1 //! A contiguous growable array type with heap-allocated contents, written
4 //! Vectors have *O*(1) indexing, amortized *O*(1) push (to the end) and
5 //! *O*(1) pop (from the end).
7 //! Vectors ensure they never allocate more than `isize::MAX` bytes.
11 //! You can explicitly create a [`Vec`] with [`Vec::new`]:
14 //! let v: Vec<i32> = Vec::new();
17 //! ...or by using the [`vec!`] macro:
20 //! let v: Vec<i32> = vec![];
22 //! let v = vec![1, 2, 3, 4, 5];
24 //! let v = vec![0; 10]; // ten zeroes
27 //! You can [`push`] values onto the end of a vector (which will grow the vector
31 //! let mut v = vec![1, 2];
36 //! Popping values works in much the same way:
39 //! let mut v = vec![1, 2];
41 //! let two = v.pop();
44 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
47 //! let mut v = vec![1, 2, 3];
52 //! [`push`]: Vec::push
54 #![stable(feature = "rust1", since = "1.0.0")]
56 #[cfg(not(no_global_oom_handling))]
58 use core
::cmp
::Ordering
;
59 use core
::convert
::TryFrom
;
61 use core
::hash
::{Hash, Hasher}
;
62 use core
::intrinsics
::{arith_offset, assume}
;
64 #[cfg(not(no_global_oom_handling))]
65 use core
::iter
::FromIterator
;
66 use core
::marker
::PhantomData
;
67 use core
::mem
::{self, ManuallyDrop, MaybeUninit}
;
68 use core
::ops
::{self, Index, IndexMut, Range, RangeBounds}
;
69 use core
::ptr
::{self, NonNull}
;
70 use core
::slice
::{self, SliceIndex}
;
72 use crate::alloc
::{Allocator, Global}
;
73 use crate::borrow
::{Cow, ToOwned}
;
74 use crate::boxed
::Box
;
75 use crate::collections
::TryReserveError
;
76 use crate::raw_vec
::RawVec
;
78 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
79 pub use self::drain_filter
::DrainFilter
;
83 #[cfg(not(no_global_oom_handling))]
84 #[stable(feature = "vec_splice", since = "1.21.0")]
85 pub use self::splice
::Splice
;
87 #[cfg(not(no_global_oom_handling))]
90 #[stable(feature = "drain", since = "1.6.0")]
91 pub use self::drain
::Drain
;
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
;
110 #[cfg(not(no_global_oom_handling))]
111 mod in_place_collect
;
115 #[cfg(not(no_global_oom_handling))]
116 use self::spec_from_elem
::SpecFromElem
;
118 #[cfg(not(no_global_oom_handling))]
121 #[cfg(not(no_global_oom_handling))]
122 use self::set_len_on_drop
::SetLenOnDrop
;
124 #[cfg(not(no_global_oom_handling))]
127 #[cfg(not(no_global_oom_handling))]
128 use self::in_place_drop
::InPlaceDrop
;
130 #[cfg(not(no_global_oom_handling))]
133 #[cfg(not(no_global_oom_handling))]
134 use self::spec_from_iter_nested
::SpecFromIterNested
;
136 #[cfg(not(no_global_oom_handling))]
137 mod spec_from_iter_nested
;
139 #[cfg(not(no_global_oom_handling))]
140 use self::spec_from_iter
::SpecFromIter
;
142 #[cfg(not(no_global_oom_handling))]
145 #[cfg(not(no_global_oom_handling))]
146 use self::spec_extend
::SpecExtend
;
148 #[cfg(not(no_global_oom_handling))]
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].iter().copied());
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 to access 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`]: ../../std/vec/struct.Vec.html#method.get
382 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.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 the specified capacity.
430 /// The vector will be able to hold exactly `capacity` elements without
431 /// reallocating. If `capacity` is 0, the vector will not allocate.
433 /// It is important to note that although the returned vector has the
434 /// *capacity* specified, the vector will have a zero *length*. For an
435 /// explanation of the difference between length and capacity, see
436 /// *[Capacity and reallocation]*.
438 /// [Capacity and reallocation]: #capacity-and-reallocation
442 /// Panics if the new capacity exceeds `isize::MAX` bytes.
447 /// let mut vec = Vec::with_capacity(10);
449 /// // The vector contains no items, even though it has capacity for more
450 /// assert_eq!(vec.len(), 0);
451 /// assert_eq!(vec.capacity(), 10);
453 /// // These are all done without reallocating...
457 /// assert_eq!(vec.len(), 10);
458 /// assert_eq!(vec.capacity(), 10);
460 /// // ...but this may make the vector reallocate
462 /// assert_eq!(vec.len(), 11);
463 /// assert!(vec.capacity() >= 11);
465 #[cfg(not(no_global_oom_handling))]
467 #[stable(feature = "rust1", since = "1.0.0")]
469 pub fn with_capacity(capacity
: usize) -> Self {
470 Self::with_capacity_in(capacity
, Global
)
473 /// Creates a `Vec<T>` directly from the raw components of another vector.
477 /// This is highly unsafe, due to the number of invariants that aren't
480 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
481 /// (at least, it's highly likely to be incorrect if it wasn't).
482 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
483 /// (`T` having a less strict alignment is not sufficient, the alignment really
484 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
485 /// allocated and deallocated with the same layout.)
486 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
487 /// to be the same size as the pointer was allocated with. (Because similar to
488 /// alignment, [`dealloc`] must be called with the same layout `size`.)
489 /// * `length` needs to be less than or equal to `capacity`.
491 /// Violating these may cause problems like corrupting the allocator's
492 /// internal data structures. For example it is **not** safe
493 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
494 /// It's also not safe to build one from a `Vec<u16>` and its length, because
495 /// the allocator cares about the alignment, and these two types have different
496 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
497 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
498 /// these issues, it is often preferable to do casting/transmuting using
499 /// [`slice::from_raw_parts`] instead.
501 /// The ownership of `ptr` is effectively transferred to the
502 /// `Vec<T>` which may then deallocate, reallocate or change the
503 /// contents of memory pointed to by the pointer at will. Ensure
504 /// that nothing else uses the pointer after calling this
507 /// [`String`]: crate::string::String
508 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
516 /// let v = vec![1, 2, 3];
518 // FIXME Update this when vec_into_raw_parts is stabilized
519 /// // Prevent running `v`'s destructor so we are in complete control
520 /// // of the allocation.
521 /// let mut v = mem::ManuallyDrop::new(v);
523 /// // Pull out the various important pieces of information about `v`
524 /// let p = v.as_mut_ptr();
525 /// let len = v.len();
526 /// let cap = v.capacity();
529 /// // Overwrite memory with 4, 5, 6
530 /// for i in 0..len as isize {
531 /// ptr::write(p.offset(i), 4 + i);
534 /// // Put everything back together into a Vec
535 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
536 /// assert_eq!(rebuilt, [4, 5, 6]);
540 #[stable(feature = "rust1", since = "1.0.0")]
541 pub unsafe fn from_raw_parts(ptr
: *mut T
, length
: usize, capacity
: usize) -> Self {
542 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
546 impl<T
, A
: Allocator
> Vec
<T
, A
> {
547 /// Constructs a new, empty `Vec<T, A>`.
549 /// The vector will not allocate until elements are pushed onto it.
554 /// #![feature(allocator_api)]
556 /// use std::alloc::System;
558 /// # #[allow(unused_mut)]
559 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
562 #[unstable(feature = "allocator_api", issue = "32838")]
563 pub const fn new_in(alloc
: A
) -> Self {
564 Vec { buf: RawVec::new_in(alloc), len: 0 }
567 /// Constructs a new, empty `Vec<T, A>` with the specified capacity with the provided
570 /// The vector will be able to hold exactly `capacity` elements without
571 /// reallocating. If `capacity` is 0, the vector will not allocate.
573 /// It is important to note that although the returned vector has the
574 /// *capacity* specified, the vector will have a zero *length*. For an
575 /// explanation of the difference between length and capacity, see
576 /// *[Capacity and reallocation]*.
578 /// [Capacity and reallocation]: #capacity-and-reallocation
582 /// Panics if the new capacity exceeds `isize::MAX` bytes.
587 /// #![feature(allocator_api)]
589 /// use std::alloc::System;
591 /// let mut vec = Vec::with_capacity_in(10, System);
593 /// // The vector contains no items, even though it has capacity for more
594 /// assert_eq!(vec.len(), 0);
595 /// assert_eq!(vec.capacity(), 10);
597 /// // These are all done without reallocating...
601 /// assert_eq!(vec.len(), 10);
602 /// assert_eq!(vec.capacity(), 10);
604 /// // ...but this may make the vector reallocate
606 /// assert_eq!(vec.len(), 11);
607 /// assert!(vec.capacity() >= 11);
609 #[cfg(not(no_global_oom_handling))]
611 #[unstable(feature = "allocator_api", issue = "32838")]
612 pub fn with_capacity_in(capacity
: usize, alloc
: A
) -> Self {
613 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
616 /// Creates a `Vec<T, A>` directly from the raw components of another vector.
620 /// This is highly unsafe, due to the number of invariants that aren't
623 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
624 /// (at least, it's highly likely to be incorrect if it wasn't).
625 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
626 /// (`T` having a less strict alignment is not sufficient, the alignment really
627 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
628 /// allocated and deallocated with the same layout.)
629 /// * `length` needs to be less than or equal to `capacity`.
630 /// * `capacity` needs to be the capacity that the pointer was allocated with.
632 /// Violating these may cause problems like corrupting the allocator's
633 /// internal data structures. For example it is **not** safe
634 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
635 /// It's also not safe to build one from a `Vec<u16>` and its length, because
636 /// the allocator cares about the alignment, and these two types have different
637 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
638 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
640 /// The ownership of `ptr` is effectively transferred to the
641 /// `Vec<T>` which may then deallocate, reallocate or change the
642 /// contents of memory pointed to by the pointer at will. Ensure
643 /// that nothing else uses the pointer after calling this
646 /// [`String`]: crate::string::String
647 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
652 /// #![feature(allocator_api)]
654 /// use std::alloc::System;
659 /// let mut v = Vec::with_capacity_in(3, System);
664 // FIXME Update this when vec_into_raw_parts is stabilized
665 /// // Prevent running `v`'s destructor so we are in complete control
666 /// // of the allocation.
667 /// let mut v = mem::ManuallyDrop::new(v);
669 /// // Pull out the various important pieces of information about `v`
670 /// let p = v.as_mut_ptr();
671 /// let len = v.len();
672 /// let cap = v.capacity();
673 /// let alloc = v.allocator();
676 /// // Overwrite memory with 4, 5, 6
677 /// for i in 0..len as isize {
678 /// ptr::write(p.offset(i), 4 + i);
681 /// // Put everything back together into a Vec
682 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
683 /// assert_eq!(rebuilt, [4, 5, 6]);
687 #[unstable(feature = "allocator_api", issue = "32838")]
688 pub unsafe fn from_raw_parts_in(ptr
: *mut T
, length
: usize, capacity
: usize, alloc
: A
) -> Self {
689 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length }
}
692 /// Decomposes a `Vec<T>` into its raw components.
694 /// Returns the raw pointer to the underlying data, the length of
695 /// the vector (in elements), and the allocated capacity of the
696 /// data (in elements). These are the same arguments in the same
697 /// order as the arguments to [`from_raw_parts`].
699 /// After calling this function, the caller is responsible for the
700 /// memory previously managed by the `Vec`. The only way to do
701 /// this is to convert the raw pointer, length, and capacity back
702 /// into a `Vec` with the [`from_raw_parts`] function, allowing
703 /// the destructor to perform the cleanup.
705 /// [`from_raw_parts`]: Vec::from_raw_parts
710 /// #![feature(vec_into_raw_parts)]
711 /// let v: Vec<i32> = vec![-1, 0, 1];
713 /// let (ptr, len, cap) = v.into_raw_parts();
715 /// let rebuilt = unsafe {
716 /// // We can now make changes to the components, such as
717 /// // transmuting the raw pointer to a compatible type.
718 /// let ptr = ptr as *mut u32;
720 /// Vec::from_raw_parts(ptr, len, cap)
722 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
724 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
725 pub fn into_raw_parts(self) -> (*mut T
, usize, usize) {
726 let mut me
= ManuallyDrop
::new(self);
727 (me
.as_mut_ptr(), me
.len(), me
.capacity())
730 /// Decomposes a `Vec<T>` into its raw components.
732 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
733 /// the allocated capacity of the data (in elements), and the allocator. These are the same
734 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
736 /// After calling this function, the caller is responsible for the
737 /// memory previously managed by the `Vec`. The only way to do
738 /// this is to convert the raw pointer, length, and capacity back
739 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
740 /// the destructor to perform the cleanup.
742 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
747 /// #![feature(allocator_api, vec_into_raw_parts)]
749 /// use std::alloc::System;
751 /// let mut v: Vec<i32, System> = Vec::new_in(System);
756 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
758 /// let rebuilt = unsafe {
759 /// // We can now make changes to the components, such as
760 /// // transmuting the raw pointer to a compatible type.
761 /// let ptr = ptr as *mut u32;
763 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
765 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
767 #[unstable(feature = "allocator_api", issue = "32838")]
768 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
769 pub fn into_raw_parts_with_alloc(self) -> (*mut T
, usize, usize, A
) {
770 let mut me
= ManuallyDrop
::new(self);
772 let capacity
= me
.capacity();
773 let ptr
= me
.as_mut_ptr();
774 let alloc
= unsafe { ptr::read(me.allocator()) }
;
775 (ptr
, len
, capacity
, alloc
)
778 /// Returns the number of elements the vector can hold without
784 /// let vec: Vec<i32> = Vec::with_capacity(10);
785 /// assert_eq!(vec.capacity(), 10);
788 #[stable(feature = "rust1", since = "1.0.0")]
789 pub fn capacity(&self) -> usize {
793 /// Reserves capacity for at least `additional` more elements to be inserted
794 /// in the given `Vec<T>`. The collection may reserve more space to avoid
795 /// frequent reallocations. After calling `reserve`, capacity will be
796 /// greater than or equal to `self.len() + additional`. Does nothing if
797 /// capacity is already sufficient.
801 /// Panics if the new capacity exceeds `isize::MAX` bytes.
806 /// let mut vec = vec![1];
808 /// assert!(vec.capacity() >= 11);
810 #[cfg(not(no_global_oom_handling))]
811 #[stable(feature = "rust1", since = "1.0.0")]
812 pub fn reserve(&mut self, additional
: usize) {
813 self.buf
.reserve(self.len
, additional
);
816 /// Reserves the minimum capacity for exactly `additional` more elements to
817 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
818 /// capacity will be greater than or equal to `self.len() + additional`.
819 /// Does nothing if the capacity is already sufficient.
821 /// Note that the allocator may give the collection more space than it
822 /// requests. Therefore, capacity can not be relied upon to be precisely
823 /// minimal. Prefer [`reserve`] if future insertions are expected.
825 /// [`reserve`]: Vec::reserve
829 /// Panics if the new capacity exceeds `isize::MAX` bytes.
834 /// let mut vec = vec![1];
835 /// vec.reserve_exact(10);
836 /// assert!(vec.capacity() >= 11);
838 #[cfg(not(no_global_oom_handling))]
839 #[stable(feature = "rust1", since = "1.0.0")]
840 pub fn reserve_exact(&mut self, additional
: usize) {
841 self.buf
.reserve_exact(self.len
, additional
);
844 /// Tries to reserve capacity for at least `additional` more elements to be inserted
845 /// in the given `Vec<T>`. The collection may reserve more space to avoid
846 /// frequent reallocations. After calling `try_reserve`, capacity will be
847 /// greater than or equal to `self.len() + additional`. Does nothing if
848 /// capacity is already sufficient.
852 /// If the capacity overflows, or the allocator reports a failure, then an error
858 /// use std::collections::TryReserveError;
860 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
861 /// let mut output = Vec::new();
863 /// // Pre-reserve the memory, exiting if we can't
864 /// output.try_reserve(data.len())?;
866 /// // Now we know this can't OOM in the middle of our complex work
867 /// output.extend(data.iter().map(|&val| {
868 /// val * 2 + 5 // very complicated
873 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
875 #[stable(feature = "try_reserve", since = "1.57.0")]
876 pub fn try_reserve(&mut self, additional
: usize) -> Result
<(), TryReserveError
> {
877 self.buf
.try_reserve(self.len
, additional
)
880 /// Tries to reserve the minimum capacity for exactly `additional`
881 /// elements to be inserted in the given `Vec<T>`. After calling
882 /// `try_reserve_exact`, capacity will be greater than or equal to
883 /// `self.len() + additional` if it returns `Ok(())`.
884 /// Does nothing if the capacity is already sufficient.
886 /// Note that the allocator may give the collection more space than it
887 /// requests. Therefore, capacity can not be relied upon to be precisely
888 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
890 /// [`try_reserve`]: Vec::try_reserve
894 /// If the capacity overflows, or the allocator reports a failure, then an error
900 /// use std::collections::TryReserveError;
902 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
903 /// let mut output = Vec::new();
905 /// // Pre-reserve the memory, exiting if we can't
906 /// output.try_reserve_exact(data.len())?;
908 /// // Now we know this can't OOM in the middle of our complex work
909 /// output.extend(data.iter().map(|&val| {
910 /// val * 2 + 5 // very complicated
915 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
917 #[stable(feature = "try_reserve", since = "1.57.0")]
918 pub fn try_reserve_exact(&mut self, additional
: usize) -> Result
<(), TryReserveError
> {
919 self.buf
.try_reserve_exact(self.len
, additional
)
922 /// Shrinks the capacity of the vector as much as possible.
924 /// It will drop down as close as possible to the length but the allocator
925 /// may still inform the vector that there is space for a few more elements.
930 /// let mut vec = Vec::with_capacity(10);
931 /// vec.extend([1, 2, 3]);
932 /// assert_eq!(vec.capacity(), 10);
933 /// vec.shrink_to_fit();
934 /// assert!(vec.capacity() >= 3);
936 #[cfg(not(no_global_oom_handling))]
937 #[stable(feature = "rust1", since = "1.0.0")]
938 pub fn shrink_to_fit(&mut self) {
939 // The capacity is never less than the length, and there's nothing to do when
940 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
941 // by only calling it with a greater capacity.
942 if self.capacity() > self.len
{
943 self.buf
.shrink_to_fit(self.len
);
947 /// Shrinks the capacity of the vector with a lower bound.
949 /// The capacity will remain at least as large as both the length
950 /// and the supplied value.
952 /// If the current capacity is less than the lower limit, this is a no-op.
957 /// let mut vec = Vec::with_capacity(10);
958 /// vec.extend([1, 2, 3]);
959 /// assert_eq!(vec.capacity(), 10);
960 /// vec.shrink_to(4);
961 /// assert!(vec.capacity() >= 4);
962 /// vec.shrink_to(0);
963 /// assert!(vec.capacity() >= 3);
965 #[cfg(not(no_global_oom_handling))]
966 #[stable(feature = "shrink_to", since = "1.56.0")]
967 pub fn shrink_to(&mut self, min_capacity
: usize) {
968 if self.capacity() > min_capacity
{
969 self.buf
.shrink_to_fit(cmp
::max(self.len
, min_capacity
));
973 /// Converts the vector into [`Box<[T]>`][owned slice].
975 /// Note that this will drop any excess capacity.
977 /// [owned slice]: Box
982 /// let v = vec![1, 2, 3];
984 /// let slice = v.into_boxed_slice();
987 /// Any excess capacity is removed:
990 /// let mut vec = Vec::with_capacity(10);
991 /// vec.extend([1, 2, 3]);
993 /// assert_eq!(vec.capacity(), 10);
994 /// let slice = vec.into_boxed_slice();
995 /// assert_eq!(slice.into_vec().capacity(), 3);
997 #[cfg(not(no_global_oom_handling))]
998 #[stable(feature = "rust1", since = "1.0.0")]
999 pub fn into_boxed_slice(mut self) -> Box
<[T
], A
> {
1001 self.shrink_to_fit();
1002 let me
= ManuallyDrop
::new(self);
1003 let buf
= ptr
::read(&me
.buf
);
1005 buf
.into_box(len
).assume_init()
1009 /// Shortens the vector, keeping the first `len` elements and dropping
1012 /// If `len` is greater than the vector's current length, this has no
1015 /// The [`drain`] method can emulate `truncate`, but causes the excess
1016 /// elements to be returned instead of dropped.
1018 /// Note that this method has no effect on the allocated capacity
1023 /// Truncating a five element vector to two elements:
1026 /// let mut vec = vec![1, 2, 3, 4, 5];
1027 /// vec.truncate(2);
1028 /// assert_eq!(vec, [1, 2]);
1031 /// No truncation occurs when `len` is greater than the vector's current
1035 /// let mut vec = vec![1, 2, 3];
1036 /// vec.truncate(8);
1037 /// assert_eq!(vec, [1, 2, 3]);
1040 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1044 /// let mut vec = vec![1, 2, 3];
1045 /// vec.truncate(0);
1046 /// assert_eq!(vec, []);
1049 /// [`clear`]: Vec::clear
1050 /// [`drain`]: Vec::drain
1051 #[stable(feature = "rust1", since = "1.0.0")]
1052 pub fn truncate(&mut self, len
: usize) {
1053 // This is safe because:
1055 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1056 // case avoids creating an invalid slice, and
1057 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1058 // such that no value will be dropped twice in case `drop_in_place`
1059 // were to panic once (if it panics twice, the program aborts).
1061 // Note: It's intentional that this is `>` and not `>=`.
1062 // Changing it to `>=` has negative performance
1063 // implications in some cases. See #78884 for more.
1067 let remaining_len
= self.len
- len
;
1068 let s
= ptr
::slice_from_raw_parts_mut(self.as_mut_ptr().add(len
), remaining_len
);
1070 ptr
::drop_in_place(s
);
1074 /// Extracts a slice containing the entire vector.
1076 /// Equivalent to `&s[..]`.
1081 /// use std::io::{self, Write};
1082 /// let buffer = vec![1, 2, 3, 5, 8];
1083 /// io::sink().write(buffer.as_slice()).unwrap();
1086 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1087 pub fn as_slice(&self) -> &[T
] {
1091 /// Extracts a mutable slice of the entire vector.
1093 /// Equivalent to `&mut s[..]`.
1098 /// use std::io::{self, Read};
1099 /// let mut buffer = vec![0; 3];
1100 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1103 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1104 pub fn as_mut_slice(&mut self) -> &mut [T
] {
1108 /// Returns a raw pointer to the vector's buffer.
1110 /// The caller must ensure that the vector outlives the pointer this
1111 /// function returns, or else it will end up pointing to garbage.
1112 /// Modifying the vector may cause its buffer to be reallocated,
1113 /// which would also make any pointers to it invalid.
1115 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1116 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1117 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1122 /// let x = vec![1, 2, 4];
1123 /// let x_ptr = x.as_ptr();
1126 /// for i in 0..x.len() {
1127 /// assert_eq!(*x_ptr.add(i), 1 << i);
1132 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1133 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1135 pub fn as_ptr(&self) -> *const T
{
1136 // We shadow the slice method of the same name to avoid going through
1137 // `deref`, which creates an intermediate reference.
1138 let ptr
= self.buf
.ptr();
1140 assume(!ptr
.is_null());
1145 /// Returns an unsafe mutable pointer to the vector's buffer.
1147 /// The caller must ensure that the vector outlives the pointer this
1148 /// function returns, or else it will end up pointing to garbage.
1149 /// Modifying the vector may cause its buffer to be reallocated,
1150 /// which would also make any pointers to it invalid.
1155 /// // Allocate vector big enough for 4 elements.
1157 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1158 /// let x_ptr = x.as_mut_ptr();
1160 /// // Initialize elements via raw pointer writes, then set length.
1162 /// for i in 0..size {
1163 /// *x_ptr.add(i) = i as i32;
1165 /// x.set_len(size);
1167 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1169 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1171 pub fn as_mut_ptr(&mut self) -> *mut T
{
1172 // We shadow the slice method of the same name to avoid going through
1173 // `deref_mut`, which creates an intermediate reference.
1174 let ptr
= self.buf
.ptr();
1176 assume(!ptr
.is_null());
1181 /// Returns a reference to the underlying allocator.
1182 #[unstable(feature = "allocator_api", issue = "32838")]
1184 pub fn allocator(&self) -> &A
{
1185 self.buf
.allocator()
1188 /// Forces the length of the vector to `new_len`.
1190 /// This is a low-level operation that maintains none of the normal
1191 /// invariants of the type. Normally changing the length of a vector
1192 /// is done using one of the safe operations instead, such as
1193 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1195 /// [`truncate`]: Vec::truncate
1196 /// [`resize`]: Vec::resize
1197 /// [`extend`]: Extend::extend
1198 /// [`clear`]: Vec::clear
1202 /// - `new_len` must be less than or equal to [`capacity()`].
1203 /// - The elements at `old_len..new_len` must be initialized.
1205 /// [`capacity()`]: Vec::capacity
1209 /// This method can be useful for situations in which the vector
1210 /// is serving as a buffer for other code, particularly over FFI:
1213 /// # #![allow(dead_code)]
1214 /// # // This is just a minimal skeleton for the doc example;
1215 /// # // don't use this as a starting point for a real library.
1216 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1217 /// # const Z_OK: i32 = 0;
1219 /// # fn deflateGetDictionary(
1220 /// # strm: *mut std::ffi::c_void,
1221 /// # dictionary: *mut u8,
1222 /// # dictLength: *mut usize,
1225 /// # impl StreamWrapper {
1226 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1227 /// // Per the FFI method's docs, "32768 bytes is always enough".
1228 /// let mut dict = Vec::with_capacity(32_768);
1229 /// let mut dict_length = 0;
1230 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1231 /// // 1. `dict_length` elements were initialized.
1232 /// // 2. `dict_length` <= the capacity (32_768)
1233 /// // which makes `set_len` safe to call.
1235 /// // Make the FFI call...
1236 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1238 /// // ...and update the length to what was initialized.
1239 /// dict.set_len(dict_length);
1249 /// While the following example is sound, there is a memory leak since
1250 /// the inner vectors were not freed prior to the `set_len` call:
1253 /// let mut vec = vec![vec![1, 0, 0],
1257 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1258 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1264 /// Normally, here, one would use [`clear`] instead to correctly drop
1265 /// the contents and thus not leak memory.
1267 #[stable(feature = "rust1", since = "1.0.0")]
1268 pub unsafe fn set_len(&mut self, new_len
: usize) {
1269 debug_assert
!(new_len
<= self.capacity());
1274 /// Removes an element from the vector and returns it.
1276 /// The removed element is replaced by the last element of the vector.
1278 /// This does not preserve ordering, but is *O*(1).
1279 /// If you need to preserve the element order, use [`remove`] instead.
1281 /// [`remove`]: Vec::remove
1285 /// Panics if `index` is out of bounds.
1290 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1292 /// assert_eq!(v.swap_remove(1), "bar");
1293 /// assert_eq!(v, ["foo", "qux", "baz"]);
1295 /// assert_eq!(v.swap_remove(0), "foo");
1296 /// assert_eq!(v, ["baz", "qux"]);
1299 #[stable(feature = "rust1", since = "1.0.0")]
1300 pub fn swap_remove(&mut self, index
: usize) -> T
{
1303 fn assert_failed(index
: usize, len
: usize) -> ! {
1304 panic
!("swap_remove index (is {index}) should be < len (is {len})");
1307 let len
= self.len();
1309 assert_failed(index
, len
);
1312 // We replace self[index] with the last element. Note that if the
1313 // bounds check above succeeds there must be a last element (which
1314 // can be self[index] itself).
1315 let value
= ptr
::read(self.as_ptr().add(index
));
1316 let base_ptr
= self.as_mut_ptr();
1317 ptr
::copy(base_ptr
.add(len
- 1), base_ptr
.add(index
), 1);
1318 self.set_len(len
- 1);
1323 /// Inserts an element at position `index` within the vector, shifting all
1324 /// elements after it to the right.
1328 /// Panics if `index > len`.
1333 /// let mut vec = vec![1, 2, 3];
1334 /// vec.insert(1, 4);
1335 /// assert_eq!(vec, [1, 4, 2, 3]);
1336 /// vec.insert(4, 5);
1337 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1339 #[cfg(not(no_global_oom_handling))]
1340 #[stable(feature = "rust1", since = "1.0.0")]
1341 pub fn insert(&mut self, index
: usize, element
: T
) {
1344 fn assert_failed(index
: usize, len
: usize) -> ! {
1345 panic
!("insertion index (is {index}) should be <= len (is {len})");
1348 let len
= self.len();
1350 assert_failed(index
, len
);
1353 // space for the new element
1354 if len
== self.buf
.capacity() {
1360 // The spot to put the new value
1362 let p
= self.as_mut_ptr().add(index
);
1363 // Shift everything over to make space. (Duplicating the
1364 // `index`th element into two consecutive places.)
1365 ptr
::copy(p
, p
.offset(1), len
- index
);
1366 // Write it in, overwriting the first copy of the `index`th
1368 ptr
::write(p
, element
);
1370 self.set_len(len
+ 1);
1374 /// Removes and returns the element at position `index` within the vector,
1375 /// shifting all elements after it to the left.
1377 /// Note: Because this shifts over the remaining elements, it has a
1378 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1379 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1380 /// elements from the beginning of the `Vec`, consider using
1381 /// [`VecDeque::pop_front`] instead.
1383 /// [`swap_remove`]: Vec::swap_remove
1384 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1388 /// Panics if `index` is out of bounds.
1393 /// let mut v = vec![1, 2, 3];
1394 /// assert_eq!(v.remove(1), 2);
1395 /// assert_eq!(v, [1, 3]);
1397 #[stable(feature = "rust1", since = "1.0.0")]
1399 pub fn remove(&mut self, index
: usize) -> T
{
1403 fn assert_failed(index
: usize, len
: usize) -> ! {
1404 panic
!("removal index (is {index}) should be < len (is {len})");
1407 let len
= self.len();
1409 assert_failed(index
, len
);
1415 // the place we are taking from.
1416 let ptr
= self.as_mut_ptr().add(index
);
1417 // copy it out, unsafely having a copy of the value on
1418 // the stack and in the vector at the same time.
1419 ret
= ptr
::read(ptr
);
1421 // Shift everything down to fill in that spot.
1422 ptr
::copy(ptr
.offset(1), ptr
, len
- index
- 1);
1424 self.set_len(len
- 1);
1429 /// Retains only the elements specified by the predicate.
1431 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1432 /// This method operates in place, visiting each element exactly once in the
1433 /// original order, and preserves the order of the retained elements.
1438 /// let mut vec = vec![1, 2, 3, 4];
1439 /// vec.retain(|&x| x % 2 == 0);
1440 /// assert_eq!(vec, [2, 4]);
1443 /// Because the elements are visited exactly once in the original order,
1444 /// external state may be used to decide which elements to keep.
1447 /// let mut vec = vec![1, 2, 3, 4, 5];
1448 /// let keep = [false, true, true, false, true];
1449 /// let mut iter = keep.iter();
1450 /// vec.retain(|_| *iter.next().unwrap());
1451 /// assert_eq!(vec, [2, 3, 5]);
1453 #[stable(feature = "rust1", since = "1.0.0")]
1454 pub fn retain
<F
>(&mut self, mut f
: F
)
1456 F
: FnMut(&T
) -> bool
,
1458 self.retain_mut(|elem
| f(elem
));
1461 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1463 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1464 /// This method operates in place, visiting each element exactly once in the
1465 /// original order, and preserves the order of the retained elements.
1470 /// let mut vec = vec![1, 2, 3, 4];
1471 /// vec.retain_mut(|x| if *x > 3 {
1477 /// assert_eq!(vec, [2, 3, 4]);
1479 #[stable(feature = "vec_retain_mut", since = "1.61.0")]
1480 pub fn retain_mut
<F
>(&mut self, mut f
: F
)
1482 F
: FnMut(&mut T
) -> bool
,
1484 let original_len
= self.len();
1485 // Avoid double drop if the drop guard is not executed,
1486 // since we may make some holes during the process.
1487 unsafe { self.set_len(0) }
;
1489 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1490 // |<- processed len ->| ^- next to check
1491 // |<- deleted cnt ->|
1492 // |<- original_len ->|
1493 // Kept: Elements which predicate returns true on.
1494 // Hole: Moved or dropped element slot.
1495 // Unchecked: Unchecked valid elements.
1497 // This drop guard will be invoked when predicate or `drop` of element panicked.
1498 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1499 // In cases when predicate and `drop` never panick, it will be optimized out.
1500 struct BackshiftOnDrop
<'a
, T
, A
: Allocator
> {
1501 v
: &'a
mut Vec
<T
, A
>,
1502 processed_len
: usize,
1504 original_len
: usize,
1507 impl<T
, A
: Allocator
> Drop
for BackshiftOnDrop
<'_
, T
, A
> {
1508 fn drop(&mut self) {
1509 if self.deleted_cnt
> 0 {
1510 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1513 self.v
.as_ptr().add(self.processed_len
),
1514 self.v
.as_mut_ptr().add(self.processed_len
- self.deleted_cnt
),
1515 self.original_len
- self.processed_len
,
1519 // SAFETY: After filling holes, all items are in contiguous memory.
1521 self.v
.set_len(self.original_len
- self.deleted_cnt
);
1526 let mut g
= BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len }
;
1528 fn process_loop
<F
, T
, A
: Allocator
, const DELETED
: bool
>(
1529 original_len
: usize,
1531 g
: &mut BackshiftOnDrop
<'_
, T
, A
>,
1533 F
: FnMut(&mut T
) -> bool
,
1535 while g
.processed_len
!= original_len
{
1536 // SAFETY: Unchecked element must be valid.
1537 let cur
= unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) }
;
1539 // Advance early to avoid double drop if `drop_in_place` panicked.
1540 g
.processed_len
+= 1;
1542 // SAFETY: We never touch this element again after dropped.
1543 unsafe { ptr::drop_in_place(cur) }
;
1544 // We already advanced the counter.
1552 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1553 // We use copy for move, and never touch this element again.
1555 let hole_slot
= g
.v
.as_mut_ptr().add(g
.processed_len
- g
.deleted_cnt
);
1556 ptr
::copy_nonoverlapping(cur
, hole_slot
, 1);
1559 g
.processed_len
+= 1;
1563 // Stage 1: Nothing was deleted.
1564 process_loop
::<F
, T
, A
, false>(original_len
, &mut f
, &mut g
);
1566 // Stage 2: Some elements were deleted.
1567 process_loop
::<F
, T
, A
, true>(original_len
, &mut f
, &mut g
);
1569 // All item are processed. This can be optimized to `set_len` by LLVM.
1573 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1576 /// If the vector is sorted, this removes all duplicates.
1581 /// let mut vec = vec![10, 20, 21, 30, 20];
1583 /// vec.dedup_by_key(|i| *i / 10);
1585 /// assert_eq!(vec, [10, 20, 30, 20]);
1587 #[stable(feature = "dedup_by", since = "1.16.0")]
1589 pub fn dedup_by_key
<F
, K
>(&mut self, mut key
: F
)
1591 F
: FnMut(&mut T
) -> K
,
1594 self.dedup_by(|a
, b
| key(a
) == key(b
))
1597 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1600 /// The `same_bucket` function is passed references to two elements from the vector and
1601 /// must determine if the elements compare equal. The elements are passed in opposite order
1602 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1604 /// If the vector is sorted, this removes all duplicates.
1609 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1611 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1613 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1615 #[stable(feature = "dedup_by", since = "1.16.0")]
1616 pub fn dedup_by
<F
>(&mut self, mut same_bucket
: F
)
1618 F
: FnMut(&mut T
, &mut T
) -> bool
,
1620 let len
= self.len();
1625 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1626 struct FillGapOnDrop
<'a
, T
, A
: core
::alloc
::Allocator
> {
1627 /* Offset of the element we want to check if it is duplicate */
1630 /* Offset of the place where we want to place the non-duplicate
1631 * when we find it. */
1634 /* The Vec that would need correction if `same_bucket` panicked */
1635 vec
: &'a
mut Vec
<T
, A
>,
1638 impl<'a
, T
, A
: core
::alloc
::Allocator
> Drop
for FillGapOnDrop
<'a
, T
, A
> {
1639 fn drop(&mut self) {
1640 /* This code gets executed when `same_bucket` panics */
1642 /* SAFETY: invariant guarantees that `read - write`
1643 * and `len - read` never overflow and that the copy is always
1646 let ptr
= self.vec
.as_mut_ptr();
1647 let len
= self.vec
.len();
1649 /* How many items were left when `same_bucket` panicked.
1650 * Basically vec[read..].len() */
1651 let items_left
= len
.wrapping_sub(self.read
);
1653 /* Pointer to first item in vec[write..write+items_left] slice */
1654 let dropped_ptr
= ptr
.add(self.write
);
1655 /* Pointer to first item in vec[read..] slice */
1656 let valid_ptr
= ptr
.add(self.read
);
1658 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1659 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1660 ptr
::copy(valid_ptr
, dropped_ptr
, items_left
);
1662 /* How many items have been already dropped
1663 * Basically vec[read..write].len() */
1664 let dropped
= self.read
.wrapping_sub(self.write
);
1666 self.vec
.set_len(len
- dropped
);
1671 let mut gap
= FillGapOnDrop { read: 1, write: 1, vec: self }
;
1672 let ptr
= gap
.vec
.as_mut_ptr();
1674 /* Drop items while going through Vec, it should be more efficient than
1675 * doing slice partition_dedup + truncate */
1677 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1678 * are always in-bounds and read_ptr never aliases prev_ptr */
1680 while gap
.read
< len
{
1681 let read_ptr
= ptr
.add(gap
.read
);
1682 let prev_ptr
= ptr
.add(gap
.write
.wrapping_sub(1));
1684 if same_bucket(&mut *read_ptr
, &mut *prev_ptr
) {
1685 // Increase `gap.read` now since the drop may panic.
1687 /* We have found duplicate, drop it in-place */
1688 ptr
::drop_in_place(read_ptr
);
1690 let write_ptr
= ptr
.add(gap
.write
);
1692 /* Because `read_ptr` can be equal to `write_ptr`, we either
1693 * have to use `copy` or conditional `copy_nonoverlapping`.
1694 * Looks like the first option is faster. */
1695 ptr
::copy(read_ptr
, write_ptr
, 1);
1697 /* We have filled that place, so go further */
1703 /* Technically we could let `gap` clean up with its Drop, but
1704 * when `same_bucket` is guaranteed to not panic, this bloats a little
1705 * the codegen, so we just do it manually */
1706 gap
.vec
.set_len(gap
.write
);
1711 /// Appends an element to the back of a collection.
1715 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1720 /// let mut vec = vec![1, 2];
1722 /// assert_eq!(vec, [1, 2, 3]);
1724 #[cfg(not(no_global_oom_handling))]
1726 #[stable(feature = "rust1", since = "1.0.0")]
1727 pub fn push(&mut self, value
: T
) {
1728 // This will panic or abort if we would allocate > isize::MAX bytes
1729 // or if the length increment would overflow for zero-sized types.
1730 if self.len
== self.buf
.capacity() {
1731 self.buf
.reserve_for_push(self.len
);
1734 let end
= self.as_mut_ptr().add(self.len
);
1735 ptr
::write(end
, value
);
1740 /// Removes the last element from a vector and returns it, or [`None`] if it
1743 /// If you'd like to pop the first element, consider using
1744 /// [`VecDeque::pop_front`] instead.
1746 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1751 /// let mut vec = vec![1, 2, 3];
1752 /// assert_eq!(vec.pop(), Some(3));
1753 /// assert_eq!(vec, [1, 2]);
1756 #[stable(feature = "rust1", since = "1.0.0")]
1757 pub fn pop(&mut self) -> Option
<T
> {
1763 Some(ptr
::read(self.as_ptr().add(self.len())))
1768 /// Moves all the elements of `other` into `self`, leaving `other` empty.
1772 /// Panics if the number of elements in the vector overflows a `usize`.
1777 /// let mut vec = vec![1, 2, 3];
1778 /// let mut vec2 = vec![4, 5, 6];
1779 /// vec.append(&mut vec2);
1780 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1781 /// assert_eq!(vec2, []);
1783 #[cfg(not(no_global_oom_handling))]
1785 #[stable(feature = "append", since = "1.4.0")]
1786 pub fn append(&mut self, other
: &mut Self) {
1788 self.append_elements(other
.as_slice() as _
);
1793 /// Appends elements to `self` from other buffer.
1794 #[cfg(not(no_global_oom_handling))]
1796 unsafe fn append_elements(&mut self, other
: *const [T
]) {
1797 let count
= unsafe { (*other).len() }
;
1798 self.reserve(count
);
1799 let len
= self.len();
1800 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) }
;
1804 /// Removes the specified range from the vector in bulk, returning all
1805 /// removed elements as an iterator. If the iterator is dropped before
1806 /// being fully consumed, it drops the remaining removed elements.
1808 /// The returned iterator keeps a mutable borrow on the vector to optimize
1809 /// its implementation.
1813 /// Panics if the starting point is greater than the end point or if
1814 /// the end point is greater than the length of the vector.
1818 /// If the returned iterator goes out of scope without being dropped (due to
1819 /// [`mem::forget`], for example), the vector may have lost and leaked
1820 /// elements arbitrarily, including elements outside the range.
1825 /// let mut v = vec![1, 2, 3];
1826 /// let u: Vec<_> = v.drain(1..).collect();
1827 /// assert_eq!(v, &[1]);
1828 /// assert_eq!(u, &[2, 3]);
1830 /// // A full range clears the vector, like `clear()` does
1832 /// assert_eq!(v, &[]);
1834 #[stable(feature = "drain", since = "1.6.0")]
1835 pub fn drain
<R
>(&mut self, range
: R
) -> Drain
<'_
, T
, A
>
1837 R
: RangeBounds
<usize>,
1841 // When the Drain is first created, it shortens the length of
1842 // the source vector to make sure no uninitialized or moved-from elements
1843 // are accessible at all if the Drain's destructor never gets to run.
1845 // Drain will ptr::read out the values to remove.
1846 // When finished, remaining tail of the vec is copied back to cover
1847 // the hole, and the vector length is restored to the new length.
1849 let len
= self.len();
1850 let Range { start, end }
= slice
::range(range
, ..len
);
1853 // set self.vec length's to start, to be safe in case Drain is leaked
1854 self.set_len(start
);
1855 // Use the borrow in the IterMut to indicate borrowing behavior of the
1856 // whole Drain iterator (like &mut T).
1857 let range_slice
= slice
::from_raw_parts_mut(self.as_mut_ptr().add(start
), end
- start
);
1860 tail_len
: len
- end
,
1861 iter
: range_slice
.iter(),
1862 vec
: NonNull
::from(self),
1867 /// Clears the vector, removing all values.
1869 /// Note that this method has no effect on the allocated capacity
1875 /// let mut v = vec![1, 2, 3];
1879 /// assert!(v.is_empty());
1882 #[stable(feature = "rust1", since = "1.0.0")]
1883 pub fn clear(&mut self) {
1887 /// Returns the number of elements in the vector, also referred to
1888 /// as its 'length'.
1893 /// let a = vec![1, 2, 3];
1894 /// assert_eq!(a.len(), 3);
1897 #[stable(feature = "rust1", since = "1.0.0")]
1898 pub fn len(&self) -> usize {
1902 /// Returns `true` if the vector contains no elements.
1907 /// let mut v = Vec::new();
1908 /// assert!(v.is_empty());
1911 /// assert!(!v.is_empty());
1913 #[stable(feature = "rust1", since = "1.0.0")]
1914 pub fn is_empty(&self) -> bool
{
1918 /// Splits the collection into two at the given index.
1920 /// Returns a newly allocated vector containing the elements in the range
1921 /// `[at, len)`. After the call, the original vector will be left containing
1922 /// the elements `[0, at)` with its previous capacity unchanged.
1926 /// Panics if `at > len`.
1931 /// let mut vec = vec![1, 2, 3];
1932 /// let vec2 = vec.split_off(1);
1933 /// assert_eq!(vec, [1]);
1934 /// assert_eq!(vec2, [2, 3]);
1936 #[cfg(not(no_global_oom_handling))]
1938 #[must_use = "use `.truncate()` if you don't need the other half"]
1939 #[stable(feature = "split_off", since = "1.4.0")]
1940 pub fn split_off(&mut self, at
: usize) -> Self
1946 fn assert_failed(at
: usize, len
: usize) -> ! {
1947 panic
!("`at` split index (is {at}) should be <= len (is {len})");
1950 if at
> self.len() {
1951 assert_failed(at
, self.len());
1955 // the new vector can take over the original buffer and avoid the copy
1956 return mem
::replace(
1958 Vec
::with_capacity_in(self.capacity(), self.allocator().clone()),
1962 let other_len
= self.len
- at
;
1963 let mut other
= Vec
::with_capacity_in(other_len
, self.allocator().clone());
1965 // Unsafely `set_len` and copy items to `other`.
1968 other
.set_len(other_len
);
1970 ptr
::copy_nonoverlapping(self.as_ptr().add(at
), other
.as_mut_ptr(), other
.len());
1975 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1977 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1978 /// difference, with each additional slot filled with the result of
1979 /// calling the closure `f`. The return values from `f` will end up
1980 /// in the `Vec` in the order they have been generated.
1982 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1984 /// This method uses a closure to create new values on every push. If
1985 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
1986 /// want to use the [`Default`] trait to generate values, you can
1987 /// pass [`Default::default`] as the second argument.
1992 /// let mut vec = vec![1, 2, 3];
1993 /// vec.resize_with(5, Default::default);
1994 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1996 /// let mut vec = vec![];
1998 /// vec.resize_with(4, || { p *= 2; p });
1999 /// assert_eq!(vec, [2, 4, 8, 16]);
2001 #[cfg(not(no_global_oom_handling))]
2002 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2003 pub fn resize_with
<F
>(&mut self, new_len
: usize, f
: F
)
2007 let len
= self.len();
2009 self.extend_with(new_len
- len
, ExtendFunc(f
));
2011 self.truncate(new_len
);
2015 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2016 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2017 /// `'a`. If the type has only static references, or none at all, then this
2018 /// may be chosen to be `'static`.
2020 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2021 /// so the leaked allocation may include unused capacity that is not part
2022 /// of the returned slice.
2024 /// This function is mainly useful for data that lives for the remainder of
2025 /// the program's life. Dropping the returned reference will cause a memory
2033 /// let x = vec![1, 2, 3];
2034 /// let static_ref: &'static mut [usize] = x.leak();
2035 /// static_ref[0] += 1;
2036 /// assert_eq!(static_ref, &[2, 2, 3]);
2038 #[cfg(not(no_global_oom_handling))]
2039 #[stable(feature = "vec_leak", since = "1.47.0")]
2041 pub fn leak
<'a
>(self) -> &'a
mut [T
]
2045 let mut me
= ManuallyDrop
::new(self);
2046 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2049 /// Returns the remaining spare capacity of the vector as a slice of
2050 /// `MaybeUninit<T>`.
2052 /// The returned slice can be used to fill the vector with data (e.g. by
2053 /// reading from a file) before marking the data as initialized using the
2054 /// [`set_len`] method.
2056 /// [`set_len`]: Vec::set_len
2061 /// // Allocate vector big enough for 10 elements.
2062 /// let mut v = Vec::with_capacity(10);
2064 /// // Fill in the first 3 elements.
2065 /// let uninit = v.spare_capacity_mut();
2066 /// uninit[0].write(0);
2067 /// uninit[1].write(1);
2068 /// uninit[2].write(2);
2070 /// // Mark the first 3 elements of the vector as being initialized.
2075 /// assert_eq!(&v, &[0, 1, 2]);
2077 #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
2079 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit
<T
>] {
2081 // This method is not implemented in terms of `split_at_spare_mut`,
2082 // to prevent invalidation of pointers to the buffer.
2084 slice
::from_raw_parts_mut(
2085 self.as_mut_ptr().add(self.len
) as *mut MaybeUninit
<T
>,
2086 self.buf
.capacity() - self.len
,
2091 /// Returns vector content as a slice of `T`, along with the remaining spare
2092 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2094 /// The returned spare capacity slice can be used to fill the vector with data
2095 /// (e.g. by reading from a file) before marking the data as initialized using
2096 /// the [`set_len`] method.
2098 /// [`set_len`]: Vec::set_len
2100 /// Note that this is a low-level API, which should be used with care for
2101 /// optimization purposes. If you need to append data to a `Vec`
2102 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2103 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2104 /// [`resize_with`], depending on your exact needs.
2106 /// [`push`]: Vec::push
2107 /// [`extend`]: Vec::extend
2108 /// [`extend_from_slice`]: Vec::extend_from_slice
2109 /// [`extend_from_within`]: Vec::extend_from_within
2110 /// [`insert`]: Vec::insert
2111 /// [`append`]: Vec::append
2112 /// [`resize`]: Vec::resize
2113 /// [`resize_with`]: Vec::resize_with
2118 /// #![feature(vec_split_at_spare)]
2120 /// let mut v = vec![1, 1, 2];
2122 /// // Reserve additional space big enough for 10 elements.
2125 /// let (init, uninit) = v.split_at_spare_mut();
2126 /// let sum = init.iter().copied().sum::<u32>();
2128 /// // Fill in the next 4 elements.
2129 /// uninit[0].write(sum);
2130 /// uninit[1].write(sum * 2);
2131 /// uninit[2].write(sum * 3);
2132 /// uninit[3].write(sum * 4);
2134 /// // Mark the 4 elements of the vector as being initialized.
2136 /// let len = v.len();
2137 /// v.set_len(len + 4);
2140 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2142 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2144 pub fn split_at_spare_mut(&mut self) -> (&mut [T
], &mut [MaybeUninit
<T
>]) {
2146 // - len is ignored and so never changed
2147 let (init
, spare
, _
) = unsafe { self.split_at_spare_mut_with_len() }
;
2151 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2153 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2154 unsafe fn split_at_spare_mut_with_len(
2156 ) -> (&mut [T
], &mut [MaybeUninit
<T
>], &mut usize) {
2157 let ptr
= self.as_mut_ptr();
2159 // - `ptr` is guaranteed to be valid for `self.len` elements
2160 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2162 let spare_ptr
= unsafe { ptr.add(self.len) }
;
2163 let spare_ptr
= spare_ptr
.cast
::<MaybeUninit
<T
>>();
2164 let spare_len
= self.buf
.capacity() - self.len
;
2167 // - `ptr` is guaranteed to be valid for `self.len` elements
2168 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2170 let initialized
= slice
::from_raw_parts_mut(ptr
, self.len
);
2171 let spare
= slice
::from_raw_parts_mut(spare_ptr
, spare_len
);
2173 (initialized
, spare
, &mut self.len
)
2178 impl<T
: Clone
, A
: Allocator
> Vec
<T
, A
> {
2179 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2181 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2182 /// difference, with each additional slot filled with `value`.
2183 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2185 /// This method requires `T` to implement [`Clone`],
2186 /// in order to be able to clone the passed value.
2187 /// If you need more flexibility (or want to rely on [`Default`] instead of
2188 /// [`Clone`]), use [`Vec::resize_with`].
2189 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2194 /// let mut vec = vec!["hello"];
2195 /// vec.resize(3, "world");
2196 /// assert_eq!(vec, ["hello", "world", "world"]);
2198 /// let mut vec = vec![1, 2, 3, 4];
2199 /// vec.resize(2, 0);
2200 /// assert_eq!(vec, [1, 2]);
2202 #[cfg(not(no_global_oom_handling))]
2203 #[stable(feature = "vec_resize", since = "1.5.0")]
2204 pub fn resize(&mut self, new_len
: usize, value
: T
) {
2205 let len
= self.len();
2208 self.extend_with(new_len
- len
, ExtendElement(value
))
2210 self.truncate(new_len
);
2214 /// Clones and appends all elements in a slice to the `Vec`.
2216 /// Iterates over the slice `other`, clones each element, and then appends
2217 /// it to this `Vec`. The `other` slice is traversed in-order.
2219 /// Note that this function is same as [`extend`] except that it is
2220 /// specialized to work with slices instead. If and when Rust gets
2221 /// specialization this function will likely be deprecated (but still
2227 /// let mut vec = vec![1];
2228 /// vec.extend_from_slice(&[2, 3, 4]);
2229 /// assert_eq!(vec, [1, 2, 3, 4]);
2232 /// [`extend`]: Vec::extend
2233 #[cfg(not(no_global_oom_handling))]
2234 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2235 pub fn extend_from_slice(&mut self, other
: &[T
]) {
2236 self.spec_extend(other
.iter())
2239 /// Copies elements from `src` range to the end of the vector.
2243 /// Panics if the starting point is greater than the end point or if
2244 /// the end point is greater than the length of the vector.
2249 /// let mut vec = vec![0, 1, 2, 3, 4];
2251 /// vec.extend_from_within(2..);
2252 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2254 /// vec.extend_from_within(..2);
2255 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2257 /// vec.extend_from_within(4..8);
2258 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2260 #[cfg(not(no_global_oom_handling))]
2261 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2262 pub fn extend_from_within
<R
>(&mut self, src
: R
)
2264 R
: RangeBounds
<usize>,
2266 let range
= slice
::range(src
, ..self.len());
2267 self.reserve(range
.len());
2270 // - `slice::range` guarantees that the given range is valid for indexing self
2272 self.spec_extend_from_within(range
);
2277 // This code generalizes `extend_with_{element,default}`.
2278 trait ExtendWith
<T
> {
2279 fn next(&mut self) -> T
;
2283 struct ExtendElement
<T
>(T
);
2284 impl<T
: Clone
> ExtendWith
<T
> for ExtendElement
<T
> {
2285 fn next(&mut self) -> T
{
2288 fn last(self) -> T
{
2293 struct ExtendFunc
<F
>(F
);
2294 impl<T
, F
: FnMut() -> T
> ExtendWith
<T
> for ExtendFunc
<F
> {
2295 fn next(&mut self) -> T
{
2298 fn last(mut self) -> T
{
2303 impl<T
, A
: Allocator
> Vec
<T
, A
> {
2304 #[cfg(not(no_global_oom_handling))]
2305 /// Extend the vector by `n` values, using the given generator.
2306 fn extend_with
<E
: ExtendWith
<T
>>(&mut self, n
: usize, mut value
: E
) {
2310 let mut ptr
= self.as_mut_ptr().add(self.len());
2311 // Use SetLenOnDrop to work around bug where compiler
2312 // might not realize the store through `ptr` through self.set_len()
2314 let mut local_len
= SetLenOnDrop
::new(&mut self.len
);
2316 // Write all elements except the last one
2318 ptr
::write(ptr
, value
.next());
2319 ptr
= ptr
.offset(1);
2320 // Increment the length in every step in case next() panics
2321 local_len
.increment_len(1);
2325 // We can write the last element directly without cloning needlessly
2326 ptr
::write(ptr
, value
.last());
2327 local_len
.increment_len(1);
2330 // len set by scope guard
2335 impl<T
: PartialEq
, A
: Allocator
> Vec
<T
, A
> {
2336 /// Removes consecutive repeated elements in the vector according to the
2337 /// [`PartialEq`] trait implementation.
2339 /// If the vector is sorted, this removes all duplicates.
2344 /// let mut vec = vec![1, 2, 2, 3, 2];
2348 /// assert_eq!(vec, [1, 2, 3, 2]);
2350 #[stable(feature = "rust1", since = "1.0.0")]
2352 pub fn dedup(&mut self) {
2353 self.dedup_by(|a
, b
| a
== b
)
2357 ////////////////////////////////////////////////////////////////////////////////
2358 // Internal methods and functions
2359 ////////////////////////////////////////////////////////////////////////////////
2362 #[cfg(not(no_global_oom_handling))]
2363 #[stable(feature = "rust1", since = "1.0.0")]
2364 pub fn from_elem
<T
: Clone
>(elem
: T
, n
: usize) -> Vec
<T
> {
2365 <T
as SpecFromElem
>::from_elem(elem
, n
, Global
)
2369 #[cfg(not(no_global_oom_handling))]
2370 #[unstable(feature = "allocator_api", issue = "32838")]
2371 pub fn from_elem_in
<T
: Clone
, A
: Allocator
>(elem
: T
, n
: usize, alloc
: A
) -> Vec
<T
, A
> {
2372 <T
as SpecFromElem
>::from_elem(elem
, n
, alloc
)
2375 trait ExtendFromWithinSpec
{
2378 /// - `src` needs to be valid index
2379 /// - `self.capacity() - self.len()` must be `>= src.len()`
2380 unsafe fn spec_extend_from_within(&mut self, src
: Range
<usize>);
2383 impl<T
: Clone
, A
: Allocator
> ExtendFromWithinSpec
for Vec
<T
, A
> {
2384 default unsafe fn spec_extend_from_within(&mut self, src
: Range
<usize>) {
2386 // - len is increased only after initializing elements
2387 let (this
, spare
, len
) = unsafe { self.split_at_spare_mut_with_len() }
;
2390 // - caller guaratees that src is a valid index
2391 let to_clone
= unsafe { this.get_unchecked(src) }
;
2393 iter
::zip(to_clone
, spare
)
2394 .map(|(src
, dst
)| dst
.write(src
.clone()))
2396 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2397 // - len is increased after each element to prevent leaks (see issue #82533)
2398 .for_each(|_
| *len
+= 1);
2402 impl<T
: Copy
, A
: Allocator
> ExtendFromWithinSpec
for Vec
<T
, A
> {
2403 unsafe fn spec_extend_from_within(&mut self, src
: Range
<usize>) {
2404 let count
= src
.len();
2406 let (init
, spare
) = self.split_at_spare_mut();
2409 // - caller guaratees that `src` is a valid index
2410 let source
= unsafe { init.get_unchecked(src) }
;
2413 // - Both pointers are created from unique slice references (`&mut [_]`)
2414 // so they are valid and do not overlap.
2415 // - Elements are :Copy so it's OK to to copy them, without doing
2416 // anything with the original values
2417 // - `count` is equal to the len of `source`, so source is valid for
2419 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2420 // is valid for `count` writes
2421 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) }
;
2425 // - The elements were just initialized by `copy_nonoverlapping`
2430 ////////////////////////////////////////////////////////////////////////////////
2431 // Common trait implementations for Vec
2432 ////////////////////////////////////////////////////////////////////////////////
2434 #[stable(feature = "rust1", since = "1.0.0")]
2435 impl<T
, A
: Allocator
> ops
::Deref
for Vec
<T
, A
> {
2438 fn deref(&self) -> &[T
] {
2439 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2443 #[stable(feature = "rust1", since = "1.0.0")]
2444 impl<T
, A
: Allocator
> ops
::DerefMut
for Vec
<T
, A
> {
2445 fn deref_mut(&mut self) -> &mut [T
] {
2446 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2450 #[cfg(not(no_global_oom_handling))]
2451 trait SpecCloneFrom
{
2452 fn clone_from(this
: &mut Self, other
: &Self);
2455 #[cfg(not(no_global_oom_handling))]
2456 impl<T
: Clone
, A
: Allocator
> SpecCloneFrom
for Vec
<T
, A
> {
2457 default fn clone_from(this
: &mut Self, other
: &Self) {
2458 // drop anything that will not be overwritten
2459 this
.truncate(other
.len());
2461 // self.len <= other.len due to the truncate above, so the
2462 // slices here are always in-bounds.
2463 let (init
, tail
) = other
.split_at(this
.len());
2465 // reuse the contained values' allocations/resources.
2466 this
.clone_from_slice(init
);
2467 this
.extend_from_slice(tail
);
2471 #[cfg(not(no_global_oom_handling))]
2472 impl<T
: Copy
, A
: Allocator
> SpecCloneFrom
for Vec
<T
, A
> {
2473 fn clone_from(this
: &mut Self, other
: &Self) {
2475 this
.extend_from_slice(other
);
2479 #[cfg(not(no_global_oom_handling))]
2480 #[stable(feature = "rust1", since = "1.0.0")]
2481 impl<T
: Clone
, A
: Allocator
+ Clone
> Clone
for Vec
<T
, A
> {
2483 fn clone(&self) -> Self {
2484 let alloc
= self.allocator().clone();
2485 <[T
]>::to_vec_in(&**self, alloc
)
2488 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2489 // required for this method definition, is not available. Instead use the
2490 // `slice::to_vec` function which is only available with cfg(test)
2491 // NB see the slice::hack module in slice.rs for more information
2493 fn clone(&self) -> Self {
2494 let alloc
= self.allocator().clone();
2495 crate::slice
::to_vec(&**self, alloc
)
2498 fn clone_from(&mut self, other
: &Self) {
2499 SpecCloneFrom
::clone_from(self, other
)
2503 /// The hash of a vector is the same as that of the corresponding slice,
2504 /// as required by the `core::borrow::Borrow` implementation.
2507 /// #![feature(build_hasher_simple_hash_one)]
2508 /// use std::hash::BuildHasher;
2510 /// let b = std::collections::hash_map::RandomState::new();
2511 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2512 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2513 /// assert_eq!(b.hash_one(v), b.hash_one(s));
2515 #[stable(feature = "rust1", since = "1.0.0")]
2516 impl<T
: Hash
, A
: Allocator
> Hash
for Vec
<T
, A
> {
2518 fn hash
<H
: Hasher
>(&self, state
: &mut H
) {
2519 Hash
::hash(&**self, state
)
2523 #[stable(feature = "rust1", since = "1.0.0")]
2524 #[rustc_on_unimplemented(
2525 message
= "vector indices are of type `usize` or ranges of `usize`",
2526 label
= "vector indices are of type `usize` or ranges of `usize`"
2528 impl<T
, I
: SliceIndex
<[T
]>, A
: Allocator
> Index
<I
> for Vec
<T
, A
> {
2529 type Output
= I
::Output
;
2532 fn index(&self, index
: I
) -> &Self::Output
{
2533 Index
::index(&**self, index
)
2537 #[stable(feature = "rust1", since = "1.0.0")]
2538 #[rustc_on_unimplemented(
2539 message
= "vector indices are of type `usize` or ranges of `usize`",
2540 label
= "vector indices are of type `usize` or ranges of `usize`"
2542 impl<T
, I
: SliceIndex
<[T
]>, A
: Allocator
> IndexMut
<I
> for Vec
<T
, A
> {
2544 fn index_mut(&mut self, index
: I
) -> &mut Self::Output
{
2545 IndexMut
::index_mut(&mut **self, index
)
2549 #[cfg(not(no_global_oom_handling))]
2550 #[stable(feature = "rust1", since = "1.0.0")]
2551 impl<T
> FromIterator
<T
> for Vec
<T
> {
2553 fn from_iter
<I
: IntoIterator
<Item
= T
>>(iter
: I
) -> Vec
<T
> {
2554 <Self as SpecFromIter
<T
, I
::IntoIter
>>::from_iter(iter
.into_iter())
2558 #[stable(feature = "rust1", since = "1.0.0")]
2559 impl<T
, A
: Allocator
> IntoIterator
for Vec
<T
, A
> {
2561 type IntoIter
= IntoIter
<T
, A
>;
2563 /// Creates a consuming iterator, that is, one that moves each value out of
2564 /// the vector (from start to end). The vector cannot be used after calling
2570 /// let v = vec!["a".to_string(), "b".to_string()];
2571 /// for s in v.into_iter() {
2572 /// // s has type String, not &String
2573 /// println!("{s}");
2577 fn into_iter(self) -> IntoIter
<T
, A
> {
2579 let mut me
= ManuallyDrop
::new(self);
2580 let alloc
= ManuallyDrop
::new(ptr
::read(me
.allocator()));
2581 let begin
= me
.as_mut_ptr();
2582 let end
= if mem
::size_of
::<T
>() == 0 {
2583 arith_offset(begin
as *const i8, me
.len() as isize) as *const T
2585 begin
.add(me
.len()) as *const T
2587 let cap
= me
.buf
.capacity();
2589 buf
: NonNull
::new_unchecked(begin
),
2590 phantom
: PhantomData
,
2600 #[stable(feature = "rust1", since = "1.0.0")]
2601 impl<'a
, T
, A
: Allocator
> IntoIterator
for &'a Vec
<T
, A
> {
2603 type IntoIter
= slice
::Iter
<'a
, T
>;
2605 fn into_iter(self) -> slice
::Iter
<'a
, T
> {
2610 #[stable(feature = "rust1", since = "1.0.0")]
2611 impl<'a
, T
, A
: Allocator
> IntoIterator
for &'a
mut Vec
<T
, A
> {
2612 type Item
= &'a
mut T
;
2613 type IntoIter
= slice
::IterMut
<'a
, T
>;
2615 fn into_iter(self) -> slice
::IterMut
<'a
, T
> {
2620 #[cfg(not(no_global_oom_handling))]
2621 #[stable(feature = "rust1", since = "1.0.0")]
2622 impl<T
, A
: Allocator
> Extend
<T
> for Vec
<T
, A
> {
2624 fn extend
<I
: IntoIterator
<Item
= T
>>(&mut self, iter
: I
) {
2625 <Self as SpecExtend
<T
, I
::IntoIter
>>::spec_extend(self, iter
.into_iter())
2629 fn extend_one(&mut self, item
: T
) {
2634 fn extend_reserve(&mut self, additional
: usize) {
2635 self.reserve(additional
);
2639 impl<T
, A
: Allocator
> Vec
<T
, A
> {
2640 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2641 // they have no further optimizations to apply
2642 #[cfg(not(no_global_oom_handling))]
2643 fn extend_desugared
<I
: Iterator
<Item
= T
>>(&mut self, mut iterator
: I
) {
2644 // This is the case for a general iterator.
2646 // This function should be the moral equivalent of:
2648 // for item in iterator {
2651 while let Some(element
) = iterator
.next() {
2652 let len
= self.len();
2653 if len
== self.capacity() {
2654 let (lower
, _
) = iterator
.size_hint();
2655 self.reserve(lower
.saturating_add(1));
2658 ptr
::write(self.as_mut_ptr().add(len
), element
);
2659 // Since next() executes user code which can panic we have to bump the length
2661 // NB can't overflow since we would have had to alloc the address space
2662 self.set_len(len
+ 1);
2667 /// Creates a splicing iterator that replaces the specified range in the vector
2668 /// with the given `replace_with` iterator and yields the removed items.
2669 /// `replace_with` does not need to be the same length as `range`.
2671 /// `range` is removed even if the iterator is not consumed until the end.
2673 /// It is unspecified how many elements are removed from the vector
2674 /// if the `Splice` value is leaked.
2676 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2678 /// This is optimal if:
2680 /// * The tail (elements in the vector after `range`) is empty,
2681 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2682 /// * or the lower bound of its `size_hint()` is exact.
2684 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2688 /// Panics if the starting point is greater than the end point or if
2689 /// the end point is greater than the length of the vector.
2694 /// let mut v = vec![1, 2, 3, 4];
2695 /// let new = [7, 8, 9];
2696 /// let u: Vec<_> = v.splice(1..3, new).collect();
2697 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
2698 /// assert_eq!(u, &[2, 3]);
2700 #[cfg(not(no_global_oom_handling))]
2702 #[stable(feature = "vec_splice", since = "1.21.0")]
2703 pub fn splice
<R
, I
>(&mut self, range
: R
, replace_with
: I
) -> Splice
<'_
, I
::IntoIter
, A
>
2705 R
: RangeBounds
<usize>,
2706 I
: IntoIterator
<Item
= T
>,
2708 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2711 /// Creates an iterator which uses a closure to determine if an element should be removed.
2713 /// If the closure returns true, then the element is removed and yielded.
2714 /// If the closure returns false, the element will remain in the vector and will not be yielded
2715 /// by the iterator.
2717 /// Using this method is equivalent to the following code:
2720 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2721 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2723 /// while i < vec.len() {
2724 /// if some_predicate(&mut vec[i]) {
2725 /// let val = vec.remove(i);
2726 /// // your code here
2732 /// # assert_eq!(vec, vec![1, 4, 5]);
2735 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2736 /// because it can backshift the elements of the array in bulk.
2738 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2739 /// regardless of whether you choose to keep or remove it.
2743 /// Splitting an array into evens and odds, reusing the original allocation:
2746 /// #![feature(drain_filter)]
2747 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2749 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2750 /// let odds = numbers;
2752 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2753 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2755 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2756 pub fn drain_filter
<F
>(&mut self, filter
: F
) -> DrainFilter
<'_
, T
, F
, A
>
2758 F
: FnMut(&mut T
) -> bool
,
2760 let old_len
= self.len();
2762 // Guard against us getting leaked (leak amplification)
2767 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2771 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2773 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2774 /// append the entire slice at once.
2776 /// [`copy_from_slice`]: slice::copy_from_slice
2777 #[cfg(not(no_global_oom_handling))]
2778 #[stable(feature = "extend_ref", since = "1.2.0")]
2779 impl<'a
, T
: Copy
+ 'a
, A
: Allocator
+ 'a
> Extend
<&'a T
> for Vec
<T
, A
> {
2780 fn extend
<I
: IntoIterator
<Item
= &'a T
>>(&mut self, iter
: I
) {
2781 self.spec_extend(iter
.into_iter())
2785 fn extend_one(&mut self, &item
: &'a T
) {
2790 fn extend_reserve(&mut self, additional
: usize) {
2791 self.reserve(additional
);
2795 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2796 #[stable(feature = "rust1", since = "1.0.0")]
2797 impl<T
: PartialOrd
, A
: Allocator
> PartialOrd
for Vec
<T
, A
> {
2799 fn partial_cmp(&self, other
: &Self) -> Option
<Ordering
> {
2800 PartialOrd
::partial_cmp(&**self, &**other
)
2804 #[stable(feature = "rust1", since = "1.0.0")]
2805 impl<T
: Eq
, A
: Allocator
> Eq
for Vec
<T
, A
> {}
2807 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2808 #[stable(feature = "rust1", since = "1.0.0")]
2809 impl<T
: Ord
, A
: Allocator
> Ord
for Vec
<T
, A
> {
2811 fn cmp(&self, other
: &Self) -> Ordering
{
2812 Ord
::cmp(&**self, &**other
)
2816 #[stable(feature = "rust1", since = "1.0.0")]
2817 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
2818 fn drop(&mut self) {
2821 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2822 // could avoid questions of validity in certain cases
2823 ptr
::drop_in_place(ptr
::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len
))
2825 // RawVec handles deallocation
2829 #[stable(feature = "rust1", since = "1.0.0")]
2830 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
2831 impl<T
> const Default
for Vec
<T
> {
2832 /// Creates an empty `Vec<T>`.
2833 fn default() -> Vec
<T
> {
2838 #[stable(feature = "rust1", since = "1.0.0")]
2839 impl<T
: fmt
::Debug
, A
: Allocator
> fmt
::Debug
for Vec
<T
, A
> {
2840 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
2841 fmt
::Debug
::fmt(&**self, f
)
2845 #[stable(feature = "rust1", since = "1.0.0")]
2846 impl<T
, A
: Allocator
> AsRef
<Vec
<T
, A
>> for Vec
<T
, A
> {
2847 fn as_ref(&self) -> &Vec
<T
, A
> {
2852 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2853 impl<T
, A
: Allocator
> AsMut
<Vec
<T
, A
>> for Vec
<T
, A
> {
2854 fn as_mut(&mut self) -> &mut Vec
<T
, A
> {
2859 #[stable(feature = "rust1", since = "1.0.0")]
2860 impl<T
, A
: Allocator
> AsRef
<[T
]> for Vec
<T
, A
> {
2861 fn as_ref(&self) -> &[T
] {
2866 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2867 impl<T
, A
: Allocator
> AsMut
<[T
]> for Vec
<T
, A
> {
2868 fn as_mut(&mut self) -> &mut [T
] {
2873 #[cfg(not(no_global_oom_handling))]
2874 #[stable(feature = "rust1", since = "1.0.0")]
2875 impl<T
: Clone
> From
<&[T
]> for Vec
<T
> {
2876 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2881 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
2884 fn from(s
: &[T
]) -> Vec
<T
> {
2888 fn from(s
: &[T
]) -> Vec
<T
> {
2889 crate::slice
::to_vec(s
, Global
)
2893 #[cfg(not(no_global_oom_handling))]
2894 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2895 impl<T
: Clone
> From
<&mut [T
]> for Vec
<T
> {
2896 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2901 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
2904 fn from(s
: &mut [T
]) -> Vec
<T
> {
2908 fn from(s
: &mut [T
]) -> Vec
<T
> {
2909 crate::slice
::to_vec(s
, Global
)
2913 #[cfg(not(no_global_oom_handling))]
2914 #[stable(feature = "vec_from_array", since = "1.44.0")]
2915 impl<T
, const N
: usize> From
<[T
; N
]> for Vec
<T
> {
2916 /// Allocate a `Vec<T>` and move `s`'s items into it.
2921 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
2924 fn from(s
: [T
; N
]) -> Vec
<T
> {
2925 <[T
]>::into_vec(box s
)
2929 fn from(s
: [T
; N
]) -> Vec
<T
> {
2930 crate::slice
::into_vec(box s
)
2934 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2935 impl<'a
, T
> From
<Cow
<'a
, [T
]>> for Vec
<T
>
2937 [T
]: ToOwned
<Owned
= Vec
<T
>>,
2939 /// Convert a clone-on-write slice into a vector.
2941 /// If `s` already owns a `Vec<T>`, it will be returned directly.
2942 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
2943 /// filled by cloning `s`'s items into it.
2948 /// # use std::borrow::Cow;
2949 /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
2950 /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
2951 /// assert_eq!(Vec::from(o), Vec::from(b));
2953 fn from(s
: Cow
<'a
, [T
]>) -> Vec
<T
> {
2958 // note: test pulls in libstd, which causes errors here
2960 #[stable(feature = "vec_from_box", since = "1.18.0")]
2961 impl<T
, A
: Allocator
> From
<Box
<[T
], A
>> for Vec
<T
, A
> {
2962 /// Convert a boxed slice into a vector by transferring ownership of
2963 /// the existing heap allocation.
2968 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
2969 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
2971 fn from(s
: Box
<[T
], A
>) -> Self {
2976 // note: test pulls in libstd, which causes errors here
2977 #[cfg(not(no_global_oom_handling))]
2979 #[stable(feature = "box_from_vec", since = "1.20.0")]
2980 impl<T
, A
: Allocator
> From
<Vec
<T
, A
>> for Box
<[T
], A
> {
2981 /// Convert a vector into a boxed slice.
2983 /// If `v` has excess capacity, its items will be moved into a
2984 /// newly-allocated buffer with exactly the right capacity.
2989 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
2991 fn from(v
: Vec
<T
, A
>) -> Self {
2992 v
.into_boxed_slice()
2996 #[cfg(not(no_global_oom_handling))]
2997 #[stable(feature = "rust1", since = "1.0.0")]
2998 impl From
<&str> for Vec
<u8> {
2999 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
3004 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
3006 fn from(s
: &str) -> Vec
<u8> {
3007 From
::from(s
.as_bytes())
3011 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
3012 impl<T
, A
: Allocator
, const N
: usize> TryFrom
<Vec
<T
, A
>> for [T
; N
] {
3013 type Error
= Vec
<T
, A
>;
3015 /// Gets the entire contents of the `Vec<T>` as an array,
3016 /// if its size exactly matches that of the requested array.
3021 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3022 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3025 /// If the length doesn't match, the input comes back in `Err`:
3027 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3028 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3031 /// If you're fine with just getting a prefix of the `Vec<T>`,
3032 /// you can call [`.truncate(N)`](Vec::truncate) first.
3034 /// let mut v = String::from("hello world").into_bytes();
3037 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3038 /// assert_eq!(a, b' ');
3039 /// assert_eq!(b, b'd');
3041 fn try_from(mut vec
: Vec
<T
, A
>) -> Result
<[T
; N
], Vec
<T
, A
>> {
3046 // SAFETY: `.set_len(0)` is always sound.
3047 unsafe { vec.set_len(0) }
;
3049 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3050 // the alignment the array needs is the same as the items.
3051 // We checked earlier that we have sufficient items.
3052 // The items will not double-drop as the `set_len`
3053 // tells the `Vec` not to also drop them.
3054 let array
= unsafe { ptr::read(vec.as_ptr() as *const [T; N]) }
;