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 normally **not** safe
493 /// to build a `Vec<u8>` from a pointer to a C `char` array with length
494 /// `size_t`, doing so is only safe if the array was initially allocated by
495 /// a `Vec` or `String`.
496 /// It's also not safe to build one from a `Vec<u16>` and its length, because
497 /// the allocator cares about the alignment, and these two types have different
498 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
499 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
500 /// these issues, it is often preferable to do casting/transmuting using
501 /// [`slice::from_raw_parts`] instead.
503 /// The ownership of `ptr` is effectively transferred to the
504 /// `Vec<T>` which may then deallocate, reallocate or change the
505 /// contents of memory pointed to by the pointer at will. Ensure
506 /// that nothing else uses the pointer after calling this
509 /// [`String`]: crate::string::String
510 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
518 /// let v = vec![1, 2, 3];
520 // FIXME Update this when vec_into_raw_parts is stabilized
521 /// // Prevent running `v`'s destructor so we are in complete control
522 /// // of the allocation.
523 /// let mut v = mem::ManuallyDrop::new(v);
525 /// // Pull out the various important pieces of information about `v`
526 /// let p = v.as_mut_ptr();
527 /// let len = v.len();
528 /// let cap = v.capacity();
531 /// // Overwrite memory with 4, 5, 6
532 /// for i in 0..len as isize {
533 /// ptr::write(p.offset(i), 4 + i);
536 /// // Put everything back together into a Vec
537 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
538 /// assert_eq!(rebuilt, [4, 5, 6]);
542 #[stable(feature = "rust1", since = "1.0.0")]
543 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
544 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
548 impl<T, A: Allocator> Vec<T, A> {
549 /// Constructs a new, empty `Vec<T, A>`.
551 /// The vector will not allocate until elements are pushed onto it.
556 /// #![feature(allocator_api)]
558 /// use std::alloc::System;
560 /// # #[allow(unused_mut)]
561 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
564 #[unstable(feature = "allocator_api", issue = "32838")]
565 pub const fn new_in(alloc: A) -> Self {
566 Vec { buf: RawVec::new_in(alloc), len: 0 }
569 /// Constructs a new, empty `Vec<T, A>` with the specified capacity with the provided
572 /// The vector will be able to hold exactly `capacity` elements without
573 /// reallocating. If `capacity` is 0, the vector will not allocate.
575 /// It is important to note that although the returned vector has the
576 /// *capacity* specified, the vector will have a zero *length*. For an
577 /// explanation of the difference between length and capacity, see
578 /// *[Capacity and reallocation]*.
580 /// [Capacity and reallocation]: #capacity-and-reallocation
584 /// Panics if the new capacity exceeds `isize::MAX` bytes.
589 /// #![feature(allocator_api)]
591 /// use std::alloc::System;
593 /// let mut vec = Vec::with_capacity_in(10, System);
595 /// // The vector contains no items, even though it has capacity for more
596 /// assert_eq!(vec.len(), 0);
597 /// assert_eq!(vec.capacity(), 10);
599 /// // These are all done without reallocating...
603 /// assert_eq!(vec.len(), 10);
604 /// assert_eq!(vec.capacity(), 10);
606 /// // ...but this may make the vector reallocate
608 /// assert_eq!(vec.len(), 11);
609 /// assert!(vec.capacity() >= 11);
611 #[cfg(not(no_global_oom_handling))]
613 #[unstable(feature = "allocator_api", issue = "32838")]
614 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
615 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
618 /// Creates a `Vec<T, A>` directly from the raw components of another vector.
622 /// This is highly unsafe, due to the number of invariants that aren't
625 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
626 /// (at least, it's highly likely to be incorrect if it wasn't).
627 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
628 /// (`T` having a less strict alignment is not sufficient, the alignment really
629 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
630 /// allocated and deallocated with the same layout.)
631 /// * `length` needs to be less than or equal to `capacity`.
632 /// * `capacity` needs to be the capacity that the pointer was allocated with.
634 /// Violating these may cause problems like corrupting the allocator's
635 /// internal data structures. For example it is **not** safe
636 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
637 /// It's also not safe to build one from a `Vec<u16>` and its length, because
638 /// the allocator cares about the alignment, and these two types have different
639 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
640 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
642 /// The ownership of `ptr` is effectively transferred to the
643 /// `Vec<T>` which may then deallocate, reallocate or change the
644 /// contents of memory pointed to by the pointer at will. Ensure
645 /// that nothing else uses the pointer after calling this
648 /// [`String`]: crate::string::String
649 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
654 /// #![feature(allocator_api)]
656 /// use std::alloc::System;
661 /// let mut v = Vec::with_capacity_in(3, System);
666 // FIXME Update this when vec_into_raw_parts is stabilized
667 /// // Prevent running `v`'s destructor so we are in complete control
668 /// // of the allocation.
669 /// let mut v = mem::ManuallyDrop::new(v);
671 /// // Pull out the various important pieces of information about `v`
672 /// let p = v.as_mut_ptr();
673 /// let len = v.len();
674 /// let cap = v.capacity();
675 /// let alloc = v.allocator();
678 /// // Overwrite memory with 4, 5, 6
679 /// for i in 0..len as isize {
680 /// ptr::write(p.offset(i), 4 + i);
683 /// // Put everything back together into a Vec
684 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
685 /// assert_eq!(rebuilt, [4, 5, 6]);
689 #[unstable(feature = "allocator_api", issue = "32838")]
690 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
691 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
694 /// Decomposes a `Vec<T>` into its raw components.
696 /// Returns the raw pointer to the underlying data, the length of
697 /// the vector (in elements), and the allocated capacity of the
698 /// data (in elements). These are the same arguments in the same
699 /// order as the arguments to [`from_raw_parts`].
701 /// After calling this function, the caller is responsible for the
702 /// memory previously managed by the `Vec`. The only way to do
703 /// this is to convert the raw pointer, length, and capacity back
704 /// into a `Vec` with the [`from_raw_parts`] function, allowing
705 /// the destructor to perform the cleanup.
707 /// [`from_raw_parts`]: Vec::from_raw_parts
712 /// #![feature(vec_into_raw_parts)]
713 /// let v: Vec<i32> = vec![-1, 0, 1];
715 /// let (ptr, len, cap) = v.into_raw_parts();
717 /// let rebuilt = unsafe {
718 /// // We can now make changes to the components, such as
719 /// // transmuting the raw pointer to a compatible type.
720 /// let ptr = ptr as *mut u32;
722 /// Vec::from_raw_parts(ptr, len, cap)
724 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
726 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
727 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
728 let mut me = ManuallyDrop::new(self);
729 (me.as_mut_ptr(), me.len(), me.capacity())
732 /// Decomposes a `Vec<T>` into its raw components.
734 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
735 /// the allocated capacity of the data (in elements), and the allocator. These are the same
736 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
738 /// After calling this function, the caller is responsible for the
739 /// memory previously managed by the `Vec`. The only way to do
740 /// this is to convert the raw pointer, length, and capacity back
741 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
742 /// the destructor to perform the cleanup.
744 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
749 /// #![feature(allocator_api, vec_into_raw_parts)]
751 /// use std::alloc::System;
753 /// let mut v: Vec<i32, System> = Vec::new_in(System);
758 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
760 /// let rebuilt = unsafe {
761 /// // We can now make changes to the components, such as
762 /// // transmuting the raw pointer to a compatible type.
763 /// let ptr = ptr as *mut u32;
765 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
767 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
769 #[unstable(feature = "allocator_api", issue = "32838")]
770 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
771 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
772 let mut me = ManuallyDrop::new(self);
774 let capacity = me.capacity();
775 let ptr = me.as_mut_ptr();
776 let alloc = unsafe { ptr::read(me.allocator()) };
777 (ptr, len, capacity, alloc)
780 /// Returns the number of elements the vector can hold without
786 /// let vec: Vec<i32> = Vec::with_capacity(10);
787 /// assert_eq!(vec.capacity(), 10);
790 #[stable(feature = "rust1", since = "1.0.0")]
791 pub fn capacity(&self) -> usize {
795 /// Reserves capacity for at least `additional` more elements to be inserted
796 /// in the given `Vec<T>`. The collection may reserve more space to avoid
797 /// frequent reallocations. After calling `reserve`, capacity will be
798 /// greater than or equal to `self.len() + additional`. Does nothing if
799 /// capacity is already sufficient.
803 /// Panics if the new capacity exceeds `isize::MAX` bytes.
808 /// let mut vec = vec![1];
810 /// assert!(vec.capacity() >= 11);
812 #[cfg(not(no_global_oom_handling))]
813 #[stable(feature = "rust1", since = "1.0.0")]
814 pub fn reserve(&mut self, additional: usize) {
815 self.buf.reserve(self.len, additional);
818 /// Reserves the minimum capacity for exactly `additional` more elements to
819 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
820 /// capacity will be greater than or equal to `self.len() + additional`.
821 /// Does nothing if the capacity is already sufficient.
823 /// Note that the allocator may give the collection more space than it
824 /// requests. Therefore, capacity can not be relied upon to be precisely
825 /// minimal. Prefer [`reserve`] if future insertions are expected.
827 /// [`reserve`]: Vec::reserve
831 /// Panics if the new capacity exceeds `isize::MAX` bytes.
836 /// let mut vec = vec![1];
837 /// vec.reserve_exact(10);
838 /// assert!(vec.capacity() >= 11);
840 #[cfg(not(no_global_oom_handling))]
841 #[stable(feature = "rust1", since = "1.0.0")]
842 pub fn reserve_exact(&mut self, additional: usize) {
843 self.buf.reserve_exact(self.len, additional);
846 /// Tries to reserve capacity for at least `additional` more elements to be inserted
847 /// in the given `Vec<T>`. The collection may reserve more space to avoid
848 /// frequent reallocations. After calling `try_reserve`, capacity will be
849 /// greater than or equal to `self.len() + additional`. Does nothing if
850 /// capacity is already sufficient.
854 /// If the capacity overflows, or the allocator reports a failure, then an error
860 /// use std::collections::TryReserveError;
862 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
863 /// let mut output = Vec::new();
865 /// // Pre-reserve the memory, exiting if we can't
866 /// output.try_reserve(data.len())?;
868 /// // Now we know this can't OOM in the middle of our complex work
869 /// output.extend(data.iter().map(|&val| {
870 /// val * 2 + 5 // very complicated
875 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
877 #[stable(feature = "try_reserve", since = "1.57.0")]
878 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
879 self.buf.try_reserve(self.len, additional)
882 /// Tries to reserve the minimum capacity for exactly `additional`
883 /// elements to be inserted in the given `Vec<T>`. After calling
884 /// `try_reserve_exact`, capacity will be greater than or equal to
885 /// `self.len() + additional` if it returns `Ok(())`.
886 /// Does nothing if the capacity is already sufficient.
888 /// Note that the allocator may give the collection more space than it
889 /// requests. Therefore, capacity can not be relied upon to be precisely
890 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
892 /// [`try_reserve`]: Vec::try_reserve
896 /// If the capacity overflows, or the allocator reports a failure, then an error
902 /// use std::collections::TryReserveError;
904 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
905 /// let mut output = Vec::new();
907 /// // Pre-reserve the memory, exiting if we can't
908 /// output.try_reserve_exact(data.len())?;
910 /// // Now we know this can't OOM in the middle of our complex work
911 /// output.extend(data.iter().map(|&val| {
912 /// val * 2 + 5 // very complicated
917 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
919 #[stable(feature = "try_reserve", since = "1.57.0")]
920 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
921 self.buf.try_reserve_exact(self.len, additional)
924 /// Shrinks the capacity of the vector as much as possible.
926 /// It will drop down as close as possible to the length but the allocator
927 /// may still inform the vector that there is space for a few more elements.
932 /// let mut vec = Vec::with_capacity(10);
933 /// vec.extend([1, 2, 3]);
934 /// assert_eq!(vec.capacity(), 10);
935 /// vec.shrink_to_fit();
936 /// assert!(vec.capacity() >= 3);
938 #[cfg(not(no_global_oom_handling))]
939 #[stable(feature = "rust1", since = "1.0.0")]
940 pub fn shrink_to_fit(&mut self) {
941 // The capacity is never less than the length, and there's nothing to do when
942 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
943 // by only calling it with a greater capacity.
944 if self.capacity() > self.len {
945 self.buf.shrink_to_fit(self.len);
949 /// Shrinks the capacity of the vector with a lower bound.
951 /// The capacity will remain at least as large as both the length
952 /// and the supplied value.
954 /// If the current capacity is less than the lower limit, this is a no-op.
959 /// let mut vec = Vec::with_capacity(10);
960 /// vec.extend([1, 2, 3]);
961 /// assert_eq!(vec.capacity(), 10);
962 /// vec.shrink_to(4);
963 /// assert!(vec.capacity() >= 4);
964 /// vec.shrink_to(0);
965 /// assert!(vec.capacity() >= 3);
967 #[cfg(not(no_global_oom_handling))]
968 #[stable(feature = "shrink_to", since = "1.56.0")]
969 pub fn shrink_to(&mut self, min_capacity: usize) {
970 if self.capacity() > min_capacity {
971 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
975 /// Converts the vector into [`Box<[T]>`][owned slice].
977 /// Note that this will drop any excess capacity.
979 /// [owned slice]: Box
984 /// let v = vec![1, 2, 3];
986 /// let slice = v.into_boxed_slice();
989 /// Any excess capacity is removed:
992 /// let mut vec = Vec::with_capacity(10);
993 /// vec.extend([1, 2, 3]);
995 /// assert_eq!(vec.capacity(), 10);
996 /// let slice = vec.into_boxed_slice();
997 /// assert_eq!(slice.into_vec().capacity(), 3);
999 #[cfg(not(no_global_oom_handling))]
1000 #[stable(feature = "rust1", since = "1.0.0")]
1001 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
1003 self.shrink_to_fit();
1004 let me = ManuallyDrop::new(self);
1005 let buf = ptr::read(&me.buf);
1007 buf.into_box(len).assume_init()
1011 /// Shortens the vector, keeping the first `len` elements and dropping
1014 /// If `len` is greater than the vector's current length, this has no
1017 /// The [`drain`] method can emulate `truncate`, but causes the excess
1018 /// elements to be returned instead of dropped.
1020 /// Note that this method has no effect on the allocated capacity
1025 /// Truncating a five element vector to two elements:
1028 /// let mut vec = vec![1, 2, 3, 4, 5];
1029 /// vec.truncate(2);
1030 /// assert_eq!(vec, [1, 2]);
1033 /// No truncation occurs when `len` is greater than the vector's current
1037 /// let mut vec = vec![1, 2, 3];
1038 /// vec.truncate(8);
1039 /// assert_eq!(vec, [1, 2, 3]);
1042 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1046 /// let mut vec = vec![1, 2, 3];
1047 /// vec.truncate(0);
1048 /// assert_eq!(vec, []);
1051 /// [`clear`]: Vec::clear
1052 /// [`drain`]: Vec::drain
1053 #[stable(feature = "rust1", since = "1.0.0")]
1054 pub fn truncate(&mut self, len: usize) {
1055 // This is safe because:
1057 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1058 // case avoids creating an invalid slice, and
1059 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1060 // such that no value will be dropped twice in case `drop_in_place`
1061 // were to panic once (if it panics twice, the program aborts).
1063 // Note: It's intentional that this is `>` and not `>=`.
1064 // Changing it to `>=` has negative performance
1065 // implications in some cases. See #78884 for more.
1069 let remaining_len = self.len - len;
1070 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1072 ptr::drop_in_place(s);
1076 /// Extracts a slice containing the entire vector.
1078 /// Equivalent to `&s[..]`.
1083 /// use std::io::{self, Write};
1084 /// let buffer = vec![1, 2, 3, 5, 8];
1085 /// io::sink().write(buffer.as_slice()).unwrap();
1088 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1089 pub fn as_slice(&self) -> &[T] {
1093 /// Extracts a mutable slice of the entire vector.
1095 /// Equivalent to `&mut s[..]`.
1100 /// use std::io::{self, Read};
1101 /// let mut buffer = vec![0; 3];
1102 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1105 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1106 pub fn as_mut_slice(&mut self) -> &mut [T] {
1110 /// Returns a raw pointer to the vector's buffer.
1112 /// The caller must ensure that the vector outlives the pointer this
1113 /// function returns, or else it will end up pointing to garbage.
1114 /// Modifying the vector may cause its buffer to be reallocated,
1115 /// which would also make any pointers to it invalid.
1117 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1118 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1119 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1124 /// let x = vec![1, 2, 4];
1125 /// let x_ptr = x.as_ptr();
1128 /// for i in 0..x.len() {
1129 /// assert_eq!(*x_ptr.add(i), 1 << i);
1134 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1135 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1137 pub fn as_ptr(&self) -> *const T {
1138 // We shadow the slice method of the same name to avoid going through
1139 // `deref`, which creates an intermediate reference.
1140 let ptr = self.buf.ptr();
1142 assume(!ptr.is_null());
1147 /// Returns an unsafe mutable pointer to the vector's buffer.
1149 /// The caller must ensure that the vector outlives the pointer this
1150 /// function returns, or else it will end up pointing to garbage.
1151 /// Modifying the vector may cause its buffer to be reallocated,
1152 /// which would also make any pointers to it invalid.
1157 /// // Allocate vector big enough for 4 elements.
1159 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1160 /// let x_ptr = x.as_mut_ptr();
1162 /// // Initialize elements via raw pointer writes, then set length.
1164 /// for i in 0..size {
1165 /// *x_ptr.add(i) = i as i32;
1167 /// x.set_len(size);
1169 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1171 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1173 pub fn as_mut_ptr(&mut self) -> *mut T {
1174 // We shadow the slice method of the same name to avoid going through
1175 // `deref_mut`, which creates an intermediate reference.
1176 let ptr = self.buf.ptr();
1178 assume(!ptr.is_null());
1183 /// Returns a reference to the underlying allocator.
1184 #[unstable(feature = "allocator_api", issue = "32838")]
1186 pub fn allocator(&self) -> &A {
1187 self.buf.allocator()
1190 /// Forces the length of the vector to `new_len`.
1192 /// This is a low-level operation that maintains none of the normal
1193 /// invariants of the type. Normally changing the length of a vector
1194 /// is done using one of the safe operations instead, such as
1195 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1197 /// [`truncate`]: Vec::truncate
1198 /// [`resize`]: Vec::resize
1199 /// [`extend`]: Extend::extend
1200 /// [`clear`]: Vec::clear
1204 /// - `new_len` must be less than or equal to [`capacity()`].
1205 /// - The elements at `old_len..new_len` must be initialized.
1207 /// [`capacity()`]: Vec::capacity
1211 /// This method can be useful for situations in which the vector
1212 /// is serving as a buffer for other code, particularly over FFI:
1215 /// # #![allow(dead_code)]
1216 /// # // This is just a minimal skeleton for the doc example;
1217 /// # // don't use this as a starting point for a real library.
1218 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1219 /// # const Z_OK: i32 = 0;
1221 /// # fn deflateGetDictionary(
1222 /// # strm: *mut std::ffi::c_void,
1223 /// # dictionary: *mut u8,
1224 /// # dictLength: *mut usize,
1227 /// # impl StreamWrapper {
1228 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1229 /// // Per the FFI method's docs, "32768 bytes is always enough".
1230 /// let mut dict = Vec::with_capacity(32_768);
1231 /// let mut dict_length = 0;
1232 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1233 /// // 1. `dict_length` elements were initialized.
1234 /// // 2. `dict_length` <= the capacity (32_768)
1235 /// // which makes `set_len` safe to call.
1237 /// // Make the FFI call...
1238 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1240 /// // ...and update the length to what was initialized.
1241 /// dict.set_len(dict_length);
1251 /// While the following example is sound, there is a memory leak since
1252 /// the inner vectors were not freed prior to the `set_len` call:
1255 /// let mut vec = vec![vec![1, 0, 0],
1259 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1260 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1266 /// Normally, here, one would use [`clear`] instead to correctly drop
1267 /// the contents and thus not leak memory.
1269 #[stable(feature = "rust1", since = "1.0.0")]
1270 pub unsafe fn set_len(&mut self, new_len: usize) {
1271 debug_assert!(new_len <= self.capacity());
1276 /// Removes an element from the vector and returns it.
1278 /// The removed element is replaced by the last element of the vector.
1280 /// This does not preserve ordering, but is *O*(1).
1281 /// If you need to preserve the element order, use [`remove`] instead.
1283 /// [`remove`]: Vec::remove
1287 /// Panics if `index` is out of bounds.
1292 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1294 /// assert_eq!(v.swap_remove(1), "bar");
1295 /// assert_eq!(v, ["foo", "qux", "baz"]);
1297 /// assert_eq!(v.swap_remove(0), "foo");
1298 /// assert_eq!(v, ["baz", "qux"]);
1301 #[stable(feature = "rust1", since = "1.0.0")]
1302 pub fn swap_remove(&mut self, index: usize) -> T {
1305 fn assert_failed(index: usize, len: usize) -> ! {
1306 panic!("swap_remove index (is {index}) should be < len (is {len})");
1309 let len = self.len();
1311 assert_failed(index, len);
1314 // We replace self[index] with the last element. Note that if the
1315 // bounds check above succeeds there must be a last element (which
1316 // can be self[index] itself).
1317 let value = ptr::read(self.as_ptr().add(index));
1318 let base_ptr = self.as_mut_ptr();
1319 ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
1320 self.set_len(len - 1);
1325 /// Inserts an element at position `index` within the vector, shifting all
1326 /// elements after it to the right.
1330 /// Panics if `index > len`.
1335 /// let mut vec = vec![1, 2, 3];
1336 /// vec.insert(1, 4);
1337 /// assert_eq!(vec, [1, 4, 2, 3]);
1338 /// vec.insert(4, 5);
1339 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1341 #[cfg(not(no_global_oom_handling))]
1342 #[stable(feature = "rust1", since = "1.0.0")]
1343 pub fn insert(&mut self, index: usize, element: T) {
1346 fn assert_failed(index: usize, len: usize) -> ! {
1347 panic!("insertion index (is {index}) should be <= len (is {len})");
1350 let len = self.len();
1352 assert_failed(index, len);
1355 // space for the new element
1356 if len == self.buf.capacity() {
1362 // The spot to put the new value
1364 let p = self.as_mut_ptr().add(index);
1365 // Shift everything over to make space. (Duplicating the
1366 // `index`th element into two consecutive places.)
1367 ptr::copy(p, p.offset(1), len - index);
1368 // Write it in, overwriting the first copy of the `index`th
1370 ptr::write(p, element);
1372 self.set_len(len + 1);
1376 /// Removes and returns the element at position `index` within the vector,
1377 /// shifting all elements after it to the left.
1379 /// Note: Because this shifts over the remaining elements, it has a
1380 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1381 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1382 /// elements from the beginning of the `Vec`, consider using
1383 /// [`VecDeque::pop_front`] instead.
1385 /// [`swap_remove`]: Vec::swap_remove
1386 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1390 /// Panics if `index` is out of bounds.
1395 /// let mut v = vec![1, 2, 3];
1396 /// assert_eq!(v.remove(1), 2);
1397 /// assert_eq!(v, [1, 3]);
1399 #[stable(feature = "rust1", since = "1.0.0")]
1401 pub fn remove(&mut self, index: usize) -> T {
1405 fn assert_failed(index: usize, len: usize) -> ! {
1406 panic!("removal index (is {index}) should be < len (is {len})");
1409 let len = self.len();
1411 assert_failed(index, len);
1417 // the place we are taking from.
1418 let ptr = self.as_mut_ptr().add(index);
1419 // copy it out, unsafely having a copy of the value on
1420 // the stack and in the vector at the same time.
1421 ret = ptr::read(ptr);
1423 // Shift everything down to fill in that spot.
1424 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1426 self.set_len(len - 1);
1431 /// Retains only the elements specified by the predicate.
1433 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1434 /// This method operates in place, visiting each element exactly once in the
1435 /// original order, and preserves the order of the retained elements.
1440 /// let mut vec = vec![1, 2, 3, 4];
1441 /// vec.retain(|&x| x % 2 == 0);
1442 /// assert_eq!(vec, [2, 4]);
1445 /// Because the elements are visited exactly once in the original order,
1446 /// external state may be used to decide which elements to keep.
1449 /// let mut vec = vec![1, 2, 3, 4, 5];
1450 /// let keep = [false, true, true, false, true];
1451 /// let mut iter = keep.iter();
1452 /// vec.retain(|_| *iter.next().unwrap());
1453 /// assert_eq!(vec, [2, 3, 5]);
1455 #[stable(feature = "rust1", since = "1.0.0")]
1456 pub fn retain<F>(&mut self, mut f: F)
1458 F: FnMut(&T) -> bool,
1460 self.retain_mut(|elem| f(elem));
1463 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1465 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1466 /// This method operates in place, visiting each element exactly once in the
1467 /// original order, and preserves the order of the retained elements.
1472 /// let mut vec = vec![1, 2, 3, 4];
1473 /// vec.retain_mut(|x| if *x > 3 {
1479 /// assert_eq!(vec, [2, 3, 4]);
1481 #[stable(feature = "vec_retain_mut", since = "1.61.0")]
1482 pub fn retain_mut<F>(&mut self, mut f: F)
1484 F: FnMut(&mut T) -> bool,
1486 let original_len = self.len();
1487 // Avoid double drop if the drop guard is not executed,
1488 // since we may make some holes during the process.
1489 unsafe { self.set_len(0) };
1491 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1492 // |<- processed len ->| ^- next to check
1493 // |<- deleted cnt ->|
1494 // |<- original_len ->|
1495 // Kept: Elements which predicate returns true on.
1496 // Hole: Moved or dropped element slot.
1497 // Unchecked: Unchecked valid elements.
1499 // This drop guard will be invoked when predicate or `drop` of element panicked.
1500 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1501 // In cases when predicate and `drop` never panick, it will be optimized out.
1502 struct BackshiftOnDrop<'a, T, A: Allocator> {
1503 v: &'a mut Vec<T, A>,
1504 processed_len: usize,
1506 original_len: usize,
1509 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1510 fn drop(&mut self) {
1511 if self.deleted_cnt > 0 {
1512 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1515 self.v.as_ptr().add(self.processed_len),
1516 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1517 self.original_len - self.processed_len,
1521 // SAFETY: After filling holes, all items are in contiguous memory.
1523 self.v.set_len(self.original_len - self.deleted_cnt);
1528 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1530 fn process_loop<F, T, A: Allocator, const DELETED: bool>(
1531 original_len: usize,
1533 g: &mut BackshiftOnDrop<'_, T, A>,
1535 F: FnMut(&mut T) -> bool,
1537 while g.processed_len != original_len {
1538 // SAFETY: Unchecked element must be valid.
1539 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1541 // Advance early to avoid double drop if `drop_in_place` panicked.
1542 g.processed_len += 1;
1544 // SAFETY: We never touch this element again after dropped.
1545 unsafe { ptr::drop_in_place(cur) };
1546 // We already advanced the counter.
1554 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1555 // We use copy for move, and never touch this element again.
1557 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1558 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1561 g.processed_len += 1;
1565 // Stage 1: Nothing was deleted.
1566 process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
1568 // Stage 2: Some elements were deleted.
1569 process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
1571 // All item are processed. This can be optimized to `set_len` by LLVM.
1575 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1578 /// If the vector is sorted, this removes all duplicates.
1583 /// let mut vec = vec![10, 20, 21, 30, 20];
1585 /// vec.dedup_by_key(|i| *i / 10);
1587 /// assert_eq!(vec, [10, 20, 30, 20]);
1589 #[stable(feature = "dedup_by", since = "1.16.0")]
1591 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1593 F: FnMut(&mut T) -> K,
1596 self.dedup_by(|a, b| key(a) == key(b))
1599 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1602 /// The `same_bucket` function is passed references to two elements from the vector and
1603 /// must determine if the elements compare equal. The elements are passed in opposite order
1604 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1606 /// If the vector is sorted, this removes all duplicates.
1611 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1613 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1615 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1617 #[stable(feature = "dedup_by", since = "1.16.0")]
1618 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1620 F: FnMut(&mut T, &mut T) -> bool,
1622 let len = self.len();
1627 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1628 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1629 /* Offset of the element we want to check if it is duplicate */
1632 /* Offset of the place where we want to place the non-duplicate
1633 * when we find it. */
1636 /* The Vec that would need correction if `same_bucket` panicked */
1637 vec: &'a mut Vec<T, A>,
1640 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1641 fn drop(&mut self) {
1642 /* This code gets executed when `same_bucket` panics */
1644 /* SAFETY: invariant guarantees that `read - write`
1645 * and `len - read` never overflow and that the copy is always
1648 let ptr = self.vec.as_mut_ptr();
1649 let len = self.vec.len();
1651 /* How many items were left when `same_bucket` panicked.
1652 * Basically vec[read..].len() */
1653 let items_left = len.wrapping_sub(self.read);
1655 /* Pointer to first item in vec[write..write+items_left] slice */
1656 let dropped_ptr = ptr.add(self.write);
1657 /* Pointer to first item in vec[read..] slice */
1658 let valid_ptr = ptr.add(self.read);
1660 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1661 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1662 ptr::copy(valid_ptr, dropped_ptr, items_left);
1664 /* How many items have been already dropped
1665 * Basically vec[read..write].len() */
1666 let dropped = self.read.wrapping_sub(self.write);
1668 self.vec.set_len(len - dropped);
1673 let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
1674 let ptr = gap.vec.as_mut_ptr();
1676 /* Drop items while going through Vec, it should be more efficient than
1677 * doing slice partition_dedup + truncate */
1679 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1680 * are always in-bounds and read_ptr never aliases prev_ptr */
1682 while gap.read < len {
1683 let read_ptr = ptr.add(gap.read);
1684 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1686 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1687 // Increase `gap.read` now since the drop may panic.
1689 /* We have found duplicate, drop it in-place */
1690 ptr::drop_in_place(read_ptr);
1692 let write_ptr = ptr.add(gap.write);
1694 /* Because `read_ptr` can be equal to `write_ptr`, we either
1695 * have to use `copy` or conditional `copy_nonoverlapping`.
1696 * Looks like the first option is faster. */
1697 ptr::copy(read_ptr, write_ptr, 1);
1699 /* We have filled that place, so go further */
1705 /* Technically we could let `gap` clean up with its Drop, but
1706 * when `same_bucket` is guaranteed to not panic, this bloats a little
1707 * the codegen, so we just do it manually */
1708 gap.vec.set_len(gap.write);
1713 /// Appends an element to the back of a collection.
1717 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1722 /// let mut vec = vec![1, 2];
1724 /// assert_eq!(vec, [1, 2, 3]);
1726 #[cfg(not(no_global_oom_handling))]
1728 #[stable(feature = "rust1", since = "1.0.0")]
1729 pub fn push(&mut self, value: T) {
1730 // This will panic or abort if we would allocate > isize::MAX bytes
1731 // or if the length increment would overflow for zero-sized types.
1732 if self.len == self.buf.capacity() {
1733 self.buf.reserve_for_push(self.len);
1736 let end = self.as_mut_ptr().add(self.len);
1737 ptr::write(end, value);
1742 /// Removes the last element from a vector and returns it, or [`None`] if it
1745 /// If you'd like to pop the first element, consider using
1746 /// [`VecDeque::pop_front`] instead.
1748 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1753 /// let mut vec = vec![1, 2, 3];
1754 /// assert_eq!(vec.pop(), Some(3));
1755 /// assert_eq!(vec, [1, 2]);
1758 #[stable(feature = "rust1", since = "1.0.0")]
1759 pub fn pop(&mut self) -> Option<T> {
1765 Some(ptr::read(self.as_ptr().add(self.len())))
1770 /// Moves all the elements of `other` into `self`, leaving `other` empty.
1774 /// Panics if the number of elements in the vector overflows a `usize`.
1779 /// let mut vec = vec![1, 2, 3];
1780 /// let mut vec2 = vec![4, 5, 6];
1781 /// vec.append(&mut vec2);
1782 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1783 /// assert_eq!(vec2, []);
1785 #[cfg(not(no_global_oom_handling))]
1787 #[stable(feature = "append", since = "1.4.0")]
1788 pub fn append(&mut self, other: &mut Self) {
1790 self.append_elements(other.as_slice() as _);
1795 /// Appends elements to `self` from other buffer.
1796 #[cfg(not(no_global_oom_handling))]
1798 unsafe fn append_elements(&mut self, other: *const [T]) {
1799 let count = unsafe { (*other).len() };
1800 self.reserve(count);
1801 let len = self.len();
1802 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1806 /// Removes the specified range from the vector in bulk, returning all
1807 /// removed elements as an iterator. If the iterator is dropped before
1808 /// being fully consumed, it drops the remaining removed elements.
1810 /// The returned iterator keeps a mutable borrow on the vector to optimize
1811 /// its implementation.
1815 /// Panics if the starting point is greater than the end point or if
1816 /// the end point is greater than the length of the vector.
1820 /// If the returned iterator goes out of scope without being dropped (due to
1821 /// [`mem::forget`], for example), the vector may have lost and leaked
1822 /// elements arbitrarily, including elements outside the range.
1827 /// let mut v = vec![1, 2, 3];
1828 /// let u: Vec<_> = v.drain(1..).collect();
1829 /// assert_eq!(v, &[1]);
1830 /// assert_eq!(u, &[2, 3]);
1832 /// // A full range clears the vector, like `clear()` does
1834 /// assert_eq!(v, &[]);
1836 #[stable(feature = "drain", since = "1.6.0")]
1837 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1839 R: RangeBounds<usize>,
1843 // When the Drain is first created, it shortens the length of
1844 // the source vector to make sure no uninitialized or moved-from elements
1845 // are accessible at all if the Drain's destructor never gets to run.
1847 // Drain will ptr::read out the values to remove.
1848 // When finished, remaining tail of the vec is copied back to cover
1849 // the hole, and the vector length is restored to the new length.
1851 let len = self.len();
1852 let Range { start, end } = slice::range(range, ..len);
1855 // set self.vec length's to start, to be safe in case Drain is leaked
1856 self.set_len(start);
1857 // Use the borrow in the IterMut to indicate borrowing behavior of the
1858 // whole Drain iterator (like &mut T).
1859 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1862 tail_len: len - end,
1863 iter: range_slice.iter(),
1864 vec: NonNull::from(self),
1869 /// Clears the vector, removing all values.
1871 /// Note that this method has no effect on the allocated capacity
1877 /// let mut v = vec![1, 2, 3];
1881 /// assert!(v.is_empty());
1884 #[stable(feature = "rust1", since = "1.0.0")]
1885 pub fn clear(&mut self) {
1886 let elems: *mut [T] = self.as_mut_slice();
1889 // - `elems` comes directly from `as_mut_slice` and is therefore valid.
1890 // - Setting `self.len` before calling `drop_in_place` means that,
1891 // if an element's `Drop` impl panics, the vector's `Drop` impl will
1892 // do nothing (leaking the rest of the elements) instead of dropping
1896 ptr::drop_in_place(elems);
1900 /// Returns the number of elements in the vector, also referred to
1901 /// as its 'length'.
1906 /// let a = vec![1, 2, 3];
1907 /// assert_eq!(a.len(), 3);
1910 #[stable(feature = "rust1", since = "1.0.0")]
1911 pub fn len(&self) -> usize {
1915 /// Returns `true` if the vector contains no elements.
1920 /// let mut v = Vec::new();
1921 /// assert!(v.is_empty());
1924 /// assert!(!v.is_empty());
1926 #[stable(feature = "rust1", since = "1.0.0")]
1927 pub fn is_empty(&self) -> bool {
1931 /// Splits the collection into two at the given index.
1933 /// Returns a newly allocated vector containing the elements in the range
1934 /// `[at, len)`. After the call, the original vector will be left containing
1935 /// the elements `[0, at)` with its previous capacity unchanged.
1939 /// Panics if `at > len`.
1944 /// let mut vec = vec![1, 2, 3];
1945 /// let vec2 = vec.split_off(1);
1946 /// assert_eq!(vec, [1]);
1947 /// assert_eq!(vec2, [2, 3]);
1949 #[cfg(not(no_global_oom_handling))]
1951 #[must_use = "use `.truncate()` if you don't need the other half"]
1952 #[stable(feature = "split_off", since = "1.4.0")]
1953 pub fn split_off(&mut self, at: usize) -> Self
1959 fn assert_failed(at: usize, len: usize) -> ! {
1960 panic!("`at` split index (is {at}) should be <= len (is {len})");
1963 if at > self.len() {
1964 assert_failed(at, self.len());
1968 // the new vector can take over the original buffer and avoid the copy
1969 return mem::replace(
1971 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
1975 let other_len = self.len - at;
1976 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
1978 // Unsafely `set_len` and copy items to `other`.
1981 other.set_len(other_len);
1983 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1988 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1990 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1991 /// difference, with each additional slot filled with the result of
1992 /// calling the closure `f`. The return values from `f` will end up
1993 /// in the `Vec` in the order they have been generated.
1995 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1997 /// This method uses a closure to create new values on every push. If
1998 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
1999 /// want to use the [`Default`] trait to generate values, you can
2000 /// pass [`Default::default`] as the second argument.
2005 /// let mut vec = vec![1, 2, 3];
2006 /// vec.resize_with(5, Default::default);
2007 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
2009 /// let mut vec = vec![];
2011 /// vec.resize_with(4, || { p *= 2; p });
2012 /// assert_eq!(vec, [2, 4, 8, 16]);
2014 #[cfg(not(no_global_oom_handling))]
2015 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2016 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
2020 let len = self.len();
2022 self.extend_with(new_len - len, ExtendFunc(f));
2024 self.truncate(new_len);
2028 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2029 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2030 /// `'a`. If the type has only static references, or none at all, then this
2031 /// may be chosen to be `'static`.
2033 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2034 /// so the leaked allocation may include unused capacity that is not part
2035 /// of the returned slice.
2037 /// This function is mainly useful for data that lives for the remainder of
2038 /// the program's life. Dropping the returned reference will cause a memory
2046 /// let x = vec![1, 2, 3];
2047 /// let static_ref: &'static mut [usize] = x.leak();
2048 /// static_ref[0] += 1;
2049 /// assert_eq!(static_ref, &[2, 2, 3]);
2051 #[cfg(not(no_global_oom_handling))]
2052 #[stable(feature = "vec_leak", since = "1.47.0")]
2054 pub fn leak<'a>(self) -> &'a mut [T]
2058 let mut me = ManuallyDrop::new(self);
2059 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2062 /// Returns the remaining spare capacity of the vector as a slice of
2063 /// `MaybeUninit<T>`.
2065 /// The returned slice can be used to fill the vector with data (e.g. by
2066 /// reading from a file) before marking the data as initialized using the
2067 /// [`set_len`] method.
2069 /// [`set_len`]: Vec::set_len
2074 /// // Allocate vector big enough for 10 elements.
2075 /// let mut v = Vec::with_capacity(10);
2077 /// // Fill in the first 3 elements.
2078 /// let uninit = v.spare_capacity_mut();
2079 /// uninit[0].write(0);
2080 /// uninit[1].write(1);
2081 /// uninit[2].write(2);
2083 /// // Mark the first 3 elements of the vector as being initialized.
2088 /// assert_eq!(&v, &[0, 1, 2]);
2090 #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
2092 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2094 // This method is not implemented in terms of `split_at_spare_mut`,
2095 // to prevent invalidation of pointers to the buffer.
2097 slice::from_raw_parts_mut(
2098 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2099 self.buf.capacity() - self.len,
2104 /// Returns vector content as a slice of `T`, along with the remaining spare
2105 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2107 /// The returned spare capacity slice can be used to fill the vector with data
2108 /// (e.g. by reading from a file) before marking the data as initialized using
2109 /// the [`set_len`] method.
2111 /// [`set_len`]: Vec::set_len
2113 /// Note that this is a low-level API, which should be used with care for
2114 /// optimization purposes. If you need to append data to a `Vec`
2115 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2116 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2117 /// [`resize_with`], depending on your exact needs.
2119 /// [`push`]: Vec::push
2120 /// [`extend`]: Vec::extend
2121 /// [`extend_from_slice`]: Vec::extend_from_slice
2122 /// [`extend_from_within`]: Vec::extend_from_within
2123 /// [`insert`]: Vec::insert
2124 /// [`append`]: Vec::append
2125 /// [`resize`]: Vec::resize
2126 /// [`resize_with`]: Vec::resize_with
2131 /// #![feature(vec_split_at_spare)]
2133 /// let mut v = vec![1, 1, 2];
2135 /// // Reserve additional space big enough for 10 elements.
2138 /// let (init, uninit) = v.split_at_spare_mut();
2139 /// let sum = init.iter().copied().sum::<u32>();
2141 /// // Fill in the next 4 elements.
2142 /// uninit[0].write(sum);
2143 /// uninit[1].write(sum * 2);
2144 /// uninit[2].write(sum * 3);
2145 /// uninit[3].write(sum * 4);
2147 /// // Mark the 4 elements of the vector as being initialized.
2149 /// let len = v.len();
2150 /// v.set_len(len + 4);
2153 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2155 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2157 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2159 // - len is ignored and so never changed
2160 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2164 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2166 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2167 unsafe fn split_at_spare_mut_with_len(
2169 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2170 let ptr = self.as_mut_ptr();
2172 // - `ptr` is guaranteed to be valid for `self.len` elements
2173 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2175 let spare_ptr = unsafe { ptr.add(self.len) };
2176 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2177 let spare_len = self.buf.capacity() - self.len;
2180 // - `ptr` is guaranteed to be valid for `self.len` elements
2181 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2183 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2184 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2186 (initialized, spare, &mut self.len)
2191 impl<T: Clone, A: Allocator> Vec<T, A> {
2192 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2194 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2195 /// difference, with each additional slot filled with `value`.
2196 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2198 /// This method requires `T` to implement [`Clone`],
2199 /// in order to be able to clone the passed value.
2200 /// If you need more flexibility (or want to rely on [`Default`] instead of
2201 /// [`Clone`]), use [`Vec::resize_with`].
2202 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2207 /// let mut vec = vec!["hello"];
2208 /// vec.resize(3, "world");
2209 /// assert_eq!(vec, ["hello", "world", "world"]);
2211 /// let mut vec = vec![1, 2, 3, 4];
2212 /// vec.resize(2, 0);
2213 /// assert_eq!(vec, [1, 2]);
2215 #[cfg(not(no_global_oom_handling))]
2216 #[stable(feature = "vec_resize", since = "1.5.0")]
2217 pub fn resize(&mut self, new_len: usize, value: T) {
2218 let len = self.len();
2221 self.extend_with(new_len - len, ExtendElement(value))
2223 self.truncate(new_len);
2227 /// Clones and appends all elements in a slice to the `Vec`.
2229 /// Iterates over the slice `other`, clones each element, and then appends
2230 /// it to this `Vec`. The `other` slice is traversed in-order.
2232 /// Note that this function is same as [`extend`] except that it is
2233 /// specialized to work with slices instead. If and when Rust gets
2234 /// specialization this function will likely be deprecated (but still
2240 /// let mut vec = vec![1];
2241 /// vec.extend_from_slice(&[2, 3, 4]);
2242 /// assert_eq!(vec, [1, 2, 3, 4]);
2245 /// [`extend`]: Vec::extend
2246 #[cfg(not(no_global_oom_handling))]
2247 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2248 pub fn extend_from_slice(&mut self, other: &[T]) {
2249 self.spec_extend(other.iter())
2252 /// Copies elements from `src` range to the end of the vector.
2256 /// Panics if the starting point is greater than the end point or if
2257 /// the end point is greater than the length of the vector.
2262 /// let mut vec = vec![0, 1, 2, 3, 4];
2264 /// vec.extend_from_within(2..);
2265 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2267 /// vec.extend_from_within(..2);
2268 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2270 /// vec.extend_from_within(4..8);
2271 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2273 #[cfg(not(no_global_oom_handling))]
2274 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2275 pub fn extend_from_within<R>(&mut self, src: R)
2277 R: RangeBounds<usize>,
2279 let range = slice::range(src, ..self.len());
2280 self.reserve(range.len());
2283 // - `slice::range` guarantees that the given range is valid for indexing self
2285 self.spec_extend_from_within(range);
2290 impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
2291 /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
2295 /// Panics if the length of the resulting vector would overflow a `usize`.
2297 /// This is only possible when flattening a vector of arrays of zero-sized
2298 /// types, and thus tends to be irrelevant in practice. If
2299 /// `size_of::<T>() > 0`, this will never panic.
2304 /// #![feature(slice_flatten)]
2306 /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
2307 /// assert_eq!(vec.pop(), Some([7, 8, 9]));
2309 /// let mut flattened = vec.into_flattened();
2310 /// assert_eq!(flattened.pop(), Some(6));
2312 #[unstable(feature = "slice_flatten", issue = "95629")]
2313 pub fn into_flattened(self) -> Vec<T, A> {
2314 let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
2315 let (new_len, new_cap) = if mem::size_of::<T>() == 0 {
2316 (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
2319 // - `cap * N` cannot overflow because the allocation is already in
2320 // the address space.
2321 // - Each `[T; N]` has `N` valid elements, so there are `len * N`
2322 // valid elements in the allocation.
2323 unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
2326 // - `ptr` was allocated by `self`
2327 // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
2328 // - `new_cap` refers to the same sized allocation as `cap` because
2329 // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
2330 // - `len` <= `cap`, so `len * N` <= `cap * N`.
2331 unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
2335 // This code generalizes `extend_with_{element,default}`.
2336 trait ExtendWith<T> {
2337 fn next(&mut self) -> T;
2341 struct ExtendElement<T>(T);
2342 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2343 fn next(&mut self) -> T {
2346 fn last(self) -> T {
2351 struct ExtendFunc<F>(F);
2352 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
2353 fn next(&mut self) -> T {
2356 fn last(mut self) -> T {
2361 impl<T, A: Allocator> Vec<T, A> {
2362 #[cfg(not(no_global_oom_handling))]
2363 /// Extend the vector by `n` values, using the given generator.
2364 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2368 let mut ptr = self.as_mut_ptr().add(self.len());
2369 // Use SetLenOnDrop to work around bug where compiler
2370 // might not realize the store through `ptr` through self.set_len()
2372 let mut local_len = SetLenOnDrop::new(&mut self.len);
2374 // Write all elements except the last one
2376 ptr::write(ptr, value.next());
2377 ptr = ptr.offset(1);
2378 // Increment the length in every step in case next() panics
2379 local_len.increment_len(1);
2383 // We can write the last element directly without cloning needlessly
2384 ptr::write(ptr, value.last());
2385 local_len.increment_len(1);
2388 // len set by scope guard
2393 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2394 /// Removes consecutive repeated elements in the vector according to the
2395 /// [`PartialEq`] trait implementation.
2397 /// If the vector is sorted, this removes all duplicates.
2402 /// let mut vec = vec![1, 2, 2, 3, 2];
2406 /// assert_eq!(vec, [1, 2, 3, 2]);
2408 #[stable(feature = "rust1", since = "1.0.0")]
2410 pub fn dedup(&mut self) {
2411 self.dedup_by(|a, b| a == b)
2415 ////////////////////////////////////////////////////////////////////////////////
2416 // Internal methods and functions
2417 ////////////////////////////////////////////////////////////////////////////////
2420 #[cfg(not(no_global_oom_handling))]
2421 #[stable(feature = "rust1", since = "1.0.0")]
2422 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2423 <T as SpecFromElem>::from_elem(elem, n, Global)
2427 #[cfg(not(no_global_oom_handling))]
2428 #[unstable(feature = "allocator_api", issue = "32838")]
2429 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2430 <T as SpecFromElem>::from_elem(elem, n, alloc)
2433 trait ExtendFromWithinSpec {
2436 /// - `src` needs to be valid index
2437 /// - `self.capacity() - self.len()` must be `>= src.len()`
2438 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2441 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2442 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2444 // - len is increased only after initializing elements
2445 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2448 // - caller guaratees that src is a valid index
2449 let to_clone = unsafe { this.get_unchecked(src) };
2451 iter::zip(to_clone, spare)
2452 .map(|(src, dst)| dst.write(src.clone()))
2454 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2455 // - len is increased after each element to prevent leaks (see issue #82533)
2456 .for_each(|_| *len += 1);
2460 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2461 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2462 let count = src.len();
2464 let (init, spare) = self.split_at_spare_mut();
2467 // - caller guaratees that `src` is a valid index
2468 let source = unsafe { init.get_unchecked(src) };
2471 // - Both pointers are created from unique slice references (`&mut [_]`)
2472 // so they are valid and do not overlap.
2473 // - Elements are :Copy so it's OK to to copy them, without doing
2474 // anything with the original values
2475 // - `count` is equal to the len of `source`, so source is valid for
2477 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2478 // is valid for `count` writes
2479 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2483 // - The elements were just initialized by `copy_nonoverlapping`
2488 ////////////////////////////////////////////////////////////////////////////////
2489 // Common trait implementations for Vec
2490 ////////////////////////////////////////////////////////////////////////////////
2492 #[stable(feature = "rust1", since = "1.0.0")]
2493 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2496 fn deref(&self) -> &[T] {
2497 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2501 #[stable(feature = "rust1", since = "1.0.0")]
2502 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2503 fn deref_mut(&mut self) -> &mut [T] {
2504 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2508 #[cfg(not(no_global_oom_handling))]
2509 trait SpecCloneFrom {
2510 fn clone_from(this: &mut Self, other: &Self);
2513 #[cfg(not(no_global_oom_handling))]
2514 impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
2515 default fn clone_from(this: &mut Self, other: &Self) {
2516 // drop anything that will not be overwritten
2517 this.truncate(other.len());
2519 // self.len <= other.len due to the truncate above, so the
2520 // slices here are always in-bounds.
2521 let (init, tail) = other.split_at(this.len());
2523 // reuse the contained values' allocations/resources.
2524 this.clone_from_slice(init);
2525 this.extend_from_slice(tail);
2529 #[cfg(not(no_global_oom_handling))]
2530 impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
2531 fn clone_from(this: &mut Self, other: &Self) {
2533 this.extend_from_slice(other);
2537 #[cfg(not(no_global_oom_handling))]
2538 #[stable(feature = "rust1", since = "1.0.0")]
2539 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2541 fn clone(&self) -> Self {
2542 let alloc = self.allocator().clone();
2543 <[T]>::to_vec_in(&**self, alloc)
2546 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2547 // required for this method definition, is not available. Instead use the
2548 // `slice::to_vec` function which is only available with cfg(test)
2549 // NB see the slice::hack module in slice.rs for more information
2551 fn clone(&self) -> Self {
2552 let alloc = self.allocator().clone();
2553 crate::slice::to_vec(&**self, alloc)
2556 fn clone_from(&mut self, other: &Self) {
2557 SpecCloneFrom::clone_from(self, other)
2561 /// The hash of a vector is the same as that of the corresponding slice,
2562 /// as required by the `core::borrow::Borrow` implementation.
2565 /// #![feature(build_hasher_simple_hash_one)]
2566 /// use std::hash::BuildHasher;
2568 /// let b = std::collections::hash_map::RandomState::new();
2569 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2570 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2571 /// assert_eq!(b.hash_one(v), b.hash_one(s));
2573 #[stable(feature = "rust1", since = "1.0.0")]
2574 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2576 fn hash<H: Hasher>(&self, state: &mut H) {
2577 Hash::hash(&**self, state)
2581 #[stable(feature = "rust1", since = "1.0.0")]
2582 #[rustc_on_unimplemented(
2583 message = "vector indices are of type `usize` or ranges of `usize`",
2584 label = "vector indices are of type `usize` or ranges of `usize`"
2586 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2587 type Output = I::Output;
2590 fn index(&self, index: I) -> &Self::Output {
2591 Index::index(&**self, index)
2595 #[stable(feature = "rust1", since = "1.0.0")]
2596 #[rustc_on_unimplemented(
2597 message = "vector indices are of type `usize` or ranges of `usize`",
2598 label = "vector indices are of type `usize` or ranges of `usize`"
2600 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2602 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2603 IndexMut::index_mut(&mut **self, index)
2607 #[cfg(not(no_global_oom_handling))]
2608 #[stable(feature = "rust1", since = "1.0.0")]
2609 impl<T> FromIterator<T> for Vec<T> {
2611 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2612 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2616 #[stable(feature = "rust1", since = "1.0.0")]
2617 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2619 type IntoIter = IntoIter<T, A>;
2621 /// Creates a consuming iterator, that is, one that moves each value out of
2622 /// the vector (from start to end). The vector cannot be used after calling
2628 /// let v = vec!["a".to_string(), "b".to_string()];
2629 /// for s in v.into_iter() {
2630 /// // s has type String, not &String
2631 /// println!("{s}");
2635 fn into_iter(self) -> IntoIter<T, A> {
2637 let mut me = ManuallyDrop::new(self);
2638 let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
2639 let begin = me.as_mut_ptr();
2640 let end = if mem::size_of::<T>() == 0 {
2641 arith_offset(begin as *const i8, me.len() as isize) as *const T
2643 begin.add(me.len()) as *const T
2645 let cap = me.buf.capacity();
2647 buf: NonNull::new_unchecked(begin),
2648 phantom: PhantomData,
2658 #[stable(feature = "rust1", since = "1.0.0")]
2659 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2661 type IntoIter = slice::Iter<'a, T>;
2663 fn into_iter(self) -> slice::Iter<'a, T> {
2668 #[stable(feature = "rust1", since = "1.0.0")]
2669 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2670 type Item = &'a mut T;
2671 type IntoIter = slice::IterMut<'a, T>;
2673 fn into_iter(self) -> slice::IterMut<'a, T> {
2678 #[cfg(not(no_global_oom_handling))]
2679 #[stable(feature = "rust1", since = "1.0.0")]
2680 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2682 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2683 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2687 fn extend_one(&mut self, item: T) {
2692 fn extend_reserve(&mut self, additional: usize) {
2693 self.reserve(additional);
2697 impl<T, A: Allocator> Vec<T, A> {
2698 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2699 // they have no further optimizations to apply
2700 #[cfg(not(no_global_oom_handling))]
2701 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2702 // This is the case for a general iterator.
2704 // This function should be the moral equivalent of:
2706 // for item in iterator {
2709 while let Some(element) = iterator.next() {
2710 let len = self.len();
2711 if len == self.capacity() {
2712 let (lower, _) = iterator.size_hint();
2713 self.reserve(lower.saturating_add(1));
2716 ptr::write(self.as_mut_ptr().add(len), element);
2717 // Since next() executes user code which can panic we have to bump the length
2719 // NB can't overflow since we would have had to alloc the address space
2720 self.set_len(len + 1);
2725 /// Creates a splicing iterator that replaces the specified range in the vector
2726 /// with the given `replace_with` iterator and yields the removed items.
2727 /// `replace_with` does not need to be the same length as `range`.
2729 /// `range` is removed even if the iterator is not consumed until the end.
2731 /// It is unspecified how many elements are removed from the vector
2732 /// if the `Splice` value is leaked.
2734 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2736 /// This is optimal if:
2738 /// * The tail (elements in the vector after `range`) is empty,
2739 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2740 /// * or the lower bound of its `size_hint()` is exact.
2742 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2746 /// Panics if the starting point is greater than the end point or if
2747 /// the end point is greater than the length of the vector.
2752 /// let mut v = vec![1, 2, 3, 4];
2753 /// let new = [7, 8, 9];
2754 /// let u: Vec<_> = v.splice(1..3, new).collect();
2755 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
2756 /// assert_eq!(u, &[2, 3]);
2758 #[cfg(not(no_global_oom_handling))]
2760 #[stable(feature = "vec_splice", since = "1.21.0")]
2761 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2763 R: RangeBounds<usize>,
2764 I: IntoIterator<Item = T>,
2766 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2769 /// Creates an iterator which uses a closure to determine if an element should be removed.
2771 /// If the closure returns true, then the element is removed and yielded.
2772 /// If the closure returns false, the element will remain in the vector and will not be yielded
2773 /// by the iterator.
2775 /// Using this method is equivalent to the following code:
2778 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2779 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2781 /// while i < vec.len() {
2782 /// if some_predicate(&mut vec[i]) {
2783 /// let val = vec.remove(i);
2784 /// // your code here
2790 /// # assert_eq!(vec, vec![1, 4, 5]);
2793 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2794 /// because it can backshift the elements of the array in bulk.
2796 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2797 /// regardless of whether you choose to keep or remove it.
2801 /// Splitting an array into evens and odds, reusing the original allocation:
2804 /// #![feature(drain_filter)]
2805 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2807 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2808 /// let odds = numbers;
2810 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2811 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2813 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2814 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
2816 F: FnMut(&mut T) -> bool,
2818 let old_len = self.len();
2820 // Guard against us getting leaked (leak amplification)
2825 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2829 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2831 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2832 /// append the entire slice at once.
2834 /// [`copy_from_slice`]: slice::copy_from_slice
2835 #[cfg(not(no_global_oom_handling))]
2836 #[stable(feature = "extend_ref", since = "1.2.0")]
2837 impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
2838 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2839 self.spec_extend(iter.into_iter())
2843 fn extend_one(&mut self, &item: &'a T) {
2848 fn extend_reserve(&mut self, additional: usize) {
2849 self.reserve(additional);
2853 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2854 #[stable(feature = "rust1", since = "1.0.0")]
2855 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
2857 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2858 PartialOrd::partial_cmp(&**self, &**other)
2862 #[stable(feature = "rust1", since = "1.0.0")]
2863 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
2865 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2866 #[stable(feature = "rust1", since = "1.0.0")]
2867 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
2869 fn cmp(&self, other: &Self) -> Ordering {
2870 Ord::cmp(&**self, &**other)
2874 #[stable(feature = "rust1", since = "1.0.0")]
2875 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
2876 fn drop(&mut self) {
2879 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2880 // could avoid questions of validity in certain cases
2881 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
2883 // RawVec handles deallocation
2887 #[stable(feature = "rust1", since = "1.0.0")]
2888 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
2889 impl<T> const Default for Vec<T> {
2890 /// Creates an empty `Vec<T>`.
2891 fn default() -> Vec<T> {
2896 #[stable(feature = "rust1", since = "1.0.0")]
2897 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
2898 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2899 fmt::Debug::fmt(&**self, f)
2903 #[stable(feature = "rust1", since = "1.0.0")]
2904 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
2905 fn as_ref(&self) -> &Vec<T, A> {
2910 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2911 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
2912 fn as_mut(&mut self) -> &mut Vec<T, A> {
2917 #[stable(feature = "rust1", since = "1.0.0")]
2918 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
2919 fn as_ref(&self) -> &[T] {
2924 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2925 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
2926 fn as_mut(&mut self) -> &mut [T] {
2931 #[cfg(not(no_global_oom_handling))]
2932 #[stable(feature = "rust1", since = "1.0.0")]
2933 impl<T: Clone> From<&[T]> for Vec<T> {
2934 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2939 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
2942 fn from(s: &[T]) -> Vec<T> {
2946 fn from(s: &[T]) -> Vec<T> {
2947 crate::slice::to_vec(s, Global)
2951 #[cfg(not(no_global_oom_handling))]
2952 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2953 impl<T: Clone> From<&mut [T]> for Vec<T> {
2954 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2959 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
2962 fn from(s: &mut [T]) -> Vec<T> {
2966 fn from(s: &mut [T]) -> Vec<T> {
2967 crate::slice::to_vec(s, Global)
2971 #[cfg(not(no_global_oom_handling))]
2972 #[stable(feature = "vec_from_array", since = "1.44.0")]
2973 impl<T, const N: usize> From<[T; N]> for Vec<T> {
2974 /// Allocate a `Vec<T>` and move `s`'s items into it.
2979 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
2982 fn from(s: [T; N]) -> Vec<T> {
2983 <[T]>::into_vec(box s)
2987 fn from(s: [T; N]) -> Vec<T> {
2988 crate::slice::into_vec(box s)
2992 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2993 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2995 [T]: ToOwned<Owned = Vec<T>>,
2997 /// Convert a clone-on-write slice into a vector.
2999 /// If `s` already owns a `Vec<T>`, it will be returned directly.
3000 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
3001 /// filled by cloning `s`'s items into it.
3006 /// # use std::borrow::Cow;
3007 /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
3008 /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
3009 /// assert_eq!(Vec::from(o), Vec::from(b));
3011 fn from(s: Cow<'a, [T]>) -> Vec<T> {
3016 // note: test pulls in libstd, which causes errors here
3018 #[stable(feature = "vec_from_box", since = "1.18.0")]
3019 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
3020 /// Convert a boxed slice into a vector by transferring ownership of
3021 /// the existing heap allocation.
3026 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
3027 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
3029 fn from(s: Box<[T], A>) -> Self {
3034 // note: test pulls in libstd, which causes errors here
3035 #[cfg(not(no_global_oom_handling))]
3037 #[stable(feature = "box_from_vec", since = "1.20.0")]
3038 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
3039 /// Convert a vector into a boxed slice.
3041 /// If `v` has excess capacity, its items will be moved into a
3042 /// newly-allocated buffer with exactly the right capacity.
3047 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
3049 fn from(v: Vec<T, A>) -> Self {
3050 v.into_boxed_slice()
3054 #[cfg(not(no_global_oom_handling))]
3055 #[stable(feature = "rust1", since = "1.0.0")]
3056 impl From<&str> for Vec<u8> {
3057 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
3062 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
3064 fn from(s: &str) -> Vec<u8> {
3065 From::from(s.as_bytes())
3069 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
3070 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
3071 type Error = Vec<T, A>;
3073 /// Gets the entire contents of the `Vec<T>` as an array,
3074 /// if its size exactly matches that of the requested array.
3079 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3080 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3083 /// If the length doesn't match, the input comes back in `Err`:
3085 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3086 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3089 /// If you're fine with just getting a prefix of the `Vec<T>`,
3090 /// you can call [`.truncate(N)`](Vec::truncate) first.
3092 /// let mut v = String::from("hello world").into_bytes();
3095 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3096 /// assert_eq!(a, b' ');
3097 /// assert_eq!(b, b'd');
3099 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
3104 // SAFETY: `.set_len(0)` is always sound.
3105 unsafe { vec.set_len(0) };
3107 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3108 // the alignment the array needs is the same as the items.
3109 // We checked earlier that we have sufficient items.
3110 // The items will not double-drop as the `set_len`
3111 // tells the `Vec` not to also drop them.
3112 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };