v.as_slice())
2453 #[stable(feature = "rust1", since = "1.0.0")]
2454 impl<'a, T> FromIterator<T> for Cow<'a, [T]>
2458 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2459 Cow::Owned(FromIterator::from_iter(it))
2463 ////////////////////////////////////////////////////////////////////////////////
2465 ////////////////////////////////////////////////////////////////////////////////
2467 /// An iterator that moves out of a vector.
2469 /// This `struct` is created by the `into_iter` method on [`Vec`] (provided
2470 /// by the [`IntoIterator`] trait).
2472 /// [`Vec`]: struct.Vec.html
2473 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2474 #[stable(feature = "rust1", since = "1.0.0")]
2475 pub struct IntoIter<T> {
2477 phantom: PhantomData<T>,
2483 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2484 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2485 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2486 f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
2490 impl<T> IntoIter<T> {
2491 /// Returns the remaining items of this iterator as a slice.
2496 /// let vec = vec!['a', 'b', 'c'];
2497 /// let mut into_iter = vec.into_iter();
2498 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2499 /// let _ = into_iter.next().unwrap();
2500 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2502 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2503 pub fn as_slice(&self) -> &[T] {
2504 unsafe { slice::from_raw_parts(self.ptr, self.len()) }
2507 /// Returns the remaining items of this iterator as a mutable slice.
2512 /// let vec = vec!['a', 'b', 'c'];
2513 /// let mut into_iter = vec.into_iter();
2514 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2515 /// into_iter.as_mut_slice()[2] = 'z';
2516 /// assert_eq!(into_iter.next().unwrap(), 'a');
2517 /// assert_eq!(into_iter.next().unwrap(), 'b');
2518 /// assert_eq!(into_iter.next().unwrap(), 'z');
2520 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2521 pub fn as_mut_slice(&mut self) -> &mut [T] {
2522 unsafe { slice::from_raw_parts_mut(self.ptr as *mut T, self.len()) }
2526 #[stable(feature = "rust1", since = "1.0.0")]
2527 unsafe impl<T: Send> Send for IntoIter<T> {}
2528 #[stable(feature = "rust1", since = "1.0.0")]
2529 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2531 #[stable(feature = "rust1", since = "1.0.0")]
2532 impl<T> Iterator for IntoIter<T> {
2536 fn next(&mut self) -> Option<T> {
2538 if self.ptr as *const _ == self.end {
2541 if mem::size_of::<T>() == 0 {
2542 // purposefully don't use 'ptr.offset' because for
2543 // vectors with 0-size elements this would return the
2545 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2547 // Make up a value of this ZST.
2551 self.ptr = self.ptr.offset(1);
2553 Some(ptr::read(old))
2560 fn size_hint(&self) -> (usize, Option<usize>) {
2561 let exact = if mem::size_of::<T>() == 0 {
2562 (self.end as usize).wrapping_sub(self.ptr as usize)
2564 unsafe { self.end.offset_from(self.ptr) as usize }
2566 (exact, Some(exact))
2570 fn count(self) -> usize {
2575 #[stable(feature = "rust1", since = "1.0.0")]
2576 impl<T> DoubleEndedIterator for IntoIter<T> {
2578 fn next_back(&mut self) -> Option<T> {
2580 if self.end == self.ptr {
2583 if mem::size_of::<T>() == 0 {
2584 // See above for why 'ptr.offset' isn't used
2585 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2587 // Make up a value of this ZST.
2590 self.end = self.end.offset(-1);
2592 Some(ptr::read(self.end))
2599 #[stable(feature = "rust1", since = "1.0.0")]
2600 impl<T> ExactSizeIterator for IntoIter<T> {
2601 fn is_empty(&self) -> bool {
2602 self.ptr == self.end
2606 #[stable(feature = "fused", since = "1.26.0")]
2607 impl<T> FusedIterator for IntoIter<T> {}
2609 #[unstable(feature = "trusted_len", issue = "37572")]
2610 unsafe impl<T> TrustedLen for IntoIter<T> {}
2612 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2613 impl<T: Clone> Clone for IntoIter<T> {
2614 fn clone(&self) -> IntoIter<T> {
2615 self.as_slice().to_owned().into_iter()
2619 #[stable(feature = "rust1", since = "1.0.0")]
2620 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2621 fn drop(&mut self) {
2622 // destroy the remaining elements
2623 for _x in self.by_ref() {}
2625 // RawVec handles deallocation
2626 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2630 /// A draining iterator for `Vec<T>`.
2632 /// This `struct` is created by the [`drain`] method on [`Vec`].
2634 /// [`drain`]: struct.Vec.html#method.drain
2635 /// [`Vec`]: struct.Vec.html
2636 #[stable(feature = "drain", since = "1.6.0")]
2637 pub struct Drain<'a, T: 'a> {
2638 /// Index of tail to preserve
2642 /// Current remaining range to remove
2643 iter: slice::Iter<'a, T>,
2644 vec: NonNull<Vec<T>>,
2647 #[stable(feature = "collection_debug", since = "1.17.0")]
2648 impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
2649 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2650 f.debug_tuple("Drain").field(&self.iter.as_slice()).finish()
2654 impl<'a, T> Drain<'a, T> {
2655 /// Returns the remaining items of this iterator as a slice.
2660 /// # #![feature(vec_drain_as_slice)]
2661 /// let mut vec = vec!['a', 'b', 'c'];
2662 /// let mut drain = vec.drain(..);
2663 /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']);
2664 /// let _ = drain.next().unwrap();
2665 /// assert_eq!(drain.as_slice(), &['b', 'c']);
2667 #[unstable(feature = "vec_drain_as_slice", reason = "recently added", issue = "58957")]
2668 pub fn as_slice(&self) -> &[T] {
2669 self.iter.as_slice()
2673 #[stable(feature = "drain", since = "1.6.0")]
2674 unsafe impl<T: Sync> Sync for Drain<'_, T> {}
2675 #[stable(feature = "drain", since = "1.6.0")]
2676 unsafe impl<T: Send> Send for Drain<'_, T> {}
2678 #[stable(feature = "drain", since = "1.6.0")]
2679 impl<T> Iterator for Drain<'_, T> {
2683 fn next(&mut self) -> Option<T> {
2684 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2687 fn size_hint(&self) -> (usize, Option<usize>) {
2688 self.iter.size_hint()
2692 #[stable(feature = "drain", since = "1.6.0")]
2693 impl<T> DoubleEndedIterator for Drain<'_, T> {
2695 fn next_back(&mut self) -> Option<T> {
2696 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2700 #[stable(feature = "drain", since = "1.6.0")]
2701 impl<T> Drop for Drain<'_, T> {
2702 fn drop(&mut self) {
2703 // exhaust self first
2704 self.for_each(drop);
2706 if self.tail_len > 0 {
2708 let source_vec = self.vec.as_mut();
2709 // memmove back untouched tail, update to new length
2710 let start = source_vec.len();
2711 let tail = self.tail_start;
2713 let src = source_vec.as_ptr().add(tail);
2714 let dst = source_vec.as_mut_ptr().add(start);
2715 ptr::copy(src, dst, self.tail_len);
2717 source_vec.set_len(start + self.tail_len);
2723 #[stable(feature = "drain", since = "1.6.0")]
2724 impl<T> ExactSizeIterator for Drain<'_, T> {
2725 fn is_empty(&self) -> bool {
2726 self.iter.is_empty()
2730 #[unstable(feature = "trusted_len", issue = "37572")]
2731 unsafe impl<T> TrustedLen for Drain<'_, T> {}
2733 #[stable(feature = "fused", since = "1.26.0")]
2734 impl<T> FusedIterator for Drain<'_, T> {}
2736 /// A splicing iterator for `Vec`.
2738 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2739 /// documentation for more.
2741 /// [`splice()`]: struct.Vec.html#method.splice
2742 /// [`Vec`]: struct.Vec.html
2744 #[stable(feature = "vec_splice", since = "1.21.0")]
2745 pub struct Splice<'a, I: Iterator + 'a> {
2746 drain: Drain<'a, I::Item>,
2750 #[stable(feature = "vec_splice", since = "1.21.0")]
2751 impl<I: Iterator> Iterator for Splice<'_, I> {
2752 type Item = I::Item;
2754 fn next(&mut self) -> Option<Self::Item> {
2758 fn size_hint(&self) -> (usize, Option<usize>) {
2759 self.drain.size_hint()
2763 #[stable(feature = "vec_splice", since = "1.21.0")]
2764 impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
2765 fn next_back(&mut self) -> Option<Self::Item> {
2766 self.drain.next_back()
2770 #[stable(feature = "vec_splice", since = "1.21.0")]
2771 impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}
2773 #[stable(feature = "vec_splice", since = "1.21.0")]
2774 impl<I: Iterator> Drop for Splice<'_, I> {
2775 fn drop(&mut self) {
2776 self.drain.by_ref().for_each(drop);
2779 if self.drain.tail_len == 0 {
2780 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2784 // First fill the range left by drain().
2785 if !self.drain.fill(&mut self.replace_with) {
2789 // There may be more elements. Use the lower bound as an estimate.
2790 // FIXME: Is the upper bound a better guess? Or something else?
2791 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2792 if lower_bound > 0 {
2793 self.drain.move_tail(lower_bound);
2794 if !self.drain.fill(&mut self.replace_with) {
2799 // Collect any remaining elements.
2800 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2801 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2802 // Now we have an exact count.
2803 if collected.len() > 0 {
2804 self.drain.move_tail(collected.len());
2805 let filled = self.drain.fill(&mut collected);
2806 debug_assert!(filled);
2807 debug_assert_eq!(collected.len(), 0);
2810 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2814 /// Private helper methods for `Splice::drop`
2815 impl<T> Drain<'_, T> {
2816 /// The range from `self.vec.len` to `self.tail_start` contains elements
2817 /// that have been moved out.
2818 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2819 /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2820 unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool {
2821 let vec = self.vec.as_mut();
2822 let range_start = vec.len;
2823 let range_end = self.tail_start;
2825 slice::from_raw_parts_mut(vec.as_mut_ptr().add(range_start), range_end - range_start);
2827 for place in range_slice {
2828 if let Some(new_item) = replace_with.next() {
2829 ptr::write(place, new_item);
2838 /// Makes room for inserting more elements before the tail.
2839 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2840 let vec = self.vec.as_mut();
2841 let used_capacity = self.tail_start + self.tail_len;
2842 vec.buf.reserve(used_capacity, extra_capacity);
2844 let new_tail_start = self.tail_start + extra_capacity;
2845 let src = vec.as_ptr().add(self.tail_start);
2846 let dst = vec.as_mut_ptr().add(new_tail_start);
2847 ptr::copy(src, dst, self.tail_len);
2848 self.tail_start = new_tail_start;
2852 /// An iterator produced by calling `drain_filter` on Vec.
2853 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2855 pub struct DrainFilter<'a, T, F>
2857 F: FnMut(&mut T) -> bool,
2859 vec: &'a mut Vec<T>,
2860 /// The index of the item that will be inspected by the next call to `next`.
2862 /// The number of items that have been drained (removed) thus far.
2864 /// The original length of `vec` prior to draining.
2866 /// The filter test predicate.
2868 /// A flag that indicates a panic has occurred in the filter test prodicate.
2869 /// This is used as a hint in the drop implmentation to prevent consumption
2870 /// of the remainder of the `DrainFilter`. Any unprocessed items will be
2871 /// backshifted in the `vec`, but no further items will be dropped or
2872 /// tested by the filter predicate.
2876 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2877 impl<T, F> Iterator for DrainFilter<'_, T, F>
2879 F: FnMut(&mut T) -> bool,
2883 fn next(&mut self) -> Option<T> {
2885 while self.idx < self.old_len {
2887 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2888 self.panic_flag = true;
2889 let drained = (self.pred)(&mut v[i]);
2890 self.panic_flag = false;
2891 // Update the index *after* the predicate is called. If the index
2892 // is updated prior and the predicate panics, the element at this
2893 // index would be leaked.
2897 return Some(ptr::read(&v[i]));
2898 } else if self.del > 0 {
2900 let src: *const T = &v[i];
2901 let dst: *mut T = &mut v[i - del];
2902 ptr::copy_nonoverlapping(src, dst, 1);
2909 fn size_hint(&self) -> (usize, Option<usize>) {
2910 (0, Some(self.old_len - self.idx))
2914 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2915 impl<T, F> Drop for DrainFilter<'_, T, F>
2917 F: FnMut(&mut T) -> bool,
2919 fn drop(&mut self) {
2920 struct BackshiftOnDrop<'a, 'b, T, F>
2922 F: FnMut(&mut T) -> bool,
2924 drain: &'b mut DrainFilter<'a, T, F>,
2927 impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F>
2929 F: FnMut(&mut T) -> bool,
2931 fn drop(&mut self) {
2933 if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
2934 // This is a pretty messed up state, and there isn't really an
2935 // obviously right thing to do. We don't want to keep trying
2936 // to execute `pred`, so we just backshift all the unprocessed
2937 // elements and tell the vec that they still exist. The backshift
2938 // is required to prevent a double-drop of the last successfully
2939 // drained item prior to a panic in the predicate.
2940 let ptr = self.drain.vec.as_mut_ptr();
2941 let src = ptr.add(self.drain.idx);
2942 let dst = src.sub(self.drain.del);
2943 let tail_len = self.drain.old_len - self.drain.idx;
2944 src.copy_to(dst, tail_len);
2946 self.drain.vec.set_len(self.drain.old_len - self.drain.del);
2951 let backshift = BackshiftOnDrop { drain: self };
2953 // Attempt to consume any remaining elements if the filter predicate
2954 // has not yet panicked. We'll backshift any remaining elements
2955 // whether we've already panicked or if the consumption here panics.
2956 if !backshift.drain.panic_flag {
2957 backshift.drain.for_each(drop);