1 // SPDX-License-Identifier: Apache-2.0 OR MIT
3 //! A contiguous growable array type with heap-allocated contents, written
6 //! Vectors have *O*(1) indexing, amortized *O*(1) push (to the end) and
7 //! *O*(1) pop (from the end).
9 //! Vectors ensure they never allocate more than `isize::MAX` bytes.
13 //! You can explicitly create a [`Vec`] with [`Vec::new`]:
16 //! let v: Vec<i32> = Vec::new();
19 //! ...or by using the [`vec!`] macro:
22 //! let v: Vec<i32> = vec![];
24 //! let v = vec![1, 2, 3, 4, 5];
26 //! let v = vec![0; 10]; // ten zeroes
29 //! You can [`push`] values onto the end of a vector (which will grow the vector
33 //! let mut v = vec![1, 2];
38 //! Popping values works in much the same way:
41 //! let mut v = vec![1, 2];
43 //! let two = v.pop();
46 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
49 //! let mut v = vec![1, 2, 3];
54 //! [`push`]: Vec::push
56 #![stable(feature = "rust1", since = "1.0.0")]
58 #[cfg(not(no_global_oom_handling))]
60 use core::cmp::Ordering;
62 use core::hash::{Hash, Hasher};
64 use core::marker::PhantomData;
65 use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
66 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
67 use core::ptr::{self, NonNull};
68 use core::slice::{self, SliceIndex};
70 use crate::alloc::{Allocator, Global};
71 #[cfg(not(no_borrow))]
72 use crate::borrow::{Cow, ToOwned};
73 use crate::boxed::Box;
74 use crate::collections::{TryReserveError, TryReserveErrorKind};
75 use crate::raw_vec::RawVec;
77 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
78 pub use self::extract_if::ExtractIf;
82 #[cfg(not(no_global_oom_handling))]
83 #[stable(feature = "vec_splice", since = "1.21.0")]
84 pub use self::splice::Splice;
86 #[cfg(not(no_global_oom_handling))]
89 #[stable(feature = "drain", since = "1.6.0")]
90 pub use self::drain::Drain;
94 #[cfg(not(no_borrow))]
95 #[cfg(not(no_global_oom_handling))]
98 #[cfg(not(no_global_oom_handling))]
99 pub(crate) use self::in_place_collect::AsVecIntoIter;
100 #[stable(feature = "rust1", since = "1.0.0")]
101 pub use self::into_iter::IntoIter;
105 #[cfg(not(no_global_oom_handling))]
106 use self::is_zero::IsZero;
108 #[cfg(not(no_global_oom_handling))]
111 #[cfg(not(no_global_oom_handling))]
112 mod in_place_collect;
116 #[cfg(not(no_global_oom_handling))]
117 use self::spec_from_elem::SpecFromElem;
119 #[cfg(not(no_global_oom_handling))]
122 use self::set_len_on_drop::SetLenOnDrop;
126 #[cfg(not(no_global_oom_handling))]
127 use self::in_place_drop::{InPlaceDrop, InPlaceDstDataSrcBufDrop};
129 #[cfg(not(no_global_oom_handling))]
132 #[cfg(not(no_global_oom_handling))]
133 use self::spec_from_iter_nested::SpecFromIterNested;
135 #[cfg(not(no_global_oom_handling))]
136 mod spec_from_iter_nested;
138 #[cfg(not(no_global_oom_handling))]
139 use self::spec_from_iter::SpecFromIter;
141 #[cfg(not(no_global_oom_handling))]
144 #[cfg(not(no_global_oom_handling))]
145 use self::spec_extend::SpecExtend;
147 use self::spec_extend::TrySpecExtend;
151 /// A contiguous growable array type, written as `Vec<T>`, short for 'vector'.
156 /// let mut vec = Vec::new();
160 /// assert_eq!(vec.len(), 2);
161 /// assert_eq!(vec[0], 1);
163 /// assert_eq!(vec.pop(), Some(2));
164 /// assert_eq!(vec.len(), 1);
167 /// assert_eq!(vec[0], 7);
169 /// vec.extend([1, 2, 3]);
174 /// assert_eq!(vec, [7, 1, 2, 3]);
177 /// The [`vec!`] macro is provided for convenient initialization:
180 /// let mut vec1 = vec![1, 2, 3];
182 /// let vec2 = Vec::from([1, 2, 3, 4]);
183 /// assert_eq!(vec1, vec2);
186 /// It can also initialize each element of a `Vec<T>` with a given value.
187 /// This may be more efficient than performing allocation and initialization
188 /// in separate steps, especially when initializing a vector of zeros:
191 /// let vec = vec![0; 5];
192 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
194 /// // The following is equivalent, but potentially slower:
195 /// let mut vec = Vec::with_capacity(5);
196 /// vec.resize(5, 0);
197 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
200 /// For more information, see
201 /// [Capacity and Reallocation](#capacity-and-reallocation).
203 /// Use a `Vec<T>` as an efficient stack:
206 /// let mut stack = Vec::new();
212 /// while let Some(top) = stack.pop() {
213 /// // Prints 3, 2, 1
214 /// println!("{top}");
220 /// The `Vec` type allows access to values by index, because it implements the
221 /// [`Index`] trait. An example will be more explicit:
224 /// let v = vec![0, 2, 4, 6];
225 /// println!("{}", v[1]); // it will display '2'
228 /// However be careful: if you try to access an index which isn't in the `Vec`,
229 /// your software will panic! You cannot do this:
232 /// let v = vec![0, 2, 4, 6];
233 /// println!("{}", v[6]); // it will panic!
236 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
241 /// A `Vec` can be mutable. On the other hand, slices are read-only objects.
242 /// To get a [slice][prim@slice], use [`&`]. Example:
245 /// fn read_slice(slice: &[usize]) {
249 /// let v = vec![0, 1];
252 /// // ... and that's all!
253 /// // you can also do it like this:
254 /// let u: &[usize] = &v;
256 /// let u: &[_] = &v;
259 /// In Rust, it's more common to pass slices as arguments rather than vectors
260 /// when you just want to provide read access. The same goes for [`String`] and
263 /// # Capacity and reallocation
265 /// The capacity of a vector is the amount of space allocated for any future
266 /// elements that will be added onto the vector. This is not to be confused with
267 /// the *length* of a vector, which specifies the number of actual elements
268 /// within the vector. If a vector's length exceeds its capacity, its capacity
269 /// will automatically be increased, but its elements will have to be
272 /// For example, a vector with capacity 10 and length 0 would be an empty vector
273 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
274 /// vector will not change its capacity or cause reallocation to occur. However,
275 /// if the vector's length is increased to 11, it will have to reallocate, which
276 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
277 /// whenever possible to specify how big the vector is expected to get.
281 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
282 /// about its design. This ensures that it's as low-overhead as possible in
283 /// the general case, and can be correctly manipulated in primitive ways
284 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
285 /// If additional type parameters are added (e.g., to support custom allocators),
286 /// overriding their defaults may change the behavior.
288 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
289 /// triplet. No more, no less. The order of these fields is completely
290 /// unspecified, and you should use the appropriate methods to modify these.
291 /// The pointer will never be null, so this type is null-pointer-optimized.
293 /// However, the pointer might not actually point to allocated memory. In particular,
294 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
295 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
296 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
297 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
298 /// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
299 /// if <code>[mem::size_of::\<T>]\() * [capacity]\() > 0</code>. In general, `Vec`'s allocation
300 /// details are very subtle --- if you intend to allocate memory using a `Vec`
301 /// and use it for something else (either to pass to unsafe code, or to build your
302 /// own memory-backed collection), be sure to deallocate this memory by using
303 /// `from_raw_parts` to recover the `Vec` and then dropping it.
305 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
306 /// (as defined by the allocator Rust is configured to use by default), and its
307 /// pointer points to [`len`] initialized, contiguous elements in order (what
308 /// you would see if you coerced it to a slice), followed by <code>[capacity] - [len]</code>
309 /// logically uninitialized, contiguous elements.
311 /// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
312 /// visualized as below. The top part is the `Vec` struct, it contains a
313 /// pointer to the head of the allocation in the heap, length and capacity.
314 /// The bottom part is the allocation on the heap, a contiguous memory block.
318 /// +--------+--------+--------+
319 /// | 0x0123 | 2 | 4 |
320 /// +--------+--------+--------+
323 /// Heap +--------+--------+--------+--------+
324 /// | 'a' | 'b' | uninit | uninit |
325 /// +--------+--------+--------+--------+
328 /// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
329 /// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
330 /// layout (including the order of fields).
332 /// `Vec` will never perform a "small optimization" where elements are actually
333 /// stored on the stack for two reasons:
335 /// * It would make it more difficult for unsafe code to correctly manipulate
336 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
337 /// only moved, and it would be more difficult to determine if a `Vec` had
338 /// actually allocated memory.
340 /// * It would penalize the general case, incurring an additional branch
343 /// `Vec` will never automatically shrink itself, even if completely empty. This
344 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
345 /// and then filling it back up to the same [`len`] should incur no calls to
346 /// the allocator. If you wish to free up unused memory, use
347 /// [`shrink_to_fit`] or [`shrink_to`].
349 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
350 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
351 /// <code>[len] == [capacity]</code>. That is, the reported capacity is completely
352 /// accurate, and can be relied on. It can even be used to manually free the memory
353 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
354 /// when not necessary.
356 /// `Vec` does not guarantee any particular growth strategy when reallocating
357 /// when full, nor when [`reserve`] is called. The current strategy is basic
358 /// and it may prove desirable to use a non-constant growth factor. Whatever
359 /// strategy is used will of course guarantee *O*(1) amortized [`push`].
361 /// `vec![x; n]`, `vec![a, b, c, d]`, and
362 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
363 /// with exactly the requested capacity. If <code>[len] == [capacity]</code>,
364 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
365 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
367 /// `Vec` will not specifically overwrite any data that is removed from it,
368 /// but also won't specifically preserve it. Its uninitialized memory is
369 /// scratch space that it may use however it wants. It will generally just do
370 /// whatever is most efficient or otherwise easy to implement. Do not rely on
371 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
372 /// buffer may simply be reused by another allocation. Even if you zero a `Vec`'s memory
373 /// first, that might not actually happen because the optimizer does not consider
374 /// this a side-effect that must be preserved. There is one case which we will
375 /// not break, however: using `unsafe` code to write to the excess capacity,
376 /// and then increasing the length to match, is always valid.
378 /// Currently, `Vec` does not guarantee the order in which elements are dropped.
379 /// The order has changed in the past and may change again.
381 /// [`get`]: slice::get
382 /// [`get_mut`]: slice::get_mut
383 /// [`String`]: crate::string::String
384 /// [`&str`]: type@str
385 /// [`shrink_to_fit`]: Vec::shrink_to_fit
386 /// [`shrink_to`]: Vec::shrink_to
387 /// [capacity]: Vec::capacity
388 /// [`capacity`]: Vec::capacity
389 /// [mem::size_of::\<T>]: core::mem::size_of
391 /// [`len`]: Vec::len
392 /// [`push`]: Vec::push
393 /// [`insert`]: Vec::insert
394 /// [`reserve`]: Vec::reserve
395 /// [`MaybeUninit`]: core::mem::MaybeUninit
396 /// [owned slice]: Box
397 #[stable(feature = "rust1", since = "1.0.0")]
398 #[cfg_attr(not(test), rustc_diagnostic_item = "Vec")]
399 #[rustc_insignificant_dtor]
400 pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
405 ////////////////////////////////////////////////////////////////////////////////
407 ////////////////////////////////////////////////////////////////////////////////
410 /// Constructs a new, empty `Vec<T>`.
412 /// The vector will not allocate until elements are pushed onto it.
417 /// # #![allow(unused_mut)]
418 /// let mut vec: Vec<i32> = Vec::new();
421 #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
422 #[stable(feature = "rust1", since = "1.0.0")]
424 pub const fn new() -> Self {
425 Vec { buf: RawVec::NEW, len: 0 }
428 /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
430 /// The vector will be able to hold at least `capacity` elements without
431 /// reallocating. This method is allowed to allocate for more elements than
432 /// `capacity`. If `capacity` is 0, the vector will not allocate.
434 /// It is important to note that although the returned vector has the
435 /// minimum *capacity* specified, the vector will have a zero *length*. For
436 /// an explanation of the difference between length and capacity, see
437 /// *[Capacity and reallocation]*.
439 /// If it is important to know the exact allocated capacity of a `Vec`,
440 /// always use the [`capacity`] method after construction.
442 /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
443 /// and the capacity will always be `usize::MAX`.
445 /// [Capacity and reallocation]: #capacity-and-reallocation
446 /// [`capacity`]: Vec::capacity
450 /// Panics if the new capacity exceeds `isize::MAX` bytes.
455 /// let mut vec = Vec::with_capacity(10);
457 /// // The vector contains no items, even though it has capacity for more
458 /// assert_eq!(vec.len(), 0);
459 /// assert!(vec.capacity() >= 10);
461 /// // These are all done without reallocating...
465 /// assert_eq!(vec.len(), 10);
466 /// assert!(vec.capacity() >= 10);
468 /// // ...but this may make the vector reallocate
470 /// assert_eq!(vec.len(), 11);
471 /// assert!(vec.capacity() >= 11);
473 /// // A vector of a zero-sized type will always over-allocate, since no
474 /// // allocation is necessary
475 /// let vec_units = Vec::<()>::with_capacity(10);
476 /// assert_eq!(vec_units.capacity(), usize::MAX);
478 #[cfg(not(no_global_oom_handling))]
480 #[stable(feature = "rust1", since = "1.0.0")]
482 pub fn with_capacity(capacity: usize) -> Self {
483 Self::with_capacity_in(capacity, Global)
486 /// Tries to construct a new, empty `Vec<T>` with at least the specified capacity.
488 /// The vector will be able to hold at least `capacity` elements without
489 /// reallocating. This method is allowed to allocate for more elements than
490 /// `capacity`. If `capacity` is 0, the vector will not allocate.
492 /// It is important to note that although the returned vector has the
493 /// minimum *capacity* specified, the vector will have a zero *length*. For
494 /// an explanation of the difference between length and capacity, see
495 /// *[Capacity and reallocation]*.
497 /// If it is important to know the exact allocated capacity of a `Vec`,
498 /// always use the [`capacity`] method after construction.
500 /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
501 /// and the capacity will always be `usize::MAX`.
503 /// [Capacity and reallocation]: #capacity-and-reallocation
504 /// [`capacity`]: Vec::capacity
509 /// let mut vec = Vec::try_with_capacity(10).unwrap();
511 /// // The vector contains no items, even though it has capacity for more
512 /// assert_eq!(vec.len(), 0);
513 /// assert!(vec.capacity() >= 10);
515 /// // These are all done without reallocating...
519 /// assert_eq!(vec.len(), 10);
520 /// assert!(vec.capacity() >= 10);
522 /// // ...but this may make the vector reallocate
524 /// assert_eq!(vec.len(), 11);
525 /// assert!(vec.capacity() >= 11);
527 /// let mut result = Vec::try_with_capacity(usize::MAX);
528 /// assert!(result.is_err());
530 /// // A vector of a zero-sized type will always over-allocate, since no
531 /// // allocation is necessary
532 /// let vec_units = Vec::<()>::try_with_capacity(10).unwrap();
533 /// assert_eq!(vec_units.capacity(), usize::MAX);
536 #[stable(feature = "kernel", since = "1.0.0")]
537 pub fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError> {
538 Self::try_with_capacity_in(capacity, Global)
541 /// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
545 /// This is highly unsafe, due to the number of invariants that aren't
548 /// * `ptr` must have been allocated using the global allocator, such as via
549 /// the [`alloc::alloc`] function.
550 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
551 /// (`T` having a less strict alignment is not sufficient, the alignment really
552 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
553 /// allocated and deallocated with the same layout.)
554 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
555 /// to be the same size as the pointer was allocated with. (Because similar to
556 /// alignment, [`dealloc`] must be called with the same layout `size`.)
557 /// * `length` needs to be less than or equal to `capacity`.
558 /// * The first `length` values must be properly initialized values of type `T`.
559 /// * `capacity` needs to be the capacity that the pointer was allocated with.
560 /// * The allocated size in bytes must be no larger than `isize::MAX`.
561 /// See the safety documentation of [`pointer::offset`].
563 /// These requirements are always upheld by any `ptr` that has been allocated
564 /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
567 /// Violating these may cause problems like corrupting the allocator's
568 /// internal data structures. For example it is normally **not** safe
569 /// to build a `Vec<u8>` from a pointer to a C `char` array with length
570 /// `size_t`, doing so is only safe if the array was initially allocated by
571 /// a `Vec` or `String`.
572 /// It's also not safe to build one from a `Vec<u16>` and its length, because
573 /// the allocator cares about the alignment, and these two types have different
574 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
575 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
576 /// these issues, it is often preferable to do casting/transmuting using
577 /// [`slice::from_raw_parts`] instead.
579 /// The ownership of `ptr` is effectively transferred to the
580 /// `Vec<T>` which may then deallocate, reallocate or change the
581 /// contents of memory pointed to by the pointer at will. Ensure
582 /// that nothing else uses the pointer after calling this
585 /// [`String`]: crate::string::String
586 /// [`alloc::alloc`]: crate::alloc::alloc
587 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
595 /// let v = vec![1, 2, 3];
597 // FIXME Update this when vec_into_raw_parts is stabilized
598 /// // Prevent running `v`'s destructor so we are in complete control
599 /// // of the allocation.
600 /// let mut v = mem::ManuallyDrop::new(v);
602 /// // Pull out the various important pieces of information about `v`
603 /// let p = v.as_mut_ptr();
604 /// let len = v.len();
605 /// let cap = v.capacity();
608 /// // Overwrite memory with 4, 5, 6
609 /// for i in 0..len {
610 /// ptr::write(p.add(i), 4 + i);
613 /// // Put everything back together into a Vec
614 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
615 /// assert_eq!(rebuilt, [4, 5, 6]);
619 /// Using memory that was allocated elsewhere:
622 /// use std::alloc::{alloc, Layout};
625 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
627 /// let vec = unsafe {
628 /// let mem = alloc(layout).cast::<u32>();
629 /// if mem.is_null() {
633 /// mem.write(1_000_000);
635 /// Vec::from_raw_parts(mem, 1, 16)
638 /// assert_eq!(vec, &[1_000_000]);
639 /// assert_eq!(vec.capacity(), 16);
643 #[stable(feature = "rust1", since = "1.0.0")]
644 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
645 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
649 impl<T, A: Allocator> Vec<T, A> {
650 /// Constructs a new, empty `Vec<T, A>`.
652 /// The vector will not allocate until elements are pushed onto it.
657 /// #![feature(allocator_api)]
659 /// use std::alloc::System;
661 /// # #[allow(unused_mut)]
662 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
665 #[unstable(feature = "allocator_api", issue = "32838")]
666 pub const fn new_in(alloc: A) -> Self {
667 Vec { buf: RawVec::new_in(alloc), len: 0 }
670 /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
671 /// with the provided allocator.
673 /// The vector will be able to hold at least `capacity` elements without
674 /// reallocating. This method is allowed to allocate for more elements than
675 /// `capacity`. If `capacity` is 0, the vector will not allocate.
677 /// It is important to note that although the returned vector has the
678 /// minimum *capacity* specified, the vector will have a zero *length*. For
679 /// an explanation of the difference between length and capacity, see
680 /// *[Capacity and reallocation]*.
682 /// If it is important to know the exact allocated capacity of a `Vec`,
683 /// always use the [`capacity`] method after construction.
685 /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
686 /// and the capacity will always be `usize::MAX`.
688 /// [Capacity and reallocation]: #capacity-and-reallocation
689 /// [`capacity`]: Vec::capacity
693 /// Panics if the new capacity exceeds `isize::MAX` bytes.
698 /// #![feature(allocator_api)]
700 /// use std::alloc::System;
702 /// let mut vec = Vec::with_capacity_in(10, System);
704 /// // The vector contains no items, even though it has capacity for more
705 /// assert_eq!(vec.len(), 0);
706 /// assert!(vec.capacity() >= 10);
708 /// // These are all done without reallocating...
712 /// assert_eq!(vec.len(), 10);
713 /// assert!(vec.capacity() >= 10);
715 /// // ...but this may make the vector reallocate
717 /// assert_eq!(vec.len(), 11);
718 /// assert!(vec.capacity() >= 11);
720 /// // A vector of a zero-sized type will always over-allocate, since no
721 /// // allocation is necessary
722 /// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
723 /// assert_eq!(vec_units.capacity(), usize::MAX);
725 #[cfg(not(no_global_oom_handling))]
727 #[unstable(feature = "allocator_api", issue = "32838")]
728 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
729 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
732 /// Tries to construct a new, empty `Vec<T, A>` with at least the specified capacity
733 /// with the provided allocator.
735 /// The vector will be able to hold at least `capacity` elements without
736 /// reallocating. This method is allowed to allocate for more elements than
737 /// `capacity`. If `capacity` is 0, the vector will not allocate.
739 /// It is important to note that although the returned vector has the
740 /// minimum *capacity* specified, the vector will have a zero *length*. For
741 /// an explanation of the difference between length and capacity, see
742 /// *[Capacity and reallocation]*.
744 /// If it is important to know the exact allocated capacity of a `Vec`,
745 /// always use the [`capacity`] method after construction.
747 /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
748 /// and the capacity will always be `usize::MAX`.
750 /// [Capacity and reallocation]: #capacity-and-reallocation
751 /// [`capacity`]: Vec::capacity
756 /// #![feature(allocator_api)]
758 /// use std::alloc::System;
760 /// let mut vec = Vec::try_with_capacity_in(10, System).unwrap();
762 /// // The vector contains no items, even though it has capacity for more
763 /// assert_eq!(vec.len(), 0);
764 /// assert!(vec.capacity() >= 10);
766 /// // These are all done without reallocating...
770 /// assert_eq!(vec.len(), 10);
771 /// assert!(vec.capacity() >= 10);
773 /// // ...but this may make the vector reallocate
775 /// assert_eq!(vec.len(), 11);
776 /// assert!(vec.capacity() >= 11);
778 /// let mut result = Vec::try_with_capacity_in(usize::MAX, System);
779 /// assert!(result.is_err());
781 /// // A vector of a zero-sized type will always over-allocate, since no
782 /// // allocation is necessary
783 /// let vec_units = Vec::<(), System>::try_with_capacity_in(10, System).unwrap();
784 /// assert_eq!(vec_units.capacity(), usize::MAX);
787 #[stable(feature = "kernel", since = "1.0.0")]
788 pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
789 Ok(Vec { buf: RawVec::try_with_capacity_in(capacity, alloc)?, len: 0 })
792 /// Creates a `Vec<T, A>` directly from a pointer, a capacity, a length,
793 /// and an allocator.
797 /// This is highly unsafe, due to the number of invariants that aren't
800 /// * `ptr` must be [*currently allocated*] via the given allocator `alloc`.
801 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
802 /// (`T` having a less strict alignment is not sufficient, the alignment really
803 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
804 /// allocated and deallocated with the same layout.)
805 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
806 /// to be the same size as the pointer was allocated with. (Because similar to
807 /// alignment, [`dealloc`] must be called with the same layout `size`.)
808 /// * `length` needs to be less than or equal to `capacity`.
809 /// * The first `length` values must be properly initialized values of type `T`.
810 /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
811 /// * The allocated size in bytes must be no larger than `isize::MAX`.
812 /// See the safety documentation of [`pointer::offset`].
814 /// These requirements are always upheld by any `ptr` that has been allocated
815 /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
818 /// Violating these may cause problems like corrupting the allocator's
819 /// internal data structures. For example it is **not** safe
820 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
821 /// It's also not safe to build one from a `Vec<u16>` and its length, because
822 /// the allocator cares about the alignment, and these two types have different
823 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
824 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
826 /// The ownership of `ptr` is effectively transferred to the
827 /// `Vec<T>` which may then deallocate, reallocate or change the
828 /// contents of memory pointed to by the pointer at will. Ensure
829 /// that nothing else uses the pointer after calling this
832 /// [`String`]: crate::string::String
833 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
834 /// [*currently allocated*]: crate::alloc::Allocator#currently-allocated-memory
835 /// [*fit*]: crate::alloc::Allocator#memory-fitting
840 /// #![feature(allocator_api)]
842 /// use std::alloc::System;
847 /// let mut v = Vec::with_capacity_in(3, System);
852 // FIXME Update this when vec_into_raw_parts is stabilized
853 /// // Prevent running `v`'s destructor so we are in complete control
854 /// // of the allocation.
855 /// let mut v = mem::ManuallyDrop::new(v);
857 /// // Pull out the various important pieces of information about `v`
858 /// let p = v.as_mut_ptr();
859 /// let len = v.len();
860 /// let cap = v.capacity();
861 /// let alloc = v.allocator();
864 /// // Overwrite memory with 4, 5, 6
865 /// for i in 0..len {
866 /// ptr::write(p.add(i), 4 + i);
869 /// // Put everything back together into a Vec
870 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
871 /// assert_eq!(rebuilt, [4, 5, 6]);
875 /// Using memory that was allocated elsewhere:
878 /// #![feature(allocator_api)]
880 /// use std::alloc::{AllocError, Allocator, Global, Layout};
883 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
885 /// let vec = unsafe {
886 /// let mem = match Global.allocate(layout) {
887 /// Ok(mem) => mem.cast::<u32>().as_ptr(),
888 /// Err(AllocError) => return,
891 /// mem.write(1_000_000);
893 /// Vec::from_raw_parts_in(mem, 1, 16, Global)
896 /// assert_eq!(vec, &[1_000_000]);
897 /// assert_eq!(vec.capacity(), 16);
901 #[unstable(feature = "allocator_api", issue = "32838")]
902 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
903 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
906 /// Decomposes a `Vec<T>` into its raw components.
908 /// Returns the raw pointer to the underlying data, the length of
909 /// the vector (in elements), and the allocated capacity of the
910 /// data (in elements). These are the same arguments in the same
911 /// order as the arguments to [`from_raw_parts`].
913 /// After calling this function, the caller is responsible for the
914 /// memory previously managed by the `Vec`. The only way to do
915 /// this is to convert the raw pointer, length, and capacity back
916 /// into a `Vec` with the [`from_raw_parts`] function, allowing
917 /// the destructor to perform the cleanup.
919 /// [`from_raw_parts`]: Vec::from_raw_parts
924 /// #![feature(vec_into_raw_parts)]
925 /// let v: Vec<i32> = vec![-1, 0, 1];
927 /// let (ptr, len, cap) = v.into_raw_parts();
929 /// let rebuilt = unsafe {
930 /// // We can now make changes to the components, such as
931 /// // transmuting the raw pointer to a compatible type.
932 /// let ptr = ptr as *mut u32;
934 /// Vec::from_raw_parts(ptr, len, cap)
936 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
938 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
939 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
940 let mut me = ManuallyDrop::new(self);
941 (me.as_mut_ptr(), me.len(), me.capacity())
944 /// Decomposes a `Vec<T>` into its raw components.
946 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
947 /// the allocated capacity of the data (in elements), and the allocator. These are the same
948 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
950 /// After calling this function, the caller is responsible for the
951 /// memory previously managed by the `Vec`. The only way to do
952 /// this is to convert the raw pointer, length, and capacity back
953 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
954 /// the destructor to perform the cleanup.
956 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
961 /// #![feature(allocator_api, vec_into_raw_parts)]
963 /// use std::alloc::System;
965 /// let mut v: Vec<i32, System> = Vec::new_in(System);
970 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
972 /// let rebuilt = unsafe {
973 /// // We can now make changes to the components, such as
974 /// // transmuting the raw pointer to a compatible type.
975 /// let ptr = ptr as *mut u32;
977 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
979 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
981 #[unstable(feature = "allocator_api", issue = "32838")]
982 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
983 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
984 let mut me = ManuallyDrop::new(self);
986 let capacity = me.capacity();
987 let ptr = me.as_mut_ptr();
988 let alloc = unsafe { ptr::read(me.allocator()) };
989 (ptr, len, capacity, alloc)
992 /// Returns the total number of elements the vector can hold without
998 /// let mut vec: Vec<i32> = Vec::with_capacity(10);
1000 /// assert!(vec.capacity() >= 10);
1003 #[stable(feature = "rust1", since = "1.0.0")]
1004 pub fn capacity(&self) -> usize {
1008 /// Reserves capacity for at least `additional` more elements to be inserted
1009 /// in the given `Vec<T>`. The collection may reserve more space to
1010 /// speculatively avoid frequent reallocations. After calling `reserve`,
1011 /// capacity will be greater than or equal to `self.len() + additional`.
1012 /// Does nothing if capacity is already sufficient.
1016 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1021 /// let mut vec = vec![1];
1022 /// vec.reserve(10);
1023 /// assert!(vec.capacity() >= 11);
1025 #[cfg(not(no_global_oom_handling))]
1026 #[stable(feature = "rust1", since = "1.0.0")]
1027 pub fn reserve(&mut self, additional: usize) {
1028 self.buf.reserve(self.len, additional);
1031 /// Reserves the minimum capacity for at least `additional` more elements to
1032 /// be inserted in the given `Vec<T>`. Unlike [`reserve`], this will not
1033 /// deliberately over-allocate to speculatively avoid frequent allocations.
1034 /// After calling `reserve_exact`, capacity will be greater than or equal to
1035 /// `self.len() + additional`. Does nothing if the capacity is already
1038 /// Note that the allocator may give the collection more space than it
1039 /// requests. Therefore, capacity can not be relied upon to be precisely
1040 /// minimal. Prefer [`reserve`] if future insertions are expected.
1042 /// [`reserve`]: Vec::reserve
1046 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1051 /// let mut vec = vec![1];
1052 /// vec.reserve_exact(10);
1053 /// assert!(vec.capacity() >= 11);
1055 #[cfg(not(no_global_oom_handling))]
1056 #[stable(feature = "rust1", since = "1.0.0")]
1057 pub fn reserve_exact(&mut self, additional: usize) {
1058 self.buf.reserve_exact(self.len, additional);
1061 /// Tries to reserve capacity for at least `additional` more elements to be inserted
1062 /// in the given `Vec<T>`. The collection may reserve more space to speculatively avoid
1063 /// frequent reallocations. After calling `try_reserve`, capacity will be
1064 /// greater than or equal to `self.len() + additional` if it returns
1065 /// `Ok(())`. Does nothing if capacity is already sufficient. This method
1066 /// preserves the contents even if an error occurs.
1070 /// If the capacity overflows, or the allocator reports a failure, then an error
1076 /// use std::collections::TryReserveError;
1078 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
1079 /// let mut output = Vec::new();
1081 /// // Pre-reserve the memory, exiting if we can't
1082 /// output.try_reserve(data.len())?;
1084 /// // Now we know this can't OOM in the middle of our complex work
1085 /// output.extend(data.iter().map(|&val| {
1086 /// val * 2 + 5 // very complicated
1091 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
1093 #[stable(feature = "try_reserve", since = "1.57.0")]
1094 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
1095 self.buf.try_reserve(self.len, additional)
1098 /// Tries to reserve the minimum capacity for at least `additional`
1099 /// elements to be inserted in the given `Vec<T>`. Unlike [`try_reserve`],
1100 /// this will not deliberately over-allocate to speculatively avoid frequent
1101 /// allocations. After calling `try_reserve_exact`, capacity will be greater
1102 /// than or equal to `self.len() + additional` if it returns `Ok(())`.
1103 /// Does nothing if the capacity is already sufficient.
1105 /// Note that the allocator may give the collection more space than it
1106 /// requests. Therefore, capacity can not be relied upon to be precisely
1107 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
1109 /// [`try_reserve`]: Vec::try_reserve
1113 /// If the capacity overflows, or the allocator reports a failure, then an error
1119 /// use std::collections::TryReserveError;
1121 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
1122 /// let mut output = Vec::new();
1124 /// // Pre-reserve the memory, exiting if we can't
1125 /// output.try_reserve_exact(data.len())?;
1127 /// // Now we know this can't OOM in the middle of our complex work
1128 /// output.extend(data.iter().map(|&val| {
1129 /// val * 2 + 5 // very complicated
1134 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
1136 #[stable(feature = "try_reserve", since = "1.57.0")]
1137 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1138 self.buf.try_reserve_exact(self.len, additional)
1141 /// Shrinks the capacity of the vector as much as possible.
1143 /// It will drop down as close as possible to the length but the allocator
1144 /// may still inform the vector that there is space for a few more elements.
1149 /// let mut vec = Vec::with_capacity(10);
1150 /// vec.extend([1, 2, 3]);
1151 /// assert!(vec.capacity() >= 10);
1152 /// vec.shrink_to_fit();
1153 /// assert!(vec.capacity() >= 3);
1155 #[cfg(not(no_global_oom_handling))]
1156 #[stable(feature = "rust1", since = "1.0.0")]
1157 pub fn shrink_to_fit(&mut self) {
1158 // The capacity is never less than the length, and there's nothing to do when
1159 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
1160 // by only calling it with a greater capacity.
1161 if self.capacity() > self.len {
1162 self.buf.shrink_to_fit(self.len);
1166 /// Shrinks the capacity of the vector with a lower bound.
1168 /// The capacity will remain at least as large as both the length
1169 /// and the supplied value.
1171 /// If the current capacity is less than the lower limit, this is a no-op.
1176 /// let mut vec = Vec::with_capacity(10);
1177 /// vec.extend([1, 2, 3]);
1178 /// assert!(vec.capacity() >= 10);
1179 /// vec.shrink_to(4);
1180 /// assert!(vec.capacity() >= 4);
1181 /// vec.shrink_to(0);
1182 /// assert!(vec.capacity() >= 3);
1184 #[cfg(not(no_global_oom_handling))]
1185 #[stable(feature = "shrink_to", since = "1.56.0")]
1186 pub fn shrink_to(&mut self, min_capacity: usize) {
1187 if self.capacity() > min_capacity {
1188 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
1192 /// Converts the vector into [`Box<[T]>`][owned slice].
1194 /// If the vector has excess capacity, its items will be moved into a
1195 /// newly-allocated buffer with exactly the right capacity.
1197 /// [owned slice]: Box
1202 /// let v = vec![1, 2, 3];
1204 /// let slice = v.into_boxed_slice();
1207 /// Any excess capacity is removed:
1210 /// let mut vec = Vec::with_capacity(10);
1211 /// vec.extend([1, 2, 3]);
1213 /// assert!(vec.capacity() >= 10);
1214 /// let slice = vec.into_boxed_slice();
1215 /// assert_eq!(slice.into_vec().capacity(), 3);
1217 #[cfg(not(no_global_oom_handling))]
1218 #[stable(feature = "rust1", since = "1.0.0")]
1219 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
1221 self.shrink_to_fit();
1222 let me = ManuallyDrop::new(self);
1223 let buf = ptr::read(&me.buf);
1225 buf.into_box(len).assume_init()
1229 /// Shortens the vector, keeping the first `len` elements and dropping
1232 /// If `len` is greater or equal to the vector's current length, this has
1235 /// The [`drain`] method can emulate `truncate`, but causes the excess
1236 /// elements to be returned instead of dropped.
1238 /// Note that this method has no effect on the allocated capacity
1243 /// Truncating a five element vector to two elements:
1246 /// let mut vec = vec![1, 2, 3, 4, 5];
1247 /// vec.truncate(2);
1248 /// assert_eq!(vec, [1, 2]);
1251 /// No truncation occurs when `len` is greater than the vector's current
1255 /// let mut vec = vec![1, 2, 3];
1256 /// vec.truncate(8);
1257 /// assert_eq!(vec, [1, 2, 3]);
1260 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1264 /// let mut vec = vec![1, 2, 3];
1265 /// vec.truncate(0);
1266 /// assert_eq!(vec, []);
1269 /// [`clear`]: Vec::clear
1270 /// [`drain`]: Vec::drain
1271 #[stable(feature = "rust1", since = "1.0.0")]
1272 pub fn truncate(&mut self, len: usize) {
1273 // This is safe because:
1275 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1276 // case avoids creating an invalid slice, and
1277 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1278 // such that no value will be dropped twice in case `drop_in_place`
1279 // were to panic once (if it panics twice, the program aborts).
1281 // Note: It's intentional that this is `>` and not `>=`.
1282 // Changing it to `>=` has negative performance
1283 // implications in some cases. See #78884 for more.
1287 let remaining_len = self.len - len;
1288 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1290 ptr::drop_in_place(s);
1294 /// Extracts a slice containing the entire vector.
1296 /// Equivalent to `&s[..]`.
1301 /// use std::io::{self, Write};
1302 /// let buffer = vec![1, 2, 3, 5, 8];
1303 /// io::sink().write(buffer.as_slice()).unwrap();
1306 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1307 pub fn as_slice(&self) -> &[T] {
1311 /// Extracts a mutable slice of the entire vector.
1313 /// Equivalent to `&mut s[..]`.
1318 /// use std::io::{self, Read};
1319 /// let mut buffer = vec![0; 3];
1320 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1323 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1324 pub fn as_mut_slice(&mut self) -> &mut [T] {
1328 /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
1329 /// valid for zero sized reads if the vector didn't allocate.
1331 /// The caller must ensure that the vector outlives the pointer this
1332 /// function returns, or else it will end up pointing to garbage.
1333 /// Modifying the vector may cause its buffer to be reallocated,
1334 /// which would also make any pointers to it invalid.
1336 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1337 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1338 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1340 /// This method guarantees that for the purpose of the aliasing model, this method
1341 /// does not materialize a reference to the underlying slice, and thus the returned pointer
1342 /// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
1343 /// Note that calling other methods that materialize mutable references to the slice,
1344 /// or mutable references to specific elements you are planning on accessing through this pointer,
1345 /// as well as writing to those elements, may still invalidate this pointer.
1346 /// See the second example below for how this guarantee can be used.
1352 /// let x = vec![1, 2, 4];
1353 /// let x_ptr = x.as_ptr();
1356 /// for i in 0..x.len() {
1357 /// assert_eq!(*x_ptr.add(i), 1 << i);
1362 /// Due to the aliasing guarantee, the following code is legal:
1366 /// let mut v = vec![0, 1, 2];
1367 /// let ptr1 = v.as_ptr();
1368 /// let _ = ptr1.read();
1369 /// let ptr2 = v.as_mut_ptr().offset(2);
1371 /// // Notably, the write to `ptr2` did *not* invalidate `ptr1`
1372 /// // because it mutated a different element:
1373 /// let _ = ptr1.read();
1377 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1378 /// [`as_ptr`]: Vec::as_ptr
1379 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1380 #[rustc_never_returns_null_ptr]
1382 pub fn as_ptr(&self) -> *const T {
1383 // We shadow the slice method of the same name to avoid going through
1384 // `deref`, which creates an intermediate reference.
1388 /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
1389 /// raw pointer valid for zero sized reads if the vector didn't allocate.
1391 /// The caller must ensure that the vector outlives the pointer this
1392 /// function returns, or else it will end up pointing to garbage.
1393 /// Modifying the vector may cause its buffer to be reallocated,
1394 /// which would also make any pointers to it invalid.
1396 /// This method guarantees that for the purpose of the aliasing model, this method
1397 /// does not materialize a reference to the underlying slice, and thus the returned pointer
1398 /// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
1399 /// Note that calling other methods that materialize references to the slice,
1400 /// or references to specific elements you are planning on accessing through this pointer,
1401 /// may still invalidate this pointer.
1402 /// See the second example below for how this guarantee can be used.
1408 /// // Allocate vector big enough for 4 elements.
1410 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1411 /// let x_ptr = x.as_mut_ptr();
1413 /// // Initialize elements via raw pointer writes, then set length.
1415 /// for i in 0..size {
1416 /// *x_ptr.add(i) = i as i32;
1418 /// x.set_len(size);
1420 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1423 /// Due to the aliasing guarantee, the following code is legal:
1427 /// let mut v = vec![0];
1428 /// let ptr1 = v.as_mut_ptr();
1430 /// let ptr2 = v.as_mut_ptr();
1432 /// // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
1437 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1438 /// [`as_ptr`]: Vec::as_ptr
1439 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1440 #[rustc_never_returns_null_ptr]
1442 pub fn as_mut_ptr(&mut self) -> *mut T {
1443 // We shadow the slice method of the same name to avoid going through
1444 // `deref_mut`, which creates an intermediate reference.
1448 /// Returns a reference to the underlying allocator.
1449 #[unstable(feature = "allocator_api", issue = "32838")]
1451 pub fn allocator(&self) -> &A {
1452 self.buf.allocator()
1455 /// Forces the length of the vector to `new_len`.
1457 /// This is a low-level operation that maintains none of the normal
1458 /// invariants of the type. Normally changing the length of a vector
1459 /// is done using one of the safe operations instead, such as
1460 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1462 /// [`truncate`]: Vec::truncate
1463 /// [`resize`]: Vec::resize
1464 /// [`extend`]: Extend::extend
1465 /// [`clear`]: Vec::clear
1469 /// - `new_len` must be less than or equal to [`capacity()`].
1470 /// - The elements at `old_len..new_len` must be initialized.
1472 /// [`capacity()`]: Vec::capacity
1476 /// This method can be useful for situations in which the vector
1477 /// is serving as a buffer for other code, particularly over FFI:
1480 /// # #![allow(dead_code)]
1481 /// # // This is just a minimal skeleton for the doc example;
1482 /// # // don't use this as a starting point for a real library.
1483 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1484 /// # const Z_OK: i32 = 0;
1486 /// # fn deflateGetDictionary(
1487 /// # strm: *mut std::ffi::c_void,
1488 /// # dictionary: *mut u8,
1489 /// # dictLength: *mut usize,
1492 /// # impl StreamWrapper {
1493 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1494 /// // Per the FFI method's docs, "32768 bytes is always enough".
1495 /// let mut dict = Vec::with_capacity(32_768);
1496 /// let mut dict_length = 0;
1497 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1498 /// // 1. `dict_length` elements were initialized.
1499 /// // 2. `dict_length` <= the capacity (32_768)
1500 /// // which makes `set_len` safe to call.
1502 /// // Make the FFI call...
1503 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1505 /// // ...and update the length to what was initialized.
1506 /// dict.set_len(dict_length);
1516 /// While the following example is sound, there is a memory leak since
1517 /// the inner vectors were not freed prior to the `set_len` call:
1520 /// let mut vec = vec![vec![1, 0, 0],
1524 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1525 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1531 /// Normally, here, one would use [`clear`] instead to correctly drop
1532 /// the contents and thus not leak memory.
1534 #[stable(feature = "rust1", since = "1.0.0")]
1535 pub unsafe fn set_len(&mut self, new_len: usize) {
1536 debug_assert!(new_len <= self.capacity());
1541 /// Removes an element from the vector and returns it.
1543 /// The removed element is replaced by the last element of the vector.
1545 /// This does not preserve ordering, but is *O*(1).
1546 /// If you need to preserve the element order, use [`remove`] instead.
1548 /// [`remove`]: Vec::remove
1552 /// Panics if `index` is out of bounds.
1557 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1559 /// assert_eq!(v.swap_remove(1), "bar");
1560 /// assert_eq!(v, ["foo", "qux", "baz"]);
1562 /// assert_eq!(v.swap_remove(0), "foo");
1563 /// assert_eq!(v, ["baz", "qux"]);
1566 #[stable(feature = "rust1", since = "1.0.0")]
1567 pub fn swap_remove(&mut self, index: usize) -> T {
1569 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
1571 fn assert_failed(index: usize, len: usize) -> ! {
1572 panic!("swap_remove index (is {index}) should be < len (is {len})");
1575 let len = self.len();
1577 assert_failed(index, len);
1580 // We replace self[index] with the last element. Note that if the
1581 // bounds check above succeeds there must be a last element (which
1582 // can be self[index] itself).
1583 let value = ptr::read(self.as_ptr().add(index));
1584 let base_ptr = self.as_mut_ptr();
1585 ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
1586 self.set_len(len - 1);
1591 /// Inserts an element at position `index` within the vector, shifting all
1592 /// elements after it to the right.
1596 /// Panics if `index > len`.
1601 /// let mut vec = vec![1, 2, 3];
1602 /// vec.insert(1, 4);
1603 /// assert_eq!(vec, [1, 4, 2, 3]);
1604 /// vec.insert(4, 5);
1605 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1607 #[cfg(not(no_global_oom_handling))]
1608 #[stable(feature = "rust1", since = "1.0.0")]
1609 pub fn insert(&mut self, index: usize, element: T) {
1611 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
1613 fn assert_failed(index: usize, len: usize) -> ! {
1614 panic!("insertion index (is {index}) should be <= len (is {len})");
1617 let len = self.len();
1619 // space for the new element
1620 if len == self.buf.capacity() {
1626 // The spot to put the new value
1628 let p = self.as_mut_ptr().add(index);
1630 // Shift everything over to make space. (Duplicating the
1631 // `index`th element into two consecutive places.)
1632 ptr::copy(p, p.add(1), len - index);
1633 } else if index == len {
1634 // No elements need shifting.
1636 assert_failed(index, len);
1638 // Write it in, overwriting the first copy of the `index`th
1640 ptr::write(p, element);
1642 self.set_len(len + 1);
1646 /// Removes and returns the element at position `index` within the vector,
1647 /// shifting all elements after it to the left.
1649 /// Note: Because this shifts over the remaining elements, it has a
1650 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1651 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1652 /// elements from the beginning of the `Vec`, consider using
1653 /// [`VecDeque::pop_front`] instead.
1655 /// [`swap_remove`]: Vec::swap_remove
1656 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1660 /// Panics if `index` is out of bounds.
1665 /// let mut v = vec![1, 2, 3];
1666 /// assert_eq!(v.remove(1), 2);
1667 /// assert_eq!(v, [1, 3]);
1669 #[stable(feature = "rust1", since = "1.0.0")]
1671 pub fn remove(&mut self, index: usize) -> T {
1673 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
1675 fn assert_failed(index: usize, len: usize) -> ! {
1676 panic!("removal index (is {index}) should be < len (is {len})");
1679 let len = self.len();
1681 assert_failed(index, len);
1687 // the place we are taking from.
1688 let ptr = self.as_mut_ptr().add(index);
1689 // copy it out, unsafely having a copy of the value on
1690 // the stack and in the vector at the same time.
1691 ret = ptr::read(ptr);
1693 // Shift everything down to fill in that spot.
1694 ptr::copy(ptr.add(1), ptr, len - index - 1);
1696 self.set_len(len - 1);
1701 /// Retains only the elements specified by the predicate.
1703 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1704 /// This method operates in place, visiting each element exactly once in the
1705 /// original order, and preserves the order of the retained elements.
1710 /// let mut vec = vec![1, 2, 3, 4];
1711 /// vec.retain(|&x| x % 2 == 0);
1712 /// assert_eq!(vec, [2, 4]);
1715 /// Because the elements are visited exactly once in the original order,
1716 /// external state may be used to decide which elements to keep.
1719 /// let mut vec = vec![1, 2, 3, 4, 5];
1720 /// let keep = [false, true, true, false, true];
1721 /// let mut iter = keep.iter();
1722 /// vec.retain(|_| *iter.next().unwrap());
1723 /// assert_eq!(vec, [2, 3, 5]);
1725 #[stable(feature = "rust1", since = "1.0.0")]
1726 pub fn retain<F>(&mut self, mut f: F)
1728 F: FnMut(&T) -> bool,
1730 self.retain_mut(|elem| f(elem));
1733 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1735 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1736 /// This method operates in place, visiting each element exactly once in the
1737 /// original order, and preserves the order of the retained elements.
1742 /// let mut vec = vec![1, 2, 3, 4];
1743 /// vec.retain_mut(|x| if *x <= 3 {
1749 /// assert_eq!(vec, [2, 3, 4]);
1751 #[stable(feature = "vec_retain_mut", since = "1.61.0")]
1752 pub fn retain_mut<F>(&mut self, mut f: F)
1754 F: FnMut(&mut T) -> bool,
1756 let original_len = self.len();
1757 // Avoid double drop if the drop guard is not executed,
1758 // since we may make some holes during the process.
1759 unsafe { self.set_len(0) };
1761 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1762 // |<- processed len ->| ^- next to check
1763 // |<- deleted cnt ->|
1764 // |<- original_len ->|
1765 // Kept: Elements which predicate returns true on.
1766 // Hole: Moved or dropped element slot.
1767 // Unchecked: Unchecked valid elements.
1769 // This drop guard will be invoked when predicate or `drop` of element panicked.
1770 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1771 // In cases when predicate and `drop` never panick, it will be optimized out.
1772 struct BackshiftOnDrop<'a, T, A: Allocator> {
1773 v: &'a mut Vec<T, A>,
1774 processed_len: usize,
1776 original_len: usize,
1779 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1780 fn drop(&mut self) {
1781 if self.deleted_cnt > 0 {
1782 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1785 self.v.as_ptr().add(self.processed_len),
1786 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1787 self.original_len - self.processed_len,
1791 // SAFETY: After filling holes, all items are in contiguous memory.
1793 self.v.set_len(self.original_len - self.deleted_cnt);
1798 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1800 fn process_loop<F, T, A: Allocator, const DELETED: bool>(
1801 original_len: usize,
1803 g: &mut BackshiftOnDrop<'_, T, A>,
1805 F: FnMut(&mut T) -> bool,
1807 while g.processed_len != original_len {
1808 // SAFETY: Unchecked element must be valid.
1809 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1811 // Advance early to avoid double drop if `drop_in_place` panicked.
1812 g.processed_len += 1;
1814 // SAFETY: We never touch this element again after dropped.
1815 unsafe { ptr::drop_in_place(cur) };
1816 // We already advanced the counter.
1824 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1825 // We use copy for move, and never touch this element again.
1827 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1828 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1831 g.processed_len += 1;
1835 // Stage 1: Nothing was deleted.
1836 process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
1838 // Stage 2: Some elements were deleted.
1839 process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
1841 // All item are processed. This can be optimized to `set_len` by LLVM.
1845 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1848 /// If the vector is sorted, this removes all duplicates.
1853 /// let mut vec = vec![10, 20, 21, 30, 20];
1855 /// vec.dedup_by_key(|i| *i / 10);
1857 /// assert_eq!(vec, [10, 20, 30, 20]);
1859 #[stable(feature = "dedup_by", since = "1.16.0")]
1861 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1863 F: FnMut(&mut T) -> K,
1866 self.dedup_by(|a, b| key(a) == key(b))
1869 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1872 /// The `same_bucket` function is passed references to two elements from the vector and
1873 /// must determine if the elements compare equal. The elements are passed in opposite order
1874 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1876 /// If the vector is sorted, this removes all duplicates.
1881 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1883 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1885 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1887 #[stable(feature = "dedup_by", since = "1.16.0")]
1888 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1890 F: FnMut(&mut T, &mut T) -> bool,
1892 let len = self.len();
1897 // Check if we ever want to remove anything.
1898 // This allows to use copy_non_overlapping in next cycle.
1899 // And avoids any memory writes if we don't need to remove anything.
1900 let mut first_duplicate_idx: usize = 1;
1901 let start = self.as_mut_ptr();
1902 while first_duplicate_idx != len {
1903 let found_duplicate = unsafe {
1904 // SAFETY: first_duplicate always in range [1..len)
1905 // Note that we start iteration from 1 so we never overflow.
1906 let prev = start.add(first_duplicate_idx.wrapping_sub(1));
1907 let current = start.add(first_duplicate_idx);
1908 // We explicitly say in docs that references are reversed.
1909 same_bucket(&mut *current, &mut *prev)
1911 if found_duplicate {
1914 first_duplicate_idx += 1;
1916 // Don't need to remove anything.
1917 // We cannot get bigger than len.
1918 if first_duplicate_idx == len {
1922 /* INVARIANT: vec.len() > read > write > write-1 >= 0 */
1923 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1924 /* Offset of the element we want to check if it is duplicate */
1927 /* Offset of the place where we want to place the non-duplicate
1928 * when we find it. */
1931 /* The Vec that would need correction if `same_bucket` panicked */
1932 vec: &'a mut Vec<T, A>,
1935 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1936 fn drop(&mut self) {
1937 /* This code gets executed when `same_bucket` panics */
1939 /* SAFETY: invariant guarantees that `read - write`
1940 * and `len - read` never overflow and that the copy is always
1943 let ptr = self.vec.as_mut_ptr();
1944 let len = self.vec.len();
1946 /* How many items were left when `same_bucket` panicked.
1947 * Basically vec[read..].len() */
1948 let items_left = len.wrapping_sub(self.read);
1950 /* Pointer to first item in vec[write..write+items_left] slice */
1951 let dropped_ptr = ptr.add(self.write);
1952 /* Pointer to first item in vec[read..] slice */
1953 let valid_ptr = ptr.add(self.read);
1955 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1956 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1957 ptr::copy(valid_ptr, dropped_ptr, items_left);
1959 /* How many items have been already dropped
1960 * Basically vec[read..write].len() */
1961 let dropped = self.read.wrapping_sub(self.write);
1963 self.vec.set_len(len - dropped);
1968 /* Drop items while going through Vec, it should be more efficient than
1969 * doing slice partition_dedup + truncate */
1971 // Construct gap first and then drop item to avoid memory corruption if `T::drop` panics.
1973 FillGapOnDrop { read: first_duplicate_idx + 1, write: first_duplicate_idx, vec: self };
1975 // SAFETY: we checked that first_duplicate_idx in bounds before.
1976 // If drop panics, `gap` would remove this item without drop.
1977 ptr::drop_in_place(start.add(first_duplicate_idx));
1980 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1981 * are always in-bounds and read_ptr never aliases prev_ptr */
1983 while gap.read < len {
1984 let read_ptr = start.add(gap.read);
1985 let prev_ptr = start.add(gap.write.wrapping_sub(1));
1987 // We explicitly say in docs that references are reversed.
1988 let found_duplicate = same_bucket(&mut *read_ptr, &mut *prev_ptr);
1989 if found_duplicate {
1990 // Increase `gap.read` now since the drop may panic.
1992 /* We have found duplicate, drop it in-place */
1993 ptr::drop_in_place(read_ptr);
1995 let write_ptr = start.add(gap.write);
1997 /* read_ptr cannot be equal to write_ptr because at this point
1998 * we guaranteed to skip at least one element (before loop starts).
2000 ptr::copy_nonoverlapping(read_ptr, write_ptr, 1);
2002 /* We have filled that place, so go further */
2008 /* Technically we could let `gap` clean up with its Drop, but
2009 * when `same_bucket` is guaranteed to not panic, this bloats a little
2010 * the codegen, so we just do it manually */
2011 gap.vec.set_len(gap.write);
2016 /// Appends an element to the back of a collection.
2020 /// Panics if the new capacity exceeds `isize::MAX` bytes.
2025 /// let mut vec = vec![1, 2];
2027 /// assert_eq!(vec, [1, 2, 3]);
2029 #[cfg(not(no_global_oom_handling))]
2031 #[stable(feature = "rust1", since = "1.0.0")]
2032 pub fn push(&mut self, value: T) {
2033 // This will panic or abort if we would allocate > isize::MAX bytes
2034 // or if the length increment would overflow for zero-sized types.
2035 if self.len == self.buf.capacity() {
2036 self.buf.reserve_for_push(self.len);
2039 let end = self.as_mut_ptr().add(self.len);
2040 ptr::write(end, value);
2045 /// Tries to append an element to the back of a collection.
2050 /// let mut vec = vec![1, 2];
2051 /// vec.try_push(3).unwrap();
2052 /// assert_eq!(vec, [1, 2, 3]);
2055 #[stable(feature = "kernel", since = "1.0.0")]
2056 pub fn try_push(&mut self, value: T) -> Result<(), TryReserveError> {
2057 if self.len == self.buf.capacity() {
2058 self.buf.try_reserve_for_push(self.len)?;
2061 let end = self.as_mut_ptr().add(self.len);
2062 ptr::write(end, value);
2068 /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
2069 /// with the element.
2071 /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
2072 /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
2074 /// [`push`]: Vec::push
2075 /// [`reserve`]: Vec::reserve
2076 /// [`try_reserve`]: Vec::try_reserve
2080 /// A manual, panic-free alternative to [`FromIterator`]:
2083 /// #![feature(vec_push_within_capacity)]
2085 /// use std::collections::TryReserveError;
2086 /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
2087 /// let mut vec = Vec::new();
2088 /// for value in iter {
2089 /// if let Err(value) = vec.push_within_capacity(value) {
2090 /// vec.try_reserve(1)?;
2091 /// // this cannot fail, the previous line either returned or added at least 1 free slot
2092 /// let _ = vec.push_within_capacity(value);
2097 /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
2100 #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
2101 pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
2102 if self.len == self.buf.capacity() {
2106 let end = self.as_mut_ptr().add(self.len);
2107 ptr::write(end, value);
2113 /// Removes the last element from a vector and returns it, or [`None`] if it
2116 /// If you'd like to pop the first element, consider using
2117 /// [`VecDeque::pop_front`] instead.
2119 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
2124 /// let mut vec = vec![1, 2, 3];
2125 /// assert_eq!(vec.pop(), Some(3));
2126 /// assert_eq!(vec, [1, 2]);
2129 #[stable(feature = "rust1", since = "1.0.0")]
2130 pub fn pop(&mut self) -> Option<T> {
2136 core::intrinsics::assume(self.len < self.capacity());
2137 Some(ptr::read(self.as_ptr().add(self.len())))
2142 /// Moves all the elements of `other` into `self`, leaving `other` empty.
2146 /// Panics if the new capacity exceeds `isize::MAX` bytes.
2151 /// let mut vec = vec![1, 2, 3];
2152 /// let mut vec2 = vec![4, 5, 6];
2153 /// vec.append(&mut vec2);
2154 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
2155 /// assert_eq!(vec2, []);
2157 #[cfg(not(no_global_oom_handling))]
2159 #[stable(feature = "append", since = "1.4.0")]
2160 pub fn append(&mut self, other: &mut Self) {
2162 self.append_elements(other.as_slice() as _);
2167 /// Appends elements to `self` from other buffer.
2168 #[cfg(not(no_global_oom_handling))]
2170 unsafe fn append_elements(&mut self, other: *const [T]) {
2171 let count = unsafe { (*other).len() };
2172 self.reserve(count);
2173 let len = self.len();
2174 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
2178 /// Tries to append elements to `self` from other buffer.
2180 unsafe fn try_append_elements(&mut self, other: *const [T]) -> Result<(), TryReserveError> {
2181 let count = unsafe { (*other).len() };
2182 self.try_reserve(count)?;
2183 let len = self.len();
2184 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
2189 /// Removes the specified range from the vector in bulk, returning all
2190 /// removed elements as an iterator. If the iterator is dropped before
2191 /// being fully consumed, it drops the remaining removed elements.
2193 /// The returned iterator keeps a mutable borrow on the vector to optimize
2194 /// its implementation.
2198 /// Panics if the starting point is greater than the end point or if
2199 /// the end point is greater than the length of the vector.
2203 /// If the returned iterator goes out of scope without being dropped (due to
2204 /// [`mem::forget`], for example), the vector may have lost and leaked
2205 /// elements arbitrarily, including elements outside the range.
2210 /// let mut v = vec![1, 2, 3];
2211 /// let u: Vec<_> = v.drain(1..).collect();
2212 /// assert_eq!(v, &[1]);
2213 /// assert_eq!(u, &[2, 3]);
2215 /// // A full range clears the vector, like `clear()` does
2217 /// assert_eq!(v, &[]);
2219 #[stable(feature = "drain", since = "1.6.0")]
2220 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
2222 R: RangeBounds<usize>,
2226 // When the Drain is first created, it shortens the length of
2227 // the source vector to make sure no uninitialized or moved-from elements
2228 // are accessible at all if the Drain's destructor never gets to run.
2230 // Drain will ptr::read out the values to remove.
2231 // When finished, remaining tail of the vec is copied back to cover
2232 // the hole, and the vector length is restored to the new length.
2234 let len = self.len();
2235 let Range { start, end } = slice::range(range, ..len);
2238 // set self.vec length's to start, to be safe in case Drain is leaked
2239 self.set_len(start);
2240 let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
2243 tail_len: len - end,
2244 iter: range_slice.iter(),
2245 vec: NonNull::from(self),
2250 /// Clears the vector, removing all values.
2252 /// Note that this method has no effect on the allocated capacity
2258 /// let mut v = vec![1, 2, 3];
2262 /// assert!(v.is_empty());
2265 #[stable(feature = "rust1", since = "1.0.0")]
2266 pub fn clear(&mut self) {
2267 let elems: *mut [T] = self.as_mut_slice();
2270 // - `elems` comes directly from `as_mut_slice` and is therefore valid.
2271 // - Setting `self.len` before calling `drop_in_place` means that,
2272 // if an element's `Drop` impl panics, the vector's `Drop` impl will
2273 // do nothing (leaking the rest of the elements) instead of dropping
2277 ptr::drop_in_place(elems);
2281 /// Returns the number of elements in the vector, also referred to
2282 /// as its 'length'.
2287 /// let a = vec![1, 2, 3];
2288 /// assert_eq!(a.len(), 3);
2291 #[stable(feature = "rust1", since = "1.0.0")]
2292 pub fn len(&self) -> usize {
2296 /// Returns `true` if the vector contains no elements.
2301 /// let mut v = Vec::new();
2302 /// assert!(v.is_empty());
2305 /// assert!(!v.is_empty());
2307 #[stable(feature = "rust1", since = "1.0.0")]
2308 pub fn is_empty(&self) -> bool {
2312 /// Splits the collection into two at the given index.
2314 /// Returns a newly allocated vector containing the elements in the range
2315 /// `[at, len)`. After the call, the original vector will be left containing
2316 /// the elements `[0, at)` with its previous capacity unchanged.
2320 /// Panics if `at > len`.
2325 /// let mut vec = vec![1, 2, 3];
2326 /// let vec2 = vec.split_off(1);
2327 /// assert_eq!(vec, [1]);
2328 /// assert_eq!(vec2, [2, 3]);
2330 #[cfg(not(no_global_oom_handling))]
2332 #[must_use = "use `.truncate()` if you don't need the other half"]
2333 #[stable(feature = "split_off", since = "1.4.0")]
2334 pub fn split_off(&mut self, at: usize) -> Self
2339 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
2341 fn assert_failed(at: usize, len: usize) -> ! {
2342 panic!("`at` split index (is {at}) should be <= len (is {len})");
2345 if at > self.len() {
2346 assert_failed(at, self.len());
2350 // the new vector can take over the original buffer and avoid the copy
2351 return mem::replace(
2353 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
2357 let other_len = self.len - at;
2358 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
2360 // Unsafely `set_len` and copy items to `other`.
2363 other.set_len(other_len);
2365 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
2370 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2372 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2373 /// difference, with each additional slot filled with the result of
2374 /// calling the closure `f`. The return values from `f` will end up
2375 /// in the `Vec` in the order they have been generated.
2377 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2379 /// This method uses a closure to create new values on every push. If
2380 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
2381 /// want to use the [`Default`] trait to generate values, you can
2382 /// pass [`Default::default`] as the second argument.
2387 /// let mut vec = vec![1, 2, 3];
2388 /// vec.resize_with(5, Default::default);
2389 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
2391 /// let mut vec = vec![];
2393 /// vec.resize_with(4, || { p *= 2; p });
2394 /// assert_eq!(vec, [2, 4, 8, 16]);
2396 #[cfg(not(no_global_oom_handling))]
2397 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2398 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
2402 let len = self.len();
2404 self.extend_trusted(iter::repeat_with(f).take(new_len - len));
2406 self.truncate(new_len);
2410 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2411 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2412 /// `'a`. If the type has only static references, or none at all, then this
2413 /// may be chosen to be `'static`.
2415 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2416 /// so the leaked allocation may include unused capacity that is not part
2417 /// of the returned slice.
2419 /// This function is mainly useful for data that lives for the remainder of
2420 /// the program's life. Dropping the returned reference will cause a memory
2428 /// let x = vec![1, 2, 3];
2429 /// let static_ref: &'static mut [usize] = x.leak();
2430 /// static_ref[0] += 1;
2431 /// assert_eq!(static_ref, &[2, 2, 3]);
2433 #[stable(feature = "vec_leak", since = "1.47.0")]
2435 pub fn leak<'a>(self) -> &'a mut [T]
2439 let mut me = ManuallyDrop::new(self);
2440 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2443 /// Returns the remaining spare capacity of the vector as a slice of
2444 /// `MaybeUninit<T>`.
2446 /// The returned slice can be used to fill the vector with data (e.g. by
2447 /// reading from a file) before marking the data as initialized using the
2448 /// [`set_len`] method.
2450 /// [`set_len`]: Vec::set_len
2455 /// // Allocate vector big enough for 10 elements.
2456 /// let mut v = Vec::with_capacity(10);
2458 /// // Fill in the first 3 elements.
2459 /// let uninit = v.spare_capacity_mut();
2460 /// uninit[0].write(0);
2461 /// uninit[1].write(1);
2462 /// uninit[2].write(2);
2464 /// // Mark the first 3 elements of the vector as being initialized.
2469 /// assert_eq!(&v, &[0, 1, 2]);
2471 #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
2473 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2475 // This method is not implemented in terms of `split_at_spare_mut`,
2476 // to prevent invalidation of pointers to the buffer.
2478 slice::from_raw_parts_mut(
2479 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2480 self.buf.capacity() - self.len,
2485 /// Returns vector content as a slice of `T`, along with the remaining spare
2486 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2488 /// The returned spare capacity slice can be used to fill the vector with data
2489 /// (e.g. by reading from a file) before marking the data as initialized using
2490 /// the [`set_len`] method.
2492 /// [`set_len`]: Vec::set_len
2494 /// Note that this is a low-level API, which should be used with care for
2495 /// optimization purposes. If you need to append data to a `Vec`
2496 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2497 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2498 /// [`resize_with`], depending on your exact needs.
2500 /// [`push`]: Vec::push
2501 /// [`extend`]: Vec::extend
2502 /// [`extend_from_slice`]: Vec::extend_from_slice
2503 /// [`extend_from_within`]: Vec::extend_from_within
2504 /// [`insert`]: Vec::insert
2505 /// [`append`]: Vec::append
2506 /// [`resize`]: Vec::resize
2507 /// [`resize_with`]: Vec::resize_with
2512 /// #![feature(vec_split_at_spare)]
2514 /// let mut v = vec![1, 1, 2];
2516 /// // Reserve additional space big enough for 10 elements.
2519 /// let (init, uninit) = v.split_at_spare_mut();
2520 /// let sum = init.iter().copied().sum::<u32>();
2522 /// // Fill in the next 4 elements.
2523 /// uninit[0].write(sum);
2524 /// uninit[1].write(sum * 2);
2525 /// uninit[2].write(sum * 3);
2526 /// uninit[3].write(sum * 4);
2528 /// // Mark the 4 elements of the vector as being initialized.
2530 /// let len = v.len();
2531 /// v.set_len(len + 4);
2534 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2536 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2538 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2540 // - len is ignored and so never changed
2541 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2545 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2547 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2548 unsafe fn split_at_spare_mut_with_len(
2550 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2551 let ptr = self.as_mut_ptr();
2553 // - `ptr` is guaranteed to be valid for `self.len` elements
2554 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2556 let spare_ptr = unsafe { ptr.add(self.len) };
2557 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2558 let spare_len = self.buf.capacity() - self.len;
2561 // - `ptr` is guaranteed to be valid for `self.len` elements
2562 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2564 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2565 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2567 (initialized, spare, &mut self.len)
2572 impl<T: Clone, A: Allocator> Vec<T, A> {
2573 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2575 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2576 /// difference, with each additional slot filled with `value`.
2577 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2579 /// This method requires `T` to implement [`Clone`],
2580 /// in order to be able to clone the passed value.
2581 /// If you need more flexibility (or want to rely on [`Default`] instead of
2582 /// [`Clone`]), use [`Vec::resize_with`].
2583 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2588 /// let mut vec = vec!["hello"];
2589 /// vec.resize(3, "world");
2590 /// assert_eq!(vec, ["hello", "world", "world"]);
2592 /// let mut vec = vec![1, 2, 3, 4];
2593 /// vec.resize(2, 0);
2594 /// assert_eq!(vec, [1, 2]);
2596 #[cfg(not(no_global_oom_handling))]
2597 #[stable(feature = "vec_resize", since = "1.5.0")]
2598 pub fn resize(&mut self, new_len: usize, value: T) {
2599 let len = self.len();
2602 self.extend_with(new_len - len, value)
2604 self.truncate(new_len);
2608 /// Tries to resize the `Vec` in-place so that `len` is equal to `new_len`.
2610 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2611 /// difference, with each additional slot filled with `value`.
2612 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2614 /// This method requires `T` to implement [`Clone`],
2615 /// in order to be able to clone the passed value.
2616 /// If you need more flexibility (or want to rely on [`Default`] instead of
2617 /// [`Clone`]), use [`Vec::resize_with`].
2618 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2623 /// let mut vec = vec!["hello"];
2624 /// vec.try_resize(3, "world").unwrap();
2625 /// assert_eq!(vec, ["hello", "world", "world"]);
2627 /// let mut vec = vec![1, 2, 3, 4];
2628 /// vec.try_resize(2, 0).unwrap();
2629 /// assert_eq!(vec, [1, 2]);
2631 /// let mut vec = vec![42];
2632 /// let result = vec.try_resize(usize::MAX, 0);
2633 /// assert!(result.is_err());
2635 #[stable(feature = "kernel", since = "1.0.0")]
2636 pub fn try_resize(&mut self, new_len: usize, value: T) -> Result<(), TryReserveError> {
2637 let len = self.len();
2640 self.try_extend_with(new_len - len, value)
2642 self.truncate(new_len);
2647 /// Clones and appends all elements in a slice to the `Vec`.
2649 /// Iterates over the slice `other`, clones each element, and then appends
2650 /// it to this `Vec`. The `other` slice is traversed in-order.
2652 /// Note that this function is same as [`extend`] except that it is
2653 /// specialized to work with slices instead. If and when Rust gets
2654 /// specialization this function will likely be deprecated (but still
2660 /// let mut vec = vec![1];
2661 /// vec.extend_from_slice(&[2, 3, 4]);
2662 /// assert_eq!(vec, [1, 2, 3, 4]);
2665 /// [`extend`]: Vec::extend
2666 #[cfg(not(no_global_oom_handling))]
2667 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2668 pub fn extend_from_slice(&mut self, other: &[T]) {
2669 self.spec_extend(other.iter())
2672 /// Tries to clone and append all elements in a slice to the `Vec`.
2674 /// Iterates over the slice `other`, clones each element, and then appends
2675 /// it to this `Vec`. The `other` slice is traversed in-order.
2677 /// Note that this function is same as [`extend`] except that it is
2678 /// specialized to work with slices instead. If and when Rust gets
2679 /// specialization this function will likely be deprecated (but still
2685 /// let mut vec = vec![1];
2686 /// vec.try_extend_from_slice(&[2, 3, 4]).unwrap();
2687 /// assert_eq!(vec, [1, 2, 3, 4]);
2690 /// [`extend`]: Vec::extend
2691 #[stable(feature = "kernel", since = "1.0.0")]
2692 pub fn try_extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError> {
2693 self.try_spec_extend(other.iter())
2696 /// Copies elements from `src` range to the end of the vector.
2700 /// Panics if the starting point is greater than the end point or if
2701 /// the end point is greater than the length of the vector.
2706 /// let mut vec = vec![0, 1, 2, 3, 4];
2708 /// vec.extend_from_within(2..);
2709 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2711 /// vec.extend_from_within(..2);
2712 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2714 /// vec.extend_from_within(4..8);
2715 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2717 #[cfg(not(no_global_oom_handling))]
2718 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2719 pub fn extend_from_within<R>(&mut self, src: R)
2721 R: RangeBounds<usize>,
2723 let range = slice::range(src, ..self.len());
2724 self.reserve(range.len());
2727 // - `slice::range` guarantees that the given range is valid for indexing self
2729 self.spec_extend_from_within(range);
2734 impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
2735 /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
2739 /// Panics if the length of the resulting vector would overflow a `usize`.
2741 /// This is only possible when flattening a vector of arrays of zero-sized
2742 /// types, and thus tends to be irrelevant in practice. If
2743 /// `size_of::<T>() > 0`, this will never panic.
2748 /// #![feature(slice_flatten)]
2750 /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
2751 /// assert_eq!(vec.pop(), Some([7, 8, 9]));
2753 /// let mut flattened = vec.into_flattened();
2754 /// assert_eq!(flattened.pop(), Some(6));
2756 #[unstable(feature = "slice_flatten", issue = "95629")]
2757 pub fn into_flattened(self) -> Vec<T, A> {
2758 let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
2759 let (new_len, new_cap) = if T::IS_ZST {
2760 (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
2763 // - `cap * N` cannot overflow because the allocation is already in
2764 // the address space.
2765 // - Each `[T; N]` has `N` valid elements, so there are `len * N`
2766 // valid elements in the allocation.
2767 unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
2770 // - `ptr` was allocated by `self`
2771 // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
2772 // - `new_cap` refers to the same sized allocation as `cap` because
2773 // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
2774 // - `len` <= `cap`, so `len * N` <= `cap * N`.
2775 unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
2779 impl<T: Clone, A: Allocator> Vec<T, A> {
2780 #[cfg(not(no_global_oom_handling))]
2781 /// Extend the vector by `n` clones of value.
2782 fn extend_with(&mut self, n: usize, value: T) {
2786 let mut ptr = self.as_mut_ptr().add(self.len());
2787 // Use SetLenOnDrop to work around bug where compiler
2788 // might not realize the store through `ptr` through self.set_len()
2790 let mut local_len = SetLenOnDrop::new(&mut self.len);
2792 // Write all elements except the last one
2794 ptr::write(ptr, value.clone());
2796 // Increment the length in every step in case clone() panics
2797 local_len.increment_len(1);
2801 // We can write the last element directly without cloning needlessly
2802 ptr::write(ptr, value);
2803 local_len.increment_len(1);
2806 // len set by scope guard
2810 /// Try to extend the vector by `n` clones of value.
2811 fn try_extend_with(&mut self, n: usize, value: T) -> Result<(), TryReserveError> {
2812 self.try_reserve(n)?;
2815 let mut ptr = self.as_mut_ptr().add(self.len());
2816 // Use SetLenOnDrop to work around bug where compiler
2817 // might not realize the store through `ptr` through self.set_len()
2819 let mut local_len = SetLenOnDrop::new(&mut self.len);
2821 // Write all elements except the last one
2823 ptr::write(ptr, value.clone());
2825 // Increment the length in every step in case clone() panics
2826 local_len.increment_len(1);
2830 // We can write the last element directly without cloning needlessly
2831 ptr::write(ptr, value);
2832 local_len.increment_len(1);
2835 // len set by scope guard
2841 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2842 /// Removes consecutive repeated elements in the vector according to the
2843 /// [`PartialEq`] trait implementation.
2845 /// If the vector is sorted, this removes all duplicates.
2850 /// let mut vec = vec![1, 2, 2, 3, 2];
2854 /// assert_eq!(vec, [1, 2, 3, 2]);
2856 #[stable(feature = "rust1", since = "1.0.0")]
2858 pub fn dedup(&mut self) {
2859 self.dedup_by(|a, b| a == b)
2863 ////////////////////////////////////////////////////////////////////////////////
2864 // Internal methods and functions
2865 ////////////////////////////////////////////////////////////////////////////////
2868 #[cfg(not(no_global_oom_handling))]
2869 #[stable(feature = "rust1", since = "1.0.0")]
2870 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2871 <T as SpecFromElem>::from_elem(elem, n, Global)
2875 #[cfg(not(no_global_oom_handling))]
2876 #[unstable(feature = "allocator_api", issue = "32838")]
2877 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2878 <T as SpecFromElem>::from_elem(elem, n, alloc)
2881 #[cfg(not(no_global_oom_handling))]
2882 trait ExtendFromWithinSpec {
2885 /// - `src` needs to be valid index
2886 /// - `self.capacity() - self.len()` must be `>= src.len()`
2887 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2890 #[cfg(not(no_global_oom_handling))]
2891 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2892 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2894 // - len is increased only after initializing elements
2895 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2898 // - caller guarantees that src is a valid index
2899 let to_clone = unsafe { this.get_unchecked(src) };
2901 iter::zip(to_clone, spare)
2902 .map(|(src, dst)| dst.write(src.clone()))
2904 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2905 // - len is increased after each element to prevent leaks (see issue #82533)
2906 .for_each(|_| *len += 1);
2910 #[cfg(not(no_global_oom_handling))]
2911 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2912 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2913 let count = src.len();
2915 let (init, spare) = self.split_at_spare_mut();
2918 // - caller guarantees that `src` is a valid index
2919 let source = unsafe { init.get_unchecked(src) };
2922 // - Both pointers are created from unique slice references (`&mut [_]`)
2923 // so they are valid and do not overlap.
2924 // - Elements are :Copy so it's OK to copy them, without doing
2925 // anything with the original values
2926 // - `count` is equal to the len of `source`, so source is valid for
2928 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2929 // is valid for `count` writes
2930 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2934 // - The elements were just initialized by `copy_nonoverlapping`
2939 ////////////////////////////////////////////////////////////////////////////////
2940 // Common trait implementations for Vec
2941 ////////////////////////////////////////////////////////////////////////////////
2943 #[stable(feature = "rust1", since = "1.0.0")]
2944 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2948 fn deref(&self) -> &[T] {
2949 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2953 #[stable(feature = "rust1", since = "1.0.0")]
2954 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2956 fn deref_mut(&mut self) -> &mut [T] {
2957 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2961 #[cfg(not(no_global_oom_handling))]
2962 #[stable(feature = "rust1", since = "1.0.0")]
2963 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2965 fn clone(&self) -> Self {
2966 let alloc = self.allocator().clone();
2967 <[T]>::to_vec_in(&**self, alloc)
2970 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2971 // required for this method definition, is not available. Instead use the
2972 // `slice::to_vec` function which is only available with cfg(test)
2973 // NB see the slice::hack module in slice.rs for more information
2975 fn clone(&self) -> Self {
2976 let alloc = self.allocator().clone();
2977 crate::slice::to_vec(&**self, alloc)
2980 fn clone_from(&mut self, other: &Self) {
2981 crate::slice::SpecCloneIntoVec::clone_into(other.as_slice(), self);
2985 /// The hash of a vector is the same as that of the corresponding slice,
2986 /// as required by the `core::borrow::Borrow` implementation.
2989 /// use std::hash::BuildHasher;
2991 /// let b = std::hash::RandomState::new();
2992 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2993 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2994 /// assert_eq!(b.hash_one(v), b.hash_one(s));
2996 #[stable(feature = "rust1", since = "1.0.0")]
2997 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2999 fn hash<H: Hasher>(&self, state: &mut H) {
3000 Hash::hash(&**self, state)
3004 #[stable(feature = "rust1", since = "1.0.0")]
3005 #[rustc_on_unimplemented(
3006 message = "vector indices are of type `usize` or ranges of `usize`",
3007 label = "vector indices are of type `usize` or ranges of `usize`"
3009 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
3010 type Output = I::Output;
3013 fn index(&self, index: I) -> &Self::Output {
3014 Index::index(&**self, index)
3018 #[stable(feature = "rust1", since = "1.0.0")]
3019 #[rustc_on_unimplemented(
3020 message = "vector indices are of type `usize` or ranges of `usize`",
3021 label = "vector indices are of type `usize` or ranges of `usize`"
3023 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
3025 fn index_mut(&mut self, index: I) -> &mut Self::Output {
3026 IndexMut::index_mut(&mut **self, index)
3030 #[cfg(not(no_global_oom_handling))]
3031 #[stable(feature = "rust1", since = "1.0.0")]
3032 impl<T> FromIterator<T> for Vec<T> {
3034 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
3035 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
3039 #[stable(feature = "rust1", since = "1.0.0")]
3040 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
3042 type IntoIter = IntoIter<T, A>;
3044 /// Creates a consuming iterator, that is, one that moves each value out of
3045 /// the vector (from start to end). The vector cannot be used after calling
3051 /// let v = vec!["a".to_string(), "b".to_string()];
3052 /// let mut v_iter = v.into_iter();
3054 /// let first_element: Option<String> = v_iter.next();
3056 /// assert_eq!(first_element, Some("a".to_string()));
3057 /// assert_eq!(v_iter.next(), Some("b".to_string()));
3058 /// assert_eq!(v_iter.next(), None);
3061 fn into_iter(self) -> Self::IntoIter {
3063 let mut me = ManuallyDrop::new(self);
3064 let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
3065 let begin = me.as_mut_ptr();
3066 let end = if T::IS_ZST {
3067 begin.wrapping_byte_add(me.len())
3069 begin.add(me.len()) as *const T
3071 let cap = me.buf.capacity();
3073 buf: NonNull::new_unchecked(begin),
3074 phantom: PhantomData,
3084 #[stable(feature = "rust1", since = "1.0.0")]
3085 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
3087 type IntoIter = slice::Iter<'a, T>;
3089 fn into_iter(self) -> Self::IntoIter {
3094 #[stable(feature = "rust1", since = "1.0.0")]
3095 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
3096 type Item = &'a mut T;
3097 type IntoIter = slice::IterMut<'a, T>;
3099 fn into_iter(self) -> Self::IntoIter {
3104 #[cfg(not(no_global_oom_handling))]
3105 #[stable(feature = "rust1", since = "1.0.0")]
3106 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
3108 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
3109 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
3113 fn extend_one(&mut self, item: T) {
3118 fn extend_reserve(&mut self, additional: usize) {
3119 self.reserve(additional);
3123 impl<T, A: Allocator> Vec<T, A> {
3124 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
3125 // they have no further optimizations to apply
3126 #[cfg(not(no_global_oom_handling))]
3127 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
3128 // This is the case for a general iterator.
3130 // This function should be the moral equivalent of:
3132 // for item in iterator {
3135 while let Some(element) = iterator.next() {
3136 let len = self.len();
3137 if len == self.capacity() {
3138 let (lower, _) = iterator.size_hint();
3139 self.reserve(lower.saturating_add(1));
3142 ptr::write(self.as_mut_ptr().add(len), element);
3143 // Since next() executes user code which can panic we have to bump the length
3145 // NB can't overflow since we would have had to alloc the address space
3146 self.set_len(len + 1);
3151 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
3152 // they have no further optimizations to apply
3153 fn try_extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) -> Result<(), TryReserveError> {
3154 // This is the case for a general iterator.
3156 // This function should be the moral equivalent of:
3158 // for item in iterator {
3161 while let Some(element) = iterator.next() {
3162 let len = self.len();
3163 if len == self.capacity() {
3164 let (lower, _) = iterator.size_hint();
3165 self.try_reserve(lower.saturating_add(1))?;
3168 ptr::write(self.as_mut_ptr().add(len), element);
3169 // Since next() executes user code which can panic we have to bump the length
3171 // NB can't overflow since we would have had to alloc the address space
3172 self.set_len(len + 1);
3179 // specific extend for `TrustedLen` iterators, called both by the specializations
3180 // and internal places where resolving specialization makes compilation slower
3181 #[cfg(not(no_global_oom_handling))]
3182 fn extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) {
3183 let (low, high) = iterator.size_hint();
3184 if let Some(additional) = high {
3188 "TrustedLen iterator's size hint is not exact: {:?}",
3191 self.reserve(additional);
3193 let ptr = self.as_mut_ptr();
3194 let mut local_len = SetLenOnDrop::new(&mut self.len);
3195 iterator.for_each(move |element| {
3196 ptr::write(ptr.add(local_len.current_len()), element);
3197 // Since the loop executes user code which can panic we have to update
3198 // the length every step to correctly drop what we've written.
3199 // NB can't overflow since we would have had to alloc the address space
3200 local_len.increment_len(1);
3204 // Per TrustedLen contract a `None` upper bound means that the iterator length
3205 // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
3206 // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
3207 // This avoids additional codegen for a fallback code path which would eventually
3209 panic!("capacity overflow");
3213 // specific extend for `TrustedLen` iterators, called both by the specializations
3214 // and internal places where resolving specialization makes compilation slower
3215 fn try_extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) -> Result<(), TryReserveError> {
3216 let (low, high) = iterator.size_hint();
3217 if let Some(additional) = high {
3221 "TrustedLen iterator's size hint is not exact: {:?}",
3224 self.try_reserve(additional)?;
3226 let ptr = self.as_mut_ptr();
3227 let mut local_len = SetLenOnDrop::new(&mut self.len);
3228 iterator.for_each(move |element| {
3229 ptr::write(ptr.add(local_len.current_len()), element);
3230 // Since the loop executes user code which can panic we have to update
3231 // the length every step to correctly drop what we've written.
3232 // NB can't overflow since we would have had to alloc the address space
3233 local_len.increment_len(1);
3238 Err(TryReserveErrorKind::CapacityOverflow.into())
3242 /// Creates a splicing iterator that replaces the specified range in the vector
3243 /// with the given `replace_with` iterator and yields the removed items.
3244 /// `replace_with` does not need to be the same length as `range`.
3246 /// `range` is removed even if the iterator is not consumed until the end.
3248 /// It is unspecified how many elements are removed from the vector
3249 /// if the `Splice` value is leaked.
3251 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
3253 /// This is optimal if:
3255 /// * The tail (elements in the vector after `range`) is empty,
3256 /// * or `replace_with` yields fewer or equal elements than `range`’s length
3257 /// * or the lower bound of its `size_hint()` is exact.
3259 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
3263 /// Panics if the starting point is greater than the end point or if
3264 /// the end point is greater than the length of the vector.
3269 /// let mut v = vec![1, 2, 3, 4];
3270 /// let new = [7, 8, 9];
3271 /// let u: Vec<_> = v.splice(1..3, new).collect();
3272 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
3273 /// assert_eq!(u, &[2, 3]);
3275 #[cfg(not(no_global_oom_handling))]
3277 #[stable(feature = "vec_splice", since = "1.21.0")]
3278 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
3280 R: RangeBounds<usize>,
3281 I: IntoIterator<Item = T>,
3283 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
3286 /// Creates an iterator which uses a closure to determine if an element should be removed.
3288 /// If the closure returns true, then the element is removed and yielded.
3289 /// If the closure returns false, the element will remain in the vector and will not be yielded
3290 /// by the iterator.
3292 /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
3293 /// or the iteration short-circuits, then the remaining elements will be retained.
3294 /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
3296 /// [`retain`]: Vec::retain
3298 /// Using this method is equivalent to the following code:
3301 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
3302 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
3304 /// while i < vec.len() {
3305 /// if some_predicate(&mut vec[i]) {
3306 /// let val = vec.remove(i);
3307 /// // your code here
3313 /// # assert_eq!(vec, vec![1, 4, 5]);
3316 /// But `extract_if` is easier to use. `extract_if` is also more efficient,
3317 /// because it can backshift the elements of the array in bulk.
3319 /// Note that `extract_if` also lets you mutate every element in the filter closure,
3320 /// regardless of whether you choose to keep or remove it.
3324 /// Splitting an array into evens and odds, reusing the original allocation:
3327 /// #![feature(extract_if)]
3328 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
3330 /// let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
3331 /// let odds = numbers;
3333 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
3334 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
3336 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
3337 pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A>
3339 F: FnMut(&mut T) -> bool,
3341 let old_len = self.len();
3343 // Guard against us getting leaked (leak amplification)
3348 ExtractIf { vec: self, idx: 0, del: 0, old_len, pred: filter }
3352 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
3354 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
3355 /// append the entire slice at once.
3357 /// [`copy_from_slice`]: slice::copy_from_slice
3358 #[cfg(not(no_global_oom_handling))]
3359 #[stable(feature = "extend_ref", since = "1.2.0")]
3360 impl<'a, T: Copy + 'a, A: Allocator> Extend<&'a T> for Vec<T, A> {
3361 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
3362 self.spec_extend(iter.into_iter())
3366 fn extend_one(&mut self, &item: &'a T) {
3371 fn extend_reserve(&mut self, additional: usize) {
3372 self.reserve(additional);
3376 /// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
3377 #[stable(feature = "rust1", since = "1.0.0")]
3378 impl<T, A1, A2> PartialOrd<Vec<T, A2>> for Vec<T, A1>
3385 fn partial_cmp(&self, other: &Vec<T, A2>) -> Option<Ordering> {
3386 PartialOrd::partial_cmp(&**self, &**other)
3390 #[stable(feature = "rust1", since = "1.0.0")]
3391 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
3393 /// Implements ordering of vectors, [lexicographically](Ord#lexicographical-comparison).
3394 #[stable(feature = "rust1", since = "1.0.0")]
3395 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
3397 fn cmp(&self, other: &Self) -> Ordering {
3398 Ord::cmp(&**self, &**other)
3402 #[stable(feature = "rust1", since = "1.0.0")]
3403 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
3404 fn drop(&mut self) {
3407 // use a raw slice to refer to the elements of the vector as weakest necessary type;
3408 // could avoid questions of validity in certain cases
3409 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
3411 // RawVec handles deallocation
3415 #[stable(feature = "rust1", since = "1.0.0")]
3416 impl<T> Default for Vec<T> {
3417 /// Creates an empty `Vec<T>`.
3419 /// The vector will not allocate until elements are pushed onto it.
3420 fn default() -> Vec<T> {
3425 #[stable(feature = "rust1", since = "1.0.0")]
3426 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
3427 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3428 fmt::Debug::fmt(&**self, f)
3432 #[stable(feature = "rust1", since = "1.0.0")]
3433 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
3434 fn as_ref(&self) -> &Vec<T, A> {
3439 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3440 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
3441 fn as_mut(&mut self) -> &mut Vec<T, A> {
3446 #[stable(feature = "rust1", since = "1.0.0")]
3447 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
3448 fn as_ref(&self) -> &[T] {
3453 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3454 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
3455 fn as_mut(&mut self) -> &mut [T] {
3460 #[cfg(not(no_global_oom_handling))]
3461 #[stable(feature = "rust1", since = "1.0.0")]
3462 impl<T: Clone> From<&[T]> for Vec<T> {
3463 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3468 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
3471 fn from(s: &[T]) -> Vec<T> {
3475 fn from(s: &[T]) -> Vec<T> {
3476 crate::slice::to_vec(s, Global)
3480 #[cfg(not(no_global_oom_handling))]
3481 #[stable(feature = "vec_from_mut", since = "1.19.0")]
3482 impl<T: Clone> From<&mut [T]> for Vec<T> {
3483 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3488 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
3491 fn from(s: &mut [T]) -> Vec<T> {
3495 fn from(s: &mut [T]) -> Vec<T> {
3496 crate::slice::to_vec(s, Global)
3500 #[cfg(not(no_global_oom_handling))]
3501 #[stable(feature = "vec_from_array_ref", since = "1.74.0")]
3502 impl<T: Clone, const N: usize> From<&[T; N]> for Vec<T> {
3503 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3508 /// assert_eq!(Vec::from(&[1, 2, 3]), vec![1, 2, 3]);
3510 fn from(s: &[T; N]) -> Vec<T> {
3511 Self::from(s.as_slice())
3515 #[cfg(not(no_global_oom_handling))]
3516 #[stable(feature = "vec_from_array_ref", since = "1.74.0")]
3517 impl<T: Clone, const N: usize> From<&mut [T; N]> for Vec<T> {
3518 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3523 /// assert_eq!(Vec::from(&mut [1, 2, 3]), vec![1, 2, 3]);
3525 fn from(s: &mut [T; N]) -> Vec<T> {
3526 Self::from(s.as_mut_slice())
3530 #[cfg(not(no_global_oom_handling))]
3531 #[stable(feature = "vec_from_array", since = "1.44.0")]
3532 impl<T, const N: usize> From<[T; N]> for Vec<T> {
3533 /// Allocate a `Vec<T>` and move `s`'s items into it.
3538 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
3541 fn from(s: [T; N]) -> Vec<T> {
3542 <[T]>::into_vec(Box::new(s))
3546 fn from(s: [T; N]) -> Vec<T> {
3547 crate::slice::into_vec(Box::new(s))
3551 #[cfg(not(no_borrow))]
3552 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
3553 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
3555 [T]: ToOwned<Owned = Vec<T>>,
3557 /// Convert a clone-on-write slice into a vector.
3559 /// If `s` already owns a `Vec<T>`, it will be returned directly.
3560 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
3561 /// filled by cloning `s`'s items into it.
3566 /// # use std::borrow::Cow;
3567 /// let o: Cow<'_, [i32]> = Cow::Owned(vec![1, 2, 3]);
3568 /// let b: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);
3569 /// assert_eq!(Vec::from(o), Vec::from(b));
3571 fn from(s: Cow<'a, [T]>) -> Vec<T> {
3576 // note: test pulls in std, which causes errors here
3578 #[stable(feature = "vec_from_box", since = "1.18.0")]
3579 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
3580 /// Convert a boxed slice into a vector by transferring ownership of
3581 /// the existing heap allocation.
3586 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
3587 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
3589 fn from(s: Box<[T], A>) -> Self {
3594 // note: test pulls in std, which causes errors here
3595 #[cfg(not(no_global_oom_handling))]
3597 #[stable(feature = "box_from_vec", since = "1.20.0")]
3598 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
3599 /// Convert a vector into a boxed slice.
3601 /// If `v` has excess capacity, its items will be moved into a
3602 /// newly-allocated buffer with exactly the right capacity.
3607 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
3610 /// Any excess capacity is removed:
3612 /// let mut vec = Vec::with_capacity(10);
3613 /// vec.extend([1, 2, 3]);
3615 /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
3617 fn from(v: Vec<T, A>) -> Self {
3618 v.into_boxed_slice()
3622 #[cfg(not(no_global_oom_handling))]
3623 #[stable(feature = "rust1", since = "1.0.0")]
3624 impl From<&str> for Vec<u8> {
3625 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
3630 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
3632 fn from(s: &str) -> Vec<u8> {
3633 From::from(s.as_bytes())
3637 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
3638 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
3639 type Error = Vec<T, A>;
3641 /// Gets the entire contents of the `Vec<T>` as an array,
3642 /// if its size exactly matches that of the requested array.
3647 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3648 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3651 /// If the length doesn't match, the input comes back in `Err`:
3653 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3654 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3657 /// If you're fine with just getting a prefix of the `Vec<T>`,
3658 /// you can call [`.truncate(N)`](Vec::truncate) first.
3660 /// let mut v = String::from("hello world").into_bytes();
3663 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3664 /// assert_eq!(a, b' ');
3665 /// assert_eq!(b, b'd');
3667 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
3672 // SAFETY: `.set_len(0)` is always sound.
3673 unsafe { vec.set_len(0) };
3675 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3676 // the alignment the array needs is the same as the items.
3677 // We checked earlier that we have sufficient items.
3678 // The items will not double-drop as the `set_len`
3679 // tells the `Vec` not to also drop them.
3680 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };