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::cmp::{self, Ordering};
61 use core::hash::{self, Hash};
62 use core::intrinsics::{arith_offset, assume};
63 use core::iter::{FromIterator, FusedIterator, TrustedLen};
64 use core::marker::PhantomData;
66 use core::ops::{self, Index, IndexMut, RangeBounds};
67 use core::ops::Bound::{Excluded, Included, Unbounded};
68 use core::ptr::{self, NonNull};
69 use core::slice::{self, SliceIndex};
71 use crate::borrow::{ToOwned, Cow};
72 use crate::collections::CollectionAllocErr;
73 use crate::boxed::Box;
74 use crate::raw_vec::RawVec;
76 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
81 /// let mut vec = Vec::new();
85 /// assert_eq!(vec.len(), 2);
86 /// assert_eq!(vec[0], 1);
88 /// assert_eq!(vec.pop(), Some(2));
89 /// assert_eq!(vec.len(), 1);
92 /// assert_eq!(vec[0], 7);
94 /// vec.extend([1, 2, 3].iter().cloned());
97 /// println!("{}", x);
99 /// assert_eq!(vec, [7, 1, 2, 3]);
102 /// The [`vec!`] macro is provided to make initialization more convenient:
105 /// let mut vec = vec![1, 2, 3];
107 /// assert_eq!(vec, [1, 2, 3, 4]);
110 /// It can also initialize each element of a `Vec<T>` with a given value.
111 /// This may be more efficient than performing allocation and initialization
112 /// in separate steps, especially when initializing a vector of zeros:
115 /// let vec = vec![0; 5];
116 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
118 /// // The following is equivalent, but potentially slower:
119 /// let mut vec1 = Vec::with_capacity(5);
120 /// vec1.resize(5, 0);
123 /// Use a `Vec<T>` as an efficient stack:
126 /// let mut stack = Vec::new();
132 /// while let Some(top) = stack.pop() {
133 /// // Prints 3, 2, 1
134 /// println!("{}", top);
140 /// The `Vec` type allows to access values by index, because it implements the
141 /// [`Index`] trait. An example will be more explicit:
144 /// let v = vec![0, 2, 4, 6];
145 /// println!("{}", v[1]); // it will display '2'
148 /// However be careful: if you try to access an index which isn't in the `Vec`,
149 /// your software will panic! You cannot do this:
152 /// let v = vec![0, 2, 4, 6];
153 /// println!("{}", v[6]); // it will panic!
156 /// In conclusion: always check if the index you want to get really exists
161 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
162 /// To get a slice, use `&`. Example:
165 /// fn read_slice(slice: &[usize]) {
169 /// let v = vec![0, 1];
172 /// // ... and that's all!
173 /// // you can also do it like this:
174 /// let x : &[usize] = &v;
177 /// In Rust, it's more common to pass slices as arguments rather than vectors
178 /// when you just want to provide a read access. The same goes for [`String`] and
181 /// # Capacity and reallocation
183 /// The capacity of a vector is the amount of space allocated for any future
184 /// elements that will be added onto the vector. This is not to be confused with
185 /// the *length* of a vector, which specifies the number of actual elements
186 /// within the vector. If a vector's length exceeds its capacity, its capacity
187 /// will automatically be increased, but its elements will have to be
190 /// For example, a vector with capacity 10 and length 0 would be an empty vector
191 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
192 /// vector will not change its capacity or cause reallocation to occur. However,
193 /// if the vector's length is increased to 11, it will have to reallocate, which
194 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
195 /// whenever possible to specify how big the vector is expected to get.
199 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
200 /// about its design. This ensures that it's as low-overhead as possible in
201 /// the general case, and can be correctly manipulated in primitive ways
202 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
203 /// If additional type parameters are added (e.g., to support custom allocators),
204 /// overriding their defaults may change the behavior.
206 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
207 /// triplet. No more, no less. The order of these fields is completely
208 /// unspecified, and you should use the appropriate methods to modify these.
209 /// The pointer will never be null, so this type is null-pointer-optimized.
211 /// However, the pointer may not actually point to allocated memory. In particular,
212 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
213 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
214 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
215 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
216 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
217 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
218 /// details are very subtle — if you intend to allocate memory using a `Vec`
219 /// and use it for something else (either to pass to unsafe code, or to build your
220 /// own memory-backed collection), be sure to deallocate this memory by using
221 /// `from_raw_parts` to recover the `Vec` and then dropping it.
223 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
224 /// (as defined by the allocator Rust is configured to use by default), and its
225 /// pointer points to [`len`] initialized, contiguous elements in order (what
226 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
227 /// `[`len`] logically uninitialized, contiguous elements.
229 /// `Vec` will never perform a "small optimization" where elements are actually
230 /// stored on the stack for two reasons:
232 /// * It would make it more difficult for unsafe code to correctly manipulate
233 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
234 /// only moved, and it would be more difficult to determine if a `Vec` had
235 /// actually allocated memory.
237 /// * It would penalize the general case, incurring an additional branch
240 /// `Vec` will never automatically shrink itself, even if completely empty. This
241 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
242 /// and then filling it back up to the same [`len`] should incur no calls to
243 /// the allocator. If you wish to free up unused memory, use
244 /// [`shrink_to_fit`][`shrink_to_fit`].
246 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
247 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
248 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
249 /// accurate, and can be relied on. It can even be used to manually free the memory
250 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
251 /// when not necessary.
253 /// `Vec` does not guarantee any particular growth strategy when reallocating
254 /// when full, nor when [`reserve`] is called. The current strategy is basic
255 /// and it may prove desirable to use a non-constant growth factor. Whatever
256 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
258 /// `vec![x; n]`, `vec![a, b, c, d]`, and
259 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
260 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
261 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
262 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
264 /// `Vec` will not specifically overwrite any data that is removed from it,
265 /// but also won't specifically preserve it. Its uninitialized memory is
266 /// scratch space that it may use however it wants. It will generally just do
267 /// whatever is most efficient or otherwise easy to implement. Do not rely on
268 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
269 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
270 /// first, that may not actually happen because the optimizer does not consider
271 /// this a side-effect that must be preserved. There is one case which we will
272 /// not break, however: using `unsafe` code to write to the excess capacity,
273 /// and then increasing the length to match, is always valid.
275 /// `Vec` does not currently guarantee the order in which elements are dropped.
276 /// The order has changed in the past and may change again.
278 /// [`vec!`]: ../../std/macro.vec.html
279 /// [`Index`]: ../../std/ops/trait.Index.html
280 /// [`String`]: ../../std/string/struct.String.html
281 /// [`&str`]: ../../std/primitive.str.html
282 /// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
283 /// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
284 /// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
285 /// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
286 /// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
287 /// [`len`]: ../../std/vec/struct.Vec.html#method.len
288 /// [`push`]: ../../std/vec/struct.Vec.html#method.push
289 /// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
290 /// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
291 /// [owned slice]: ../../std/boxed/struct.Box.html
292 #[stable(feature = "rust1", since = "1.0.0")]
298 ////////////////////////////////////////////////////////////////////////////////
300 ////////////////////////////////////////////////////////////////////////////////
303 /// Constructs a new, empty `Vec<T>`.
305 /// The vector will not allocate until elements are pushed onto it.
310 /// # #![allow(unused_mut)]
311 /// let mut vec: Vec<i32> = Vec::new();
314 #[stable(feature = "rust1", since = "1.0.0")]
315 #[rustc_const_unstable(feature = "const_vec_new")]
316 pub const fn new() -> Vec<T> {
323 /// Constructs a new, empty `Vec<T>` with the specified capacity.
325 /// The vector will be able to hold exactly `capacity` elements without
326 /// reallocating. If `capacity` is 0, the vector will not allocate.
328 /// It is important to note that although the returned vector has the
329 /// *capacity* specified, the vector will have a zero *length*. For an
330 /// explanation of the difference between length and capacity, see
331 /// *[Capacity and reallocation]*.
333 /// [Capacity and reallocation]: #capacity-and-reallocation
338 /// let mut vec = Vec::with_capacity(10);
340 /// // The vector contains no items, even though it has capacity for more
341 /// assert_eq!(vec.len(), 0);
343 /// // These are all done without reallocating...
348 /// // ...but this may make the vector reallocate
352 #[stable(feature = "rust1", since = "1.0.0")]
353 pub fn with_capacity(capacity: usize) -> Vec<T> {
355 buf: RawVec::with_capacity(capacity),
360 /// Creates a `Vec<T>` directly from the raw components of another vector.
364 /// This is highly unsafe, due to the number of invariants that aren't
367 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
368 /// (at least, it's highly likely to be incorrect if it wasn't).
369 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
370 /// * `length` needs to be less than or equal to `capacity`.
371 /// * `capacity` needs to be the capacity that the pointer was allocated with.
373 /// Violating these may cause problems like corrupting the allocator's
374 /// internal data structures. For example it is **not** safe
375 /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
377 /// The ownership of `ptr` is effectively transferred to the
378 /// `Vec<T>` which may then deallocate, reallocate or change the
379 /// contents of memory pointed to by the pointer at will. Ensure
380 /// that nothing else uses the pointer after calling this
383 /// [`String`]: ../../std/string/struct.String.html
392 /// let mut v = vec![1, 2, 3];
394 /// // Pull out the various important pieces of information about `v`
395 /// let p = v.as_mut_ptr();
396 /// let len = v.len();
397 /// let cap = v.capacity();
400 /// // Cast `v` into the void: no destructor run, so we are in
401 /// // complete control of the allocation to which `p` points.
404 /// // Overwrite memory with 4, 5, 6
405 /// for i in 0..len as isize {
406 /// ptr::write(p.offset(i), 4 + i);
409 /// // Put everything back together into a Vec
410 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
411 /// assert_eq!(rebuilt, [4, 5, 6]);
415 #[stable(feature = "rust1", since = "1.0.0")]
416 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
418 buf: RawVec::from_raw_parts(ptr, capacity),
423 /// Returns the number of elements the vector can hold without
429 /// let vec: Vec<i32> = Vec::with_capacity(10);
430 /// assert_eq!(vec.capacity(), 10);
433 #[stable(feature = "rust1", since = "1.0.0")]
434 pub fn capacity(&self) -> usize {
438 /// Reserves capacity for at least `additional` more elements to be inserted
439 /// in the given `Vec<T>`. The collection may reserve more space to avoid
440 /// frequent reallocations. After calling `reserve`, capacity will be
441 /// greater than or equal to `self.len() + additional`. Does nothing if
442 /// capacity is already sufficient.
446 /// Panics if the new capacity overflows `usize`.
451 /// let mut vec = vec![1];
453 /// assert!(vec.capacity() >= 11);
455 #[stable(feature = "rust1", since = "1.0.0")]
456 pub fn reserve(&mut self, additional: usize) {
457 self.buf.reserve(self.len, additional);
460 /// Reserves the minimum capacity for exactly `additional` more elements to
461 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
462 /// capacity will be greater than or equal to `self.len() + additional`.
463 /// Does nothing if the capacity is already sufficient.
465 /// Note that the allocator may give the collection more space than it
466 /// requests. Therefore, capacity can not be relied upon to be precisely
467 /// minimal. Prefer `reserve` if future insertions are expected.
471 /// Panics if the new capacity overflows `usize`.
476 /// let mut vec = vec![1];
477 /// vec.reserve_exact(10);
478 /// assert!(vec.capacity() >= 11);
480 #[stable(feature = "rust1", since = "1.0.0")]
481 pub fn reserve_exact(&mut self, additional: usize) {
482 self.buf.reserve_exact(self.len, additional);
485 /// Tries to reserve capacity for at least `additional` more elements to be inserted
486 /// in the given `Vec<T>`. The collection may reserve more space to avoid
487 /// frequent reallocations. After calling `reserve`, capacity will be
488 /// greater than or equal to `self.len() + additional`. Does nothing if
489 /// capacity is already sufficient.
493 /// If the capacity overflows, or the allocator reports a failure, then an error
499 /// #![feature(try_reserve)]
500 /// use std::collections::CollectionAllocErr;
502 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
503 /// let mut output = Vec::new();
505 /// // Pre-reserve the memory, exiting if we can't
506 /// output.try_reserve(data.len())?;
508 /// // Now we know this can't OOM in the middle of our complex work
509 /// output.extend(data.iter().map(|&val| {
510 /// val * 2 + 5 // very complicated
515 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
517 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
518 pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
519 self.buf.try_reserve(self.len, additional)
522 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
523 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
524 /// capacity will be greater than or equal to `self.len() + additional`.
525 /// Does nothing if the capacity is already sufficient.
527 /// Note that the allocator may give the collection more space than it
528 /// requests. Therefore, capacity can not be relied upon to be precisely
529 /// minimal. Prefer `reserve` if future insertions are expected.
533 /// If the capacity overflows, or the allocator reports a failure, then an error
539 /// #![feature(try_reserve)]
540 /// use std::collections::CollectionAllocErr;
542 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
543 /// let mut output = Vec::new();
545 /// // Pre-reserve the memory, exiting if we can't
546 /// output.try_reserve(data.len())?;
548 /// // Now we know this can't OOM in the middle of our complex work
549 /// output.extend(data.iter().map(|&val| {
550 /// val * 2 + 5 // very complicated
555 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
557 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
558 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
559 self.buf.try_reserve_exact(self.len, additional)
562 /// Shrinks the capacity of the vector as much as possible.
564 /// It will drop down as close as possible to the length but the allocator
565 /// may still inform the vector that there is space for a few more elements.
570 /// let mut vec = Vec::with_capacity(10);
571 /// vec.extend([1, 2, 3].iter().cloned());
572 /// assert_eq!(vec.capacity(), 10);
573 /// vec.shrink_to_fit();
574 /// assert!(vec.capacity() >= 3);
576 #[stable(feature = "rust1", since = "1.0.0")]
577 pub fn shrink_to_fit(&mut self) {
578 if self.capacity() != self.len {
579 self.buf.shrink_to_fit(self.len);
583 /// Shrinks the capacity of the vector with a lower bound.
585 /// The capacity will remain at least as large as both the length
586 /// and the supplied value.
588 /// Panics if the current capacity is smaller than the supplied
589 /// minimum capacity.
594 /// #![feature(shrink_to)]
595 /// let mut vec = Vec::with_capacity(10);
596 /// vec.extend([1, 2, 3].iter().cloned());
597 /// assert_eq!(vec.capacity(), 10);
598 /// vec.shrink_to(4);
599 /// assert!(vec.capacity() >= 4);
600 /// vec.shrink_to(0);
601 /// assert!(vec.capacity() >= 3);
603 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
604 pub fn shrink_to(&mut self, min_capacity: usize) {
605 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
608 /// Converts the vector into [`Box<[T]>`][owned slice].
610 /// Note that this will drop any excess capacity.
612 /// [owned slice]: ../../std/boxed/struct.Box.html
617 /// let v = vec![1, 2, 3];
619 /// let slice = v.into_boxed_slice();
622 /// Any excess capacity is removed:
625 /// let mut vec = Vec::with_capacity(10);
626 /// vec.extend([1, 2, 3].iter().cloned());
628 /// assert_eq!(vec.capacity(), 10);
629 /// let slice = vec.into_boxed_slice();
630 /// assert_eq!(slice.into_vec().capacity(), 3);
632 #[stable(feature = "rust1", since = "1.0.0")]
633 pub fn into_boxed_slice(mut self) -> Box<[T]> {
635 self.shrink_to_fit();
636 let buf = ptr::read(&self.buf);
642 /// Shortens the vector, keeping the first `len` elements and dropping
645 /// If `len` is greater than the vector's current length, this has no
648 /// The [`drain`] method can emulate `truncate`, but causes the excess
649 /// elements to be returned instead of dropped.
651 /// Note that this method has no effect on the allocated capacity
656 /// Truncating a five element vector to two elements:
659 /// let mut vec = vec![1, 2, 3, 4, 5];
661 /// assert_eq!(vec, [1, 2]);
664 /// No truncation occurs when `len` is greater than the vector's current
668 /// let mut vec = vec![1, 2, 3];
670 /// assert_eq!(vec, [1, 2, 3]);
673 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
677 /// let mut vec = vec![1, 2, 3];
679 /// assert_eq!(vec, []);
682 /// [`clear`]: #method.clear
683 /// [`drain`]: #method.drain
684 #[stable(feature = "rust1", since = "1.0.0")]
685 pub fn truncate(&mut self, len: usize) {
686 let current_len = self.len;
688 let mut ptr = self.as_mut_ptr().add(self.len);
689 // Set the final length at the end, keeping in mind that
690 // dropping an element might panic. Works around a missed
691 // optimization, as seen in the following issue:
692 // https://github.com/rust-lang/rust/issues/51802
693 let mut local_len = SetLenOnDrop::new(&mut self.len);
695 // drop any extra elements
696 for _ in len..current_len {
697 local_len.decrement_len(1);
698 ptr = ptr.offset(-1);
699 ptr::drop_in_place(ptr);
704 /// Extracts a slice containing the entire vector.
706 /// Equivalent to `&s[..]`.
711 /// use std::io::{self, Write};
712 /// let buffer = vec![1, 2, 3, 5, 8];
713 /// io::sink().write(buffer.as_slice()).unwrap();
716 #[stable(feature = "vec_as_slice", since = "1.7.0")]
717 pub fn as_slice(&self) -> &[T] {
721 /// Extracts a mutable slice of the entire vector.
723 /// Equivalent to `&mut s[..]`.
728 /// use std::io::{self, Read};
729 /// let mut buffer = vec![0; 3];
730 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
733 #[stable(feature = "vec_as_slice", since = "1.7.0")]
734 pub fn as_mut_slice(&mut self) -> &mut [T] {
738 /// Forces the length of the vector to `new_len`.
740 /// This is a low-level operation that maintains none of the normal
741 /// invariants of the type. Normally changing the length of a vector
742 /// is done using one of the safe operations instead, such as
743 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
745 /// [`truncate`]: #method.truncate
746 /// [`resize`]: #method.resize
747 /// [`extend`]: #method.extend-1
748 /// [`clear`]: #method.clear
752 /// - `new_len` must be less than or equal to [`capacity()`].
753 /// - The elements at `old_len..new_len` must be initialized.
755 /// [`capacity()`]: #method.capacity
759 /// This method can be useful for situations in which the vector
760 /// is serving as a buffer for other code, particularly over FFI:
763 /// # #![allow(dead_code)]
764 /// # // This is just a minimal skeleton for the doc example;
765 /// # // don't use this as a starting point for a real library.
766 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
767 /// # const Z_OK: i32 = 0;
769 /// # fn deflateGetDictionary(
770 /// # strm: *mut std::ffi::c_void,
771 /// # dictionary: *mut u8,
772 /// # dictLength: *mut usize,
775 /// # impl StreamWrapper {
776 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
777 /// // Per the FFI method's docs, "32768 bytes is always enough".
778 /// let mut dict = Vec::with_capacity(32_768);
779 /// let mut dict_length = 0;
780 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
781 /// // 1. `dict_length` elements were initialized.
782 /// // 2. `dict_length` <= the capacity (32_768)
783 /// // which makes `set_len` safe to call.
785 /// // Make the FFI call...
786 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
788 /// // ...and update the length to what was initialized.
789 /// dict.set_len(dict_length);
799 /// While the following example is sound, there is a memory leak since
800 /// the inner vectors were not freed prior to the `set_len` call:
803 /// let mut vec = vec![vec![1, 0, 0],
807 /// // 1. `old_len..0` is empty so no elements need to be initialized.
808 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
814 /// Normally, here, one would use [`clear`] instead to correctly drop
815 /// the contents and thus not leak memory.
817 #[stable(feature = "rust1", since = "1.0.0")]
818 pub unsafe fn set_len(&mut self, new_len: usize) {
819 debug_assert!(new_len <= self.capacity());
824 /// Removes an element from the vector and returns it.
826 /// The removed element is replaced by the last element of the vector.
828 /// This does not preserve ordering, but is O(1).
832 /// Panics if `index` is out of bounds.
837 /// let mut v = vec!["foo", "bar", "baz", "qux"];
839 /// assert_eq!(v.swap_remove(1), "bar");
840 /// assert_eq!(v, ["foo", "qux", "baz"]);
842 /// assert_eq!(v.swap_remove(0), "foo");
843 /// assert_eq!(v, ["baz", "qux"]);
846 #[stable(feature = "rust1", since = "1.0.0")]
847 pub fn swap_remove(&mut self, index: usize) -> T {
849 // We replace self[index] with the last element. Note that if the
850 // bounds check on hole succeeds there must be a last element (which
851 // can be self[index] itself).
852 let hole: *mut T = &mut self[index];
853 let last = ptr::read(self.get_unchecked(self.len - 1));
855 ptr::replace(hole, last)
859 /// Inserts an element at position `index` within the vector, shifting all
860 /// elements after it to the right.
864 /// Panics if `index > len`.
869 /// let mut vec = vec![1, 2, 3];
870 /// vec.insert(1, 4);
871 /// assert_eq!(vec, [1, 4, 2, 3]);
872 /// vec.insert(4, 5);
873 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
875 #[stable(feature = "rust1", since = "1.0.0")]
876 pub fn insert(&mut self, index: usize, element: T) {
877 let len = self.len();
878 assert!(index <= len);
880 // space for the new element
881 if len == self.buf.cap() {
887 // The spot to put the new value
889 let p = self.as_mut_ptr().add(index);
890 // Shift everything over to make space. (Duplicating the
891 // `index`th element into two consecutive places.)
892 ptr::copy(p, p.offset(1), len - index);
893 // Write it in, overwriting the first copy of the `index`th
895 ptr::write(p, element);
897 self.set_len(len + 1);
901 /// Removes and returns the element at position `index` within the vector,
902 /// shifting all elements after it to the left.
906 /// Panics if `index` is out of bounds.
911 /// let mut v = vec![1, 2, 3];
912 /// assert_eq!(v.remove(1), 2);
913 /// assert_eq!(v, [1, 3]);
915 #[stable(feature = "rust1", since = "1.0.0")]
916 pub fn remove(&mut self, index: usize) -> T {
917 let len = self.len();
918 assert!(index < len);
923 // the place we are taking from.
924 let ptr = self.as_mut_ptr().add(index);
925 // copy it out, unsafely having a copy of the value on
926 // the stack and in the vector at the same time.
927 ret = ptr::read(ptr);
929 // Shift everything down to fill in that spot.
930 ptr::copy(ptr.offset(1), ptr, len - index - 1);
932 self.set_len(len - 1);
937 /// Retains only the elements specified by the predicate.
939 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
940 /// This method operates in place and preserves the order of the retained
946 /// let mut vec = vec![1, 2, 3, 4];
947 /// vec.retain(|&x| x%2 == 0);
948 /// assert_eq!(vec, [2, 4]);
950 #[stable(feature = "rust1", since = "1.0.0")]
951 pub fn retain<F>(&mut self, mut f: F)
952 where F: FnMut(&T) -> bool
954 self.drain_filter(|x| !f(x));
957 /// Removes all but the first of consecutive elements in the vector that resolve to the same
960 /// If the vector is sorted, this removes all duplicates.
965 /// let mut vec = vec![10, 20, 21, 30, 20];
967 /// vec.dedup_by_key(|i| *i / 10);
969 /// assert_eq!(vec, [10, 20, 30, 20]);
971 #[stable(feature = "dedup_by", since = "1.16.0")]
973 pub fn dedup_by_key<F, K>(&mut self, mut key: F) where F: FnMut(&mut T) -> K, K: PartialEq {
974 self.dedup_by(|a, b| key(a) == key(b))
977 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
980 /// The `same_bucket` function is passed references to two elements from the vector and
981 /// must determine if the elements compare equal. The elements are passed in opposite order
982 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
984 /// If the vector is sorted, this removes all duplicates.
989 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
991 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
993 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
995 #[stable(feature = "dedup_by", since = "1.16.0")]
996 pub fn dedup_by<F>(&mut self, same_bucket: F) where F: FnMut(&mut T, &mut T) -> bool {
998 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
1004 /// Appends an element to the back of a collection.
1008 /// Panics if the number of elements in the vector overflows a `usize`.
1013 /// let mut vec = vec![1, 2];
1015 /// assert_eq!(vec, [1, 2, 3]);
1018 #[stable(feature = "rust1", since = "1.0.0")]
1019 pub fn push(&mut self, value: T) {
1020 // This will panic or abort if we would allocate > isize::MAX bytes
1021 // or if the length increment would overflow for zero-sized types.
1022 if self.len == self.buf.cap() {
1026 let end = self.as_mut_ptr().add(self.len);
1027 ptr::write(end, value);
1032 /// Removes the last element from a vector and returns it, or [`None`] if it
1035 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1040 /// let mut vec = vec![1, 2, 3];
1041 /// assert_eq!(vec.pop(), Some(3));
1042 /// assert_eq!(vec, [1, 2]);
1045 #[stable(feature = "rust1", since = "1.0.0")]
1046 pub fn pop(&mut self) -> Option<T> {
1052 Some(ptr::read(self.get_unchecked(self.len())))
1057 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1061 /// Panics if the number of elements in the vector overflows a `usize`.
1066 /// let mut vec = vec![1, 2, 3];
1067 /// let mut vec2 = vec![4, 5, 6];
1068 /// vec.append(&mut vec2);
1069 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1070 /// assert_eq!(vec2, []);
1073 #[stable(feature = "append", since = "1.4.0")]
1074 pub fn append(&mut self, other: &mut Self) {
1076 self.append_elements(other.as_slice() as _);
1081 /// Appends elements to `Self` from other buffer.
1083 unsafe fn append_elements(&mut self, other: *const [T]) {
1084 let count = (*other).len();
1085 self.reserve(count);
1086 let len = self.len();
1087 ptr::copy_nonoverlapping(other as *const T, self.get_unchecked_mut(len), count);
1091 /// Creates a draining iterator that removes the specified range in the vector
1092 /// and yields the removed items.
1094 /// Note 1: The element range is removed even if the iterator is only
1095 /// partially consumed or not consumed at all.
1097 /// Note 2: It is unspecified how many elements are removed from the vector
1098 /// if the `Drain` value is leaked.
1102 /// Panics if the starting point is greater than the end point or if
1103 /// the end point is greater than the length of the vector.
1108 /// let mut v = vec![1, 2, 3];
1109 /// let u: Vec<_> = v.drain(1..).collect();
1110 /// assert_eq!(v, &[1]);
1111 /// assert_eq!(u, &[2, 3]);
1113 /// // A full range clears the vector
1115 /// assert_eq!(v, &[]);
1117 #[stable(feature = "drain", since = "1.6.0")]
1118 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1119 where R: RangeBounds<usize>
1123 // When the Drain is first created, it shortens the length of
1124 // the source vector to make sure no uninitialized or moved-from elements
1125 // are accessible at all if the Drain's destructor never gets to run.
1127 // Drain will ptr::read out the values to remove.
1128 // When finished, remaining tail of the vec is copied back to cover
1129 // the hole, and the vector length is restored to the new length.
1131 let len = self.len();
1132 let start = match range.start_bound() {
1134 Excluded(&n) => n + 1,
1137 let end = match range.end_bound() {
1138 Included(&n) => n + 1,
1142 assert!(start <= end);
1143 assert!(end <= len);
1146 // set self.vec length's to start, to be safe in case Drain is leaked
1147 self.set_len(start);
1148 // Use the borrow in the IterMut to indicate borrowing behavior of the
1149 // whole Drain iterator (like &mut T).
1150 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start),
1154 tail_len: len - end,
1155 iter: range_slice.iter(),
1156 vec: NonNull::from(self),
1161 /// Clears the vector, removing all values.
1163 /// Note that this method has no effect on the allocated capacity
1169 /// let mut v = vec![1, 2, 3];
1173 /// assert!(v.is_empty());
1176 #[stable(feature = "rust1", since = "1.0.0")]
1177 pub fn clear(&mut self) {
1181 /// Returns the number of elements in the vector, also referred to
1182 /// as its 'length'.
1187 /// let a = vec![1, 2, 3];
1188 /// assert_eq!(a.len(), 3);
1191 #[stable(feature = "rust1", since = "1.0.0")]
1192 pub fn len(&self) -> usize {
1196 /// Returns `true` if the vector contains no elements.
1201 /// let mut v = Vec::new();
1202 /// assert!(v.is_empty());
1205 /// assert!(!v.is_empty());
1207 #[stable(feature = "rust1", since = "1.0.0")]
1208 pub fn is_empty(&self) -> bool {
1212 /// Splits the collection into two at the given index.
1214 /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
1215 /// and the returned `Self` contains elements `[at, len)`.
1217 /// Note that the capacity of `self` does not change.
1221 /// Panics if `at > len`.
1226 /// let mut vec = vec![1,2,3];
1227 /// let vec2 = vec.split_off(1);
1228 /// assert_eq!(vec, [1]);
1229 /// assert_eq!(vec2, [2, 3]);
1232 #[stable(feature = "split_off", since = "1.4.0")]
1233 pub fn split_off(&mut self, at: usize) -> Self {
1234 assert!(at <= self.len(), "`at` out of bounds");
1236 let other_len = self.len - at;
1237 let mut other = Vec::with_capacity(other_len);
1239 // Unsafely `set_len` and copy items to `other`.
1242 other.set_len(other_len);
1244 ptr::copy_nonoverlapping(self.as_ptr().add(at),
1251 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1253 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1254 /// difference, with each additional slot filled with the result of
1255 /// calling the closure `f`. The return values from `f` will end up
1256 /// in the `Vec` in the order they have been generated.
1258 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1260 /// This method uses a closure to create new values on every push. If
1261 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1262 /// to use the [`Default`] trait to generate values, you can pass
1263 /// [`Default::default()`] as the second argument..
1268 /// let mut vec = vec![1, 2, 3];
1269 /// vec.resize_with(5, Default::default);
1270 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1272 /// let mut vec = vec![];
1274 /// vec.resize_with(4, || { p *= 2; p });
1275 /// assert_eq!(vec, [2, 4, 8, 16]);
1278 /// [`resize`]: #method.resize
1279 /// [`Clone`]: ../../std/clone/trait.Clone.html
1280 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1281 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1282 where F: FnMut() -> T
1284 let len = self.len();
1286 self.extend_with(new_len - len, ExtendFunc(f));
1288 self.truncate(new_len);
1293 impl<T: Clone> Vec<T> {
1294 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1296 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1297 /// difference, with each additional slot filled with `value`.
1298 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1300 /// This method requires [`Clone`] to be able clone the passed value. If
1301 /// you need more flexibility (or want to rely on [`Default`] instead of
1302 /// [`Clone`]), use [`resize_with`].
1307 /// let mut vec = vec!["hello"];
1308 /// vec.resize(3, "world");
1309 /// assert_eq!(vec, ["hello", "world", "world"]);
1311 /// let mut vec = vec![1, 2, 3, 4];
1312 /// vec.resize(2, 0);
1313 /// assert_eq!(vec, [1, 2]);
1316 /// [`Clone`]: ../../std/clone/trait.Clone.html
1317 /// [`Default`]: ../../std/default/trait.Default.html
1318 /// [`resize_with`]: #method.resize_with
1319 #[stable(feature = "vec_resize", since = "1.5.0")]
1320 pub fn resize(&mut self, new_len: usize, value: T) {
1321 let len = self.len();
1324 self.extend_with(new_len - len, ExtendElement(value))
1326 self.truncate(new_len);
1330 /// Clones and appends all elements in a slice to the `Vec`.
1332 /// Iterates over the slice `other`, clones each element, and then appends
1333 /// it to this `Vec`. The `other` vector is traversed in-order.
1335 /// Note that this function is same as [`extend`] except that it is
1336 /// specialized to work with slices instead. If and when Rust gets
1337 /// specialization this function will likely be deprecated (but still
1343 /// let mut vec = vec![1];
1344 /// vec.extend_from_slice(&[2, 3, 4]);
1345 /// assert_eq!(vec, [1, 2, 3, 4]);
1348 /// [`extend`]: #method.extend
1349 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1350 pub fn extend_from_slice(&mut self, other: &[T]) {
1351 self.spec_extend(other.iter())
1355 impl<T: Default> Vec<T> {
1356 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1358 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1359 /// difference, with each additional slot filled with [`Default::default()`].
1360 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1362 /// This method uses [`Default`] to create new values on every push. If
1363 /// you'd rather [`Clone`] a given value, use [`resize`].
1368 /// # #![allow(deprecated)]
1369 /// #![feature(vec_resize_default)]
1371 /// let mut vec = vec![1, 2, 3];
1372 /// vec.resize_default(5);
1373 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1375 /// let mut vec = vec![1, 2, 3, 4];
1376 /// vec.resize_default(2);
1377 /// assert_eq!(vec, [1, 2]);
1380 /// [`resize`]: #method.resize
1381 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1382 /// [`Default`]: ../../std/default/trait.Default.html
1383 /// [`Clone`]: ../../std/clone/trait.Clone.html
1384 #[unstable(feature = "vec_resize_default", issue = "41758")]
1385 #[rustc_deprecated(reason = "This is moving towards being removed in favor \
1386 of `.resize_with(Default::default)`. If you disagree, please comment \
1387 in the tracking issue.", since = "1.33.0")]
1388 pub fn resize_default(&mut self, new_len: usize) {
1389 let len = self.len();
1392 self.extend_with(new_len - len, ExtendDefault);
1394 self.truncate(new_len);
1399 // This code generalises `extend_with_{element,default}`.
1400 trait ExtendWith<T> {
1401 fn next(&mut self) -> T;
1405 struct ExtendElement<T>(T);
1406 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1407 fn next(&mut self) -> T { self.0.clone() }
1408 fn last(self) -> T { self.0 }
1411 struct ExtendDefault;
1412 impl<T: Default> ExtendWith<T> for ExtendDefault {
1413 fn next(&mut self) -> T { Default::default() }
1414 fn last(self) -> T { Default::default() }
1417 struct ExtendFunc<F>(F);
1418 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1419 fn next(&mut self) -> T { (self.0)() }
1420 fn last(mut self) -> T { (self.0)() }
1424 /// Extend the vector by `n` values, using the given generator.
1425 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1429 let mut ptr = self.as_mut_ptr().add(self.len());
1430 // Use SetLenOnDrop to work around bug where compiler
1431 // may not realize the store through `ptr` through self.set_len()
1433 let mut local_len = SetLenOnDrop::new(&mut self.len);
1435 // Write all elements except the last one
1437 ptr::write(ptr, value.next());
1438 ptr = ptr.offset(1);
1439 // Increment the length in every step in case next() panics
1440 local_len.increment_len(1);
1444 // We can write the last element directly without cloning needlessly
1445 ptr::write(ptr, value.last());
1446 local_len.increment_len(1);
1449 // len set by scope guard
1454 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1456 // The idea is: The length field in SetLenOnDrop is a local variable
1457 // that the optimizer will see does not alias with any stores through the Vec's data
1458 // pointer. This is a workaround for alias analysis issue #32155
1459 struct SetLenOnDrop<'a> {
1464 impl<'a> SetLenOnDrop<'a> {
1466 fn new(len: &'a mut usize) -> Self {
1467 SetLenOnDrop { local_len: *len, len: len }
1471 fn increment_len(&mut self, increment: usize) {
1472 self.local_len += increment;
1476 fn decrement_len(&mut self, decrement: usize) {
1477 self.local_len -= decrement;
1481 impl Drop for SetLenOnDrop<'_> {
1483 fn drop(&mut self) {
1484 *self.len = self.local_len;
1488 impl<T: PartialEq> Vec<T> {
1489 /// Removes consecutive repeated elements in the vector according to the
1490 /// [`PartialEq`] trait implementation.
1492 /// If the vector is sorted, this removes all duplicates.
1497 /// let mut vec = vec![1, 2, 2, 3, 2];
1501 /// assert_eq!(vec, [1, 2, 3, 2]);
1503 #[stable(feature = "rust1", since = "1.0.0")]
1505 pub fn dedup(&mut self) {
1506 self.dedup_by(|a, b| a == b)
1509 /// Removes the first instance of `item` from the vector if the item exists.
1514 /// # #![feature(vec_remove_item)]
1515 /// let mut vec = vec![1, 2, 3, 1];
1517 /// vec.remove_item(&1);
1519 /// assert_eq!(vec, vec![2, 3, 1]);
1521 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1522 pub fn remove_item(&mut self, item: &T) -> Option<T> {
1523 let pos = self.iter().position(|x| *x == *item)?;
1524 Some(self.remove(pos))
1528 ////////////////////////////////////////////////////////////////////////////////
1529 // Internal methods and functions
1530 ////////////////////////////////////////////////////////////////////////////////
1533 #[stable(feature = "rust1", since = "1.0.0")]
1534 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1535 <T as SpecFromElem>::from_elem(elem, n)
1538 // Specialization trait used for Vec::from_elem
1539 trait SpecFromElem: Sized {
1540 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1543 impl<T: Clone> SpecFromElem for T {
1544 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1545 let mut v = Vec::with_capacity(n);
1546 v.extend_with(n, ExtendElement(elem));
1551 impl SpecFromElem for u8 {
1553 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1556 buf: RawVec::with_capacity_zeroed(n),
1561 let mut v = Vec::with_capacity(n);
1562 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1569 impl<T: Clone + IsZero> SpecFromElem for T {
1571 fn from_elem(elem: T, n: usize) -> Vec<T> {
1574 buf: RawVec::with_capacity_zeroed(n),
1578 let mut v = Vec::with_capacity(n);
1579 v.extend_with(n, ExtendElement(elem));
1584 unsafe trait IsZero {
1585 /// Whether this value is zero
1586 fn is_zero(&self) -> bool;
1589 macro_rules! impl_is_zero {
1590 ($t: ty, $is_zero: expr) => {
1591 unsafe impl IsZero for $t {
1593 fn is_zero(&self) -> bool {
1600 impl_is_zero!(i8, |x| x == 0);
1601 impl_is_zero!(i16, |x| x == 0);
1602 impl_is_zero!(i32, |x| x == 0);
1603 impl_is_zero!(i64, |x| x == 0);
1604 impl_is_zero!(i128, |x| x == 0);
1605 impl_is_zero!(isize, |x| x == 0);
1607 impl_is_zero!(u16, |x| x == 0);
1608 impl_is_zero!(u32, |x| x == 0);
1609 impl_is_zero!(u64, |x| x == 0);
1610 impl_is_zero!(u128, |x| x == 0);
1611 impl_is_zero!(usize, |x| x == 0);
1613 impl_is_zero!(bool, |x| x == false);
1614 impl_is_zero!(char, |x| x == '\0');
1616 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1617 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1619 unsafe impl<T: ?Sized> IsZero for *const T {
1621 fn is_zero(&self) -> bool {
1626 unsafe impl<T: ?Sized> IsZero for *mut T {
1628 fn is_zero(&self) -> bool {
1634 ////////////////////////////////////////////////////////////////////////////////
1635 // Common trait implementations for Vec
1636 ////////////////////////////////////////////////////////////////////////////////
1638 #[stable(feature = "rust1", since = "1.0.0")]
1639 impl<T: Clone> Clone for Vec<T> {
1641 fn clone(&self) -> Vec<T> {
1642 <[T]>::to_vec(&**self)
1645 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1646 // required for this method definition, is not available. Instead use the
1647 // `slice::to_vec` function which is only available with cfg(test)
1648 // NB see the slice::hack module in slice.rs for more information
1650 fn clone(&self) -> Vec<T> {
1651 crate::slice::to_vec(&**self)
1654 fn clone_from(&mut self, other: &Vec<T>) {
1655 other.as_slice().clone_into(self);
1659 #[stable(feature = "rust1", since = "1.0.0")]
1660 impl<T: Hash> Hash for Vec<T> {
1662 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1663 Hash::hash(&**self, state)
1667 #[stable(feature = "rust1", since = "1.0.0")]
1668 #[rustc_on_unimplemented(
1669 message="vector indices are of type `usize` or ranges of `usize`",
1670 label="vector indices are of type `usize` or ranges of `usize`",
1672 impl<T, I: SliceIndex<[T]>> Index<I> for Vec<T> {
1673 type Output = I::Output;
1676 fn index(&self, index: I) -> &Self::Output {
1677 Index::index(&**self, index)
1681 #[stable(feature = "rust1", since = "1.0.0")]
1682 #[rustc_on_unimplemented(
1683 message="vector indices are of type `usize` or ranges of `usize`",
1684 label="vector indices are of type `usize` or ranges of `usize`",
1686 impl<T, I: SliceIndex<[T]>> IndexMut<I> for Vec<T> {
1688 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1689 IndexMut::index_mut(&mut **self, index)
1693 #[stable(feature = "rust1", since = "1.0.0")]
1694 impl<T> ops::Deref for Vec<T> {
1697 fn deref(&self) -> &[T] {
1699 let p = self.buf.ptr();
1700 assume(!p.is_null());
1701 slice::from_raw_parts(p, self.len)
1706 #[stable(feature = "rust1", since = "1.0.0")]
1707 impl<T> ops::DerefMut for Vec<T> {
1708 fn deref_mut(&mut self) -> &mut [T] {
1710 let ptr = self.buf.ptr();
1711 assume(!ptr.is_null());
1712 slice::from_raw_parts_mut(ptr, self.len)
1717 #[stable(feature = "rust1", since = "1.0.0")]
1718 impl<T> FromIterator<T> for Vec<T> {
1720 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1721 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1725 #[stable(feature = "rust1", since = "1.0.0")]
1726 impl<T> IntoIterator for Vec<T> {
1728 type IntoIter = IntoIter<T>;
1730 /// Creates a consuming iterator, that is, one that moves each value out of
1731 /// the vector (from start to end). The vector cannot be used after calling
1737 /// let v = vec!["a".to_string(), "b".to_string()];
1738 /// for s in v.into_iter() {
1739 /// // s has type String, not &String
1740 /// println!("{}", s);
1744 fn into_iter(mut self) -> IntoIter<T> {
1746 let begin = self.as_mut_ptr();
1747 assume(!begin.is_null());
1748 let end = if mem::size_of::<T>() == 0 {
1749 arith_offset(begin as *const i8, self.len() as isize) as *const T
1751 begin.add(self.len()) as *const T
1753 let cap = self.buf.cap();
1756 buf: NonNull::new_unchecked(begin),
1757 phantom: PhantomData,
1766 #[stable(feature = "rust1", since = "1.0.0")]
1767 impl<'a, T> IntoIterator for &'a Vec<T> {
1769 type IntoIter = slice::Iter<'a, T>;
1771 fn into_iter(self) -> slice::Iter<'a, T> {
1776 #[stable(feature = "rust1", since = "1.0.0")]
1777 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1778 type Item = &'a mut T;
1779 type IntoIter = slice::IterMut<'a, T>;
1781 fn into_iter(self) -> slice::IterMut<'a, T> {
1786 #[stable(feature = "rust1", since = "1.0.0")]
1787 impl<T> Extend<T> for Vec<T> {
1789 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1790 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1794 // Specialization trait used for Vec::from_iter and Vec::extend
1795 trait SpecExtend<T, I> {
1796 fn from_iter(iter: I) -> Self;
1797 fn spec_extend(&mut self, iter: I);
1800 impl<T, I> SpecExtend<T, I> for Vec<T>
1801 where I: Iterator<Item=T>,
1803 default fn from_iter(mut iterator: I) -> Self {
1804 // Unroll the first iteration, as the vector is going to be
1805 // expanded on this iteration in every case when the iterable is not
1806 // empty, but the loop in extend_desugared() is not going to see the
1807 // vector being full in the few subsequent loop iterations.
1808 // So we get better branch prediction.
1809 let mut vector = match iterator.next() {
1810 None => return Vec::new(),
1812 let (lower, _) = iterator.size_hint();
1813 let mut vector = Vec::with_capacity(lower.saturating_add(1));
1815 ptr::write(vector.get_unchecked_mut(0), element);
1821 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
1825 default fn spec_extend(&mut self, iter: I) {
1826 self.extend_desugared(iter)
1830 impl<T, I> SpecExtend<T, I> for Vec<T>
1831 where I: TrustedLen<Item=T>,
1833 default fn from_iter(iterator: I) -> Self {
1834 let mut vector = Vec::new();
1835 vector.spec_extend(iterator);
1839 default fn spec_extend(&mut self, iterator: I) {
1840 // This is the case for a TrustedLen iterator.
1841 let (low, high) = iterator.size_hint();
1842 if let Some(high_value) = high {
1843 debug_assert_eq!(low, high_value,
1844 "TrustedLen iterator's size hint is not exact: {:?}",
1847 if let Some(additional) = high {
1848 self.reserve(additional);
1850 let mut ptr = self.as_mut_ptr().add(self.len());
1851 let mut local_len = SetLenOnDrop::new(&mut self.len);
1852 iterator.for_each(move |element| {
1853 ptr::write(ptr, element);
1854 ptr = ptr.offset(1);
1855 // NB can't overflow since we would have had to alloc the address space
1856 local_len.increment_len(1);
1860 self.extend_desugared(iterator)
1865 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
1866 fn from_iter(iterator: IntoIter<T>) -> Self {
1867 // A common case is passing a vector into a function which immediately
1868 // re-collects into a vector. We can short circuit this if the IntoIter
1869 // has not been advanced at all.
1870 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
1872 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
1875 mem::forget(iterator);
1879 let mut vector = Vec::new();
1880 vector.spec_extend(iterator);
1885 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
1887 self.append_elements(iterator.as_slice() as _);
1889 iterator.ptr = iterator.end;
1893 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
1894 where I: Iterator<Item=&'a T>,
1897 default fn from_iter(iterator: I) -> Self {
1898 SpecExtend::from_iter(iterator.cloned())
1901 default fn spec_extend(&mut self, iterator: I) {
1902 self.spec_extend(iterator.cloned())
1906 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
1909 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
1910 let slice = iterator.as_slice();
1911 self.reserve(slice.len());
1913 let len = self.len();
1914 self.set_len(len + slice.len());
1915 self.get_unchecked_mut(len..).copy_from_slice(slice);
1921 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
1922 // This is the case for a general iterator.
1924 // This function should be the moral equivalent of:
1926 // for item in iterator {
1929 while let Some(element) = iterator.next() {
1930 let len = self.len();
1931 if len == self.capacity() {
1932 let (lower, _) = iterator.size_hint();
1933 self.reserve(lower.saturating_add(1));
1936 ptr::write(self.get_unchecked_mut(len), element);
1937 // NB can't overflow since we would have had to alloc the address space
1938 self.set_len(len + 1);
1943 /// Creates a splicing iterator that replaces the specified range in the vector
1944 /// with the given `replace_with` iterator and yields the removed items.
1945 /// `replace_with` does not need to be the same length as `range`.
1947 /// Note 1: The element range is removed even if the iterator is not
1948 /// consumed until the end.
1950 /// Note 2: It is unspecified how many elements are removed from the vector,
1951 /// if the `Splice` value is leaked.
1953 /// Note 3: The input iterator `replace_with` is only consumed
1954 /// when the `Splice` value is dropped.
1956 /// Note 4: This is optimal if:
1958 /// * The tail (elements in the vector after `range`) is empty,
1959 /// * or `replace_with` yields fewer elements than `range`’s length
1960 /// * or the lower bound of its `size_hint()` is exact.
1962 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
1966 /// Panics if the starting point is greater than the end point or if
1967 /// the end point is greater than the length of the vector.
1972 /// let mut v = vec![1, 2, 3];
1973 /// let new = [7, 8];
1974 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
1975 /// assert_eq!(v, &[7, 8, 3]);
1976 /// assert_eq!(u, &[1, 2]);
1979 #[stable(feature = "vec_splice", since = "1.21.0")]
1980 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
1981 where R: RangeBounds<usize>, I: IntoIterator<Item=T>
1984 drain: self.drain(range),
1985 replace_with: replace_with.into_iter(),
1989 /// Creates an iterator which uses a closure to determine if an element should be removed.
1991 /// If the closure returns true, then the element is removed and yielded.
1992 /// If the closure returns false, the element will remain in the vector and will not be yielded
1993 /// by the iterator.
1995 /// Using this method is equivalent to the following code:
1998 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
1999 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2001 /// while i != vec.len() {
2002 /// if some_predicate(&mut vec[i]) {
2003 /// let val = vec.remove(i);
2004 /// // your code here
2010 /// # assert_eq!(vec, vec![1, 4, 5]);
2013 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2014 /// because it can backshift the elements of the array in bulk.
2016 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2017 /// regardless of whether you choose to keep or remove it.
2022 /// Splitting an array into evens and odds, reusing the original allocation:
2025 /// #![feature(drain_filter)]
2026 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2028 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2029 /// let odds = numbers;
2031 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2032 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2034 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2035 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
2036 where F: FnMut(&mut T) -> bool,
2038 let old_len = self.len();
2040 // Guard against us getting leaked (leak amplification)
2041 unsafe { self.set_len(0); }
2053 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2055 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2056 /// append the entire slice at once.
2058 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2059 #[stable(feature = "extend_ref", since = "1.2.0")]
2060 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2061 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2062 self.spec_extend(iter.into_iter())
2066 macro_rules! __impl_slice_eq1 {
2067 ($Lhs: ty, $Rhs: ty) => {
2068 __impl_slice_eq1! { $Lhs, $Rhs, Sized }
2070 ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
2071 #[stable(feature = "rust1", since = "1.0.0")]
2072 impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
2074 fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
2076 fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
2081 __impl_slice_eq1! { Vec<A>, Vec<B> }
2082 __impl_slice_eq1! { Vec<A>, &'b [B] }
2083 __impl_slice_eq1! { Vec<A>, &'b mut [B] }
2084 __impl_slice_eq1! { Cow<'a, [A]>, &'b [B], Clone }
2085 __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B], Clone }
2086 __impl_slice_eq1! { Cow<'a, [A]>, Vec<B>, Clone }
2088 macro_rules! array_impls {
2091 // NOTE: some less important impls are omitted to reduce code bloat
2092 __impl_slice_eq1! { Vec<A>, [B; $N] }
2093 __impl_slice_eq1! { Vec<A>, &'b [B; $N] }
2094 // __impl_slice_eq1! { Vec<A>, &'b mut [B; $N] }
2095 // __impl_slice_eq1! { Cow<'a, [A]>, [B; $N], Clone }
2096 // __impl_slice_eq1! { Cow<'a, [A]>, &'b [B; $N], Clone }
2097 // __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B; $N], Clone }
2104 10 11 12 13 14 15 16 17 18 19
2105 20 21 22 23 24 25 26 27 28 29
2109 /// Implements comparison of vectors, lexicographically.
2110 #[stable(feature = "rust1", since = "1.0.0")]
2111 impl<T: PartialOrd> PartialOrd for Vec<T> {
2113 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2114 PartialOrd::partial_cmp(&**self, &**other)
2118 #[stable(feature = "rust1", since = "1.0.0")]
2119 impl<T: Eq> Eq for Vec<T> {}
2121 /// Implements ordering of vectors, lexicographically.
2122 #[stable(feature = "rust1", since = "1.0.0")]
2123 impl<T: Ord> Ord for Vec<T> {
2125 fn cmp(&self, other: &Vec<T>) -> Ordering {
2126 Ord::cmp(&**self, &**other)
2130 #[stable(feature = "rust1", since = "1.0.0")]
2131 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2132 fn drop(&mut self) {
2135 ptr::drop_in_place(&mut self[..]);
2137 // RawVec handles deallocation
2141 #[stable(feature = "rust1", since = "1.0.0")]
2142 impl<T> Default for Vec<T> {
2143 /// Creates an empty `Vec<T>`.
2144 fn default() -> Vec<T> {
2149 #[stable(feature = "rust1", since = "1.0.0")]
2150 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2151 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2152 fmt::Debug::fmt(&**self, f)
2156 #[stable(feature = "rust1", since = "1.0.0")]
2157 impl<T> AsRef<Vec<T>> for Vec<T> {
2158 fn as_ref(&self) -> &Vec<T> {
2163 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2164 impl<T> AsMut<Vec<T>> for Vec<T> {
2165 fn as_mut(&mut self) -> &mut Vec<T> {
2170 #[stable(feature = "rust1", since = "1.0.0")]
2171 impl<T> AsRef<[T]> for Vec<T> {
2172 fn as_ref(&self) -> &[T] {
2177 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2178 impl<T> AsMut<[T]> for Vec<T> {
2179 fn as_mut(&mut self) -> &mut [T] {
2184 #[stable(feature = "rust1", since = "1.0.0")]
2185 impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
2187 fn from(s: &'a [T]) -> Vec<T> {
2191 fn from(s: &'a [T]) -> Vec<T> {
2192 crate::slice::to_vec(s)
2196 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2197 impl<'a, T: Clone> From<&'a mut [T]> for Vec<T> {
2199 fn from(s: &'a mut [T]) -> Vec<T> {
2203 fn from(s: &'a mut [T]) -> Vec<T> {
2204 crate::slice::to_vec(s)
2208 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2209 impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
2210 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2215 // note: test pulls in libstd, which causes errors here
2217 #[stable(feature = "vec_from_box", since = "1.18.0")]
2218 impl<T> From<Box<[T]>> for Vec<T> {
2219 fn from(s: Box<[T]>) -> Vec<T> {
2224 // note: test pulls in libstd, which causes errors here
2226 #[stable(feature = "box_from_vec", since = "1.20.0")]
2227 impl<T> From<Vec<T>> for Box<[T]> {
2228 fn from(v: Vec<T>) -> Box<[T]> {
2229 v.into_boxed_slice()
2233 #[stable(feature = "rust1", since = "1.0.0")]
2234 impl<'a> From<&'a str> for Vec<u8> {
2235 fn from(s: &'a str) -> Vec<u8> {
2236 From::from(s.as_bytes())
2240 ////////////////////////////////////////////////////////////////////////////////
2242 ////////////////////////////////////////////////////////////////////////////////
2244 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2245 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2246 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2251 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2252 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2253 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2258 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2259 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2260 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2261 Cow::Borrowed(v.as_slice())
2265 #[stable(feature = "rust1", since = "1.0.0")]
2266 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
2267 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2268 Cow::Owned(FromIterator::from_iter(it))
2272 ////////////////////////////////////////////////////////////////////////////////
2274 ////////////////////////////////////////////////////////////////////////////////
2276 /// An iterator that moves out of a vector.
2278 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
2279 /// by the [`IntoIterator`] trait).
2281 /// [`Vec`]: struct.Vec.html
2282 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2283 #[stable(feature = "rust1", since = "1.0.0")]
2284 pub struct IntoIter<T> {
2286 phantom: PhantomData<T>,
2292 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2293 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2294 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2295 f.debug_tuple("IntoIter")
2296 .field(&self.as_slice())
2301 impl<T> IntoIter<T> {
2302 /// Returns the remaining items of this iterator as a slice.
2307 /// let vec = vec!['a', 'b', 'c'];
2308 /// let mut into_iter = vec.into_iter();
2309 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2310 /// let _ = into_iter.next().unwrap();
2311 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2313 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2314 pub fn as_slice(&self) -> &[T] {
2316 slice::from_raw_parts(self.ptr, self.len())
2320 /// Returns the remaining items of this iterator as a mutable slice.
2325 /// let vec = vec!['a', 'b', 'c'];
2326 /// let mut into_iter = vec.into_iter();
2327 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2328 /// into_iter.as_mut_slice()[2] = 'z';
2329 /// assert_eq!(into_iter.next().unwrap(), 'a');
2330 /// assert_eq!(into_iter.next().unwrap(), 'b');
2331 /// assert_eq!(into_iter.next().unwrap(), 'z');
2333 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2334 pub fn as_mut_slice(&mut self) -> &mut [T] {
2336 slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
2341 #[stable(feature = "rust1", since = "1.0.0")]
2342 unsafe impl<T: Send> Send for IntoIter<T> {}
2343 #[stable(feature = "rust1", since = "1.0.0")]
2344 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2346 #[stable(feature = "rust1", since = "1.0.0")]
2347 impl<T> Iterator for IntoIter<T> {
2351 fn next(&mut self) -> Option<T> {
2353 if self.ptr as *const _ == self.end {
2356 if mem::size_of::<T>() == 0 {
2357 // purposefully don't use 'ptr.offset' because for
2358 // vectors with 0-size elements this would return the
2360 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2362 // Make up a value of this ZST.
2366 self.ptr = self.ptr.offset(1);
2368 Some(ptr::read(old))
2375 fn size_hint(&self) -> (usize, Option<usize>) {
2376 let exact = if mem::size_of::<T>() == 0 {
2377 (self.end as usize).wrapping_sub(self.ptr as usize)
2379 unsafe { self.end.offset_from(self.ptr) as usize }
2381 (exact, Some(exact))
2385 fn count(self) -> usize {
2390 #[stable(feature = "rust1", since = "1.0.0")]
2391 impl<T> DoubleEndedIterator for IntoIter<T> {
2393 fn next_back(&mut self) -> Option<T> {
2395 if self.end == self.ptr {
2398 if mem::size_of::<T>() == 0 {
2399 // See above for why 'ptr.offset' isn't used
2400 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2402 // Make up a value of this ZST.
2405 self.end = self.end.offset(-1);
2407 Some(ptr::read(self.end))
2414 #[stable(feature = "rust1", since = "1.0.0")]
2415 impl<T> ExactSizeIterator for IntoIter<T> {
2416 fn is_empty(&self) -> bool {
2417 self.ptr == self.end
2421 #[stable(feature = "fused", since = "1.26.0")]
2422 impl<T> FusedIterator for IntoIter<T> {}
2424 #[unstable(feature = "trusted_len", issue = "37572")]
2425 unsafe impl<T> TrustedLen for IntoIter<T> {}
2427 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2428 impl<T: Clone> Clone for IntoIter<T> {
2429 fn clone(&self) -> IntoIter<T> {
2430 self.as_slice().to_owned().into_iter()
2434 #[stable(feature = "rust1", since = "1.0.0")]
2435 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2436 fn drop(&mut self) {
2437 // destroy the remaining elements
2438 for _x in self.by_ref() {}
2440 // RawVec handles deallocation
2441 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2445 /// A draining iterator for `Vec<T>`.
2447 /// This `struct` is created by the [`drain`] method on [`Vec`].
2449 /// [`drain`]: struct.Vec.html#method.drain
2450 /// [`Vec`]: struct.Vec.html
2451 #[stable(feature = "drain", since = "1.6.0")]
2452 pub struct Drain<'a, T: 'a> {
2453 /// Index of tail to preserve
2457 /// Current remaining range to remove
2458 iter: slice::Iter<'a, T>,
2459 vec: NonNull<Vec<T>>,
2462 #[stable(feature = "collection_debug", since = "1.17.0")]
2463 impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
2464 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2465 f.debug_tuple("Drain")
2466 .field(&self.iter.as_slice())
2471 #[stable(feature = "drain", since = "1.6.0")]
2472 unsafe impl<T: Sync> Sync for Drain<'_, T> {}
2473 #[stable(feature = "drain", since = "1.6.0")]
2474 unsafe impl<T: Send> Send for Drain<'_, T> {}
2476 #[stable(feature = "drain", since = "1.6.0")]
2477 impl<T> Iterator for Drain<'_, T> {
2481 fn next(&mut self) -> Option<T> {
2482 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2485 fn size_hint(&self) -> (usize, Option<usize>) {
2486 self.iter.size_hint()
2490 #[stable(feature = "drain", since = "1.6.0")]
2491 impl<T> DoubleEndedIterator for Drain<'_, T> {
2493 fn next_back(&mut self) -> Option<T> {
2494 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2498 #[stable(feature = "drain", since = "1.6.0")]
2499 impl<T> Drop for Drain<'_, T> {
2500 fn drop(&mut self) {
2501 // exhaust self first
2502 self.for_each(drop);
2504 if self.tail_len > 0 {
2506 let source_vec = self.vec.as_mut();
2507 // memmove back untouched tail, update to new length
2508 let start = source_vec.len();
2509 let tail = self.tail_start;
2511 let src = source_vec.as_ptr().add(tail);
2512 let dst = source_vec.as_mut_ptr().add(start);
2513 ptr::copy(src, dst, self.tail_len);
2515 source_vec.set_len(start + self.tail_len);
2522 #[stable(feature = "drain", since = "1.6.0")]
2523 impl<T> ExactSizeIterator for Drain<'_, T> {
2524 fn is_empty(&self) -> bool {
2525 self.iter.is_empty()
2529 #[stable(feature = "fused", since = "1.26.0")]
2530 impl<T> FusedIterator for Drain<'_, T> {}
2532 /// A splicing iterator for `Vec`.
2534 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2535 /// documentation for more.
2537 /// [`splice()`]: struct.Vec.html#method.splice
2538 /// [`Vec`]: struct.Vec.html
2540 #[stable(feature = "vec_splice", since = "1.21.0")]
2541 pub struct Splice<'a, I: Iterator + 'a> {
2542 drain: Drain<'a, I::Item>,
2546 #[stable(feature = "vec_splice", since = "1.21.0")]
2547 impl<I: Iterator> Iterator for Splice<'_, I> {
2548 type Item = I::Item;
2550 fn next(&mut self) -> Option<Self::Item> {
2554 fn size_hint(&self) -> (usize, Option<usize>) {
2555 self.drain.size_hint()
2559 #[stable(feature = "vec_splice", since = "1.21.0")]
2560 impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
2561 fn next_back(&mut self) -> Option<Self::Item> {
2562 self.drain.next_back()
2566 #[stable(feature = "vec_splice", since = "1.21.0")]
2567 impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}
2570 #[stable(feature = "vec_splice", since = "1.21.0")]
2571 impl<I: Iterator> Drop for Splice<'_, I> {
2572 fn drop(&mut self) {
2573 self.drain.by_ref().for_each(drop);
2576 if self.drain.tail_len == 0 {
2577 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2581 // First fill the range left by drain().
2582 if !self.drain.fill(&mut self.replace_with) {
2586 // There may be more elements. Use the lower bound as an estimate.
2587 // FIXME: Is the upper bound a better guess? Or something else?
2588 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2589 if lower_bound > 0 {
2590 self.drain.move_tail(lower_bound);
2591 if !self.drain.fill(&mut self.replace_with) {
2596 // Collect any remaining elements.
2597 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2598 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2599 // Now we have an exact count.
2600 if collected.len() > 0 {
2601 self.drain.move_tail(collected.len());
2602 let filled = self.drain.fill(&mut collected);
2603 debug_assert!(filled);
2604 debug_assert_eq!(collected.len(), 0);
2607 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2611 /// Private helper methods for `Splice::drop`
2612 impl<T> Drain<'_, T> {
2613 /// The range from `self.vec.len` to `self.tail_start` contains elements
2614 /// that have been moved out.
2615 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2616 /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2617 unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
2618 let vec = self.vec.as_mut();
2619 let range_start = vec.len;
2620 let range_end = self.tail_start;
2621 let range_slice = slice::from_raw_parts_mut(
2622 vec.as_mut_ptr().add(range_start),
2623 range_end - range_start);
2625 for place in range_slice {
2626 if let Some(new_item) = replace_with.next() {
2627 ptr::write(place, new_item);
2636 /// Makes room for inserting more elements before the tail.
2637 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2638 let vec = self.vec.as_mut();
2639 let used_capacity = self.tail_start + self.tail_len;
2640 vec.buf.reserve(used_capacity, extra_capacity);
2642 let new_tail_start = self.tail_start + extra_capacity;
2643 let src = vec.as_ptr().add(self.tail_start);
2644 let dst = vec.as_mut_ptr().add(new_tail_start);
2645 ptr::copy(src, dst, self.tail_len);
2646 self.tail_start = new_tail_start;
2650 /// An iterator produced by calling `drain_filter` on Vec.
2651 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2653 pub struct DrainFilter<'a, T, F>
2654 where F: FnMut(&mut T) -> bool,
2656 vec: &'a mut Vec<T>,
2663 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2664 impl<T, F> Iterator for DrainFilter<'_, T, F>
2665 where F: FnMut(&mut T) -> bool,
2669 fn next(&mut self) -> Option<T> {
2671 while self.idx != self.old_len {
2674 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2675 if (self.pred)(&mut v[i]) {
2677 return Some(ptr::read(&v[i]));
2678 } else if self.del > 0 {
2680 let src: *const T = &v[i];
2681 let dst: *mut T = &mut v[i - del];
2682 // This is safe because self.vec has length 0
2683 // thus its elements will not have Drop::drop
2684 // called on them in the event of a panic.
2685 ptr::copy_nonoverlapping(src, dst, 1);
2692 fn size_hint(&self) -> (usize, Option<usize>) {
2693 (0, Some(self.old_len - self.idx))
2697 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2698 impl<T, F> Drop for DrainFilter<'_, T, F>
2699 where F: FnMut(&mut T) -> bool,
2701 fn drop(&mut self) {
2702 self.for_each(drop);
2704 self.vec.set_len(self.old_len - self.del);