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().cloned());
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 #[stable(feature = "rust1", since = "1.0.0")]
319 pub const fn new() -> Vec<T> {
326 /// Constructs a new, empty `Vec<T>` with the specified capacity.
328 /// The vector will be able to hold exactly `capacity` elements without
329 /// reallocating. If `capacity` is 0, the vector will not allocate.
331 /// It is important to note that although the returned vector has the
332 /// *capacity* specified, the vector will have a zero *length*. For an
333 /// explanation of the difference between length and capacity, see
334 /// *[Capacity and reallocation]*.
336 /// [Capacity and reallocation]: #capacity-and-reallocation
341 /// let mut vec = Vec::with_capacity(10);
343 /// // The vector contains no items, even though it has capacity for more
344 /// assert_eq!(vec.len(), 0);
346 /// // These are all done without reallocating...
351 /// // ...but this may make the vector reallocate
355 #[stable(feature = "rust1", since = "1.0.0")]
356 pub fn with_capacity(capacity: usize) -> Vec<T> {
358 buf: RawVec::with_capacity(capacity),
363 /// Decomposes a `Vec<T>` into its raw components.
365 /// Returns the raw pointer to the underlying data, the length of
366 /// the vector (in elements), and the allocated capacity of the
367 /// data (in elements). These are the same arguments in the same
368 /// order as the arguments to [`from_raw_parts`].
370 /// After calling this function, the caller is responsible for the
371 /// memory previously managed by the `Vec`. The only way to do
372 /// this is to convert the raw pointer, length, and capacity back
373 /// into a `Vec` with the [`from_raw_parts`] function, allowing
374 /// the destructor to perform the cleanup.
376 /// [`from_raw_parts`]: #method.from_raw_parts
381 /// #![feature(vec_into_raw_parts)]
382 /// let v: Vec<i32> = vec![-1, 0, 1];
384 /// let (ptr, len, cap) = v.into_raw_parts();
386 /// let rebuilt = unsafe {
387 /// // We can now make changes to the components, such as
388 /// // transmuting the raw pointer to a compatible type.
389 /// let ptr = ptr as *mut u32;
391 /// Vec::from_raw_parts(ptr, len, cap)
393 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
395 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
396 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
397 let mut me = mem::ManuallyDrop::new(self);
398 (me.as_mut_ptr(), me.len(), me.capacity())
401 /// Creates a `Vec<T>` directly from the raw components of another vector.
405 /// This is highly unsafe, due to the number of invariants that aren't
408 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
409 /// (at least, it's highly likely to be incorrect if it wasn't).
410 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
411 /// * `length` needs to be less than or equal to `capacity`.
412 /// * `capacity` needs to be the capacity that the pointer was allocated with.
414 /// Violating these may cause problems like corrupting the allocator's
415 /// internal data structures. For example it is **not** safe
416 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
417 /// It's also not safe to build one from a `Vec<u16>` and its length, because
418 /// the allocator cares about the alignment, and these two types have different
419 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
420 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
422 /// The ownership of `ptr` is effectively transferred to the
423 /// `Vec<T>` which may then deallocate, reallocate or change the
424 /// contents of memory pointed to by the pointer at will. Ensure
425 /// that nothing else uses the pointer after calling this
428 /// [`String`]: ../../std/string/struct.String.html
436 /// let v = vec![1, 2, 3];
438 // FIXME Update this when vec_into_raw_parts is stabilized
439 /// // Prevent running `v`'s destructor so we are in complete control
440 /// // of the allocation.
441 /// let mut v = mem::ManuallyDrop::new(v);
443 /// // Pull out the various important pieces of information about `v`
444 /// let p = v.as_mut_ptr();
445 /// let len = v.len();
446 /// let cap = v.capacity();
449 /// // Overwrite memory with 4, 5, 6
450 /// for i in 0..len as isize {
451 /// ptr::write(p.offset(i), 4 + i);
454 /// // Put everything back together into a Vec
455 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
456 /// assert_eq!(rebuilt, [4, 5, 6]);
459 #[stable(feature = "rust1", since = "1.0.0")]
460 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
462 buf: RawVec::from_raw_parts(ptr, capacity),
467 /// Returns the number of elements the vector can hold without
473 /// let vec: Vec<i32> = Vec::with_capacity(10);
474 /// assert_eq!(vec.capacity(), 10);
477 #[stable(feature = "rust1", since = "1.0.0")]
478 pub fn capacity(&self) -> usize {
482 /// Reserves capacity for at least `additional` more elements to be inserted
483 /// in the given `Vec<T>`. The collection may reserve more space to avoid
484 /// frequent reallocations. After calling `reserve`, capacity will be
485 /// greater than or equal to `self.len() + additional`. Does nothing if
486 /// capacity is already sufficient.
490 /// Panics if the new capacity overflows `usize`.
495 /// let mut vec = vec![1];
497 /// assert!(vec.capacity() >= 11);
499 #[stable(feature = "rust1", since = "1.0.0")]
500 pub fn reserve(&mut self, additional: usize) {
501 self.buf.reserve(self.len, additional);
504 /// Reserves the minimum capacity for exactly `additional` more elements to
505 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
506 /// capacity will be greater than or equal to `self.len() + additional`.
507 /// Does nothing if the capacity is already sufficient.
509 /// Note that the allocator may give the collection more space than it
510 /// requests. Therefore, capacity can not be relied upon to be precisely
511 /// minimal. Prefer `reserve` if future insertions are expected.
515 /// Panics if the new capacity overflows `usize`.
520 /// let mut vec = vec![1];
521 /// vec.reserve_exact(10);
522 /// assert!(vec.capacity() >= 11);
524 #[stable(feature = "rust1", since = "1.0.0")]
525 pub fn reserve_exact(&mut self, additional: usize) {
526 self.buf.reserve_exact(self.len, additional);
529 /// Tries to reserve capacity for at least `additional` more elements to be inserted
530 /// in the given `Vec<T>`. The collection may reserve more space to avoid
531 /// frequent reallocations. After calling `reserve`, capacity will be
532 /// greater than or equal to `self.len() + additional`. Does nothing if
533 /// capacity is already sufficient.
537 /// If the capacity overflows, or the allocator reports a failure, then an error
543 /// #![feature(try_reserve)]
544 /// use std::collections::TryReserveError;
546 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
547 /// let mut output = Vec::new();
549 /// // Pre-reserve the memory, exiting if we can't
550 /// output.try_reserve(data.len())?;
552 /// // Now we know this can't OOM in the middle of our complex work
553 /// output.extend(data.iter().map(|&val| {
554 /// val * 2 + 5 // very complicated
559 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
561 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
562 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
563 self.buf.try_reserve(self.len, additional)
566 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
567 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
568 /// capacity will be greater than or equal to `self.len() + additional`.
569 /// Does nothing if the capacity is already sufficient.
571 /// Note that the allocator may give the collection more space than it
572 /// requests. Therefore, capacity can not be relied upon to be precisely
573 /// minimal. Prefer `reserve` if future insertions are expected.
577 /// If the capacity overflows, or the allocator reports a failure, then an error
583 /// #![feature(try_reserve)]
584 /// use std::collections::TryReserveError;
586 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
587 /// let mut output = Vec::new();
589 /// // Pre-reserve the memory, exiting if we can't
590 /// output.try_reserve(data.len())?;
592 /// // Now we know this can't OOM in the middle of our complex work
593 /// output.extend(data.iter().map(|&val| {
594 /// val * 2 + 5 // very complicated
599 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
601 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
602 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
603 self.buf.try_reserve_exact(self.len, additional)
606 /// Shrinks the capacity of the vector as much as possible.
608 /// It will drop down as close as possible to the length but the allocator
609 /// may still inform the vector that there is space for a few more elements.
614 /// let mut vec = Vec::with_capacity(10);
615 /// vec.extend([1, 2, 3].iter().cloned());
616 /// assert_eq!(vec.capacity(), 10);
617 /// vec.shrink_to_fit();
618 /// assert!(vec.capacity() >= 3);
620 #[stable(feature = "rust1", since = "1.0.0")]
621 pub fn shrink_to_fit(&mut self) {
622 if self.capacity() != self.len {
623 self.buf.shrink_to_fit(self.len);
627 /// Shrinks the capacity of the vector with a lower bound.
629 /// The capacity will remain at least as large as both the length
630 /// and the supplied value.
632 /// Panics if the current capacity is smaller than the supplied
633 /// minimum capacity.
638 /// #![feature(shrink_to)]
639 /// let mut vec = Vec::with_capacity(10);
640 /// vec.extend([1, 2, 3].iter().cloned());
641 /// assert_eq!(vec.capacity(), 10);
642 /// vec.shrink_to(4);
643 /// assert!(vec.capacity() >= 4);
644 /// vec.shrink_to(0);
645 /// assert!(vec.capacity() >= 3);
647 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
648 pub fn shrink_to(&mut self, min_capacity: usize) {
649 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
652 /// Converts the vector into [`Box<[T]>`][owned slice].
654 /// Note that this will drop any excess capacity.
656 /// [owned slice]: ../../std/boxed/struct.Box.html
661 /// let v = vec![1, 2, 3];
663 /// let slice = v.into_boxed_slice();
666 /// Any excess capacity is removed:
669 /// let mut vec = Vec::with_capacity(10);
670 /// vec.extend([1, 2, 3].iter().cloned());
672 /// assert_eq!(vec.capacity(), 10);
673 /// let slice = vec.into_boxed_slice();
674 /// assert_eq!(slice.into_vec().capacity(), 3);
676 #[stable(feature = "rust1", since = "1.0.0")]
677 pub fn into_boxed_slice(mut self) -> Box<[T]> {
679 self.shrink_to_fit();
680 let buf = ptr::read(&self.buf);
686 /// Shortens the vector, keeping the first `len` elements and dropping
689 /// If `len` is greater than the vector's current length, this has no
692 /// The [`drain`] method can emulate `truncate`, but causes the excess
693 /// elements to be returned instead of dropped.
695 /// Note that this method has no effect on the allocated capacity
700 /// Truncating a five element vector to two elements:
703 /// let mut vec = vec![1, 2, 3, 4, 5];
705 /// assert_eq!(vec, [1, 2]);
708 /// No truncation occurs when `len` is greater than the vector's current
712 /// let mut vec = vec![1, 2, 3];
714 /// assert_eq!(vec, [1, 2, 3]);
717 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
721 /// let mut vec = vec![1, 2, 3];
723 /// assert_eq!(vec, []);
726 /// [`clear`]: #method.clear
727 /// [`drain`]: #method.drain
728 #[stable(feature = "rust1", since = "1.0.0")]
729 pub fn truncate(&mut self, len: usize) {
730 // This is safe because:
732 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
733 // case avoids creating an invalid slice, and
734 // * the `len` of the vector is shrunk before calling `drop_in_place`,
735 // such that no value will be dropped twice in case `drop_in_place`
736 // were to panic once (if it panics twice, the program aborts).
741 let s = self.get_unchecked_mut(len..) as *mut _;
743 ptr::drop_in_place(s);
747 /// Extracts a slice containing the entire vector.
749 /// Equivalent to `&s[..]`.
754 /// use std::io::{self, Write};
755 /// let buffer = vec![1, 2, 3, 5, 8];
756 /// io::sink().write(buffer.as_slice()).unwrap();
759 #[stable(feature = "vec_as_slice", since = "1.7.0")]
760 pub fn as_slice(&self) -> &[T] {
764 /// Extracts a mutable slice of the entire vector.
766 /// Equivalent to `&mut s[..]`.
771 /// use std::io::{self, Read};
772 /// let mut buffer = vec![0; 3];
773 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
776 #[stable(feature = "vec_as_slice", since = "1.7.0")]
777 pub fn as_mut_slice(&mut self) -> &mut [T] {
781 /// Returns a raw pointer to the vector's buffer.
783 /// The caller must ensure that the vector outlives the pointer this
784 /// function returns, or else it will end up pointing to garbage.
785 /// Modifying the vector may cause its buffer to be reallocated,
786 /// which would also make any pointers to it invalid.
788 /// The caller must also ensure that the memory the pointer (non-transitively) points to
789 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
790 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
795 /// let x = vec![1, 2, 4];
796 /// let x_ptr = x.as_ptr();
799 /// for i in 0..x.len() {
800 /// assert_eq!(*x_ptr.add(i), 1 << i);
805 /// [`as_mut_ptr`]: #method.as_mut_ptr
806 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
808 pub fn as_ptr(&self) -> *const T {
809 // We shadow the slice method of the same name to avoid going through
810 // `deref`, which creates an intermediate reference.
811 let ptr = self.buf.ptr();
812 unsafe { assume(!ptr.is_null()); }
816 /// Returns an unsafe mutable pointer to the vector's buffer.
818 /// The caller must ensure that the vector outlives the pointer this
819 /// function returns, or else it will end up pointing to garbage.
820 /// Modifying the vector may cause its buffer to be reallocated,
821 /// which would also make any pointers to it invalid.
826 /// // Allocate vector big enough for 4 elements.
828 /// let mut x: Vec<i32> = Vec::with_capacity(size);
829 /// let x_ptr = x.as_mut_ptr();
831 /// // Initialize elements via raw pointer writes, then set length.
833 /// for i in 0..size {
834 /// *x_ptr.add(i) = i as i32;
838 /// assert_eq!(&*x, &[0,1,2,3]);
840 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
842 pub fn as_mut_ptr(&mut self) -> *mut T {
843 // We shadow the slice method of the same name to avoid going through
844 // `deref_mut`, which creates an intermediate reference.
845 let ptr = self.buf.ptr();
846 unsafe { assume(!ptr.is_null()); }
850 /// Forces the length of the vector to `new_len`.
852 /// This is a low-level operation that maintains none of the normal
853 /// invariants of the type. Normally changing the length of a vector
854 /// is done using one of the safe operations instead, such as
855 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
857 /// [`truncate`]: #method.truncate
858 /// [`resize`]: #method.resize
859 /// [`extend`]: ../../std/iter/trait.Extend.html#tymethod.extend
860 /// [`clear`]: #method.clear
864 /// - `new_len` must be less than or equal to [`capacity()`].
865 /// - The elements at `old_len..new_len` must be initialized.
867 /// [`capacity()`]: #method.capacity
871 /// This method can be useful for situations in which the vector
872 /// is serving as a buffer for other code, particularly over FFI:
875 /// # #![allow(dead_code)]
876 /// # // This is just a minimal skeleton for the doc example;
877 /// # // don't use this as a starting point for a real library.
878 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
879 /// # const Z_OK: i32 = 0;
881 /// # fn deflateGetDictionary(
882 /// # strm: *mut std::ffi::c_void,
883 /// # dictionary: *mut u8,
884 /// # dictLength: *mut usize,
887 /// # impl StreamWrapper {
888 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
889 /// // Per the FFI method's docs, "32768 bytes is always enough".
890 /// let mut dict = Vec::with_capacity(32_768);
891 /// let mut dict_length = 0;
892 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
893 /// // 1. `dict_length` elements were initialized.
894 /// // 2. `dict_length` <= the capacity (32_768)
895 /// // which makes `set_len` safe to call.
897 /// // Make the FFI call...
898 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
900 /// // ...and update the length to what was initialized.
901 /// dict.set_len(dict_length);
911 /// While the following example is sound, there is a memory leak since
912 /// the inner vectors were not freed prior to the `set_len` call:
915 /// let mut vec = vec![vec![1, 0, 0],
919 /// // 1. `old_len..0` is empty so no elements need to be initialized.
920 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
926 /// Normally, here, one would use [`clear`] instead to correctly drop
927 /// the contents and thus not leak memory.
929 #[stable(feature = "rust1", since = "1.0.0")]
930 pub unsafe fn set_len(&mut self, new_len: usize) {
931 debug_assert!(new_len <= self.capacity());
936 /// Removes an element from the vector and returns it.
938 /// The removed element is replaced by the last element of the vector.
940 /// This does not preserve ordering, but is O(1).
944 /// Panics if `index` is out of bounds.
949 /// let mut v = vec!["foo", "bar", "baz", "qux"];
951 /// assert_eq!(v.swap_remove(1), "bar");
952 /// assert_eq!(v, ["foo", "qux", "baz"]);
954 /// assert_eq!(v.swap_remove(0), "foo");
955 /// assert_eq!(v, ["baz", "qux"]);
958 #[stable(feature = "rust1", since = "1.0.0")]
959 pub fn swap_remove(&mut self, index: usize) -> T {
961 // We replace self[index] with the last element. Note that if the
962 // bounds check on hole succeeds there must be a last element (which
963 // can be self[index] itself).
964 let hole: *mut T = &mut self[index];
965 let last = ptr::read(self.get_unchecked(self.len - 1));
967 ptr::replace(hole, last)
971 /// Inserts an element at position `index` within the vector, shifting all
972 /// elements after it to the right.
976 /// Panics if `index > len`.
981 /// let mut vec = vec![1, 2, 3];
982 /// vec.insert(1, 4);
983 /// assert_eq!(vec, [1, 4, 2, 3]);
984 /// vec.insert(4, 5);
985 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
987 #[stable(feature = "rust1", since = "1.0.0")]
988 pub fn insert(&mut self, index: usize, element: T) {
989 let len = self.len();
990 assert!(index <= len);
992 // space for the new element
993 if len == self.buf.capacity() {
999 // The spot to put the new value
1001 let p = self.as_mut_ptr().add(index);
1002 // Shift everything over to make space. (Duplicating the
1003 // `index`th element into two consecutive places.)
1004 ptr::copy(p, p.offset(1), len - index);
1005 // Write it in, overwriting the first copy of the `index`th
1007 ptr::write(p, element);
1009 self.set_len(len + 1);
1013 /// Removes and returns the element at position `index` within the vector,
1014 /// shifting all elements after it to the left.
1018 /// Panics if `index` is out of bounds.
1023 /// let mut v = vec![1, 2, 3];
1024 /// assert_eq!(v.remove(1), 2);
1025 /// assert_eq!(v, [1, 3]);
1027 #[stable(feature = "rust1", since = "1.0.0")]
1028 pub fn remove(&mut self, index: usize) -> T {
1029 let len = self.len();
1030 assert!(index < len);
1035 // the place we are taking from.
1036 let ptr = self.as_mut_ptr().add(index);
1037 // copy it out, unsafely having a copy of the value on
1038 // the stack and in the vector at the same time.
1039 ret = ptr::read(ptr);
1041 // Shift everything down to fill in that spot.
1042 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1044 self.set_len(len - 1);
1049 /// Retains only the elements specified by the predicate.
1051 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1052 /// This method operates in place, visiting each element exactly once in the
1053 /// original order, and preserves the order of the retained elements.
1058 /// let mut vec = vec![1, 2, 3, 4];
1059 /// vec.retain(|&x| x%2 == 0);
1060 /// assert_eq!(vec, [2, 4]);
1063 /// The exact order may be useful for tracking external state, like an index.
1066 /// let mut vec = vec![1, 2, 3, 4, 5];
1067 /// let keep = [false, true, true, false, true];
1069 /// vec.retain(|_| (keep[i], i += 1).0);
1070 /// assert_eq!(vec, [2, 3, 5]);
1072 #[stable(feature = "rust1", since = "1.0.0")]
1073 pub fn retain<F>(&mut self, mut f: F)
1074 where F: FnMut(&T) -> bool
1076 self.drain_filter(|x| !f(x));
1079 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1082 /// If the vector is sorted, this removes all duplicates.
1087 /// let mut vec = vec![10, 20, 21, 30, 20];
1089 /// vec.dedup_by_key(|i| *i / 10);
1091 /// assert_eq!(vec, [10, 20, 30, 20]);
1093 #[stable(feature = "dedup_by", since = "1.16.0")]
1095 pub fn dedup_by_key<F, K>(&mut self, mut key: F) where F: FnMut(&mut T) -> K, K: PartialEq {
1096 self.dedup_by(|a, b| key(a) == key(b))
1099 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1102 /// The `same_bucket` function is passed references to two elements from the vector and
1103 /// must determine if the elements compare equal. The elements are passed in opposite order
1104 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1106 /// If the vector is sorted, this removes all duplicates.
1111 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1113 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1115 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1117 #[stable(feature = "dedup_by", since = "1.16.0")]
1118 pub fn dedup_by<F>(&mut self, same_bucket: F) where F: FnMut(&mut T, &mut T) -> bool {
1120 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
1126 /// Appends an element to the back of a collection.
1130 /// Panics if the number of elements in the vector overflows a `usize`.
1135 /// let mut vec = vec![1, 2];
1137 /// assert_eq!(vec, [1, 2, 3]);
1140 #[stable(feature = "rust1", since = "1.0.0")]
1141 pub fn push(&mut self, value: T) {
1142 // This will panic or abort if we would allocate > isize::MAX bytes
1143 // or if the length increment would overflow for zero-sized types.
1144 if self.len == self.buf.capacity() {
1148 let end = self.as_mut_ptr().add(self.len);
1149 ptr::write(end, value);
1154 /// Removes the last element from a vector and returns it, or [`None`] if it
1157 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1162 /// let mut vec = vec![1, 2, 3];
1163 /// assert_eq!(vec.pop(), Some(3));
1164 /// assert_eq!(vec, [1, 2]);
1167 #[stable(feature = "rust1", since = "1.0.0")]
1168 pub fn pop(&mut self) -> Option<T> {
1174 Some(ptr::read(self.get_unchecked(self.len())))
1179 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1183 /// Panics if the number of elements in the vector overflows a `usize`.
1188 /// let mut vec = vec![1, 2, 3];
1189 /// let mut vec2 = vec![4, 5, 6];
1190 /// vec.append(&mut vec2);
1191 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1192 /// assert_eq!(vec2, []);
1195 #[stable(feature = "append", since = "1.4.0")]
1196 pub fn append(&mut self, other: &mut Self) {
1198 self.append_elements(other.as_slice() as _);
1203 /// Appends elements to `Self` from other buffer.
1205 unsafe fn append_elements(&mut self, other: *const [T]) {
1206 let count = (*other).len();
1207 self.reserve(count);
1208 let len = self.len();
1209 ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count);
1213 /// Creates a draining iterator that removes the specified range in the vector
1214 /// and yields the removed items.
1216 /// Note 1: The element range is removed even if the iterator is only
1217 /// partially consumed or not consumed at all.
1219 /// Note 2: It is unspecified how many elements are removed from the vector
1220 /// if the `Drain` value is leaked.
1224 /// Panics if the starting point is greater than the end point or if
1225 /// the end point is greater than the length of the vector.
1230 /// let mut v = vec![1, 2, 3];
1231 /// let u: Vec<_> = v.drain(1..).collect();
1232 /// assert_eq!(v, &[1]);
1233 /// assert_eq!(u, &[2, 3]);
1235 /// // A full range clears the vector
1237 /// assert_eq!(v, &[]);
1239 #[stable(feature = "drain", since = "1.6.0")]
1240 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1241 where R: RangeBounds<usize>
1245 // When the Drain is first created, it shortens the length of
1246 // the source vector to make sure no uninitialized or moved-from elements
1247 // are accessible at all if the Drain's destructor never gets to run.
1249 // Drain will ptr::read out the values to remove.
1250 // When finished, remaining tail of the vec is copied back to cover
1251 // the hole, and the vector length is restored to the new length.
1253 let len = self.len();
1254 let start = match range.start_bound() {
1256 Excluded(&n) => n + 1,
1259 let end = match range.end_bound() {
1260 Included(&n) => n + 1,
1264 assert!(start <= end);
1265 assert!(end <= len);
1268 // set self.vec length's to start, to be safe in case Drain is leaked
1269 self.set_len(start);
1270 // Use the borrow in the IterMut to indicate borrowing behavior of the
1271 // whole Drain iterator (like &mut T).
1272 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start),
1276 tail_len: len - end,
1277 iter: range_slice.iter(),
1278 vec: NonNull::from(self),
1283 /// Clears the vector, removing all values.
1285 /// Note that this method has no effect on the allocated capacity
1291 /// let mut v = vec![1, 2, 3];
1295 /// assert!(v.is_empty());
1298 #[stable(feature = "rust1", since = "1.0.0")]
1299 pub fn clear(&mut self) {
1303 /// Returns the number of elements in the vector, also referred to
1304 /// as its 'length'.
1309 /// let a = vec![1, 2, 3];
1310 /// assert_eq!(a.len(), 3);
1313 #[stable(feature = "rust1", since = "1.0.0")]
1314 pub fn len(&self) -> usize {
1318 /// Returns `true` if the vector contains no elements.
1323 /// let mut v = Vec::new();
1324 /// assert!(v.is_empty());
1327 /// assert!(!v.is_empty());
1329 #[stable(feature = "rust1", since = "1.0.0")]
1330 pub fn is_empty(&self) -> bool {
1334 /// Splits the collection into two at the given index.
1336 /// Returns a newly allocated vector containing the elements in the range
1337 /// `[at, len)`. After the call, the original vector will be left containing
1338 /// the elements `[0, at)` with its previous capacity unchanged.
1342 /// Panics if `at > len`.
1347 /// let mut vec = vec![1,2,3];
1348 /// let vec2 = vec.split_off(1);
1349 /// assert_eq!(vec, [1]);
1350 /// assert_eq!(vec2, [2, 3]);
1353 #[stable(feature = "split_off", since = "1.4.0")]
1354 pub fn split_off(&mut self, at: usize) -> Self {
1355 assert!(at <= self.len(), "`at` out of bounds");
1357 let other_len = self.len - at;
1358 let mut other = Vec::with_capacity(other_len);
1360 // Unsafely `set_len` and copy items to `other`.
1363 other.set_len(other_len);
1365 ptr::copy_nonoverlapping(self.as_ptr().add(at),
1372 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1374 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1375 /// difference, with each additional slot filled with the result of
1376 /// calling the closure `f`. The return values from `f` will end up
1377 /// in the `Vec` in the order they have been generated.
1379 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1381 /// This method uses a closure to create new values on every push. If
1382 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1383 /// to use the [`Default`] trait to generate values, you can pass
1384 /// [`Default::default()`] as the second argument.
1389 /// let mut vec = vec![1, 2, 3];
1390 /// vec.resize_with(5, Default::default);
1391 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1393 /// let mut vec = vec![];
1395 /// vec.resize_with(4, || { p *= 2; p });
1396 /// assert_eq!(vec, [2, 4, 8, 16]);
1399 /// [`resize`]: #method.resize
1400 /// [`Clone`]: ../../std/clone/trait.Clone.html
1401 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1402 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1403 where F: FnMut() -> T
1405 let len = self.len();
1407 self.extend_with(new_len - len, ExtendFunc(f));
1409 self.truncate(new_len);
1413 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1414 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1415 /// `'a`. If the type has only static references, or none at all, then this
1416 /// may be chosen to be `'static`.
1418 /// This function is similar to the `leak` function on `Box`.
1420 /// This function is mainly useful for data that lives for the remainder of
1421 /// the program's life. Dropping the returned reference will cause a memory
1429 /// #![feature(vec_leak)]
1431 /// let x = vec![1, 2, 3];
1432 /// let static_ref: &'static mut [usize] = Vec::leak(x);
1433 /// static_ref[0] += 1;
1434 /// assert_eq!(static_ref, &[2, 2, 3]);
1436 #[unstable(feature = "vec_leak", issue = "62195")]
1438 pub fn leak<'a>(vec: Vec<T>) -> &'a mut [T]
1440 T: 'a // Technically not needed, but kept to be explicit.
1442 Box::leak(vec.into_boxed_slice())
1446 impl<T: Clone> Vec<T> {
1447 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1449 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1450 /// difference, with each additional slot filled with `value`.
1451 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1453 /// This method requires [`Clone`] to be able clone the passed value. If
1454 /// you need more flexibility (or want to rely on [`Default`] instead of
1455 /// [`Clone`]), use [`resize_with`].
1460 /// let mut vec = vec!["hello"];
1461 /// vec.resize(3, "world");
1462 /// assert_eq!(vec, ["hello", "world", "world"]);
1464 /// let mut vec = vec![1, 2, 3, 4];
1465 /// vec.resize(2, 0);
1466 /// assert_eq!(vec, [1, 2]);
1469 /// [`Clone`]: ../../std/clone/trait.Clone.html
1470 /// [`Default`]: ../../std/default/trait.Default.html
1471 /// [`resize_with`]: #method.resize_with
1472 #[stable(feature = "vec_resize", since = "1.5.0")]
1473 pub fn resize(&mut self, new_len: usize, value: T) {
1474 let len = self.len();
1477 self.extend_with(new_len - len, ExtendElement(value))
1479 self.truncate(new_len);
1483 /// Clones and appends all elements in a slice to the `Vec`.
1485 /// Iterates over the slice `other`, clones each element, and then appends
1486 /// it to this `Vec`. The `other` vector is traversed in-order.
1488 /// Note that this function is same as [`extend`] except that it is
1489 /// specialized to work with slices instead. If and when Rust gets
1490 /// specialization this function will likely be deprecated (but still
1496 /// let mut vec = vec![1];
1497 /// vec.extend_from_slice(&[2, 3, 4]);
1498 /// assert_eq!(vec, [1, 2, 3, 4]);
1501 /// [`extend`]: #method.extend
1502 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1503 pub fn extend_from_slice(&mut self, other: &[T]) {
1504 self.spec_extend(other.iter())
1508 impl<T: Default> Vec<T> {
1509 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1511 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1512 /// difference, with each additional slot filled with [`Default::default()`].
1513 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1515 /// This method uses [`Default`] to create new values on every push. If
1516 /// you'd rather [`Clone`] a given value, use [`resize`].
1521 /// # #![allow(deprecated)]
1522 /// #![feature(vec_resize_default)]
1524 /// let mut vec = vec![1, 2, 3];
1525 /// vec.resize_default(5);
1526 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1528 /// let mut vec = vec![1, 2, 3, 4];
1529 /// vec.resize_default(2);
1530 /// assert_eq!(vec, [1, 2]);
1533 /// [`resize`]: #method.resize
1534 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1535 /// [`Default`]: ../../std/default/trait.Default.html
1536 /// [`Clone`]: ../../std/clone/trait.Clone.html
1537 #[unstable(feature = "vec_resize_default", issue = "41758")]
1538 #[rustc_deprecated(reason = "This is moving towards being removed in favor \
1539 of `.resize_with(Default::default)`. If you disagree, please comment \
1540 in the tracking issue.", since = "1.33.0")]
1541 pub fn resize_default(&mut self, new_len: usize) {
1542 let len = self.len();
1545 self.extend_with(new_len - len, ExtendDefault);
1547 self.truncate(new_len);
1552 // This code generalises `extend_with_{element,default}`.
1553 trait ExtendWith<T> {
1554 fn next(&mut self) -> T;
1558 struct ExtendElement<T>(T);
1559 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1560 fn next(&mut self) -> T { self.0.clone() }
1561 fn last(self) -> T { self.0 }
1564 struct ExtendDefault;
1565 impl<T: Default> ExtendWith<T> for ExtendDefault {
1566 fn next(&mut self) -> T { Default::default() }
1567 fn last(self) -> T { Default::default() }
1570 struct ExtendFunc<F>(F);
1571 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1572 fn next(&mut self) -> T { (self.0)() }
1573 fn last(mut self) -> T { (self.0)() }
1577 /// Extend the vector by `n` values, using the given generator.
1578 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1582 let mut ptr = self.as_mut_ptr().add(self.len());
1583 // Use SetLenOnDrop to work around bug where compiler
1584 // may not realize the store through `ptr` through self.set_len()
1586 let mut local_len = SetLenOnDrop::new(&mut self.len);
1588 // Write all elements except the last one
1590 ptr::write(ptr, value.next());
1591 ptr = ptr.offset(1);
1592 // Increment the length in every step in case next() panics
1593 local_len.increment_len(1);
1597 // We can write the last element directly without cloning needlessly
1598 ptr::write(ptr, value.last());
1599 local_len.increment_len(1);
1602 // len set by scope guard
1607 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1609 // The idea is: The length field in SetLenOnDrop is a local variable
1610 // that the optimizer will see does not alias with any stores through the Vec's data
1611 // pointer. This is a workaround for alias analysis issue #32155
1612 struct SetLenOnDrop<'a> {
1617 impl<'a> SetLenOnDrop<'a> {
1619 fn new(len: &'a mut usize) -> Self {
1620 SetLenOnDrop { local_len: *len, len: len }
1624 fn increment_len(&mut self, increment: usize) {
1625 self.local_len += increment;
1629 impl Drop for SetLenOnDrop<'_> {
1631 fn drop(&mut self) {
1632 *self.len = self.local_len;
1636 impl<T: PartialEq> Vec<T> {
1637 /// Removes consecutive repeated elements in the vector according to the
1638 /// [`PartialEq`] trait implementation.
1640 /// If the vector is sorted, this removes all duplicates.
1645 /// let mut vec = vec![1, 2, 2, 3, 2];
1649 /// assert_eq!(vec, [1, 2, 3, 2]);
1651 #[stable(feature = "rust1", since = "1.0.0")]
1653 pub fn dedup(&mut self) {
1654 self.dedup_by(|a, b| a == b)
1657 /// Removes the first instance of `item` from the vector if the item exists.
1662 /// # #![feature(vec_remove_item)]
1663 /// let mut vec = vec![1, 2, 3, 1];
1665 /// vec.remove_item(&1);
1667 /// assert_eq!(vec, vec![2, 3, 1]);
1669 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1670 pub fn remove_item(&mut self, item: &T) -> Option<T> {
1671 let pos = self.iter().position(|x| *x == *item)?;
1672 Some(self.remove(pos))
1676 ////////////////////////////////////////////////////////////////////////////////
1677 // Internal methods and functions
1678 ////////////////////////////////////////////////////////////////////////////////
1681 #[stable(feature = "rust1", since = "1.0.0")]
1682 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1683 <T as SpecFromElem>::from_elem(elem, n)
1686 // Specialization trait used for Vec::from_elem
1687 trait SpecFromElem: Sized {
1688 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1691 impl<T: Clone> SpecFromElem for T {
1692 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1693 let mut v = Vec::with_capacity(n);
1694 v.extend_with(n, ExtendElement(elem));
1699 impl SpecFromElem for u8 {
1701 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1704 buf: RawVec::with_capacity_zeroed(n),
1709 let mut v = Vec::with_capacity(n);
1710 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1717 impl<T: Clone + IsZero> SpecFromElem for T {
1719 fn from_elem(elem: T, n: usize) -> Vec<T> {
1722 buf: RawVec::with_capacity_zeroed(n),
1726 let mut v = Vec::with_capacity(n);
1727 v.extend_with(n, ExtendElement(elem));
1732 unsafe trait IsZero {
1733 /// Whether this value is zero
1734 fn is_zero(&self) -> bool;
1737 macro_rules! impl_is_zero {
1738 ($t: ty, $is_zero: expr) => {
1739 unsafe impl IsZero for $t {
1741 fn is_zero(&self) -> bool {
1748 impl_is_zero!(i8, |x| x == 0);
1749 impl_is_zero!(i16, |x| x == 0);
1750 impl_is_zero!(i32, |x| x == 0);
1751 impl_is_zero!(i64, |x| x == 0);
1752 impl_is_zero!(i128, |x| x == 0);
1753 impl_is_zero!(isize, |x| x == 0);
1755 impl_is_zero!(u16, |x| x == 0);
1756 impl_is_zero!(u32, |x| x == 0);
1757 impl_is_zero!(u64, |x| x == 0);
1758 impl_is_zero!(u128, |x| x == 0);
1759 impl_is_zero!(usize, |x| x == 0);
1761 impl_is_zero!(bool, |x| x == false);
1762 impl_is_zero!(char, |x| x == '\0');
1764 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1765 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1767 unsafe impl<T> IsZero for *const T {
1769 fn is_zero(&self) -> bool {
1774 unsafe impl<T> IsZero for *mut T {
1776 fn is_zero(&self) -> bool {
1781 // `Option<&T>`, `Option<&mut T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
1782 // For fat pointers, the bytes that would be the pointer metadata in the `Some` variant
1783 // are padding in the `None` variant, so ignoring them and zero-initializing instead is ok.
1785 unsafe impl<T: ?Sized> IsZero for Option<&T> {
1787 fn is_zero(&self) -> bool {
1792 unsafe impl<T: ?Sized> IsZero for Option<&mut T> {
1794 fn is_zero(&self) -> bool {
1799 unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
1801 fn is_zero(&self) -> bool {
1807 ////////////////////////////////////////////////////////////////////////////////
1808 // Common trait implementations for Vec
1809 ////////////////////////////////////////////////////////////////////////////////
1811 #[stable(feature = "rust1", since = "1.0.0")]
1812 impl<T: Clone> Clone for Vec<T> {
1814 fn clone(&self) -> Vec<T> {
1815 <[T]>::to_vec(&**self)
1818 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1819 // required for this method definition, is not available. Instead use the
1820 // `slice::to_vec` function which is only available with cfg(test)
1821 // NB see the slice::hack module in slice.rs for more information
1823 fn clone(&self) -> Vec<T> {
1824 crate::slice::to_vec(&**self)
1827 fn clone_from(&mut self, other: &Vec<T>) {
1828 other.as_slice().clone_into(self);
1832 #[stable(feature = "rust1", since = "1.0.0")]
1833 impl<T: Hash> Hash for Vec<T> {
1835 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1836 Hash::hash(&**self, state)
1840 #[stable(feature = "rust1", since = "1.0.0")]
1841 #[rustc_on_unimplemented(
1842 message="vector indices are of type `usize` or ranges of `usize`",
1843 label="vector indices are of type `usize` or ranges of `usize`",
1845 impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> {
1846 type Output = I::Output;
1849 fn index(&self, index: I) -> &Self::Output {
1850 Index::index(&**self, index)
1854 #[stable(feature = "rust1", since = "1.0.0")]
1855 #[rustc_on_unimplemented(
1856 message="vector indices are of type `usize` or ranges of `usize`",
1857 label="vector indices are of type `usize` or ranges of `usize`",
1859 impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
1861 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1862 IndexMut::index_mut(&mut **self, index)
1866 #[stable(feature = "rust1", since = "1.0.0")]
1867 impl<T> ops::Deref for Vec<T> {
1870 fn deref(&self) -> &[T] {
1872 slice::from_raw_parts(self.as_ptr(), self.len)
1877 #[stable(feature = "rust1", since = "1.0.0")]
1878 impl<T> ops::DerefMut for Vec<T> {
1879 fn deref_mut(&mut self) -> &mut [T] {
1881 slice::from_raw_parts_mut(self.as_mut_ptr(), self.len)
1886 #[stable(feature = "rust1", since = "1.0.0")]
1887 impl<T> FromIterator<T> for Vec<T> {
1889 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1890 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1894 #[stable(feature = "rust1", since = "1.0.0")]
1895 impl<T> IntoIterator for Vec<T> {
1897 type IntoIter = IntoIter<T>;
1899 /// Creates a consuming iterator, that is, one that moves each value out of
1900 /// the vector (from start to end). The vector cannot be used after calling
1906 /// let v = vec!["a".to_string(), "b".to_string()];
1907 /// for s in v.into_iter() {
1908 /// // s has type String, not &String
1909 /// println!("{}", s);
1913 fn into_iter(mut self) -> IntoIter<T> {
1915 let begin = self.as_mut_ptr();
1916 let end = if mem::size_of::<T>() == 0 {
1917 arith_offset(begin as *const i8, self.len() as isize) as *const T
1919 begin.add(self.len()) as *const T
1921 let cap = self.buf.capacity();
1924 buf: NonNull::new_unchecked(begin),
1925 phantom: PhantomData,
1934 #[stable(feature = "rust1", since = "1.0.0")]
1935 impl<'a, T> IntoIterator for &'a Vec<T> {
1937 type IntoIter = slice::Iter<'a, T>;
1939 fn into_iter(self) -> slice::Iter<'a, T> {
1944 #[stable(feature = "rust1", since = "1.0.0")]
1945 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1946 type Item = &'a mut T;
1947 type IntoIter = slice::IterMut<'a, T>;
1949 fn into_iter(self) -> slice::IterMut<'a, T> {
1954 #[stable(feature = "rust1", since = "1.0.0")]
1955 impl<T> Extend<T> for Vec<T> {
1957 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1958 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1962 // Specialization trait used for Vec::from_iter and Vec::extend
1963 trait SpecExtend<T, I> {
1964 fn from_iter(iter: I) -> Self;
1965 fn spec_extend(&mut self, iter: I);
1968 impl<T, I> SpecExtend<T, I> for Vec<T>
1969 where I: Iterator<Item=T>,
1971 default fn from_iter(mut iterator: I) -> Self {
1972 // Unroll the first iteration, as the vector is going to be
1973 // expanded on this iteration in every case when the iterable is not
1974 // empty, but the loop in extend_desugared() is not going to see the
1975 // vector being full in the few subsequent loop iterations.
1976 // So we get better branch prediction.
1977 let mut vector = match iterator.next() {
1978 None => return Vec::new(),
1980 let (lower, _) = iterator.size_hint();
1981 let mut vector = Vec::with_capacity(lower.saturating_add(1));
1983 ptr::write(vector.get_unchecked_mut(0), element);
1989 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
1993 default fn spec_extend(&mut self, iter: I) {
1994 self.extend_desugared(iter)
1998 impl<T, I> SpecExtend<T, I> for Vec<T>
1999 where I: TrustedLen<Item=T>,
2001 default fn from_iter(iterator: I) -> Self {
2002 let mut vector = Vec::new();
2003 vector.spec_extend(iterator);
2007 default fn spec_extend(&mut self, iterator: I) {
2008 // This is the case for a TrustedLen iterator.
2009 let (low, high) = iterator.size_hint();
2010 if let Some(high_value) = high {
2011 debug_assert_eq!(low, high_value,
2012 "TrustedLen iterator's size hint is not exact: {:?}",
2015 if let Some(additional) = high {
2016 self.reserve(additional);
2018 let mut ptr = self.as_mut_ptr().add(self.len());
2019 let mut local_len = SetLenOnDrop::new(&mut self.len);
2020 iterator.for_each(move |element| {
2021 ptr::write(ptr, element);
2022 ptr = ptr.offset(1);
2023 // NB can't overflow since we would have had to alloc the address space
2024 local_len.increment_len(1);
2028 self.extend_desugared(iterator)
2033 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
2034 fn from_iter(iterator: IntoIter<T>) -> Self {
2035 // A common case is passing a vector into a function which immediately
2036 // re-collects into a vector. We can short circuit this if the IntoIter
2037 // has not been advanced at all.
2038 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
2040 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
2043 mem::forget(iterator);
2047 let mut vector = Vec::new();
2048 vector.spec_extend(iterator);
2053 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
2055 self.append_elements(iterator.as_slice() as _);
2057 iterator.ptr = iterator.end;
2061 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
2062 where I: Iterator<Item=&'a T>,
2065 default fn from_iter(iterator: I) -> Self {
2066 SpecExtend::from_iter(iterator.cloned())
2069 default fn spec_extend(&mut self, iterator: I) {
2070 self.spec_extend(iterator.cloned())
2074 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
2077 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
2078 let slice = iterator.as_slice();
2079 self.reserve(slice.len());
2081 let len = self.len();
2082 self.set_len(len + slice.len());
2083 self.get_unchecked_mut(len..).copy_from_slice(slice);
2089 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2090 // This is the case for a general iterator.
2092 // This function should be the moral equivalent of:
2094 // for item in iterator {
2097 while let Some(element) = iterator.next() {
2098 let len = self.len();
2099 if len == self.capacity() {
2100 let (lower, _) = iterator.size_hint();
2101 self.reserve(lower.saturating_add(1));
2104 ptr::write(self.get_unchecked_mut(len), element);
2105 // NB can't overflow since we would have had to alloc the address space
2106 self.set_len(len + 1);
2111 /// Creates a splicing iterator that replaces the specified range in the vector
2112 /// with the given `replace_with` iterator and yields the removed items.
2113 /// `replace_with` does not need to be the same length as `range`.
2115 /// The element range is removed even if the iterator is not consumed until the end.
2117 /// It is unspecified how many elements are removed from the vector
2118 /// if the `Splice` value is leaked.
2120 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2122 /// This is optimal if:
2124 /// * The tail (elements in the vector after `range`) is empty,
2125 /// * or `replace_with` yields fewer elements than `range`’s length
2126 /// * or the lower bound of its `size_hint()` is exact.
2128 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2132 /// Panics if the starting point is greater than the end point or if
2133 /// the end point is greater than the length of the vector.
2138 /// let mut v = vec![1, 2, 3];
2139 /// let new = [7, 8];
2140 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2141 /// assert_eq!(v, &[7, 8, 3]);
2142 /// assert_eq!(u, &[1, 2]);
2145 #[stable(feature = "vec_splice", since = "1.21.0")]
2146 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
2147 where R: RangeBounds<usize>, I: IntoIterator<Item=T>
2150 drain: self.drain(range),
2151 replace_with: replace_with.into_iter(),
2155 /// Creates an iterator which uses a closure to determine if an element should be removed.
2157 /// If the closure returns true, then the element is removed and yielded.
2158 /// If the closure returns false, the element will remain in the vector and will not be yielded
2159 /// by the iterator.
2161 /// Using this method is equivalent to the following code:
2164 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2165 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2167 /// while i != vec.len() {
2168 /// if some_predicate(&mut vec[i]) {
2169 /// let val = vec.remove(i);
2170 /// // your code here
2176 /// # assert_eq!(vec, vec![1, 4, 5]);
2179 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2180 /// because it can backshift the elements of the array in bulk.
2182 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2183 /// regardless of whether you choose to keep or remove it.
2188 /// Splitting an array into evens and odds, reusing the original allocation:
2191 /// #![feature(drain_filter)]
2192 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2194 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2195 /// let odds = numbers;
2197 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2198 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2200 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2201 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
2202 where F: FnMut(&mut T) -> bool,
2204 let old_len = self.len();
2206 // Guard against us getting leaked (leak amplification)
2207 unsafe { self.set_len(0); }
2220 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2222 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2223 /// append the entire slice at once.
2225 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2226 #[stable(feature = "extend_ref", since = "1.2.0")]
2227 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2228 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2229 self.spec_extend(iter.into_iter())
2233 macro_rules! __impl_slice_eq1 {
2234 ([$($vars:tt)*] $lhs:ty, $rhs:ty, $($constraints:tt)*) => {
2235 #[stable(feature = "rust1", since = "1.0.0")]
2236 impl<A, B, $($vars)*> PartialEq<$rhs> for $lhs
2242 fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
2244 fn ne(&self, other: &$rhs) -> bool { self[..] != other[..] }
2249 __impl_slice_eq1! { [] Vec<A>, Vec<B>, }
2250 __impl_slice_eq1! { [] Vec<A>, &[B], }
2251 __impl_slice_eq1! { [] Vec<A>, &mut [B], }
2252 __impl_slice_eq1! { [] Cow<'_, [A]>, &[B], A: Clone }
2253 __impl_slice_eq1! { [] Cow<'_, [A]>, &mut [B], A: Clone }
2254 __impl_slice_eq1! { [] Cow<'_, [A]>, Vec<B>, A: Clone }
2255 __impl_slice_eq1! { [const N: usize] Vec<A>, [B; N], [B; N]: LengthAtMost32 }
2256 __impl_slice_eq1! { [const N: usize] Vec<A>, &[B; N], [B; N]: LengthAtMost32 }
2258 // NOTE: some less important impls are omitted to reduce code bloat
2259 // FIXME(Centril): Reconsider this?
2260 //__impl_slice_eq1! { [const N: usize] Vec<A>, &mut [B; N], [B; N]: LengthAtMost32 }
2261 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, [B; N], [B; N]: LengthAtMost32 }
2262 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &[B; N], [B; N]: LengthAtMost32 }
2263 //__impl_slice_eq1! { [const N: usize] Cow<'a, [A]>, &mut [B; N], [B; N]: LengthAtMost32 }
2265 /// Implements comparison of vectors, lexicographically.
2266 #[stable(feature = "rust1", since = "1.0.0")]
2267 impl<T: PartialOrd> PartialOrd for Vec<T> {
2269 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2270 PartialOrd::partial_cmp(&**self, &**other)
2274 #[stable(feature = "rust1", since = "1.0.0")]
2275 impl<T: Eq> Eq for Vec<T> {}
2277 /// Implements ordering of vectors, lexicographically.
2278 #[stable(feature = "rust1", since = "1.0.0")]
2279 impl<T: Ord> Ord for Vec<T> {
2281 fn cmp(&self, other: &Vec<T>) -> Ordering {
2282 Ord::cmp(&**self, &**other)
2286 #[stable(feature = "rust1", since = "1.0.0")]
2287 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2288 fn drop(&mut self) {
2291 ptr::drop_in_place(&mut self[..]);
2293 // RawVec handles deallocation
2297 #[stable(feature = "rust1", since = "1.0.0")]
2298 impl<T> Default for Vec<T> {
2299 /// Creates an empty `Vec<T>`.
2300 fn default() -> Vec<T> {
2305 #[stable(feature = "rust1", since = "1.0.0")]
2306 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2307 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2308 fmt::Debug::fmt(&**self, f)
2312 #[stable(feature = "rust1", since = "1.0.0")]
2313 impl<T> AsRef<Vec<T>> for Vec<T> {
2314 fn as_ref(&self) -> &Vec<T> {
2319 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2320 impl<T> AsMut<Vec<T>> for Vec<T> {
2321 fn as_mut(&mut self) -> &mut Vec<T> {
2326 #[stable(feature = "rust1", since = "1.0.0")]
2327 impl<T> AsRef<[T]> for Vec<T> {
2328 fn as_ref(&self) -> &[T] {
2333 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2334 impl<T> AsMut<[T]> for Vec<T> {
2335 fn as_mut(&mut self) -> &mut [T] {
2340 #[stable(feature = "rust1", since = "1.0.0")]
2341 impl<T: Clone> From<&[T]> for Vec<T> {
2343 fn from(s: &[T]) -> Vec<T> {
2347 fn from(s: &[T]) -> Vec<T> {
2348 crate::slice::to_vec(s)
2352 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2353 impl<T: Clone> From<&mut [T]> for Vec<T> {
2355 fn from(s: &mut [T]) -> Vec<T> {
2359 fn from(s: &mut [T]) -> Vec<T> {
2360 crate::slice::to_vec(s)
2364 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2365 impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
2366 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2371 // note: test pulls in libstd, which causes errors here
2373 #[stable(feature = "vec_from_box", since = "1.18.0")]
2374 impl<T> From<Box<[T]>> for Vec<T> {
2375 fn from(s: Box<[T]>) -> Vec<T> {
2380 // note: test pulls in libstd, which causes errors here
2382 #[stable(feature = "box_from_vec", since = "1.20.0")]
2383 impl<T> From<Vec<T>> for Box<[T]> {
2384 fn from(v: Vec<T>) -> Box<[T]> {
2385 v.into_boxed_slice()
2389 #[stable(feature = "rust1", since = "1.0.0")]
2390 impl From<&str> for Vec<u8> {
2391 fn from(s: &str) -> Vec<u8> {
2392 From::from(s.as_bytes())
2396 ////////////////////////////////////////////////////////////////////////////////
2398 ////////////////////////////////////////////////////////////////////////////////
2400 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2401 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2402 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2407 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2408 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2409 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2414 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2415 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2416 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2417 Cow::Borrowed(v.as_slice())
2421 #[stable(feature = "rust1", since = "1.0.0")]
2422 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
2423 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2424 Cow::Owned(FromIterator::from_iter(it))
2428 ////////////////////////////////////////////////////////////////////////////////
2430 ////////////////////////////////////////////////////////////////////////////////
2432 /// An iterator that moves out of a vector.
2434 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
2435 /// by the [`IntoIterator`] trait).
2437 /// [`Vec`]: struct.Vec.html
2438 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2439 #[stable(feature = "rust1", since = "1.0.0")]
2440 pub struct IntoIter<T> {
2442 phantom: PhantomData<T>,
2448 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2449 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2450 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2451 f.debug_tuple("IntoIter")
2452 .field(&self.as_slice())
2457 impl<T> IntoIter<T> {
2458 /// Returns the remaining items of this iterator as a slice.
2463 /// let vec = vec!['a', 'b', 'c'];
2464 /// let mut into_iter = vec.into_iter();
2465 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2466 /// let _ = into_iter.next().unwrap();
2467 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2469 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2470 pub fn as_slice(&self) -> &[T] {
2472 slice::from_raw_parts(self.ptr, self.len())
2476 /// Returns the remaining items of this iterator as a mutable 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 /// into_iter.as_mut_slice()[2] = 'z';
2485 /// assert_eq!(into_iter.next().unwrap(), 'a');
2486 /// assert_eq!(into_iter.next().unwrap(), 'b');
2487 /// assert_eq!(into_iter.next().unwrap(), 'z');
2489 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2490 pub fn as_mut_slice(&mut self) -> &mut [T] {
2492 slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
2497 #[stable(feature = "rust1", since = "1.0.0")]
2498 unsafe impl<T: Send> Send for IntoIter<T> {}
2499 #[stable(feature = "rust1", since = "1.0.0")]
2500 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2502 #[stable(feature = "rust1", since = "1.0.0")]
2503 impl<T> Iterator for IntoIter<T> {
2507 fn next(&mut self) -> Option<T> {
2509 if self.ptr as *const _ == self.end {
2512 if mem::size_of::<T>() == 0 {
2513 // purposefully don't use 'ptr.offset' because for
2514 // vectors with 0-size elements this would return the
2516 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2518 // Make up a value of this ZST.
2522 self.ptr = self.ptr.offset(1);
2524 Some(ptr::read(old))
2531 fn size_hint(&self) -> (usize, Option<usize>) {
2532 let exact = if mem::size_of::<T>() == 0 {
2533 (self.end as usize).wrapping_sub(self.ptr as usize)
2535 unsafe { self.end.offset_from(self.ptr) as usize }
2537 (exact, Some(exact))
2541 fn count(self) -> usize {
2546 #[stable(feature = "rust1", since = "1.0.0")]
2547 impl<T> DoubleEndedIterator for IntoIter<T> {
2549 fn next_back(&mut self) -> Option<T> {
2551 if self.end == self.ptr {
2554 if mem::size_of::<T>() == 0 {
2555 // See above for why 'ptr.offset' isn't used
2556 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2558 // Make up a value of this ZST.
2561 self.end = self.end.offset(-1);
2563 Some(ptr::read(self.end))
2570 #[stable(feature = "rust1", since = "1.0.0")]
2571 impl<T> ExactSizeIterator for IntoIter<T> {
2572 fn is_empty(&self) -> bool {
2573 self.ptr == self.end
2577 #[stable(feature = "fused", since = "1.26.0")]
2578 impl<T> FusedIterator for IntoIter<T> {}
2580 #[unstable(feature = "trusted_len", issue = "37572")]
2581 unsafe impl<T> TrustedLen for IntoIter<T> {}
2583 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2584 impl<T: Clone> Clone for IntoIter<T> {
2585 fn clone(&self) -> IntoIter<T> {
2586 self.as_slice().to_owned().into_iter()
2590 #[stable(feature = "rust1", since = "1.0.0")]
2591 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2592 fn drop(&mut self) {
2593 // destroy the remaining elements
2594 for _x in self.by_ref() {}
2596 // RawVec handles deallocation
2597 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2601 /// A draining iterator for `Vec<T>`.
2603 /// This `struct` is created by the [`drain`] method on [`Vec`].
2605 /// [`drain`]: struct.Vec.html#method.drain
2606 /// [`Vec`]: struct.Vec.html
2607 #[stable(feature = "drain", since = "1.6.0")]
2608 pub struct Drain<'a, T: 'a> {
2609 /// Index of tail to preserve
2613 /// Current remaining range to remove
2614 iter: slice::Iter<'a, T>,
2615 vec: NonNull<Vec<T>>,
2618 #[stable(feature = "collection_debug", since = "1.17.0")]
2619 impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
2620 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2621 f.debug_tuple("Drain")
2622 .field(&self.iter.as_slice())
2627 impl<'a, T> Drain<'a, T> {
2628 /// Returns the remaining items of this iterator as a slice.
2633 /// # #![feature(vec_drain_as_slice)]
2634 /// let mut vec = vec!['a', 'b', 'c'];
2635 /// let mut drain = vec.drain(..);
2636 /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']);
2637 /// let _ = drain.next().unwrap();
2638 /// assert_eq!(drain.as_slice(), &['b', 'c']);
2640 #[unstable(feature = "vec_drain_as_slice", reason = "recently added", issue = "58957")]
2641 pub fn as_slice(&self) -> &[T] {
2642 self.iter.as_slice()
2646 #[stable(feature = "drain", since = "1.6.0")]
2647 unsafe impl<T: Sync> Sync for Drain<'_, T> {}
2648 #[stable(feature = "drain", since = "1.6.0")]
2649 unsafe impl<T: Send> Send for Drain<'_, T> {}
2651 #[stable(feature = "drain", since = "1.6.0")]
2652 impl<T> Iterator for Drain<'_, T> {
2656 fn next(&mut self) -> Option<T> {
2657 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2660 fn size_hint(&self) -> (usize, Option<usize>) {
2661 self.iter.size_hint()
2665 #[stable(feature = "drain", since = "1.6.0")]
2666 impl<T> DoubleEndedIterator for Drain<'_, T> {
2668 fn next_back(&mut self) -> Option<T> {
2669 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2673 #[stable(feature = "drain", since = "1.6.0")]
2674 impl<T> Drop for Drain<'_, T> {
2675 fn drop(&mut self) {
2676 // exhaust self first
2677 self.for_each(drop);
2679 if self.tail_len > 0 {
2681 let source_vec = self.vec.as_mut();
2682 // memmove back untouched tail, update to new length
2683 let start = source_vec.len();
2684 let tail = self.tail_start;
2686 let src = source_vec.as_ptr().add(tail);
2687 let dst = source_vec.as_mut_ptr().add(start);
2688 ptr::copy(src, dst, self.tail_len);
2690 source_vec.set_len(start + self.tail_len);
2697 #[stable(feature = "drain", since = "1.6.0")]
2698 impl<T> ExactSizeIterator for Drain<'_, T> {
2699 fn is_empty(&self) -> bool {
2700 self.iter.is_empty()
2704 #[stable(feature = "fused", since = "1.26.0")]
2705 impl<T> FusedIterator for Drain<'_, T> {}
2707 /// A splicing iterator for `Vec`.
2709 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2710 /// documentation for more.
2712 /// [`splice()`]: struct.Vec.html#method.splice
2713 /// [`Vec`]: struct.Vec.html
2715 #[stable(feature = "vec_splice", since = "1.21.0")]
2716 pub struct Splice<'a, I: Iterator + 'a> {
2717 drain: Drain<'a, I::Item>,
2721 #[stable(feature = "vec_splice", since = "1.21.0")]
2722 impl<I: Iterator> Iterator for Splice<'_, I> {
2723 type Item = I::Item;
2725 fn next(&mut self) -> Option<Self::Item> {
2729 fn size_hint(&self) -> (usize, Option<usize>) {
2730 self.drain.size_hint()
2734 #[stable(feature = "vec_splice", since = "1.21.0")]
2735 impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
2736 fn next_back(&mut self) -> Option<Self::Item> {
2737 self.drain.next_back()
2741 #[stable(feature = "vec_splice", since = "1.21.0")]
2742 impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}
2745 #[stable(feature = "vec_splice", since = "1.21.0")]
2746 impl<I: Iterator> Drop for Splice<'_, I> {
2747 fn drop(&mut self) {
2748 self.drain.by_ref().for_each(drop);
2751 if self.drain.tail_len == 0 {
2752 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2756 // First fill the range left by drain().
2757 if !self.drain.fill(&mut self.replace_with) {
2761 // There may be more elements. Use the lower bound as an estimate.
2762 // FIXME: Is the upper bound a better guess? Or something else?
2763 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2764 if lower_bound > 0 {
2765 self.drain.move_tail(lower_bound);
2766 if !self.drain.fill(&mut self.replace_with) {
2771 // Collect any remaining elements.
2772 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2773 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2774 // Now we have an exact count.
2775 if collected.len() > 0 {
2776 self.drain.move_tail(collected.len());
2777 let filled = self.drain.fill(&mut collected);
2778 debug_assert!(filled);
2779 debug_assert_eq!(collected.len(), 0);
2782 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2786 /// Private helper methods for `Splice::drop`
2787 impl<T> Drain<'_, T> {
2788 /// The range from `self.vec.len` to `self.tail_start` contains elements
2789 /// that have been moved out.
2790 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2791 /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2792 unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
2793 let vec = self.vec.as_mut();
2794 let range_start = vec.len;
2795 let range_end = self.tail_start;
2796 let range_slice = slice::from_raw_parts_mut(
2797 vec.as_mut_ptr().add(range_start),
2798 range_end - range_start);
2800 for place in range_slice {
2801 if let Some(new_item) = replace_with.next() {
2802 ptr::write(place, new_item);
2811 /// Makes room for inserting more elements before the tail.
2812 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2813 let vec = self.vec.as_mut();
2814 let used_capacity = self.tail_start + self.tail_len;
2815 vec.buf.reserve(used_capacity, extra_capacity);
2817 let new_tail_start = self.tail_start + extra_capacity;
2818 let src = vec.as_ptr().add(self.tail_start);
2819 let dst = vec.as_mut_ptr().add(new_tail_start);
2820 ptr::copy(src, dst, self.tail_len);
2821 self.tail_start = new_tail_start;
2825 /// An iterator produced by calling `drain_filter` on Vec.
2826 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2828 pub struct DrainFilter<'a, T, F>
2829 where F: FnMut(&mut T) -> bool,
2831 vec: &'a mut Vec<T>,
2832 /// The index of the item that will be inspected by the next call to `next`.
2834 /// The number of items that have been drained (removed) thus far.
2836 /// The original length of `vec` prior to draining.
2838 /// The filter test predicate.
2840 /// A flag that indicates a panic has occured in the filter test prodicate.
2841 /// This is used as a hint in the drop implmentation to prevent consumption
2842 /// of the remainder of the `DrainFilter`. Any unprocessed items will be
2843 /// backshifted in the `vec`, but no further items will be dropped or
2844 /// tested by the filter predicate.
2848 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2849 impl<T, F> Iterator for DrainFilter<'_, T, F>
2850 where F: FnMut(&mut T) -> bool,
2854 fn next(&mut self) -> Option<T> {
2856 while self.idx < self.old_len {
2858 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2859 self.panic_flag = true;
2860 let drained = (self.pred)(&mut v[i]);
2861 self.panic_flag = false;
2862 // Update the index *after* the predicate is called. If the index
2863 // is updated prior and the predicate panics, the element at this
2864 // index would be leaked.
2868 return Some(ptr::read(&v[i]));
2869 } else if self.del > 0 {
2871 let src: *const T = &v[i];
2872 let dst: *mut T = &mut v[i - del];
2873 ptr::copy_nonoverlapping(src, dst, 1);
2880 fn size_hint(&self) -> (usize, Option<usize>) {
2881 (0, Some(self.old_len - self.idx))
2885 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2886 impl<T, F> Drop for DrainFilter<'_, T, F>
2887 where F: FnMut(&mut T) -> bool,
2889 fn drop(&mut self) {
2890 struct BackshiftOnDrop<'a, 'b, T, F>
2892 F: FnMut(&mut T) -> bool,
2894 drain: &'b mut DrainFilter<'a, T, F>,
2897 impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F>
2899 F: FnMut(&mut T) -> bool
2901 fn drop(&mut self) {
2903 if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
2904 // This is a pretty messed up state, and there isn't really an
2905 // obviously right thing to do. We don't want to keep trying
2906 // to execute `pred`, so we just backshift all the unprocessed
2907 // elements and tell the vec that they still exist. The backshift
2908 // is required to prevent a double-drop of the last successfully
2909 // drained item prior to a panic in the predicate.
2910 let ptr = self.drain.vec.as_mut_ptr();
2911 let src = ptr.add(self.drain.idx);
2912 let dst = src.sub(self.drain.del);
2913 let tail_len = self.drain.old_len - self.drain.idx;
2914 src.copy_to(dst, tail_len);
2916 self.drain.vec.set_len(self.drain.old_len - self.drain.del);
2921 let backshift = BackshiftOnDrop {
2925 // Attempt to consume any remaining elements if the filter predicate
2926 // has not yet panicked. We'll backshift any remaining elements
2927 // whether we've already panicked or if the consumption here panics.
2928 if !backshift.drain.panic_flag {
2929 backshift.drain.for_each(drop);