1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! A contiguous growable array type with heap-allocated contents, written
14 //! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
15 //! `O(1)` pop (from the end).
19 //! You can explicitly create a [`Vec<T>`] with [`new`]:
22 //! let v: Vec<i32> = Vec::new();
25 //! ...or by using the [`vec!`] macro:
28 //! let v: Vec<i32> = vec![];
30 //! let v = vec![1, 2, 3, 4, 5];
32 //! let v = vec![0; 10]; // ten zeroes
35 //! You can [`push`] values onto the end of a vector (which will grow the vector
39 //! let mut v = vec![1, 2];
44 //! Popping values works in much the same way:
47 //! let mut v = vec![1, 2];
49 //! let two = v.pop();
52 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
55 //! let mut v = vec![1, 2, 3];
60 //! [`Vec<T>`]: ../../std/vec/struct.Vec.html
61 //! [`new`]: ../../std/vec/struct.Vec.html#method.new
62 //! [`push`]: ../../std/vec/struct.Vec.html#method.push
63 //! [`Index`]: ../../std/ops/trait.Index.html
64 //! [`IndexMut`]: ../../std/ops/trait.IndexMut.html
65 //! [`vec!`]: ../../std/macro.vec.html
67 #![stable(feature = "rust1", since = "1.0.0")]
69 use core::cmp::{self, Ordering};
71 use core::hash::{self, Hash};
72 use core::intrinsics::{arith_offset, assume};
73 use core::iter::{FromIterator, FusedIterator, TrustedLen};
74 use core::marker::PhantomData;
76 use core::ops::Bound::{Excluded, Included, Unbounded};
77 use core::ops::{Index, IndexMut, RangeBounds};
80 use core::ptr::NonNull;
83 use collections::CollectionAllocErr;
89 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
94 /// let mut vec = Vec::new();
98 /// assert_eq!(vec.len(), 2);
99 /// assert_eq!(vec[0], 1);
101 /// assert_eq!(vec.pop(), Some(2));
102 /// assert_eq!(vec.len(), 1);
105 /// assert_eq!(vec[0], 7);
107 /// vec.extend([1, 2, 3].iter().cloned());
110 /// println!("{}", x);
112 /// assert_eq!(vec, [7, 1, 2, 3]);
115 /// The [`vec!`] macro is provided to make initialization more convenient:
118 /// let mut vec = vec![1, 2, 3];
120 /// assert_eq!(vec, [1, 2, 3, 4]);
123 /// It can also initialize each element of a `Vec<T>` with a given value.
124 /// This may be more efficient than performing allocation and initialization
125 /// in separate steps, especially when initializing a vector of zeros:
128 /// let vec = vec![0; 5];
129 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
131 /// // The following is equivalent, but potentially slower:
132 /// let mut vec1 = Vec::with_capacity(5);
133 /// vec1.resize(5, 0);
136 /// Use a `Vec<T>` as an efficient stack:
139 /// let mut stack = Vec::new();
145 /// while let Some(top) = stack.pop() {
146 /// // Prints 3, 2, 1
147 /// println!("{}", top);
153 /// The `Vec` type allows to access values by index, because it implements the
154 /// [`Index`] trait. An example will be more explicit:
157 /// let v = vec![0, 2, 4, 6];
158 /// println!("{}", v[1]); // it will display '2'
161 /// However be careful: if you try to access an index which isn't in the `Vec`,
162 /// your software will panic! You cannot do this:
165 /// let v = vec![0, 2, 4, 6];
166 /// println!("{}", v[6]); // it will panic!
169 /// In conclusion: always check if the index you want to get really exists
174 /// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
175 /// To get a slice, use `&`. Example:
178 /// fn read_slice(slice: &[usize]) {
182 /// let v = vec![0, 1];
185 /// // ... and that's all!
186 /// // you can also do it like this:
187 /// let x : &[usize] = &v;
190 /// In Rust, it's more common to pass slices as arguments rather than vectors
191 /// when you just want to provide a read access. The same goes for [`String`] and
194 /// # Capacity and reallocation
196 /// The capacity of a vector is the amount of space allocated for any future
197 /// elements that will be added onto the vector. This is not to be confused with
198 /// the *length* of a vector, which specifies the number of actual elements
199 /// within the vector. If a vector's length exceeds its capacity, its capacity
200 /// will automatically be increased, but its elements will have to be
203 /// For example, a vector with capacity 10 and length 0 would be an empty vector
204 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
205 /// vector will not change its capacity or cause reallocation to occur. However,
206 /// if the vector's length is increased to 11, it will have to reallocate, which
207 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
208 /// whenever possible to specify how big the vector is expected to get.
212 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
213 /// about its design. This ensures that it's as low-overhead as possible in
214 /// the general case, and can be correctly manipulated in primitive ways
215 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
216 /// If additional type parameters are added (e.g., to support custom allocators),
217 /// overriding their defaults may change the behavior.
219 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
220 /// triplet. No more, no less. The order of these fields is completely
221 /// unspecified, and you should use the appropriate methods to modify these.
222 /// The pointer will never be null, so this type is null-pointer-optimized.
224 /// However, the pointer may not actually point to allocated memory. In particular,
225 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
226 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
227 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
228 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
229 /// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
230 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
231 /// details are very subtle — if you intend to allocate memory using a `Vec`
232 /// and use it for something else (either to pass to unsafe code, or to build your
233 /// own memory-backed collection), be sure to deallocate this memory by using
234 /// `from_raw_parts` to recover the `Vec` and then dropping it.
236 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
237 /// (as defined by the allocator Rust is configured to use by default), and its
238 /// pointer points to [`len`] initialized, contiguous elements in order (what
239 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
240 /// `[`len`] logically uninitialized, contiguous elements.
242 /// `Vec` will never perform a "small optimization" where elements are actually
243 /// stored on the stack for two reasons:
245 /// * It would make it more difficult for unsafe code to correctly manipulate
246 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
247 /// only moved, and it would be more difficult to determine if a `Vec` had
248 /// actually allocated memory.
250 /// * It would penalize the general case, incurring an additional branch
253 /// `Vec` will never automatically shrink itself, even if completely empty. This
254 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
255 /// and then filling it back up to the same [`len`] should incur no calls to
256 /// the allocator. If you wish to free up unused memory, use
257 /// [`shrink_to_fit`][`shrink_to_fit`].
259 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
260 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
261 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
262 /// accurate, and can be relied on. It can even be used to manually free the memory
263 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
264 /// when not necessary.
266 /// `Vec` does not guarantee any particular growth strategy when reallocating
267 /// when full, nor when [`reserve`] is called. The current strategy is basic
268 /// and it may prove desirable to use a non-constant growth factor. Whatever
269 /// strategy is used will of course guarantee `O(1)` amortized [`push`].
271 /// `vec![x; n]`, `vec![a, b, c, d]`, and
272 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
273 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
274 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
275 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
277 /// `Vec` will not specifically overwrite any data that is removed from it,
278 /// but also won't specifically preserve it. Its uninitialized memory is
279 /// scratch space that it may use however it wants. It will generally just do
280 /// whatever is most efficient or otherwise easy to implement. Do not rely on
281 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
282 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
283 /// first, that may not actually happen because the optimizer does not consider
284 /// this a side-effect that must be preserved. There is one case which we will
285 /// not break, however: using `unsafe` code to write to the excess capacity,
286 /// and then increasing the length to match, is always valid.
288 /// `Vec` does not currently guarantee the order in which elements are dropped.
289 /// The order has changed in the past and may change again.
291 /// [`vec!`]: ../../std/macro.vec.html
292 /// [`Index`]: ../../std/ops/trait.Index.html
293 /// [`String`]: ../../std/string/struct.String.html
294 /// [`&str`]: ../../std/primitive.str.html
295 /// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
296 /// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
297 /// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
298 /// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
299 /// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
300 /// [`len`]: ../../std/vec/struct.Vec.html#method.len
301 /// [`push`]: ../../std/vec/struct.Vec.html#method.push
302 /// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
303 /// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
304 /// [owned slice]: ../../std/boxed/struct.Box.html
305 #[stable(feature = "rust1", since = "1.0.0")]
311 ////////////////////////////////////////////////////////////////////////////////
313 ////////////////////////////////////////////////////////////////////////////////
316 /// Constructs a new, empty `Vec<T>`.
318 /// The vector will not allocate until elements are pushed onto it.
323 /// # #![allow(unused_mut)]
324 /// let mut vec: Vec<i32> = Vec::new();
327 #[stable(feature = "rust1", since = "1.0.0")]
328 #[rustc_const_unstable(feature = "const_vec_new")]
329 pub const fn new() -> Vec<T> {
336 /// Constructs a new, empty `Vec<T>` with the specified capacity.
338 /// The vector will be able to hold exactly `capacity` elements without
339 /// reallocating. If `capacity` is 0, the vector will not allocate.
341 /// It is important to note that although the returned vector has the
342 /// *capacity* specified, the vector will have a zero *length*. For an
343 /// explanation of the difference between length and capacity, see
344 /// *[Capacity and reallocation]*.
346 /// [Capacity and reallocation]: #capacity-and-reallocation
351 /// let mut vec = Vec::with_capacity(10);
353 /// // The vector contains no items, even though it has capacity for more
354 /// assert_eq!(vec.len(), 0);
356 /// // These are all done without reallocating...
361 /// // ...but this may make the vector reallocate
365 #[stable(feature = "rust1", since = "1.0.0")]
366 pub fn with_capacity(capacity: usize) -> Vec<T> {
368 buf: RawVec::with_capacity(capacity),
373 /// Creates a `Vec<T>` directly from the raw components of another vector.
377 /// This is highly unsafe, due to the number of invariants that aren't
380 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
381 /// (at least, it's highly likely to be incorrect if it wasn't).
382 /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
383 /// * `length` needs to be less than or equal to `capacity`.
384 /// * `capacity` needs to be the capacity that the pointer was allocated with.
386 /// Violating these may cause problems like corrupting the allocator's
387 /// internal data structures. For example it is **not** safe
388 /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
390 /// The ownership of `ptr` is effectively transferred to the
391 /// `Vec<T>` which may then deallocate, reallocate or change the
392 /// contents of memory pointed to by the pointer at will. Ensure
393 /// that nothing else uses the pointer after calling this
396 /// [`String`]: ../../std/string/struct.String.html
405 /// let mut v = vec![1, 2, 3];
407 /// // Pull out the various important pieces of information about `v`
408 /// let p = v.as_mut_ptr();
409 /// let len = v.len();
410 /// let cap = v.capacity();
413 /// // Cast `v` into the void: no destructor run, so we are in
414 /// // complete control of the allocation to which `p` points.
417 /// // Overwrite memory with 4, 5, 6
418 /// for i in 0..len as isize {
419 /// ptr::write(p.offset(i), 4 + i);
422 /// // Put everything back together into a Vec
423 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
424 /// assert_eq!(rebuilt, [4, 5, 6]);
428 #[stable(feature = "rust1", since = "1.0.0")]
429 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
431 buf: RawVec::from_raw_parts(ptr, capacity),
436 /// Returns the number of elements the vector can hold without
442 /// let vec: Vec<i32> = Vec::with_capacity(10);
443 /// assert_eq!(vec.capacity(), 10);
446 #[stable(feature = "rust1", since = "1.0.0")]
447 pub fn capacity(&self) -> usize {
451 /// Reserves capacity for at least `additional` more elements to be inserted
452 /// in the given `Vec<T>`. The collection may reserve more space to avoid
453 /// frequent reallocations. After calling `reserve`, capacity will be
454 /// greater than or equal to `self.len() + additional`. Does nothing if
455 /// capacity is already sufficient.
459 /// Panics if the new capacity overflows `usize`.
464 /// let mut vec = vec![1];
466 /// assert!(vec.capacity() >= 11);
468 #[stable(feature = "rust1", since = "1.0.0")]
469 pub fn reserve(&mut self, additional: usize) {
470 self.buf.reserve(self.len, additional);
473 /// Reserves the minimum capacity for exactly `additional` more elements to
474 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
475 /// capacity will be greater than or equal to `self.len() + additional`.
476 /// Does nothing if the capacity is already sufficient.
478 /// Note that the allocator may give the collection more space than it
479 /// requests. Therefore capacity can not be relied upon to be precisely
480 /// minimal. Prefer `reserve` if future insertions are expected.
484 /// Panics if the new capacity overflows `usize`.
489 /// let mut vec = vec![1];
490 /// vec.reserve_exact(10);
491 /// assert!(vec.capacity() >= 11);
493 #[stable(feature = "rust1", since = "1.0.0")]
494 pub fn reserve_exact(&mut self, additional: usize) {
495 self.buf.reserve_exact(self.len, additional);
498 /// Tries to reserve capacity for at least `additional` more elements to be inserted
499 /// in the given `Vec<T>`. The collection may reserve more space to avoid
500 /// frequent reallocations. After calling `reserve`, capacity will be
501 /// greater than or equal to `self.len() + additional`. Does nothing if
502 /// capacity is already sufficient.
506 /// If the capacity overflows, or the allocator reports a failure, then an error
512 /// #![feature(try_reserve)]
513 /// use std::collections::CollectionAllocErr;
515 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
516 /// let mut output = Vec::new();
518 /// // Pre-reserve the memory, exiting if we can't
519 /// output.try_reserve(data.len())?;
521 /// // Now we know this can't OOM in the middle of our complex work
522 /// output.extend(data.iter().map(|&val| {
523 /// val * 2 + 5 // very complicated
528 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
530 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
531 pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
532 self.buf.try_reserve(self.len, additional)
535 /// Tries to reserves the minimum capacity for exactly `additional` more elements to
536 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
537 /// capacity will be greater than or equal to `self.len() + additional`.
538 /// Does nothing if the capacity is already sufficient.
540 /// Note that the allocator may give the collection more space than it
541 /// requests. Therefore capacity can not be relied upon to be precisely
542 /// minimal. Prefer `reserve` if future insertions are expected.
546 /// If the capacity overflows, or the allocator reports a failure, then an error
552 /// #![feature(try_reserve)]
553 /// use std::collections::CollectionAllocErr;
555 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, CollectionAllocErr> {
556 /// let mut output = Vec::new();
558 /// // Pre-reserve the memory, exiting if we can't
559 /// output.try_reserve(data.len())?;
561 /// // Now we know this can't OOM in the middle of our complex work
562 /// output.extend(data.iter().map(|&val| {
563 /// val * 2 + 5 // very complicated
568 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
570 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
571 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
572 self.buf.try_reserve_exact(self.len, additional)
575 /// Shrinks the capacity of the vector as much as possible.
577 /// It will drop down as close as possible to the length but the allocator
578 /// may still inform the vector that there is space for a few more elements.
583 /// let mut vec = Vec::with_capacity(10);
584 /// vec.extend([1, 2, 3].iter().cloned());
585 /// assert_eq!(vec.capacity(), 10);
586 /// vec.shrink_to_fit();
587 /// assert!(vec.capacity() >= 3);
589 #[stable(feature = "rust1", since = "1.0.0")]
590 pub fn shrink_to_fit(&mut self) {
591 if self.capacity() != self.len {
592 self.buf.shrink_to_fit(self.len);
596 /// Shrinks the capacity of the vector with a lower bound.
598 /// The capacity will remain at least as large as both the length
599 /// and the supplied value.
601 /// Panics if the current capacity is smaller than the supplied
602 /// minimum capacity.
607 /// #![feature(shrink_to)]
608 /// let mut vec = Vec::with_capacity(10);
609 /// vec.extend([1, 2, 3].iter().cloned());
610 /// assert_eq!(vec.capacity(), 10);
611 /// vec.shrink_to(4);
612 /// assert!(vec.capacity() >= 4);
613 /// vec.shrink_to(0);
614 /// assert!(vec.capacity() >= 3);
616 #[unstable(feature = "shrink_to", reason = "new API", issue="56431")]
617 pub fn shrink_to(&mut self, min_capacity: usize) {
618 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
621 /// Converts the vector into [`Box<[T]>`][owned slice].
623 /// Note that this will drop any excess capacity.
625 /// [owned slice]: ../../std/boxed/struct.Box.html
630 /// let v = vec![1, 2, 3];
632 /// let slice = v.into_boxed_slice();
635 /// Any excess capacity is removed:
638 /// let mut vec = Vec::with_capacity(10);
639 /// vec.extend([1, 2, 3].iter().cloned());
641 /// assert_eq!(vec.capacity(), 10);
642 /// let slice = vec.into_boxed_slice();
643 /// assert_eq!(slice.into_vec().capacity(), 3);
645 #[stable(feature = "rust1", since = "1.0.0")]
646 pub fn into_boxed_slice(mut self) -> Box<[T]> {
648 self.shrink_to_fit();
649 let buf = ptr::read(&self.buf);
655 /// Shortens the vector, keeping the first `len` elements and dropping
658 /// If `len` is greater than the vector's current length, this has no
661 /// The [`drain`] method can emulate `truncate`, but causes the excess
662 /// elements to be returned instead of dropped.
664 /// Note that this method has no effect on the allocated capacity
669 /// Truncating a five element vector to two elements:
672 /// let mut vec = vec![1, 2, 3, 4, 5];
674 /// assert_eq!(vec, [1, 2]);
677 /// No truncation occurs when `len` is greater than the vector's current
681 /// let mut vec = vec![1, 2, 3];
683 /// assert_eq!(vec, [1, 2, 3]);
686 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
690 /// let mut vec = vec![1, 2, 3];
692 /// assert_eq!(vec, []);
695 /// [`clear`]: #method.clear
696 /// [`drain`]: #method.drain
697 #[stable(feature = "rust1", since = "1.0.0")]
698 pub fn truncate(&mut self, len: usize) {
699 let current_len = self.len;
701 let mut ptr = self.as_mut_ptr().add(self.len);
702 // Set the final length at the end, keeping in mind that
703 // dropping an element might panic. Works around a missed
704 // optimization, as seen in the following issue:
705 // https://github.com/rust-lang/rust/issues/51802
706 let mut local_len = SetLenOnDrop::new(&mut self.len);
708 // drop any extra elements
709 for _ in len..current_len {
710 local_len.decrement_len(1);
711 ptr = ptr.offset(-1);
712 ptr::drop_in_place(ptr);
717 /// Extracts a slice containing the entire vector.
719 /// Equivalent to `&s[..]`.
724 /// use std::io::{self, Write};
725 /// let buffer = vec![1, 2, 3, 5, 8];
726 /// io::sink().write(buffer.as_slice()).unwrap();
729 #[stable(feature = "vec_as_slice", since = "1.7.0")]
730 pub fn as_slice(&self) -> &[T] {
734 /// Extracts a mutable slice of the entire vector.
736 /// Equivalent to `&mut s[..]`.
741 /// use std::io::{self, Read};
742 /// let mut buffer = vec![0; 3];
743 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
746 #[stable(feature = "vec_as_slice", since = "1.7.0")]
747 pub fn as_mut_slice(&mut self) -> &mut [T] {
751 /// Sets the length of a vector.
753 /// This will explicitly set the size of the vector, without actually
754 /// modifying its buffers, so it is up to the caller to ensure that the
755 /// vector is actually the specified size.
762 /// let mut vec = vec!['r', 'u', 's', 't'];
765 /// ptr::drop_in_place(&mut vec[3]);
768 /// assert_eq!(vec, ['r', 'u', 's']);
771 /// In this example, there is a memory leak since the memory locations
772 /// owned by the inner vectors were not freed prior to the `set_len` call:
775 /// let mut vec = vec![vec![1, 0, 0],
783 /// In this example, the vector gets expanded from zero to four items
784 /// without any memory allocations occurring, resulting in vector
785 /// values of unallocated memory:
788 /// let mut vec: Vec<char> = Vec::new();
795 #[stable(feature = "rust1", since = "1.0.0")]
796 pub unsafe fn set_len(&mut self, len: usize) {
800 /// Removes an element from the vector and returns it.
802 /// The removed element is replaced by the last element of the vector.
804 /// This does not preserve ordering, but is O(1).
808 /// Panics if `index` is out of bounds.
813 /// let mut v = vec!["foo", "bar", "baz", "qux"];
815 /// assert_eq!(v.swap_remove(1), "bar");
816 /// assert_eq!(v, ["foo", "qux", "baz"]);
818 /// assert_eq!(v.swap_remove(0), "foo");
819 /// assert_eq!(v, ["baz", "qux"]);
822 #[stable(feature = "rust1", since = "1.0.0")]
823 pub fn swap_remove(&mut self, index: usize) -> T {
825 // We replace self[index] with the last element. Note that if the
826 // bounds check on hole succeeds there must be a last element (which
827 // can be self[index] itself).
828 let hole: *mut T = &mut self[index];
829 let last = ptr::read(self.get_unchecked(self.len - 1));
831 ptr::replace(hole, last)
835 /// Inserts an element at position `index` within the vector, shifting all
836 /// elements after it to the right.
840 /// Panics if `index > len`.
845 /// let mut vec = vec![1, 2, 3];
846 /// vec.insert(1, 4);
847 /// assert_eq!(vec, [1, 4, 2, 3]);
848 /// vec.insert(4, 5);
849 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
851 #[stable(feature = "rust1", since = "1.0.0")]
852 pub fn insert(&mut self, index: usize, element: T) {
853 let len = self.len();
854 assert!(index <= len);
856 // space for the new element
857 if len == self.buf.cap() {
863 // The spot to put the new value
865 let p = self.as_mut_ptr().add(index);
866 // Shift everything over to make space. (Duplicating the
867 // `index`th element into two consecutive places.)
868 ptr::copy(p, p.offset(1), len - index);
869 // Write it in, overwriting the first copy of the `index`th
871 ptr::write(p, element);
873 self.set_len(len + 1);
877 /// Removes and returns the element at position `index` within the vector,
878 /// shifting all elements after it to the left.
882 /// Panics if `index` is out of bounds.
887 /// let mut v = vec![1, 2, 3];
888 /// assert_eq!(v.remove(1), 2);
889 /// assert_eq!(v, [1, 3]);
891 #[stable(feature = "rust1", since = "1.0.0")]
892 pub fn remove(&mut self, index: usize) -> T {
893 let len = self.len();
894 assert!(index < len);
899 // the place we are taking from.
900 let ptr = self.as_mut_ptr().add(index);
901 // copy it out, unsafely having a copy of the value on
902 // the stack and in the vector at the same time.
903 ret = ptr::read(ptr);
905 // Shift everything down to fill in that spot.
906 ptr::copy(ptr.offset(1), ptr, len - index - 1);
908 self.set_len(len - 1);
913 /// Retains only the elements specified by the predicate.
915 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
916 /// This method operates in place and preserves the order of the retained
922 /// let mut vec = vec![1, 2, 3, 4];
923 /// vec.retain(|&x| x%2 == 0);
924 /// assert_eq!(vec, [2, 4]);
926 #[stable(feature = "rust1", since = "1.0.0")]
927 pub fn retain<F>(&mut self, mut f: F)
928 where F: FnMut(&T) -> bool
930 self.drain_filter(|x| !f(x));
933 /// Removes all but the first of consecutive elements in the vector that resolve to the same
936 /// If the vector is sorted, this removes all duplicates.
941 /// let mut vec = vec![10, 20, 21, 30, 20];
943 /// vec.dedup_by_key(|i| *i / 10);
945 /// assert_eq!(vec, [10, 20, 30, 20]);
947 #[stable(feature = "dedup_by", since = "1.16.0")]
949 pub fn dedup_by_key<F, K>(&mut self, mut key: F) where F: FnMut(&mut T) -> K, K: PartialEq {
950 self.dedup_by(|a, b| key(a) == key(b))
953 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
956 /// The `same_bucket` function is passed references to two elements from the vector and
957 /// must determine if the elements compare equal. The elements are passed in opposite order
958 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
960 /// If the vector is sorted, this removes all duplicates.
965 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
967 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
969 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
971 #[stable(feature = "dedup_by", since = "1.16.0")]
972 pub fn dedup_by<F>(&mut self, same_bucket: F) where F: FnMut(&mut T, &mut T) -> bool {
974 let (dedup, _) = self.as_mut_slice().partition_dedup_by(same_bucket);
980 /// Appends an element to the back of a collection.
984 /// Panics if the number of elements in the vector overflows a `usize`.
989 /// let mut vec = vec![1, 2];
991 /// assert_eq!(vec, [1, 2, 3]);
994 #[stable(feature = "rust1", since = "1.0.0")]
995 pub fn push(&mut self, value: T) {
996 // This will panic or abort if we would allocate > isize::MAX bytes
997 // or if the length increment would overflow for zero-sized types.
998 if self.len == self.buf.cap() {
1002 let end = self.as_mut_ptr().add(self.len);
1003 ptr::write(end, value);
1008 /// Removes the last element from a vector and returns it, or [`None`] if it
1011 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1016 /// let mut vec = vec![1, 2, 3];
1017 /// assert_eq!(vec.pop(), Some(3));
1018 /// assert_eq!(vec, [1, 2]);
1021 #[stable(feature = "rust1", since = "1.0.0")]
1022 pub fn pop(&mut self) -> Option<T> {
1028 Some(ptr::read(self.get_unchecked(self.len())))
1033 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1037 /// Panics if the number of elements in the vector overflows a `usize`.
1042 /// let mut vec = vec![1, 2, 3];
1043 /// let mut vec2 = vec![4, 5, 6];
1044 /// vec.append(&mut vec2);
1045 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1046 /// assert_eq!(vec2, []);
1049 #[stable(feature = "append", since = "1.4.0")]
1050 pub fn append(&mut self, other: &mut Self) {
1052 self.append_elements(other.as_slice() as _);
1057 /// Appends elements to `Self` from other buffer.
1059 unsafe fn append_elements(&mut self, other: *const [T]) {
1060 let count = (*other).len();
1061 self.reserve(count);
1062 let len = self.len();
1063 ptr::copy_nonoverlapping(other as *const T, self.get_unchecked_mut(len), count);
1067 /// Creates a draining iterator that removes the specified range in the vector
1068 /// and yields the removed items.
1070 /// Note 1: The element range is removed even if the iterator is only
1071 /// partially consumed or not consumed at all.
1073 /// Note 2: It is unspecified how many elements are removed from the vector
1074 /// if the `Drain` value is leaked.
1078 /// Panics if the starting point is greater than the end point or if
1079 /// the end point is greater than the length of the vector.
1084 /// let mut v = vec![1, 2, 3];
1085 /// let u: Vec<_> = v.drain(1..).collect();
1086 /// assert_eq!(v, &[1]);
1087 /// assert_eq!(u, &[2, 3]);
1089 /// // A full range clears the vector
1091 /// assert_eq!(v, &[]);
1093 #[stable(feature = "drain", since = "1.6.0")]
1094 pub fn drain<R>(&mut self, range: R) -> Drain<T>
1095 where R: RangeBounds<usize>
1099 // When the Drain is first created, it shortens the length of
1100 // the source vector to make sure no uninitialized or moved-from elements
1101 // are accessible at all if the Drain's destructor never gets to run.
1103 // Drain will ptr::read out the values to remove.
1104 // When finished, remaining tail of the vec is copied back to cover
1105 // the hole, and the vector length is restored to the new length.
1107 let len = self.len();
1108 let start = match range.start_bound() {
1110 Excluded(&n) => n + 1,
1113 let end = match range.end_bound() {
1114 Included(&n) => n + 1,
1118 assert!(start <= end);
1119 assert!(end <= len);
1122 // set self.vec length's to start, to be safe in case Drain is leaked
1123 self.set_len(start);
1124 // Use the borrow in the IterMut to indicate borrowing behavior of the
1125 // whole Drain iterator (like &mut T).
1126 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start),
1130 tail_len: len - end,
1131 iter: range_slice.iter(),
1132 vec: NonNull::from(self),
1137 /// Clears the vector, removing all values.
1139 /// Note that this method has no effect on the allocated capacity
1145 /// let mut v = vec![1, 2, 3];
1149 /// assert!(v.is_empty());
1152 #[stable(feature = "rust1", since = "1.0.0")]
1153 pub fn clear(&mut self) {
1157 /// Returns the number of elements in the vector, also referred to
1158 /// as its 'length'.
1163 /// let a = vec![1, 2, 3];
1164 /// assert_eq!(a.len(), 3);
1167 #[stable(feature = "rust1", since = "1.0.0")]
1168 pub fn len(&self) -> usize {
1172 /// Returns `true` if the vector contains no elements.
1177 /// let mut v = Vec::new();
1178 /// assert!(v.is_empty());
1181 /// assert!(!v.is_empty());
1183 #[stable(feature = "rust1", since = "1.0.0")]
1184 pub fn is_empty(&self) -> bool {
1188 /// Splits the collection into two at the given index.
1190 /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
1191 /// and the returned `Self` contains elements `[at, len)`.
1193 /// Note that the capacity of `self` does not change.
1197 /// Panics if `at > len`.
1202 /// let mut vec = vec![1,2,3];
1203 /// let vec2 = vec.split_off(1);
1204 /// assert_eq!(vec, [1]);
1205 /// assert_eq!(vec2, [2, 3]);
1208 #[stable(feature = "split_off", since = "1.4.0")]
1209 pub fn split_off(&mut self, at: usize) -> Self {
1210 assert!(at <= self.len(), "`at` out of bounds");
1212 let other_len = self.len - at;
1213 let mut other = Vec::with_capacity(other_len);
1215 // Unsafely `set_len` and copy items to `other`.
1218 other.set_len(other_len);
1220 ptr::copy_nonoverlapping(self.as_ptr().add(at),
1227 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1229 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1230 /// difference, with each additional slot filled with the result of
1231 /// calling the closure `f`. The return values from `f` will end up
1232 /// in the `Vec` in the order they have been generated.
1234 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1236 /// This method uses a closure to create new values on every push. If
1237 /// you'd rather [`Clone`] a given value, use [`resize`]. If you want
1238 /// to use the [`Default`] trait to generate values, you can pass
1239 /// [`Default::default()`] as the second argument..
1244 /// #![feature(vec_resize_with)]
1246 /// let mut vec = vec![1, 2, 3];
1247 /// vec.resize_with(5, Default::default);
1248 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1250 /// let mut vec = vec![];
1252 /// vec.resize_with(4, || { p *= 2; p });
1253 /// assert_eq!(vec, [2, 4, 8, 16]);
1256 /// [`resize`]: #method.resize
1257 /// [`Clone`]: ../../std/clone/trait.Clone.html
1258 #[unstable(feature = "vec_resize_with", issue = "41758")]
1259 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1260 where F: FnMut() -> T
1262 let len = self.len();
1264 self.extend_with(new_len - len, ExtendFunc(f));
1266 self.truncate(new_len);
1271 impl<T: Clone> Vec<T> {
1272 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1274 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1275 /// difference, with each additional slot filled with `value`.
1276 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1278 /// This method requires [`Clone`] to be able clone the passed value. If
1279 /// you need more flexibility (or want to rely on [`Default`] instead of
1280 /// [`Clone`]), use [`resize_with`].
1285 /// let mut vec = vec!["hello"];
1286 /// vec.resize(3, "world");
1287 /// assert_eq!(vec, ["hello", "world", "world"]);
1289 /// let mut vec = vec![1, 2, 3, 4];
1290 /// vec.resize(2, 0);
1291 /// assert_eq!(vec, [1, 2]);
1294 /// [`Clone`]: ../../std/clone/trait.Clone.html
1295 /// [`Default`]: ../../std/default/trait.Default.html
1296 /// [`resize_with`]: #method.resize_with
1297 #[stable(feature = "vec_resize", since = "1.5.0")]
1298 pub fn resize(&mut self, new_len: usize, value: T) {
1299 let len = self.len();
1302 self.extend_with(new_len - len, ExtendElement(value))
1304 self.truncate(new_len);
1308 /// Clones and appends all elements in a slice to the `Vec`.
1310 /// Iterates over the slice `other`, clones each element, and then appends
1311 /// it to this `Vec`. The `other` vector is traversed in-order.
1313 /// Note that this function is same as [`extend`] except that it is
1314 /// specialized to work with slices instead. If and when Rust gets
1315 /// specialization this function will likely be deprecated (but still
1321 /// let mut vec = vec![1];
1322 /// vec.extend_from_slice(&[2, 3, 4]);
1323 /// assert_eq!(vec, [1, 2, 3, 4]);
1326 /// [`extend`]: #method.extend
1327 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
1328 pub fn extend_from_slice(&mut self, other: &[T]) {
1329 self.spec_extend(other.iter())
1333 impl<T: Default> Vec<T> {
1334 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1336 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1337 /// difference, with each additional slot filled with [`Default::default()`].
1338 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1340 /// This method uses [`Default`] to create new values on every push. If
1341 /// you'd rather [`Clone`] a given value, use [`resize`].
1346 /// #![feature(vec_resize_default)]
1348 /// let mut vec = vec![1, 2, 3];
1349 /// vec.resize_default(5);
1350 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1352 /// let mut vec = vec![1, 2, 3, 4];
1353 /// vec.resize_default(2);
1354 /// assert_eq!(vec, [1, 2]);
1357 /// [`resize`]: #method.resize
1358 /// [`Default::default()`]: ../../std/default/trait.Default.html#tymethod.default
1359 /// [`Default`]: ../../std/default/trait.Default.html
1360 /// [`Clone`]: ../../std/clone/trait.Clone.html
1361 #[unstable(feature = "vec_resize_default", issue = "41758")]
1362 pub fn resize_default(&mut self, new_len: usize) {
1363 let len = self.len();
1366 self.extend_with(new_len - len, ExtendDefault);
1368 self.truncate(new_len);
1373 // This code generalises `extend_with_{element,default}`.
1374 trait ExtendWith<T> {
1375 fn next(&mut self) -> T;
1379 struct ExtendElement<T>(T);
1380 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
1381 fn next(&mut self) -> T { self.0.clone() }
1382 fn last(self) -> T { self.0 }
1385 struct ExtendDefault;
1386 impl<T: Default> ExtendWith<T> for ExtendDefault {
1387 fn next(&mut self) -> T { Default::default() }
1388 fn last(self) -> T { Default::default() }
1391 struct ExtendFunc<F>(F);
1392 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
1393 fn next(&mut self) -> T { (self.0)() }
1394 fn last(mut self) -> T { (self.0)() }
1398 /// Extend the vector by `n` values, using the given generator.
1399 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
1403 let mut ptr = self.as_mut_ptr().add(self.len());
1404 // Use SetLenOnDrop to work around bug where compiler
1405 // may not realize the store through `ptr` through self.set_len()
1407 let mut local_len = SetLenOnDrop::new(&mut self.len);
1409 // Write all elements except the last one
1411 ptr::write(ptr, value.next());
1412 ptr = ptr.offset(1);
1413 // Increment the length in every step in case next() panics
1414 local_len.increment_len(1);
1418 // We can write the last element directly without cloning needlessly
1419 ptr::write(ptr, value.last());
1420 local_len.increment_len(1);
1423 // len set by scope guard
1428 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
1430 // The idea is: The length field in SetLenOnDrop is a local variable
1431 // that the optimizer will see does not alias with any stores through the Vec's data
1432 // pointer. This is a workaround for alias analysis issue #32155
1433 struct SetLenOnDrop<'a> {
1438 impl<'a> SetLenOnDrop<'a> {
1440 fn new(len: &'a mut usize) -> Self {
1441 SetLenOnDrop { local_len: *len, len: len }
1445 fn increment_len(&mut self, increment: usize) {
1446 self.local_len += increment;
1450 fn decrement_len(&mut self, decrement: usize) {
1451 self.local_len -= decrement;
1455 impl<'a> Drop for SetLenOnDrop<'a> {
1457 fn drop(&mut self) {
1458 *self.len = self.local_len;
1462 impl<T: PartialEq> Vec<T> {
1463 /// Removes consecutive repeated elements in the vector according to the
1464 /// [`PartialEq`] trait implementation.
1466 /// If the vector is sorted, this removes all duplicates.
1471 /// let mut vec = vec![1, 2, 2, 3, 2];
1475 /// assert_eq!(vec, [1, 2, 3, 2]);
1477 #[stable(feature = "rust1", since = "1.0.0")]
1479 pub fn dedup(&mut self) {
1480 self.dedup_by(|a, b| a == b)
1483 /// Removes the first instance of `item` from the vector if the item exists.
1488 /// # #![feature(vec_remove_item)]
1489 /// let mut vec = vec![1, 2, 3, 1];
1491 /// vec.remove_item(&1);
1493 /// assert_eq!(vec, vec![2, 3, 1]);
1495 #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
1496 pub fn remove_item(&mut self, item: &T) -> Option<T> {
1497 let pos = self.iter().position(|x| *x == *item)?;
1498 Some(self.remove(pos))
1502 ////////////////////////////////////////////////////////////////////////////////
1503 // Internal methods and functions
1504 ////////////////////////////////////////////////////////////////////////////////
1507 #[stable(feature = "rust1", since = "1.0.0")]
1508 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
1509 <T as SpecFromElem>::from_elem(elem, n)
1512 // Specialization trait used for Vec::from_elem
1513 trait SpecFromElem: Sized {
1514 fn from_elem(elem: Self, n: usize) -> Vec<Self>;
1517 impl<T: Clone> SpecFromElem for T {
1518 default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
1519 let mut v = Vec::with_capacity(n);
1520 v.extend_with(n, ExtendElement(elem));
1525 impl SpecFromElem for u8 {
1527 fn from_elem(elem: u8, n: usize) -> Vec<u8> {
1530 buf: RawVec::with_capacity_zeroed(n),
1535 let mut v = Vec::with_capacity(n);
1536 ptr::write_bytes(v.as_mut_ptr(), elem, n);
1543 impl<T: Clone + IsZero> SpecFromElem for T {
1545 fn from_elem(elem: T, n: usize) -> Vec<T> {
1548 buf: RawVec::with_capacity_zeroed(n),
1552 let mut v = Vec::with_capacity(n);
1553 v.extend_with(n, ExtendElement(elem));
1558 unsafe trait IsZero {
1559 /// Whether this value is zero
1560 fn is_zero(&self) -> bool;
1563 macro_rules! impl_is_zero {
1564 ($t: ty, $is_zero: expr) => {
1565 unsafe impl IsZero for $t {
1567 fn is_zero(&self) -> bool {
1574 impl_is_zero!(i8, |x| x == 0);
1575 impl_is_zero!(i16, |x| x == 0);
1576 impl_is_zero!(i32, |x| x == 0);
1577 impl_is_zero!(i64, |x| x == 0);
1578 impl_is_zero!(i128, |x| x == 0);
1579 impl_is_zero!(isize, |x| x == 0);
1581 impl_is_zero!(u16, |x| x == 0);
1582 impl_is_zero!(u32, |x| x == 0);
1583 impl_is_zero!(u64, |x| x == 0);
1584 impl_is_zero!(u128, |x| x == 0);
1585 impl_is_zero!(usize, |x| x == 0);
1587 impl_is_zero!(char, |x| x == '\0');
1589 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
1590 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
1592 unsafe impl<T: ?Sized> IsZero for *const T {
1594 fn is_zero(&self) -> bool {
1599 unsafe impl<T: ?Sized> IsZero for *mut T {
1601 fn is_zero(&self) -> bool {
1607 ////////////////////////////////////////////////////////////////////////////////
1608 // Common trait implementations for Vec
1609 ////////////////////////////////////////////////////////////////////////////////
1611 #[stable(feature = "rust1", since = "1.0.0")]
1612 impl<T: Clone> Clone for Vec<T> {
1614 fn clone(&self) -> Vec<T> {
1615 <[T]>::to_vec(&**self)
1618 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
1619 // required for this method definition, is not available. Instead use the
1620 // `slice::to_vec` function which is only available with cfg(test)
1621 // NB see the slice::hack module in slice.rs for more information
1623 fn clone(&self) -> Vec<T> {
1624 ::slice::to_vec(&**self)
1627 fn clone_from(&mut self, other: &Vec<T>) {
1628 other.as_slice().clone_into(self);
1632 #[stable(feature = "rust1", since = "1.0.0")]
1633 impl<T: Hash> Hash for Vec<T> {
1635 fn hash<H: hash::Hasher>(&self, state: &mut H) {
1636 Hash::hash(&**self, state)
1640 #[stable(feature = "rust1", since = "1.0.0")]
1641 #[rustc_on_unimplemented(
1642 message="vector indices are of type `usize` or ranges of `usize`",
1643 label="vector indices are of type `usize` or ranges of `usize`",
1645 impl<T, I> Index<I> for Vec<T>
1647 I: ::core::slice::SliceIndex<[T]>,
1649 type Output = I::Output;
1652 fn index(&self, index: I) -> &Self::Output {
1653 Index::index(&**self, index)
1657 #[stable(feature = "rust1", since = "1.0.0")]
1658 #[rustc_on_unimplemented(
1659 message="vector indices are of type `usize` or ranges of `usize`",
1660 label="vector indices are of type `usize` or ranges of `usize`",
1662 impl<T, I> IndexMut<I> for Vec<T>
1664 I: ::core::slice::SliceIndex<[T]>,
1667 fn index_mut(&mut self, index: I) -> &mut Self::Output {
1668 IndexMut::index_mut(&mut **self, index)
1672 #[stable(feature = "rust1", since = "1.0.0")]
1673 impl<T> ops::Deref for Vec<T> {
1676 fn deref(&self) -> &[T] {
1678 let p = self.buf.ptr();
1679 assume(!p.is_null());
1680 slice::from_raw_parts(p, self.len)
1685 #[stable(feature = "rust1", since = "1.0.0")]
1686 impl<T> ops::DerefMut for Vec<T> {
1687 fn deref_mut(&mut self) -> &mut [T] {
1689 let ptr = self.buf.ptr();
1690 assume(!ptr.is_null());
1691 slice::from_raw_parts_mut(ptr, self.len)
1696 #[stable(feature = "rust1", since = "1.0.0")]
1697 impl<T> FromIterator<T> for Vec<T> {
1699 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
1700 <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
1704 #[stable(feature = "rust1", since = "1.0.0")]
1705 impl<T> IntoIterator for Vec<T> {
1707 type IntoIter = IntoIter<T>;
1709 /// Creates a consuming iterator, that is, one that moves each value out of
1710 /// the vector (from start to end). The vector cannot be used after calling
1716 /// let v = vec!["a".to_string(), "b".to_string()];
1717 /// for s in v.into_iter() {
1718 /// // s has type String, not &String
1719 /// println!("{}", s);
1723 fn into_iter(mut self) -> IntoIter<T> {
1725 let begin = self.as_mut_ptr();
1726 assume(!begin.is_null());
1727 let end = if mem::size_of::<T>() == 0 {
1728 arith_offset(begin as *const i8, self.len() as isize) as *const T
1730 begin.add(self.len()) as *const T
1732 let cap = self.buf.cap();
1735 buf: NonNull::new_unchecked(begin),
1736 phantom: PhantomData,
1745 #[stable(feature = "rust1", since = "1.0.0")]
1746 impl<'a, T> IntoIterator for &'a Vec<T> {
1748 type IntoIter = slice::Iter<'a, T>;
1750 fn into_iter(self) -> slice::Iter<'a, T> {
1755 #[stable(feature = "rust1", since = "1.0.0")]
1756 impl<'a, T> IntoIterator for &'a mut Vec<T> {
1757 type Item = &'a mut T;
1758 type IntoIter = slice::IterMut<'a, T>;
1760 fn into_iter(self) -> slice::IterMut<'a, T> {
1765 #[stable(feature = "rust1", since = "1.0.0")]
1766 impl<T> Extend<T> for Vec<T> {
1768 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
1769 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
1773 // Specialization trait used for Vec::from_iter and Vec::extend
1774 trait SpecExtend<T, I> {
1775 fn from_iter(iter: I) -> Self;
1776 fn spec_extend(&mut self, iter: I);
1779 impl<T, I> SpecExtend<T, I> for Vec<T>
1780 where I: Iterator<Item=T>,
1782 default fn from_iter(mut iterator: I) -> Self {
1783 // Unroll the first iteration, as the vector is going to be
1784 // expanded on this iteration in every case when the iterable is not
1785 // empty, but the loop in extend_desugared() is not going to see the
1786 // vector being full in the few subsequent loop iterations.
1787 // So we get better branch prediction.
1788 let mut vector = match iterator.next() {
1789 None => return Vec::new(),
1791 let (lower, _) = iterator.size_hint();
1792 let mut vector = Vec::with_capacity(lower.saturating_add(1));
1794 ptr::write(vector.get_unchecked_mut(0), element);
1800 <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
1804 default fn spec_extend(&mut self, iter: I) {
1805 self.extend_desugared(iter)
1809 impl<T, I> SpecExtend<T, I> for Vec<T>
1810 where I: TrustedLen<Item=T>,
1812 default fn from_iter(iterator: I) -> Self {
1813 let mut vector = Vec::new();
1814 vector.spec_extend(iterator);
1818 default fn spec_extend(&mut self, iterator: I) {
1819 // This is the case for a TrustedLen iterator.
1820 let (low, high) = iterator.size_hint();
1821 if let Some(high_value) = high {
1822 debug_assert_eq!(low, high_value,
1823 "TrustedLen iterator's size hint is not exact: {:?}",
1826 if let Some(additional) = high {
1827 self.reserve(additional);
1829 let mut ptr = self.as_mut_ptr().add(self.len());
1830 let mut local_len = SetLenOnDrop::new(&mut self.len);
1831 iterator.for_each(move |element| {
1832 ptr::write(ptr, element);
1833 ptr = ptr.offset(1);
1834 // NB can't overflow since we would have had to alloc the address space
1835 local_len.increment_len(1);
1839 self.extend_desugared(iterator)
1844 impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
1845 fn from_iter(iterator: IntoIter<T>) -> Self {
1846 // A common case is passing a vector into a function which immediately
1847 // re-collects into a vector. We can short circuit this if the IntoIter
1848 // has not been advanced at all.
1849 if iterator.buf.as_ptr() as *const _ == iterator.ptr {
1851 let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
1854 mem::forget(iterator);
1858 let mut vector = Vec::new();
1859 vector.spec_extend(iterator);
1864 fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
1866 self.append_elements(iterator.as_slice() as _);
1868 iterator.ptr = iterator.end;
1872 impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
1873 where I: Iterator<Item=&'a T>,
1876 default fn from_iter(iterator: I) -> Self {
1877 SpecExtend::from_iter(iterator.cloned())
1880 default fn spec_extend(&mut self, iterator: I) {
1881 self.spec_extend(iterator.cloned())
1885 impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
1888 fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
1889 let slice = iterator.as_slice();
1890 self.reserve(slice.len());
1892 let len = self.len();
1893 self.set_len(len + slice.len());
1894 self.get_unchecked_mut(len..).copy_from_slice(slice);
1900 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
1901 // This is the case for a general iterator.
1903 // This function should be the moral equivalent of:
1905 // for item in iterator {
1908 while let Some(element) = iterator.next() {
1909 let len = self.len();
1910 if len == self.capacity() {
1911 let (lower, _) = iterator.size_hint();
1912 self.reserve(lower.saturating_add(1));
1915 ptr::write(self.get_unchecked_mut(len), element);
1916 // NB can't overflow since we would have had to alloc the address space
1917 self.set_len(len + 1);
1922 /// Creates a splicing iterator that replaces the specified range in the vector
1923 /// with the given `replace_with` iterator and yields the removed items.
1924 /// `replace_with` does not need to be the same length as `range`.
1926 /// Note 1: The element range is removed even if the iterator is not
1927 /// consumed until the end.
1929 /// Note 2: It is unspecified how many elements are removed from the vector,
1930 /// if the `Splice` value is leaked.
1932 /// Note 3: The input iterator `replace_with` is only consumed
1933 /// when the `Splice` value is dropped.
1935 /// Note 4: This is optimal if:
1937 /// * The tail (elements in the vector after `range`) is empty,
1938 /// * or `replace_with` yields fewer elements than `range`’s length
1939 /// * or the lower bound of its `size_hint()` is exact.
1941 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
1945 /// Panics if the starting point is greater than the end point or if
1946 /// the end point is greater than the length of the vector.
1951 /// let mut v = vec![1, 2, 3];
1952 /// let new = [7, 8];
1953 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
1954 /// assert_eq!(v, &[7, 8, 3]);
1955 /// assert_eq!(u, &[1, 2]);
1958 #[stable(feature = "vec_splice", since = "1.21.0")]
1959 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<I::IntoIter>
1960 where R: RangeBounds<usize>, I: IntoIterator<Item=T>
1963 drain: self.drain(range),
1964 replace_with: replace_with.into_iter(),
1968 /// Creates an iterator which uses a closure to determine if an element should be removed.
1970 /// If the closure returns true, then the element is removed and yielded.
1971 /// If the closure returns false, the element will remain in the vector and will not be yielded
1972 /// by the iterator.
1974 /// Using this method is equivalent to the following code:
1977 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
1978 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
1980 /// while i != vec.len() {
1981 /// if some_predicate(&mut vec[i]) {
1982 /// let val = vec.remove(i);
1983 /// // your code here
1989 /// # assert_eq!(vec, vec![1, 4, 5]);
1992 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
1993 /// because it can backshift the elements of the array in bulk.
1995 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
1996 /// regardless of whether you choose to keep or remove it.
2001 /// Splitting an array into evens and odds, reusing the original allocation:
2004 /// #![feature(drain_filter)]
2005 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2007 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2008 /// let odds = numbers;
2010 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2011 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2013 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2014 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<T, F>
2015 where F: FnMut(&mut T) -> bool,
2017 let old_len = self.len();
2019 // Guard against us getting leaked (leak amplification)
2020 unsafe { self.set_len(0); }
2032 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2034 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2035 /// append the entire slice at once.
2037 /// [`copy_from_slice`]: ../../std/primitive.slice.html#method.copy_from_slice
2038 #[stable(feature = "extend_ref", since = "1.2.0")]
2039 impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
2040 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2041 self.spec_extend(iter.into_iter())
2045 macro_rules! __impl_slice_eq1 {
2046 ($Lhs: ty, $Rhs: ty) => {
2047 __impl_slice_eq1! { $Lhs, $Rhs, Sized }
2049 ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
2050 #[stable(feature = "rust1", since = "1.0.0")]
2051 impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
2053 fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
2055 fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
2060 __impl_slice_eq1! { Vec<A>, Vec<B> }
2061 __impl_slice_eq1! { Vec<A>, &'b [B] }
2062 __impl_slice_eq1! { Vec<A>, &'b mut [B] }
2063 __impl_slice_eq1! { Cow<'a, [A]>, &'b [B], Clone }
2064 __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B], Clone }
2065 __impl_slice_eq1! { Cow<'a, [A]>, Vec<B>, Clone }
2067 macro_rules! array_impls {
2070 // NOTE: some less important impls are omitted to reduce code bloat
2071 __impl_slice_eq1! { Vec<A>, [B; $N] }
2072 __impl_slice_eq1! { Vec<A>, &'b [B; $N] }
2073 // __impl_slice_eq1! { Vec<A>, &'b mut [B; $N] }
2074 // __impl_slice_eq1! { Cow<'a, [A]>, [B; $N], Clone }
2075 // __impl_slice_eq1! { Cow<'a, [A]>, &'b [B; $N], Clone }
2076 // __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B; $N], Clone }
2083 10 11 12 13 14 15 16 17 18 19
2084 20 21 22 23 24 25 26 27 28 29
2088 /// Implements comparison of vectors, lexicographically.
2089 #[stable(feature = "rust1", since = "1.0.0")]
2090 impl<T: PartialOrd> PartialOrd for Vec<T> {
2092 fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
2093 PartialOrd::partial_cmp(&**self, &**other)
2097 #[stable(feature = "rust1", since = "1.0.0")]
2098 impl<T: Eq> Eq for Vec<T> {}
2100 /// Implements ordering of vectors, lexicographically.
2101 #[stable(feature = "rust1", since = "1.0.0")]
2102 impl<T: Ord> Ord for Vec<T> {
2104 fn cmp(&self, other: &Vec<T>) -> Ordering {
2105 Ord::cmp(&**self, &**other)
2109 #[stable(feature = "rust1", since = "1.0.0")]
2110 unsafe impl<#[may_dangle] T> Drop for Vec<T> {
2111 fn drop(&mut self) {
2114 ptr::drop_in_place(&mut self[..]);
2116 // RawVec handles deallocation
2120 #[stable(feature = "rust1", since = "1.0.0")]
2121 impl<T> Default for Vec<T> {
2122 /// Creates an empty `Vec<T>`.
2123 fn default() -> Vec<T> {
2128 #[stable(feature = "rust1", since = "1.0.0")]
2129 impl<T: fmt::Debug> fmt::Debug for Vec<T> {
2130 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2131 fmt::Debug::fmt(&**self, f)
2135 #[stable(feature = "rust1", since = "1.0.0")]
2136 impl<T> AsRef<Vec<T>> for Vec<T> {
2137 fn as_ref(&self) -> &Vec<T> {
2142 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2143 impl<T> AsMut<Vec<T>> for Vec<T> {
2144 fn as_mut(&mut self) -> &mut Vec<T> {
2149 #[stable(feature = "rust1", since = "1.0.0")]
2150 impl<T> AsRef<[T]> for Vec<T> {
2151 fn as_ref(&self) -> &[T] {
2156 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2157 impl<T> AsMut<[T]> for Vec<T> {
2158 fn as_mut(&mut self) -> &mut [T] {
2163 #[stable(feature = "rust1", since = "1.0.0")]
2164 impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
2166 fn from(s: &'a [T]) -> Vec<T> {
2170 fn from(s: &'a [T]) -> Vec<T> {
2175 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2176 impl<'a, T: Clone> From<&'a mut [T]> for Vec<T> {
2178 fn from(s: &'a mut [T]) -> Vec<T> {
2182 fn from(s: &'a mut [T]) -> Vec<T> {
2187 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2188 impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
2189 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2194 // note: test pulls in libstd, which causes errors here
2196 #[stable(feature = "vec_from_box", since = "1.18.0")]
2197 impl<T> From<Box<[T]>> for Vec<T> {
2198 fn from(s: Box<[T]>) -> Vec<T> {
2203 // note: test pulls in libstd, which causes errors here
2205 #[stable(feature = "box_from_vec", since = "1.20.0")]
2206 impl<T> From<Vec<T>> for Box<[T]> {
2207 fn from(v: Vec<T>) -> Box<[T]> {
2208 v.into_boxed_slice()
2212 #[stable(feature = "rust1", since = "1.0.0")]
2213 impl<'a> From<&'a str> for Vec<u8> {
2214 fn from(s: &'a str) -> Vec<u8> {
2215 From::from(s.as_bytes())
2219 ////////////////////////////////////////////////////////////////////////////////
2221 ////////////////////////////////////////////////////////////////////////////////
2223 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2224 impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
2225 fn from(s: &'a [T]) -> Cow<'a, [T]> {
2230 #[stable(feature = "cow_from_vec", since = "1.8.0")]
2231 impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
2232 fn from(v: Vec<T>) -> Cow<'a, [T]> {
2237 #[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
2238 impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
2239 fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
2240 Cow::Borrowed(v.as_slice())
2244 #[stable(feature = "rust1", since = "1.0.0")]
2245 impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
2246 fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
2247 Cow::Owned(FromIterator::from_iter(it))
2251 ////////////////////////////////////////////////////////////////////////////////
2253 ////////////////////////////////////////////////////////////////////////////////
2255 /// An iterator that moves out of a vector.
2257 /// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
2258 /// by the [`IntoIterator`] trait).
2260 /// [`Vec`]: struct.Vec.html
2261 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
2262 #[stable(feature = "rust1", since = "1.0.0")]
2263 pub struct IntoIter<T> {
2265 phantom: PhantomData<T>,
2271 #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
2272 impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
2273 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2274 f.debug_tuple("IntoIter")
2275 .field(&self.as_slice())
2280 impl<T> IntoIter<T> {
2281 /// Returns the remaining items of this iterator as a slice.
2286 /// let vec = vec!['a', 'b', 'c'];
2287 /// let mut into_iter = vec.into_iter();
2288 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2289 /// let _ = into_iter.next().unwrap();
2290 /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
2292 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2293 pub fn as_slice(&self) -> &[T] {
2295 slice::from_raw_parts(self.ptr, self.len())
2299 /// Returns the remaining items of this iterator as a mutable slice.
2304 /// let vec = vec!['a', 'b', 'c'];
2305 /// let mut into_iter = vec.into_iter();
2306 /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
2307 /// into_iter.as_mut_slice()[2] = 'z';
2308 /// assert_eq!(into_iter.next().unwrap(), 'a');
2309 /// assert_eq!(into_iter.next().unwrap(), 'b');
2310 /// assert_eq!(into_iter.next().unwrap(), 'z');
2312 #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
2313 pub fn as_mut_slice(&mut self) -> &mut [T] {
2315 slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
2320 #[stable(feature = "rust1", since = "1.0.0")]
2321 unsafe impl<T: Send> Send for IntoIter<T> {}
2322 #[stable(feature = "rust1", since = "1.0.0")]
2323 unsafe impl<T: Sync> Sync for IntoIter<T> {}
2325 #[stable(feature = "rust1", since = "1.0.0")]
2326 impl<T> Iterator for IntoIter<T> {
2330 fn next(&mut self) -> Option<T> {
2332 if self.ptr as *const _ == self.end {
2335 if mem::size_of::<T>() == 0 {
2336 // purposefully don't use 'ptr.offset' because for
2337 // vectors with 0-size elements this would return the
2339 self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
2341 // Make up a value of this ZST.
2345 self.ptr = self.ptr.offset(1);
2347 Some(ptr::read(old))
2354 fn size_hint(&self) -> (usize, Option<usize>) {
2355 let exact = if mem::size_of::<T>() == 0 {
2356 (self.end as usize).wrapping_sub(self.ptr as usize)
2358 unsafe { self.end.offset_from(self.ptr) as usize }
2360 (exact, Some(exact))
2364 fn count(self) -> usize {
2369 #[stable(feature = "rust1", since = "1.0.0")]
2370 impl<T> DoubleEndedIterator for IntoIter<T> {
2372 fn next_back(&mut self) -> Option<T> {
2374 if self.end == self.ptr {
2377 if mem::size_of::<T>() == 0 {
2378 // See above for why 'ptr.offset' isn't used
2379 self.end = arith_offset(self.end as *const i8, -1) as *mut T;
2381 // Make up a value of this ZST.
2384 self.end = self.end.offset(-1);
2386 Some(ptr::read(self.end))
2393 #[stable(feature = "rust1", since = "1.0.0")]
2394 impl<T> ExactSizeIterator for IntoIter<T> {
2395 fn is_empty(&self) -> bool {
2396 self.ptr == self.end
2400 #[stable(feature = "fused", since = "1.26.0")]
2401 impl<T> FusedIterator for IntoIter<T> {}
2403 #[unstable(feature = "trusted_len", issue = "37572")]
2404 unsafe impl<T> TrustedLen for IntoIter<T> {}
2406 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
2407 impl<T: Clone> Clone for IntoIter<T> {
2408 fn clone(&self) -> IntoIter<T> {
2409 self.as_slice().to_owned().into_iter()
2413 #[stable(feature = "rust1", since = "1.0.0")]
2414 unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
2415 fn drop(&mut self) {
2416 // destroy the remaining elements
2417 for _x in self.by_ref() {}
2419 // RawVec handles deallocation
2420 let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
2424 /// A draining iterator for `Vec<T>`.
2426 /// This `struct` is created by the [`drain`] method on [`Vec`].
2428 /// [`drain`]: struct.Vec.html#method.drain
2429 /// [`Vec`]: struct.Vec.html
2430 #[stable(feature = "drain", since = "1.6.0")]
2431 pub struct Drain<'a, T: 'a> {
2432 /// Index of tail to preserve
2436 /// Current remaining range to remove
2437 iter: slice::Iter<'a, T>,
2438 vec: NonNull<Vec<T>>,
2441 #[stable(feature = "collection_debug", since = "1.17.0")]
2442 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Drain<'a, T> {
2443 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2444 f.debug_tuple("Drain")
2445 .field(&self.iter.as_slice())
2450 #[stable(feature = "drain", since = "1.6.0")]
2451 unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
2452 #[stable(feature = "drain", since = "1.6.0")]
2453 unsafe impl<'a, T: Send> Send for Drain<'a, T> {}
2455 #[stable(feature = "drain", since = "1.6.0")]
2456 impl<'a, T> Iterator for Drain<'a, T> {
2460 fn next(&mut self) -> Option<T> {
2461 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
2464 fn size_hint(&self) -> (usize, Option<usize>) {
2465 self.iter.size_hint()
2469 #[stable(feature = "drain", since = "1.6.0")]
2470 impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
2472 fn next_back(&mut self) -> Option<T> {
2473 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
2477 #[stable(feature = "drain", since = "1.6.0")]
2478 impl<'a, T> Drop for Drain<'a, T> {
2479 fn drop(&mut self) {
2480 // exhaust self first
2481 self.for_each(drop);
2483 if self.tail_len > 0 {
2485 let source_vec = self.vec.as_mut();
2486 // memmove back untouched tail, update to new length
2487 let start = source_vec.len();
2488 let tail = self.tail_start;
2490 let src = source_vec.as_ptr().add(tail);
2491 let dst = source_vec.as_mut_ptr().add(start);
2492 ptr::copy(src, dst, self.tail_len);
2494 source_vec.set_len(start + self.tail_len);
2501 #[stable(feature = "drain", since = "1.6.0")]
2502 impl<'a, T> ExactSizeIterator for Drain<'a, T> {
2503 fn is_empty(&self) -> bool {
2504 self.iter.is_empty()
2508 #[stable(feature = "fused", since = "1.26.0")]
2509 impl<'a, T> FusedIterator for Drain<'a, T> {}
2511 /// A splicing iterator for `Vec`.
2513 /// This struct is created by the [`splice()`] method on [`Vec`]. See its
2514 /// documentation for more.
2516 /// [`splice()`]: struct.Vec.html#method.splice
2517 /// [`Vec`]: struct.Vec.html
2519 #[stable(feature = "vec_splice", since = "1.21.0")]
2520 pub struct Splice<'a, I: Iterator + 'a> {
2521 drain: Drain<'a, I::Item>,
2525 #[stable(feature = "vec_splice", since = "1.21.0")]
2526 impl<'a, I: Iterator> Iterator for Splice<'a, I> {
2527 type Item = I::Item;
2529 fn next(&mut self) -> Option<Self::Item> {
2533 fn size_hint(&self) -> (usize, Option<usize>) {
2534 self.drain.size_hint()
2538 #[stable(feature = "vec_splice", since = "1.21.0")]
2539 impl<'a, I: Iterator> DoubleEndedIterator for Splice<'a, I> {
2540 fn next_back(&mut self) -> Option<Self::Item> {
2541 self.drain.next_back()
2545 #[stable(feature = "vec_splice", since = "1.21.0")]
2546 impl<'a, I: Iterator> ExactSizeIterator for Splice<'a, I> {}
2549 #[stable(feature = "vec_splice", since = "1.21.0")]
2550 impl<'a, I: Iterator> Drop for Splice<'a, I> {
2551 fn drop(&mut self) {
2552 self.drain.by_ref().for_each(drop);
2555 if self.drain.tail_len == 0 {
2556 self.drain.vec.as_mut().extend(self.replace_with.by_ref());
2560 // First fill the range left by drain().
2561 if !self.drain.fill(&mut self.replace_with) {
2565 // There may be more elements. Use the lower bound as an estimate.
2566 // FIXME: Is the upper bound a better guess? Or something else?
2567 let (lower_bound, _upper_bound) = self.replace_with.size_hint();
2568 if lower_bound > 0 {
2569 self.drain.move_tail(lower_bound);
2570 if !self.drain.fill(&mut self.replace_with) {
2575 // Collect any remaining elements.
2576 // This is a zero-length vector which does not allocate if `lower_bound` was exact.
2577 let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
2578 // Now we have an exact count.
2579 if collected.len() > 0 {
2580 self.drain.move_tail(collected.len());
2581 let filled = self.drain.fill(&mut collected);
2582 debug_assert!(filled);
2583 debug_assert_eq!(collected.len(), 0);
2586 // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
2590 /// Private helper methods for `Splice::drop`
2591 impl<'a, T> Drain<'a, T> {
2592 /// The range from `self.vec.len` to `self.tail_start` contains elements
2593 /// that have been moved out.
2594 /// Fill that range as much as possible with new elements from the `replace_with` iterator.
2595 /// Return whether we filled the entire range. (`replace_with.next()` didn’t return `None`.)
2596 unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
2597 let vec = self.vec.as_mut();
2598 let range_start = vec.len;
2599 let range_end = self.tail_start;
2600 let range_slice = slice::from_raw_parts_mut(
2601 vec.as_mut_ptr().add(range_start),
2602 range_end - range_start);
2604 for place in range_slice {
2605 if let Some(new_item) = replace_with.next() {
2606 ptr::write(place, new_item);
2615 /// Make room for inserting more elements before the tail.
2616 unsafe fn move_tail(&mut self, extra_capacity: usize) {
2617 let vec = self.vec.as_mut();
2618 let used_capacity = self.tail_start + self.tail_len;
2619 vec.buf.reserve(used_capacity, extra_capacity);
2621 let new_tail_start = self.tail_start + extra_capacity;
2622 let src = vec.as_ptr().add(self.tail_start);
2623 let dst = vec.as_mut_ptr().add(new_tail_start);
2624 ptr::copy(src, dst, self.tail_len);
2625 self.tail_start = new_tail_start;
2629 /// An iterator produced by calling `drain_filter` on Vec.
2630 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2632 pub struct DrainFilter<'a, T: 'a, F>
2633 where F: FnMut(&mut T) -> bool,
2635 vec: &'a mut Vec<T>,
2642 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2643 impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
2644 where F: FnMut(&mut T) -> bool,
2648 fn next(&mut self) -> Option<T> {
2650 while self.idx != self.old_len {
2653 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
2654 if (self.pred)(&mut v[i]) {
2656 return Some(ptr::read(&v[i]));
2657 } else if self.del > 0 {
2659 let src: *const T = &v[i];
2660 let dst: *mut T = &mut v[i - del];
2661 // This is safe because self.vec has length 0
2662 // thus its elements will not have Drop::drop
2663 // called on them in the event of a panic.
2664 ptr::copy_nonoverlapping(src, dst, 1);
2671 fn size_hint(&self) -> (usize, Option<usize>) {
2672 (0, Some(self.old_len - self.idx))
2676 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2677 impl<'a, T, F> Drop for DrainFilter<'a, T, F>
2678 where F: FnMut(&mut T) -> bool,
2680 fn drop(&mut self) {
2681 self.for_each(drop);
2683 self.vec.set_len(self.old_len - self.del);