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::{self, Index, IndexMut, RangeBounds};
68 use core::ops::Bound::{Excluded, Included, Unbounded};
69 use core::ptr::{self, NonNull};
70 use core::slice::{self, SliceIndex};
72 use crate::borrow::{ToOwned, Cow};
73 use crate::collections::TryReserveError;
74 use crate::boxed::Box;
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`][`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> {
327 /// Constructs a new, empty `Vec<T>` with the specified capacity.
329 /// The vector will be able to hold exactly `capacity` elements without
330 /// reallocating. If `capacity` is 0, the vector will not allocate.
332 /// It is important to note that although the returned vector has the
333 /// *capacity* specified, the vector will have a zero *length*. For an
334 /// explanation of the difference between length and capacity, see
335 /// *[Capacity and reallocation]*.
337 /// [Capacity and reallocation]: #capacity-and-reallocation
342 /// let mut vec = Vec::with_capacity(10);
344 /// // The vector contains no items, even though it has capacity for more
345 /// assert_eq!(vec.len(), 0);
347 /// // These are all done without reallocating...
352 /// // ...but this may make the vector reallocate
356 #[stable(feature = "rust1", since = "1.0.0")]
357 pub fn with_capacity(capacity: usize) -> Vec<T> {
359 buf: RawVec::with_capacity(capacity),
364 /// Decomposes a `Vec<T>` into its raw components.
366 /// Returns the raw pointer to the underlying data, the length of
367 /// the vector (in elements), and the allocated capacity of the
368 /// data (in elements). These are the same arguments in the same
369 /// order as the arguments to [`from_raw_parts`].
371 /// After calling this function, the caller is responsible for the
372 /// memory previously managed by the `Vec`. The only way to do
373 /// this is to convert the raw pointer, length, and capacity back
374 /// into a `Vec` with the [`from_raw_parts`] function, allowing
375 /// the destructor to perform the cleanup.
377 /// [`from_raw_parts`]: #method.from_raw_parts
382 /// #![feature(vec_into_raw_parts)]
383 /// let v: Vec<i32> = vec![-1, 0, 1];
385 /// let (ptr, len, cap) = v.into_raw_parts();
387 /// let rebuilt = unsafe {
388 /// // We can now make changes to the components, such as
389 /// // transmuting the raw pointer to a compatible type.
390 /// let ptr = ptr as *mut u32;
392 /// Vec::from_raw_parts(ptr, len, cap)
394 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
396 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
397 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
398 let mut me = mem::ManuallyDrop::new(self);
399 (me.as_mut_ptr(), me.len(), me.capacity())
402 /// Creates a `Vec<T>` directly from the raw components of another vector.
406 /// This is highly unsafe, due to the number of invariants that aren't
409 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
410 /// (at least, it's highly likely to be incorrect if it wasn't).
411 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
412 /// * `length` needs to be less than or equal to `capacity`.
413 /// * `capacity` needs to be the capacity that the pointer was allocated with.
415 /// Violating these may cause problems like corrupting the allocator's
416 /// internal data structures. For example it is **not** safe
417 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
418 /// It's also not safe to build one from a `Vec<u16>` and its length, because
419 /// the allocator cares about the alignment, and these two types have different
420 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
421 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
423 /// The ownership of `ptr` is effectively transferred to the
424 /// `Vec<T>` which may then deallocate, reallocate or change the
425 /// contents of memory pointed to by the pointer at will. Ensure
426 /// that nothing else uses the pointer after calling this
429 /// [`String`]: ../../std/string/struct.String.html
437 /// let v = vec![1, 2, 3];
439 // FIXME Update this when vec_into_raw_parts is stabilized
440 /// // Prevent running `v`'s destructor so we are in complete control
441 /// // of the allocation.
442 /// let mut v = mem::ManuallyDrop::new(v);
444 /// // Pull out the various important pieces of information about `v`
445 /// let p = v.as_mut_ptr();
446 /// let len = v.len();
447 /// let cap = v.capacity();
450 /// // Overwrite memory with 4, 5, 6
451 /// for i in 0..len as isize {
452 /// ptr::write(p.offset(i), 4 + i);
455 /// // Put everything back together into a Vec
456 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
457 /// assert_eq!(rebuilt, [4, 5, 6]);
460 #[stable(feature = "rust1", since = "1.0.0")]
461 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
463 buf: RawVec::from_raw_parts(ptr, capacity),
468 /// Returns the number of elements the vector can hold without
474 /// let vec: Vec<i32> = Vec::with_capacity(10);
475 /// assert_eq!(vec.capacity(), 10);
478 #[stable(feature = "rust1", since = "1.0.0")]
479 pub fn capacity(&self) -> usize {
483 /// Reserves capacity for at least `additional` more elements to be inserted
484 /// in the given `Vec<T>`. The collection may reserve more space to avoid
485 /// frequent reallocations. After calling `reserve`, capacity will be
486 /// greater than or equal to `self.len() + additional`. Does nothing if
487 /// capacity is already sufficient.
491 /// Panics if the new capacity overflows `usize`.
496 /// let mut vec = vec![1];
498 /// assert!(vec.capacity() >= 11);
500 #[stable(feature = "rust1", since = "1.0.0")]
501 pub fn reserve(&mut self, additional: usize) {
502 self.buf.reserve(self.len, additional);
505 /// Reserves the minimum capacity for exactly `additional` more elements to
506 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
507 /// capacity will be greater than or equal to `self.len() + additional`.
508 /// Does nothing if the capacity is already sufficient.
510 /// Note that the allocator may give the collection more space than it
511 /// requests. Therefore, capacity can not be relied upon to be precisely
512 /// minimal. Prefer `reserve` if future insertions are expected.
516 /// Panics if the new capacity overflows `usize`.
521 /// let mut vec = vec![1];
522 /// vec.reserve_exact(10);
523 /// assert!(vec.capacity() >= 11);
525 #[stable(feature = "rust1", since = "1.0.0")]
526 pub fn reserve_exact(&mut self, additional: usize) {
527 self.buf.reserve_exact(self.len, additional);
530 /// Tries to reserve capacity for at least `additional` more elements to be inserted
531 /// in the given `Vec<T>`. The collection may reserve more space to avoid
532 /// frequent reallocations. After calling `reserve`, capacity will be
533 /// greater than or equal to `self.len() + additional`. Does nothing if
534 /// capacity is already sufficient.
538 /// If the capacity overflows, or the allocator reports a failure, then an error
544 /// #![feature(try_reserve)]
545 /// use std::collections::TryReserveError;
547 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
548 /// let mut output = Vec::new();
550 /// // Pre-reserve the memory, exiting if we can't
551 /// output.try_reserve(data.len())?;
553 /// // Now we know this can't OOM in the middle of our complex work
554 /// output.extend(data.iter().map(|&val| {
555 /// val * 2 + 5 // very complicated
560 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
562 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
563 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
564 self.buf.try_reserve(self.len, additional)
567 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
568 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
569 /// capacity will be greater than or equal to `self.len() + additional`.
570 /// Does nothing if the capacity is already sufficient.
572 /// Note that the allocator may give the collection more space than it
573 /// requests. Therefore, capacity can not be relied upon to be precisely
574 /// minimal. Prefer `reserve` if future insertions are expected.
578 /// If the capacity overflows, or the allocator reports a failure, then an error
584 /// #![feature(try_reserve)]
585 /// use std::collections::TryReserveError;
587 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
588 /// let mut output = Vec::new();
590 /// // Pre-reserve the memory, exiting if we can't
591 /// output.try_reserve(data.len())?;
593 /// // Now we know this can't OOM in the middle of our complex work
594 /// output.extend(data.iter().map(|&val| {
595 /// val * 2 + 5 // very complicated
600 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
602 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
603 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
604 self.buf.try_reserve_exact(self.len, additional)
607 /// Shrinks the capacity of the vector as much as possible.
609 /// It will drop down as close as possible to the length but the allocator
610 /// may still inform the vector that there is space for a few more elements.
615 /// let mut vec = Vec::with_capacity(10);
616 /// vec.extend([1, 2, 3].iter().cloned());
617 /// assert_eq!(vec.capacity(), 10);
618 /// vec.shrink_to_fit();
619 /// assert!(vec.capacity() >= 3);
621 #[stable(feature = "rust1", since = "1.0.0")]
622 pub fn shrink_to_fit(&mut self) {
623 if self.capacity() != self.len {
624 self.buf.shrink_to_fit(self.len);
628 /// Shrinks the capacity of the vector with a lower bound.
630 /// The capacity will remain at least as large as both the length
631 /// and the supplied value.
635 /// Panics if the current capacity is smaller than the supplied
636 /// minimum capacity.
641 /// #![feature(shrink_to)]
642 /// let mut vec = Vec::with_capacity(10);
643 /// vec.extend([1, 2, 3].iter().cloned());
644 /// assert_eq!(vec.capacity(), 10);
645 /// vec.shrink_to(4);
646 /// assert!(vec.capacity() >= 4);
647 /// vec.shrink_to(0);
648 /// assert!(vec.capacity() >= 3);
650 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
651 pub fn shrink_to(&mut self, min_capacity: usize) {
652 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
655 /// Converts the vector into [`Box<[T]>`][owned slice].
657 /// Note that this will drop any excess capacity.
659 /// [owned slice]: ../../std/boxed/struct.Box.html
664 /// let v = vec![1, 2, 3];
666 /// let slice = v.into_boxed_slice();
669 /// Any excess capacity is removed:
672 /// let mut vec = Vec::with_capacity(10);
673 /// vec.extend([1, 2, 3].iter().cloned());
675 /// assert_eq!(vec.capacity(), 10);
676 /// let slice = vec.into_boxed_slice();
677 /// assert_eq!(slice.into_vec().capacity(), 3);
679 #[stable(feature = "rust1", since = "1.0.0")]
680 pub fn into_boxed_slice(mut self) -> Box<[T]> {
682 self.shrink_to_fit();
683 let buf = ptr::read(&self.buf);
689 /// Shortens the vector, keeping the first `len` elements and dropping
692 /// If `len` is greater than the vector's current length, this has no
695 /// The [`drain`] method can emulate `truncate`, but causes the excess
696 /// elements to be returned instead of dropped.
698 /// Note that this method has no effect on the allocated capacity
703 /// Truncating a five element vector to two elements:
706 /// let mut vec = vec![1, 2, 3, 4, 5];
708 /// assert_eq!(vec, [1, 2]);
711 /// No truncation occurs when `len` is greater than the vector's current
715 /// let mut vec = vec![1, 2, 3];
717 /// assert_eq!(vec, [1, 2, 3]);
720 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
724 /// let mut vec = vec![1, 2, 3];
726 /// assert_eq!(vec, []);
729 /// [`clear`]: #method.clear
730 /// [`drain`]: #method.drain
731 #[stable(feature = "rust1", since = "1.0.0")]
732 pub fn truncate(&mut self, len: usize) {
733 // This is safe because:
735 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
736 // case avoids creating an invalid slice, and
737 // * the `len` of the vector is shrunk before calling `drop_in_place`,
738 // such that no value will be dropped twice in case `drop_in_place`
739 // were to panic once (if it panics twice, the program aborts).
744 let s = self.get_unchecked_mut(len..) as *mut _;
746 ptr::drop_in_place(s);
750 /// Extracts a slice containing the entire vector.
752 /// Equivalent to `&s[..]`.
757 /// use std::io::{self, Write};
758 /// let buffer = vec![1, 2, 3, 5, 8];
759 /// io::sink().write(buffer.as_slice()).unwrap();
762 #[stable(feature = "vec_as_slice", since = "1.7.0")]
763 pub fn as_slice(&self) -> &[T] {
767 /// Extracts a mutable slice of the entire vector.
769 /// Equivalent to `&mut s[..]`.
774 /// use std::io::{self, Read};
775 /// let mut buffer = vec![0; 3];
776 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
779 #[stable(feature = "vec_as_slice", since = "1.7.0")]
780 pub fn as_mut_slice(&mut self) -> &mut [T] {
784 /// Returns a raw pointer to the vector's buffer.
786 /// The caller must ensure that the vector outlives the pointer this
787 /// function returns, or else it will end up pointing to garbage.
788 /// Modifying the vector may cause its buffer to be reallocated,
789 /// which would also make any pointers to it invalid.
791 /// The caller must also ensure that the memory the pointer (non-transitively) points to
792 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
793 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
798 /// let x = vec![1, 2, 4];
799 /// let x_ptr = x.as_ptr();
802 /// for i in 0..x.len() {
803 /// assert_eq!(*x_ptr.add(i), 1 << i);
808 /// [`as_mut_ptr`]: #method.as_mut_ptr
809 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
811 pub fn as_ptr(&self) -> *const T {
812 // We shadow the slice method of the same name to avoid going through
813 // `deref`, which creates an intermediate reference.
814 let ptr = self.buf.ptr();
815 unsafe { 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();
849 unsafe { assume(!ptr.is_null()); }
853 /// Forces the length of the vector to `new_len`.
855 /// This is a low-level operation that maintains none of the normal
856 /// invariants of the type. Normally changing the length of a vector
857 /// is done using one of the safe operations instead, such as
858 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
860 /// [`truncate`]: #method.truncate
861 /// [`resize`]: #method.resize
862 /// [`extend`]: ../../std/iter/trait.Extend.html#tymethod.extend
863 /// [`clear`]: #method.clear
867 /// - `new_len` must be less than or equal to [`capacity()`].
868 /// - The elements at `old_len..new_len` must be initialized.
870 /// [`capacity()`]: #method.capacity
874 /// This method can be useful for situations in which the vector
875 /// is serving as a buffer for other code, particularly over FFI:
878 /// # #![allow(dead_code)]
879 /// # // This is just a minimal skeleton for the doc example;
880 /// # // don't use this as a starting point for a real library.
881 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
882 /// # const Z_OK: i32 = 0;
884 /// # fn deflateGetDictionary(
885 /// # strm: *mut std::ffi::c_void,
886 /// # dictionary: *mut u8,
887 /// # dictLength: *mut usize,
890 /// # impl StreamWrapper {
891 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
892 /// // Per the FFI method's docs, "32768 bytes is always enough".
893 /// let mut dict = Vec::with_capacity(32_768);
894 /// let mut dict_length = 0;
895 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
896 /// // 1. `dict_length` elements were initialized.
897 /// // 2. `dict_length` <= the capacity (32_768)
898 /// // which makes `set_len` safe to call.
900 /// // Make the FFI call...
901 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
903 /// // ...and update the length to what was initialized.
904 /// dict.set_len(dict_length);
914 /// While the following example is sound, there is a memory leak since
915 /// the inner vectors were not freed prior to the `set_len` call:
918 /// let mut vec = vec![vec![1, 0, 0],
922 /// // 1. `old_len..0` is empty so no elements need to be initialized.
923 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
929 /// Normally, here, one would use [`clear`] instead to correctly drop
930 /// the contents and thus not leak memory.
932 #[stable(feature = "rust1", since = "1.0.0")]
933 pub unsafe fn set_len(&mut self, new_len: usize) {
934 debug_assert!(new_len <= self.capacity());
939 /// Removes an element from the vector and returns it.
941 /// The removed element is replaced by the last element of the vector.
943 /// This does not preserve ordering, but is O(1).
947 /// Panics if `index` is out of bounds.
952 /// let mut v = vec!["foo", "bar", "baz", "qux"];
954 /// assert_eq!(v.swap_remove(1), "bar");
955 /// assert_eq!(v, ["foo", "qux", "baz"]);
957 /// assert_eq!(v.swap_remove(0), "foo");
958 /// assert_eq!(v, ["baz", "qux"]);
961 #[stable(feature = "rust1", since = "1.0.0")]
962 pub fn swap_remove(&mut self, index: usize) -> T {
964 // We replace self[index] with the last element. Note that if the
965 // bounds check on hole succeeds there must be a last element (which
966 // can be self[index] itself).
967 let hole: *mut T = &mut self[index];
968 let last = ptr::read(self.get_unchecked(self.len - 1));
970 ptr::replace(hole, last)
974 /// Inserts an element at position `index` within the vector, shifting all
975 /// elements after it to the right.
979 /// Panics if `index > len`.
984 /// let mut vec = vec![1, 2, 3];
985 /// vec.insert(1, 4);
986 /// assert_eq!(vec, [1, 4, 2, 3]);
987 /// vec.insert(4, 5);
988 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
990 #[stable(feature = "rust1", since = "1.0.0")]
991 pub fn insert(&mut self, index: usize, element: T) {
992 let len = self.len();
993 assert!(index <= len);
995 // space for the new element
996 if len == self.buf.capacity() {
1002 // The spot to put the new value
1004 let p = self.as_mut_ptr().add(index);
1005 // Shift everything over to make space. (Duplicating the
1006 // `index`th element into two consecutive places.)
1007 ptr::copy(p, p.offset(1), len - index);
1008 // Write it in, overwriting the first copy of the `index`th
1010 ptr::write(p, element);
1012 self.set_len(len + 1);
1016 /// Removes and returns the element at position `index` within the vector,
1017 /// shifting all elements after it to the left.
1021 /// Panics if `index` is out of bounds.
1026 /// let mut v = vec![1, 2, 3];
1027 /// assert_eq!(v.remove(1), 2);
1028 /// assert_eq!(v, [1, 3]);
1030 #[stable(feature = "rust1", since = "1.0.0")]
1031 pub fn remove(&mut self, index: usize) -> T {
1032 let len = self.len();
1033 assert!(index < len);
1038 // the place we are taking from.
1039 let ptr = self.as_mut_ptr().add(index);
1040 // copy it out, unsafely having a copy of the value on
1041 // the stack and in the vector at the same time.
1042 ret = ptr::read(ptr);
1044 // Shift everything down to fill in that spot.
1045 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1047 self.set_len(len - 1);
1052 /// Retains only the elements specified by the predicate.
1054 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1055 /// This method operates in place, visiting each element exactly once in the
1056 /// original order, and preserves the order of the retained elements.
1061 /// let mut vec = vec![1, 2, 3, 4];
1062 /// vec.retain(|&x| x%2 == 0);
1063 /// assert_eq!(vec, [2, 4]);
1066 /// The exact order may be useful for tracking external state, like an index.
1069 /// let mut vec = vec![1, 2, 3, 4, 5];
1070 /// let keep = [false, true, true, false, true];
1072 /// vec.retain(|_| (keep[i], i += 1).0);
1073 /// assert_eq!(vec, [2, 3, 5]);
1075 #[stable(feature = "rust1", since = "1.0.0")]
1076 pub fn retain<F>(&mut self, mut f: F)
1077 where F: FnMut(&T) -> bool
1079 let len = self.len();
1082 let v = &mut **self;
1093 self.truncate(len - del);
1097 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1100 /// If the vector is sorted, this removes all duplicates.
1105 /// let mut vec = vec![10, 20, 21, 30, 20];
1107 /// vec.dedup_by_key(|i| *i / 10);
1109 /// assert_eq!(vec, [10, 20, 30, 20]);
1111 #[stable(feature = "dedup_by", since = "1.16.0")]
1113 pub fn dedup_by_key<F, K>(&mut self, mut key: F) where F: FnMut(&mut T) -> K, K: PartialEq {
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) where F: FnMut(&mut T, &mut T) -> bool {
1138 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
1144 /// Appends an element to the back of a collection.
1148 /// Panics if the number of elements in the vector overflows a `usize`.
1153 /// let mut vec = vec![1, 2];
1155 /// assert_eq!(vec, [1, 2, 3]);
1158 #[stable(feature = "rust1", since = "1.0.0")]
1159 pub fn push(&mut self, value: T) {
1160 // This will panic or abort if we would allocate > isize::MAX bytes
1161 // or if the length increment would overflow for zero-sized types.
1162 if self.len == self.buf.capacity() {
1166 let end = self.as_mut_ptr().add(self.len);
1167 ptr::write(end, value);
1172 /// Removes the last element from a vector and returns it, or [`None`] if it
1175 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1180 /// let mut vec = vec![1, 2, 3];
1181 /// assert_eq!(vec.pop(), Some(3));
1182 /// assert_eq!(vec, [1, 2]);
1185 #[stable(feature = "rust1", since = "1.0.0")]
1186 pub fn pop(&mut self) -> Option<T> {
1192 Some(ptr::read(self.get_unchecked(self.len())))
1197 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1201 /// Panics if the number of elements in the vector overflows a `usize`.
1206 /// let mut vec = vec![1, 2, 3];
1207 /// let mut vec2 = vec![4, 5, 6];
1208 /// vec.append(&mut vec2);
1209 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1210 /// assert_eq!(vec2, []);
1213 #[stable(feature = "append", since = "1.4.0")]
1214 pub fn append(&mut self, other: &mut Self) {
1216 self.append_elements(other.as_slice() as _);
1221 /// Appends elements to `Self` from other buffer.
1223 unsafe fn append_elements(&mut self, other: *const [T]) {
1224 let count = (*other).len();
1225 self.reserve(count);
1226 let len = self.len();
1227 ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count);
1231 /// Creates a draining iterator that removes the specified range in the vector
1232 /// and yields the removed items.
1234 /// Note 1: The element range is removed even if the iterator is only
1235 /// partially consumed or not consumed at all.
1237 /// Note 2: It is unspecified how many elements are removed from the vector
1238 /// if the `Drain` value is leaked.
1242 /// Panics if the starting point is greater than the end point or if
1243 /// the end point is greater than the length of the vector.
1248 /// let mut v = vec![1, 2, 3];
1249 /// let u: Vec<_> = v.drain(1..).collect();
1250 /// assert_eq!(v, &[1]);
1251 /// assert_eq!(u, &[2, 3]);
1253 /// // A full range clears the vector
1255 /// assert_eq!(v, &[]);
1257 #[stable(feature = "drain", since = "1.6.0")]
1258 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1259 where R: RangeBounds<usize>
1263 // When the Drain is first created, it shortens the length of
1264 // the source vector to make sure no uninitialized or moved-from elements
1265 // are accessible at all if the Drain's destructor never gets to run.
1267 // Drain will ptr::read out the values to remove.
1268 // When finished, remaining tail of the vec is copied back to cover
1269 // the hole, and the vector length is restored to the new length.
1271 let len = self.len();
1272 let start = match range.start_bound() {
1274 Excluded(&n) => n + 1,
1277 let end = match range.end_bound() {
1278 Included(&n) => n + 1,
1282 assert!(start <= end);
1283 assert!(end <= len);
1286 // set self.vec length's to start, to be safe in case Drain is leaked
1287 self.set_len(start);
1288 // Use the borrow in the IterMut to indicate borrowing behavior of the
1289 // whole Drain iterator (like &mut T).
1290 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start),
1294 tail_len: len - end,
1295 iter: range_slice.iter(),
1296 vec: NonNull::from(self),
1301 /// Clears the vector, removing all values.
1303 /// Note that this method has no effect on the allocated capacity
1309 /// let mut v = vec![1, 2, 3];
1313 /// assert!(v.is_empty());
1316 #[stable(feature = "rust1", since = "1.0.0")]
1317 pub fn clear(&mut self) {
1321 /// Returns the number of elements in the vector, also referred to
1322 /// as its 'length'.
1327 /// let a = vec![1, 2, 3];
1328 /// assert_eq!(a.len(), 3);
1331 #[stable(feature = "rust1", since = "1.0.0")]
1332 pub fn len(&self) -> usize {
1336 /// Returns `true` if the vector contains no elements.
1341 /// let mut v = Vec::new();
1342 /// assert!(v.is_empty());
1345 /// assert!(!v.is_empty());
1347 #[stable(feature = "rust1", since = "1.0.0")]
1348 pub fn is_empty(&self) -> bool {
1352 /// Splits the collection into two at the given index.
1354 /// Returns a newly allocated vector containing the elements in the range
1355 /// `[at, len)`. After the call, the original vector will be left containing
1356 /// the elements `[0, at)` with its previous capacity unchanged.
1360 /// Panics if `at > len`.
1365 /// let mut vec = vec![1,2,3];
1366 /// let vec2 = vec.split_off(1);
1367 /// assert_eq!(vec, [1]);
1368 /// assert_eq!(vec2, [2, 3]);
1371 #[stable(feature = "split_off", since = "1.4.0")]
1372 pub fn split_off(&mut self, at: usize) -> Self {
1373 assert!(at <= self.len(), "`at` out of bounds");
1375 let other_len = self.len - at;
1376 let mut other = Vec::with_capacity(other_len);
1378 // Unsafely `set_len` and copy items to `other`.
1381 other.set_len(other_len);
1383 ptr::copy_nonoverlapping(self.as_ptr().add(at),
1390 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1392 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1393 /// difference, with each additional slot filled with the result of
1394 /// calling the closure `f`. The return values from `f` will end up
1395 /// in the `Vec` in the order they have been generated.
1397 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1399 /// This method uses a closure to create new values on every push. If
1400 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1401 /// to use the [`Default`] trait to generate values, you can pass
1402 /// [`Default::default()`] as the second argument.
1407 /// let mut vec = vec![1, 2, 3];
1408 /// vec.resize_with(5, Default::default);
1409 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1411 /// let mut vec = vec![];
1413 /// vec.resize_with(4, || { p *= 2; p });
1414 /// assert_eq!(vec, [2, 4, 8, 16]);
1417 /// [`resize`]: #method.resize
1418 /// [`Clone`]: ../../std/clone/trait.Clone.html
1419 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1420 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1421 where F: FnMut() -> T
1423 let len = self.len();
1425 self.extend_with(new_len - len, ExtendFunc(f));
1427 self.truncate(new_len);
1431 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1432 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1433 /// `'a`. If the type has only static references, or none at all, then this
1434 /// may be chosen to be `'static`.
1436 /// This function is similar to the `leak` function on `Box`.
1438 /// This function is mainly useful for data that lives for the remainder of
1439 /// the program's life. Dropping the returned reference will cause a memory
1447 /// #![feature(vec_leak)]
1449 /// let x = vec![1, 2, 3];
1450 /// let static_ref: &'static mut [usize] = Vec::leak(x);
1451 /// static_ref[0] += 1;
1452 /// assert_eq!(static_ref, &[2, 2, 3]);
1454 #[unstable(feature = "vec_leak", issue = "62195")]
1456 pub fn leak<'a>(vec: Vec<T>) -> &'a mut [T]
1458 T: 'a // Technically not needed, but kept to be explicit.
1460 Box::leak(vec.into_boxed_slice())
1464 impl<T: Clone> Vec<T> {
1465 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1467 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1468 /// difference, with each additional slot filled with `value`.
1469 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1471 /// This method requires [`Clone`] to be able clone the passed value. If
1472 /// you need more flexibility (or want to rely on [`Default`] instead of
1473 /// [`Clone`]), use [`resize_with`].
1478 /// let mut vec = vec!["hello"];
1479 /// vec.resize(3, "world");
1480 /// assert_eq!(vec, ["hello", "world", "world"]);
1482 /// let mut vec = vec![1, 2, 3, 4];
1483 /// vec.resize(2, 0);
1484 /// assert_eq!(vec, [1, 2]);
1487 /// [`Clone`]: ../../std/clone/trait.Clone.html
1488 /// [`Default`]: ../../std/default/trait.Default.html
1489 /// [`resize_with`]: #method.resize_with
1490 #[stable(feature = "vec_resize", since = "1.5.0")]
1491 pub fn resize(&mut self, new_len: usize, value: T) {
1492 let len = self.len();
1495 self.extend_with(new_len - len, ExtendElement(value))
1497 self.truncate(new_len);
1501 /// Clones and appends all elements in a slice to the `Vec`.
1503 /// Iterates over the slice `other`, clones each element, and then appends
1504 /// it to this `Vec`. The `other` vector is traversed in-order.
1506 /// Note that this function is same as [`extend`] except that it is
1507 /// specialized to work with slices instead. If and when Rust gets
1508 /// specialization this function will likely be deprecated (but still
1514 /// let mut vec = vec![1];
1515 /// vec.extend_from_slice(&[2, 3, 4]);
1516 /// assert_eq!(vec, [1, 2, 3, 4]);
1519 /// [`extend`]: #method.extend
1520 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1521 pub fn extend_from_slice(&mut self, other: &[T]) {
1522 self.spec_extend(other.iter())
1526 impl<T: Default> Vec<T> {
1527 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1529 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1530 /// difference, with each additional slot filled with [`Default::default()`].
1531 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1533 /// This method uses [`Default`] to create new values on every push. If
1534 /// you'd rather [`Clone`] a given value, use [`resize`].
1539 /// # #![allow(deprecated)]
1540 /// #![feature(vec_resize_default)]
1542 /// let mut vec = vec![1, 2, 3];
1543 /// vec.resize_default(5);
1544 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1546 /// let mut vec = vec![1, 2, 3, 4];
1547 /// vec.resize_default(2);
1548 /// assert_eq!(vec, [1, 2]);
1551 /// [`resize`]: #method.resize
1552 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1553 /// [`Default`]: ../../std/default/trait.Default.html
1554 /// [`Clone`]: ../../std/clone/trait.Clone.html
1555 #[unstable(feature = "vec_resize_default", issue = "41758")]
1556 #[rustc_deprecated(reason = "This is moving towards being removed in favor \
1557 of `.resize_with(Default::default)`. If you disagree, please comment \
1558 in the tracking issue.", since = "1.33.0")]
1559 pub fn resize_default(&mut self, new_len: usize) {
1560 let len = self.len();
1563 self.extend_with(new_len - len, ExtendDefault);
1565 self.truncate(new_len);
1570 // This code generalises `extend_with_{element,default}`.
1571 trait ExtendWith<T> {
1572 fn next(&mut self) -> T;
1576 struct ExtendElement<T>(T);
1577 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1578 fn next(&mut self) -> T { self.0.clone() }
1579 fn last(self) -> T { self.0 }
1582 struct ExtendDefault;
1583 impl<T: Default> ExtendWith<T> for ExtendDefault {
1584 fn next(&mut self) -> T { Default::default() }
1585 fn last(self) -> T { Default::default() }
1588 struct ExtendFunc<F>(F);
1589 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1590 fn next(&mut self) -> T { (self.0)() }
1591 fn last(mut self) -> T { (self.0)() }
1595 /// Extend the vector by `n` values, using the given generator.
1596 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1600 let mut ptr = self.as_mut_ptr().add(self.len());
1601 // Use SetLenOnDrop to work around bug where compiler
1602 // may not realize the store through `ptr` through self.set_len()
1604 let mut local_len = SetLenOnDrop::new(&mut self.len);
1606 // Write all elements except the last one
1608 ptr::write(ptr, value.next());
1609 ptr = ptr.offset(1);
1610 // Increment the length in every step in case next() panics
1611 local_len.increment_len(1);
1615 // We can write the last element directly without cloning needlessly
1616 ptr::write(ptr, value.last());
1617 local_len.increment_len(1);
1620 // len set by scope guard
1625 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1627 // The idea is: The length field in SetLenOnDrop is a local variable
1628 // that the optimizer will see does not alias with any stores through the Vec's data
1629 // pointer. This is a workaround for alias analysis issue #32155
1630 struct SetLenOnDrop<'a> {
1635 impl<'a> SetLenOnDrop<'a> {
1637 fn new(len: &'a mut usize) -> Self {
1638 SetLenOnDrop { local_len: *len, len: len }
1642 fn increment_len(&mut self, increment: usize) {
1643 self.local_len += increment;
1647 impl Drop for SetLenOnDrop<'_> {
1649 fn drop(&mut self) {
1650 *self.len = self.local_len;
1654 impl<T: PartialEq> Vec<T> {
1655 /// Removes consecutive repeated elements in the vector according to the
1656 /// [`PartialEq`] trait implementation.
1658 /// If the vector is sorted, this removes all duplicates.
1663 /// let mut vec = vec![1, 2, 2, 3, 2];
1667 /// assert_eq!(vec, [1, 2, 3, 2]);
1669 #[stable(feature = "rust1", since = "1.0.0")]
1671 pub fn dedup(&mut self) {
1672 self.dedup_by(|a, b| a == b)
1675 /// Removes the first instance of `item` from the vector if the item exists.
1680 /// # #![feature(vec_remove_item)]
1681 /// let mut vec = vec![1, 2, 3, 1];
1683 /// vec.remove_item(&1);
1685 /// assert_eq!(vec, vec![2, 3, 1]);
1687 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1688 pub fn remove_item(&mut self, item: &T) -> Option<T> {
1689 let pos = self.iter().position(|x| *x == *item)?;
1690 Some(self.remove(pos))
1694 ////////////////////////////////////////////////////////////////////////////////
1695 // Internal methods and functions
1696 ////////////////////////////////////////////////////////////////////////////////
1699 #[stable(feature = "rust1", since = "1.0.0")]
1700 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1701 <T as SpecFromElem>::from_elem(elem, n)
1704 // Specialization trait used for Vec::from_elem
1705 trait SpecFromElem: Sized {
1706 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1709 impl<T: Clone> SpecFromElem for T {
1710 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1711 let mut v = Vec::with_capacity(n);
1712 v.extend_with(n, ExtendElement(elem));
1717 impl SpecFromElem for u8 {
1719 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1722 buf: RawVec::with_capacity_zeroed(n),
1727 let mut v = Vec::with_capacity(n);
1728 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1735 impl<T: Clone + IsZero> SpecFromElem for T {
1737 fn from_elem(elem: T, n: usize) -> Vec<T> {
1740 buf: RawVec::with_capacity_zeroed(n),
1744 let mut v = Vec::with_capacity(n);
1745 v.extend_with(n, ExtendElement(elem));
1750 unsafe trait IsZero {
1751 /// Whether this value is zero
1752 fn is_zero(&self) -> bool;
1755 macro_rules! impl_is_zero {
1756 ($t: ty, $is_zero: expr) => {
1757 unsafe impl IsZero for $t {
1759 fn is_zero(&self) -> bool {
1766 impl_is_zero!(i8, |x| x == 0);
1767 impl_is_zero!(i16, |x| x == 0);
1768 impl_is_zero!(i32, |x| x == 0);
1769 impl_is_zero!(i64, |x| x == 0);
1770 impl_is_zero!(i128, |x| x == 0);
1771 impl_is_zero!(isize, |x| x == 0);
1773 impl_is_zero!(u16, |x| x == 0);
1774 impl_is_zero!(u32, |x| x == 0);
1775 impl_is_zero!(u64, |x| x == 0);
1776 impl_is_zero!(u128, |x| x == 0);
1777 impl_is_zero!(usize, |x| x == 0);
1779 impl_is_zero!(bool, |x| x == false);
1780 impl_is_zero!(char, |x| x == '\0');
1782 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1783 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1785 unsafe impl<T> IsZero for *const T {
1787 fn is_zero(&self) -> bool {
1792 unsafe impl<T> IsZero for *mut T {
1794 fn is_zero(&self) -> bool {
1799 // `Option<&T>`, `Option<&mut T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
1800 // For fat pointers, the bytes that would be the pointer metadata in the `Some` variant
1801 // are padding in the `None` variant, so ignoring them and zero-initializing instead is ok.
1803 unsafe impl<T: ?Sized> IsZero for Option<&T> {
1805 fn is_zero(&self) -> bool {
1810 unsafe impl<T: ?Sized> IsZero for Option<&mut T> {
1812 fn is_zero(&self) -> bool {
1817 unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
1819 fn is_zero(&self) -> bool {
1825 ////////////////////////////////////////////////////////////////////////////////
1826 // Common trait implementations for Vec
1827 ////////////////////////////////////////////////////////////////////////////////
1829 #[stable(feature = "rust1", since = "1.0.0")]
1830 impl<T: Clone> Clone for Vec<T> {
1832 fn clone(&self) -> Vec<T> {
1833 <[T]>::to_vec(&**self)
1836 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1837 // required for this method definition, is not available. Instead use the
1838 // `slice::to_vec` function which is only available with cfg(test)
1839 // NB see the slice::hack module in slice.rs for more information
1841 fn clone(&self) -> Vec<T> {
1842 crate::slice::to_vec(&**self)
1845 fn clone_from(&mut self, other: &Vec<T>) {
1846 other.as_slice().clone_into(self);
1850 #[stable(feature = "rust1", since = "1.0.0")]
1851 impl<T: Hash> Hash for Vec<T> {
1853 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1854 Hash::hash(&**self, state)
1858 #[stable(feature = "rust1", since = "1.0.0")]
1859 #[rustc_on_unimplemented(
1860 message="vector indices are of type `usize` or ranges of `usize`",
1861 label="vector indices are of type `usize` or ranges of `usize`",
1863 impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> {
1864 type Output = I::Output;
1867 fn index(&self, index: I) -> &Self::Output {
1868 Index::index(&**self, index)
1872 #[stable(feature = "rust1", since = "1.0.0")]
1873 #[rustc_on_unimplemented(
1874 message="vector indices are of type `usize` or ranges of `usize`",
1875 label="vector indices are of type `usize` or ranges of `usize`",
1877 impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
1879 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1880 IndexMut::index_mut(&mut **self, index)
1884 #[stable(feature = "rust1", since = "1.0.0")]
1885 impl<T> ops::Deref for Vec<T> {
1888 fn deref(&self) -> &[T] {
1890 slice::from_raw_parts(self.as_ptr(), self.len)
1895 #[stable(feature = "rust1", since = "1.0.0")]
1896 impl<T> ops::DerefMut for Vec<T> {
1897 fn deref_mut(&mut self) -> &mut [T] {
1899 slice::from_raw_parts_mut(self.as_mut_ptr(), self.len)
1904 #[stable(feature = "rust1", since = "1.0.0")]
1905 impl<T> FromIterator<T> for Vec<T> {
1907 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1908 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1912 #[stable(feature = "rust1", since = "1.0.0")]
1913 impl<T> IntoIterator for Vec<T> {
1915 type IntoIter = IntoIter<T>;
1917 /// Creates a consuming iterator, that is, one that moves each value out of
1918 /// the vector (from start to end). The vector cannot be used after calling
1924 /// let v = vec!["a".to_string(), "b".to_string()];
1925 /// for s in v.into_iter() {
1926 /// // s has type String, not &String
1927 /// println!("{}", s);
1931 fn into_iter(mut self) -> IntoIter<T> {
1933 let begin = self.as_mut_ptr();
1934 let end = if mem::size_of::<T>() == 0 {
1935 arith_offset(begin as *const i8, self.len() as isize) as *const T
1937 begin.add(self.len()) as *const T
1939 let cap = self.buf.capacity();
1942 buf: NonNull::new_unchecked(begin),
1943 phantom: PhantomData,
1952 #[stable(feature = "rust1", since = "1.0.0")]
1953 impl<'a, T> IntoIterator for &'a Vec<T> {
1955 type IntoIter = slice::Iter<'a, T>;
1957 fn into_iter(self) -> slice::Iter<'a, T> {
1962 #[stable(feature = "rust1", since = "1.0.0")]
1963 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1964 type Item = &'a mut T;
1965 type IntoIter = slice::IterMut<'a, T>;
1967 fn into_iter(self) -> slice::IterMut<'a, T> {
1972 #[stable(feature = "rust1", since = "1.0.0")]
1973 impl<T> Extend<T> for Vec<T> {
1975 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1976 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1980 // Specialization trait used for Vec::from_iter and Vec::extend
1981 trait SpecExtend<T, I> {
1982 fn from_iter(iter: I) -> Self;
1983 fn spec_extend(&mut self, iter: I);
1986 impl<T, I> SpecExtend<T, I> for Vec<T>
1987 where I: Iterator<Item=T>,
1989 default fn from_iter(mut iterator: I) -> Self {
1990 // Unroll the first iteration, as the vector is going to be
1991 // expanded on this iteration in every case when the iterable is not
1992 // empty, but the loop in extend_desugared() is not going to see the
1993 // vector being full in the few subsequent loop iterations.
1994 // So we get better branch prediction.
1995 let mut vector = match iterator.next() {
1996 None => return Vec::new(),
1998 let (lower, _) = iterator.size_hint();
1999 let mut vector = Vec::with_capacity(lower.saturating_add(1));
2001 ptr::write(vector.get_unchecked_mut(0), element);
2007 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
2011 default fn spec_extend(&mut self, iter: I) {
2012 self.extend_desugared(iter)
2016 impl<T, I> SpecExtend<T, I> for Vec<T>
2017 where I: TrustedLen<Item=T>,
2019 default fn from_iter(iterator: I) -> Self {
2020 let mut vector = Vec::new();
2021 vector.spec_extend(iterator);
2025 default fn spec_extend(&mut self, iterator: I) {
2026 // This is the case for a TrustedLen iterator.
2027 let (low, high) = iterator.size_hint();
2028 if let Some(high_value) = high {
2029 debug_assert_eq!(low, high_value,
2030 "TrustedLen iterator's size hint is not exact: {:?}",
2033 if let Some(additional) = high {
2034 self.reserve(additional);
2036 let mut ptr = self.as_mut_ptr().add(self.len());
2037 let mut local_len = SetLenOnDrop::new(&mut self.len);
2038 iterator.for_each(move |element| {
2039 ptr::write(ptr, element);
2040 ptr = ptr.offset(1);
2041 // NB can't overflow since we would have had to alloc the address space
2042 local_len.increment_len(1);
2046 self.extend_desugared(iterator)
2051 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
2052 fn from_iter(iterator: IntoIter<T>) -> Self {
2053 // A common case is passing a vector into a function which immediately
2054 // re-collects into a vector. We can short circuit this if the IntoIter
2055 // has not been advanced at all.
2056 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
2058 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
2061 mem::forget(iterator);
2065 let mut vector = Vec::new();
2066 vector.spec_extend(iterator);
2071 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
2073 self.append_elements(iterator.as_slice() as _);
2075 iterator.ptr = iterator.end;
2079 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
2080 where I: Iterator<Item=&'a T>,
2083 default fn from_iter(iterator: I) -> Self {
2084 SpecExtend::from_iter(iterator.cloned())
2087 default fn spec_extend(&mut self, iterator: I) {
2088 self.spec_extend(iterator.cloned())
2092 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
2095 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
2096 let slice = iterator.as_slice();
2097 self.reserve(slice.len());
2099 let len = self.len();
2100 self.set_len(len + slice.len());
2101 self.get_unchecked_mut(len..).copy_from_slice(slice);
2107 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2108 // This is the case for a general iterator.
2110 // This function should be the moral equivalent of:
2112 // for item in iterator {
2115 while let Some(element) = iterator.next() {
2116 let len = self.len();
2117 if len == self.capacity() {
2118 let (lower, _) = iterator.size_hint();
2119 self.reserve(lower.saturating_add(1));
2122 ptr::write(self.get_unchecked_mut(len), element);
2123 // NB can't overflow since we would have had to alloc the address space
2124 self.set_len(len + 1);
2129 /// Creates a splicing iterator that replaces the specified range in the vector
2130 /// with the given `replace_with` iterator and yields the removed items.
2131 /// `replace_with` does not need to be the same length as `range`.
2133 /// The element range is removed even if the iterator is not consumed until the end.
2135 /// It is unspecified how many elements are removed from the vector
2136 /// if the `Splice` value is leaked.
2138 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2140 /// This is optimal if:
2142 /// * The tail (elements in the vector after `range`) is empty,
2143 /// * or `replace_with` yields fewer elements than `range`’s length
2144 /// * or the lower bound of its `size_hint()` is exact.
2146 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2150 /// Panics if the starting point is greater than the end point or if
2151 /// the end point is greater than the length of the vector.
2156 /// let mut v = vec![1, 2, 3];
2157 /// let new = [7, 8];
2158 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2159 /// assert_eq!(v, &[7, 8, 3]);
2160 /// assert_eq!(u, &[1, 2]);
2163 #[stable(feature = "vec_splice", since = "1.21.0")]
2164 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
2165 where R: RangeBounds<usize>, I: IntoIterator<Item=T>
2168 drain: self.drain(range),
2169 replace_with: replace_with.into_iter(),
2173 /// Creates an iterator which uses a closure to determine if an element should be removed.
2175 /// If the closure returns true, then the element is removed and yielded.
2176 /// If the closure returns false, the element will remain in the vector and will not be yielded
2177 /// by the iterator.
2179 /// Using this method is equivalent to the following code:
2182 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2183 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2185 /// while i != vec.len() {
2186 /// if some_predicate(&mut vec[i]) {
2187 /// let val = vec.remove(i);
2188 /// // your code here
2194 /// # assert_eq!(vec, vec![1, 4, 5]);
2197 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2198 /// because it can backshift the elements of the array in bulk.
2200 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2201 /// regardless of whether you choose to keep or remove it.
2206 /// Splitting an array into evens and odds, reusing the original allocation:
2209 /// #![feature(drain_filter)]
2210 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2212 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2213 /// let odds = numbers;
2215 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2216 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2218 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2219 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
2220 where F: FnMut(&mut T) -> bool,
2222 let old_len = self.len();
2224 // Guard against us getting leaked (leak amplification)
2225 unsafe { self.set_len(0); }
2238 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2240 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2241 /// append the entire slice at once.
2243 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2244 #[stable(feature = "extend_ref", since = "1.2.0")]
2245 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2246 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2247 self.spec_extend(iter.into_iter())
2251 macro_rules! __impl_slice_eq1 {
2252 ([$($vars:tt)*] $lhs:ty, $rhs:ty, $($constraints:tt)*) => {
2253 #[stable(feature = "rust1", since = "1.0.0")]
2254 impl<A, B, $($vars)*> PartialEq<$rhs> for $lhs
2260 fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
2262 fn ne(&self, other: &$rhs) -> bool { self[..] != other[..] }
2267 __impl_slice_eq1! { [] Vec<A>, Vec<B>, }
2268 __impl_slice_eq1! { [] Vec<A>, &[B], }
2269 __impl_slice_eq1! { [] Vec<A>, &mut [B], }
2270 __impl_slice_eq1! { [] Cow<'_, [A]>, &[B], A: Clone }
2271 __impl_slice_eq1! { [] Cow<'_, [A]>, &mut [B], A: Clone }
2272 __impl_slice_eq1! { [] Cow<'_, [A]>, Vec<B>, A: Clone }
2273 __impl_slice_eq1! { [const N: usize] Vec<A>, [B; N], [B; N]: LengthAtMost32 }
2274 __impl_slice_eq1! { [const N: usize] Vec<A>, &[B; N], [B; N]: LengthAtMost32 }
2276 // NOTE: some less important impls are omitted to reduce code bloat
2277 // FIXME(Centril): Reconsider this?
2278 //__impl_slice_eq1! { [const N: usize] Vec<A>, &mut [B; N], [B; N]: LengthAtMost32 }
2279 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, [B; N], [B; N]: LengthAtMost32 }
2280 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &[B; N], [B; N]: LengthAtMost32 }
2281 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &mut [B; N], [B; N]: LengthAtMost32 }
2283 /// Implements comparison of vectors, lexicographically.
2284 #[stable(feature = "rust1", since = "1.0.0")]
2285 impl<T: PartialOrd> PartialOrd for Vec<T> {
2287 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2288 PartialOrd::partial_cmp(&**self, &**other)
2292 #[stable(feature = "rust1", since = "1.0.0")]
2293 impl<T: Eq> Eq for Vec<T> {}
2295 /// Implements ordering of vectors, lexicographically.
2296 #[stable(feature = "rust1", since = "1.0.0")]
2297 impl<T: Ord> Ord for Vec<T> {
2299 fn cmp(&self, other: &Vec<T>) -> Ordering {
2300 Ord::cmp(&**self, &**other)
2304 #[stable(feature = "rust1", since = "1.0.0")]
2305 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2306 fn drop(&mut self) {
2309 ptr::drop_in_place(&mut self[..]);
2311 // RawVec handles deallocation
2315 #[stable(feature = "rust1", since = "1.0.0")]
2316 impl<T> Default for Vec<T> {
2317 /// Creates an empty `Vec<T>`.
2318 fn default() -> Vec<T> {
2323 #[stable(feature = "rust1", since = "1.0.0")]
2324 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2325 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2326 fmt::Debug::fmt(&**self, f)
2330 #[stable(feature = "rust1", since = "1.0.0")]
2331 impl<T> AsRef<Vec<T>> for Vec<T> {
2332 fn as_ref(&self) -> &Vec<T> {
2337 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2338 impl<T> AsMut<Vec<T>> for Vec<T> {
2339 fn as_mut(&mut self) -> &mut Vec<T> {
2344 #[stable(feature = "rust1", since = "1.0.0")]
2345 impl<T> AsRef<[T]> for Vec<T> {
2346 fn as_ref(&self) -> &[T] {
2351 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2352 impl<T> AsMut<[T]> for Vec<T> {
2353 fn as_mut(&mut self) -> &mut [T] {
2358 #[stable(feature = "rust1", since = "1.0.0")]
2359 impl<T: Clone> From<&[T]> for Vec<T> {
2361 fn from(s: &[T]) -> Vec<T> {
2365 fn from(s: &[T]) -> Vec<T> {
2366 crate::slice::to_vec(s)
2370 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2371 impl<T: Clone> From<&mut [T]> for Vec<T> {
2373 fn from(s: &mut [T]) -> Vec<T> {
2377 fn from(s: &mut [T]) -> Vec<T> {
2378 crate::slice::to_vec(s)
2382 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2383 impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
2384 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2389 // note: test pulls in libstd, which causes errors here
2391 #[stable(feature = "vec_from_box", since = "1.18.0")]
2392 impl<T> From<Box<[T]>> for Vec<T> {
2393 fn from(s: Box<[T]>) -> Vec<T> {
2398 // note: test pulls in libstd, which causes errors here
2400 #[stable(feature = "box_from_vec", since = "1.20.0")]
2401 impl<T> From<Vec<T>> for Box<[T]> {
2402 fn from(v: Vec<T>) -> Box<[T]> {
2403 v.into_boxed_slice()
2407 #[stable(feature = "rust1", since = "1.0.0")]
2408 impl From<&str> for Vec<u8> {
2409 fn from(s: &str) -> Vec<u8> {
2410 From::from(s.as_bytes())
2414 ////////////////////////////////////////////////////////////////////////////////
2416 ////////////////////////////////////////////////////////////////////////////////
2418 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2419 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2420 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2425 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2426 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2427 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2432 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2433 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2434 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2435 Cow::Borrowed(v.as_slice())
2439 #[stable(feature = "rust1", since = "1.0.0")]
2440 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
2441 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2442 Cow::Owned(FromIterator::from_iter(it))
2446 ////////////////////////////////////////////////////////////////////////////////
2448 ////////////////////////////////////////////////////////////////////////////////
2450 /// An iterator that moves out of a vector.
2452 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
2453 /// by the [`IntoIterator`] trait).
2455 /// [`Vec`]: struct.Vec.html
2456 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2457 #[stable(feature = "rust1", since = "1.0.0")]
2458 pub struct IntoIter<T> {
2460 phantom: PhantomData<T>,
2466 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2467 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2468 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2469 f.debug_tuple("IntoIter")
2470 .field(&self.as_slice())
2475 impl<T> IntoIter<T> {
2476 /// Returns the remaining items of this iterator as a slice.
2481 /// let vec = vec!['a', 'b', 'c'];
2482 /// let mut into_iter = vec.into_iter();
2483 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2484 /// let _ = into_iter.next().unwrap();
2485 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2487 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2488 pub fn as_slice(&self) -> &[T] {
2490 slice::from_raw_parts(self.ptr, self.len())
2494 /// Returns the remaining items of this iterator as a mutable slice.
2499 /// let vec = vec!['a', 'b', 'c'];
2500 /// let mut into_iter = vec.into_iter();
2501 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2502 /// into_iter.as_mut_slice()[2] = 'z';
2503 /// assert_eq!(into_iter.next().unwrap(), 'a');
2504 /// assert_eq!(into_iter.next().unwrap(), 'b');
2505 /// assert_eq!(into_iter.next().unwrap(), 'z');
2507 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2508 pub fn as_mut_slice(&mut self) -> &mut [T] {
2510 slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
2515 #[stable(feature = "rust1", since = "1.0.0")]
2516 unsafe impl<T: Send> Send for IntoIter<T> {}
2517 #[stable(feature = "rust1", since = "1.0.0")]
2518 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2520 #[stable(feature = "rust1", since = "1.0.0")]
2521 impl<T> Iterator for IntoIter<T> {
2525 fn next(&mut self) -> Option<T> {
2527 if self.ptr as *const _ == self.end {
2530 if mem::size_of::<T>() == 0 {
2531 // purposefully don't use 'ptr.offset' because for
2532 // vectors with 0-size elements this would return the
2534 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2536 // Make up a value of this ZST.
2540 self.ptr = self.ptr.offset(1);
2542 Some(ptr::read(old))
2549 fn size_hint(&self) -> (usize, Option<usize>) {
2550 let exact = if mem::size_of::<T>() == 0 {
2551 (self.end as usize).wrapping_sub(self.ptr as usize)
2553 unsafe { self.end.offset_from(self.ptr) as usize }
2555 (exact, Some(exact))
2559 fn count(self) -> usize {
2564 #[stable(feature = "rust1", since = "1.0.0")]
2565 impl<T> DoubleEndedIterator for IntoIter<T> {
2567 fn next_back(&mut self) -> Option<T> {
2569 if self.end == self.ptr {
2572 if mem::size_of::<T>() == 0 {
2573 // See above for why 'ptr.offset' isn't used
2574 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2576 // Make up a value of this ZST.
2579 self.end = self.end.offset(-1);
2581 Some(ptr::read(self.end))
2588 #[stable(feature = "rust1", since = "1.0.0")]
2589 impl<T> ExactSizeIterator for IntoIter<T> {
2590 fn is_empty(&self) -> bool {
2591 self.ptr == self.end
2595 #[stable(feature = "fused", since = "1.26.0")]
2596 impl<T> FusedIterator for IntoIter<T> {}
2598 #[unstable(feature = "trusted_len", issue = "37572")]
2599 unsafe impl<T> TrustedLen for IntoIter<T> {}
2601 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2602 impl<T: Clone> Clone for IntoIter<T> {
2603 fn clone(&self) -> IntoIter<T> {
2604 self.as_slice().to_owned().into_iter()
2608 #[stable(feature = "rust1", since = "1.0.0")]
2609 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2610 fn drop(&mut self) {
2611 // destroy the remaining elements
2612 for _x in self.by_ref() {}
2614 // RawVec handles deallocation
2615 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2619 /// A draining iterator for `Vec<T>`.
2621 /// This `struct` is created by the [`drain`] method on [`Vec`].
2623 /// [`drain`]: struct.Vec.html#method.drain
2624 /// [`Vec`]: struct.Vec.html
2625 #[stable(feature = "drain", since = "1.6.0")]
2626 pub struct Drain<'a, T: 'a> {
2627 /// Index of tail to preserve
2631 /// Current remaining range to remove
2632 iter: slice::Iter<'a, T>,
2633 vec: NonNull<Vec<T>>,
2636 #[stable(feature = "collection_debug", since = "1.17.0")]
2637 impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
2638 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2639 f.debug_tuple("Drain")
2640 .field(&self.iter.as_slice())
2645 impl<'a, T> Drain<'a, T> {
2646 /// Returns the remaining items of this iterator as a slice.
2651 /// # #![feature(vec_drain_as_slice)]
2652 /// let mut vec = vec!['a', 'b', 'c'];
2653 /// let mut drain = vec.drain(..);
2654 /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']);
2655 /// let _ = drain.next().unwrap();
2656 /// assert_eq!(drain.as_slice(), &['b', 'c']);
2658 #[unstable(feature = "vec_drain_as_slice", reason = "recently added", issue = "58957")]
2659 pub fn as_slice(&self) -> &[T] {
2660 self.iter.as_slice()
2664 #[stable(feature = "drain", since = "1.6.0")]
2665 unsafe impl<T: Sync> Sync for Drain<'_, T> {}
2666 #[stable(feature = "drain", since = "1.6.0")]
2667 unsafe impl<T: Send> Send for Drain<'_, T> {}
2669 #[stable(feature = "drain", since = "1.6.0")]
2670 impl<T> Iterator for Drain<'_, T> {
2674 fn next(&mut self) -> Option<T> {
2675 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2678 fn size_hint(&self) -> (usize, Option<usize>) {
2679 self.iter.size_hint()
2683 #[stable(feature = "drain", since = "1.6.0")]
2684 impl<T> DoubleEndedIterator for Drain<'_, T> {
2686 fn next_back(&mut self) -> Option<T> {
2687 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2691 #[stable(feature = "drain", since = "1.6.0")]
2692 impl<T> Drop for Drain<'_, T> {
2693 fn drop(&mut self) {
2694 // exhaust self first
2695 self.for_each(drop);
2697 if self.tail_len > 0 {
2699 let source_vec = self.vec.as_mut();
2700 // memmove back untouched tail, update to new length
2701 let start = source_vec.len();
2702 let tail = self.tail_start;
2704 let src = source_vec.as_ptr().add(tail);
2705 let dst = source_vec.as_mut_ptr().add(start);
2706 ptr::copy(src, dst, self.tail_len);
2708 source_vec.set_len(start + self.tail_len);
2715 #[stable(feature = "drain", since = "1.6.0")]
2716 impl<T> ExactSizeIterator for Drain<'_, T> {
2717 fn is_empty(&self) -> bool {
2718 self.iter.is_empty()
2722 #[unstable(feature = "trusted_len", issue = "37572")]
2723 unsafe impl<T> TrustedLen for Drain<'_, T> {}
2725 #[stable(feature = "fused", since = "1.26.0")]
2726 impl<T> FusedIterator for Drain<'_, T> {}
2728 /// A splicing iterator for `Vec`.
2730 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2731 /// documentation for more.
2733 /// [`splice()`]: struct.Vec.html#method.splice
2734 /// [`Vec`]: struct.Vec.html
2736 #[stable(feature = "vec_splice", since = "1.21.0")]
2737 pub struct Splice<'a, I: Iterator + 'a> {
2738 drain: Drain<'a, I::Item>,
2742 #[stable(feature = "vec_splice", since = "1.21.0")]
2743 impl<I: Iterator> Iterator for Splice<'_, I> {
2744 type Item = I::Item;
2746 fn next(&mut self) -> Option<Self::Item> {
2750 fn size_hint(&self) -> (usize, Option<usize>) {
2751 self.drain.size_hint()
2755 #[stable(feature = "vec_splice", since = "1.21.0")]
2756 impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
2757 fn next_back(&mut self) -> Option<Self::Item> {
2758 self.drain.next_back()
2762 #[stable(feature = "vec_splice", since = "1.21.0")]
2763 impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}
2766 #[stable(feature = "vec_splice", since = "1.21.0")]
2767 impl<I: Iterator> Drop for Splice<'_, I> {
2768 fn drop(&mut self) {
2769 self.drain.by_ref().for_each(drop);
2772 if self.drain.tail_len == 0 {
2773 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2777 // First fill the range left by drain().
2778 if !self.drain.fill(&mut self.replace_with) {
2782 // There may be more elements. Use the lower bound as an estimate.
2783 // FIXME: Is the upper bound a better guess? Or something else?
2784 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2785 if lower_bound > 0 {
2786 self.drain.move_tail(lower_bound);
2787 if !self.drain.fill(&mut self.replace_with) {
2792 // Collect any remaining elements.
2793 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2794 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2795 // Now we have an exact count.
2796 if collected.len() > 0 {
2797 self.drain.move_tail(collected.len());
2798 let filled = self.drain.fill(&mut collected);
2799 debug_assert!(filled);
2800 debug_assert_eq!(collected.len(), 0);
2803 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2807 /// Private helper methods for `Splice::drop`
2808 impl<T> Drain<'_, T> {
2809 /// The range from `self.vec.len` to `self.tail_start` contains elements
2810 /// that have been moved out.
2811 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2812 /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2813 unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
2814 let vec = self.vec.as_mut();
2815 let range_start = vec.len;
2816 let range_end = self.tail_start;
2817 let range_slice = slice::from_raw_parts_mut(
2818 vec.as_mut_ptr().add(range_start),
2819 range_end - range_start);
2821 for place in range_slice {
2822 if let Some(new_item) = replace_with.next() {
2823 ptr::write(place, new_item);
2832 /// Makes room for inserting more elements before the tail.
2833 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2834 let vec = self.vec.as_mut();
2835 let used_capacity = self.tail_start + self.tail_len;
2836 vec.buf.reserve(used_capacity, extra_capacity);
2838 let new_tail_start = self.tail_start + extra_capacity;
2839 let src = vec.as_ptr().add(self.tail_start);
2840 let dst = vec.as_mut_ptr().add(new_tail_start);
2841 ptr::copy(src, dst, self.tail_len);
2842 self.tail_start = new_tail_start;
2846 /// An iterator produced by calling `drain_filter` on Vec.
2847 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2849 pub struct DrainFilter<'a, T, F>
2850 where F: FnMut(&mut T) -> bool,
2852 vec: &'a mut Vec<T>,
2853 /// The index of the item that will be inspected by the next call to `next`.
2855 /// The number of items that have been drained (removed) thus far.
2857 /// The original length of `vec` prior to draining.
2859 /// The filter test predicate.
2861 /// A flag that indicates a panic has occurred in the filter test prodicate.
2862 /// This is used as a hint in the drop implmentation to prevent consumption
2863 /// of the remainder of the `DrainFilter`. Any unprocessed items will be
2864 /// backshifted in the `vec`, but no further items will be dropped or
2865 /// tested by the filter predicate.
2869 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2870 impl<T, F> Iterator for DrainFilter<'_, T, F>
2871 where F: FnMut(&mut T) -> bool,
2875 fn next(&mut self) -> Option<T> {
2877 while self.idx < self.old_len {
2879 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2880 self.panic_flag = true;
2881 let drained = (self.pred)(&mut v[i]);
2882 self.panic_flag = false;
2883 // Update the index *after* the predicate is called. If the index
2884 // is updated prior and the predicate panics, the element at this
2885 // index would be leaked.
2889 return Some(ptr::read(&v[i]));
2890 } else if self.del > 0 {
2892 let src: *const T = &v[i];
2893 let dst: *mut T = &mut v[i - del];
2894 ptr::copy_nonoverlapping(src, dst, 1);
2901 fn size_hint(&self) -> (usize, Option<usize>) {
2902 (0, Some(self.old_len - self.idx))
2906 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2907 impl<T, F> Drop for DrainFilter<'_, T, F>
2908 where F: FnMut(&mut T) -> bool,
2910 fn drop(&mut self) {
2911 struct BackshiftOnDrop<'a, 'b, T, F>
2913 F: FnMut(&mut T) -> bool,
2915 drain: &'b mut DrainFilter<'a, T, F>,
2918 impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F>
2920 F: FnMut(&mut T) -> bool
2922 fn drop(&mut self) {
2924 if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
2925 // This is a pretty messed up state, and there isn't really an
2926 // obviously right thing to do. We don't want to keep trying
2927 // to execute `pred`, so we just backshift all the unprocessed
2928 // elements and tell the vec that they still exist. The backshift
2929 // is required to prevent a double-drop of the last successfully
2930 // drained item prior to a panic in the predicate.
2931 let ptr = self.drain.vec.as_mut_ptr();
2932 let src = ptr.add(self.drain.idx);
2933 let dst = src.sub(self.drain.del);
2934 let tail_len = self.drain.old_len - self.drain.idx;
2935 src.copy_to(dst, tail_len);
2937 self.drain.vec.set_len(self.drain.old_len - self.drain.del);
2942 let backshift = BackshiftOnDrop {
2946 // Attempt to consume any remaining elements if the filter predicate
2947 // has not yet panicked. We'll backshift any remaining elements
2948 // whether we've already panicked or if the consumption here panics.
2949 if !backshift.drain.panic_flag {
2950 backshift.drain.for_each(drop);