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::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, SizedTypeProperties};
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, InPlaceDstBufDrop};
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]);
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 at least the specified capacity.
430 /// The vector will be able to hold at least `capacity` elements without
431 /// reallocating. This method is allowed to allocate for more elements than
432 /// `capacity`. If `capacity` is 0, the vector will not allocate.
434 /// It is important to note that although the returned vector has the
435 /// minimum *capacity* specified, the vector will have a zero *length*. For
436 /// an explanation of the difference between length and capacity, see
437 /// *[Capacity and reallocation]*.
439 /// If it is important to know the exact allocated capacity of a `Vec`,
440 /// always use the [`capacity`] method after construction.
442 /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
443 /// and the capacity will always be `usize::MAX`.
445 /// [Capacity and reallocation]: #capacity-and-reallocation
446 /// [`capacity`]: Vec::capacity
450 /// Panics if the new capacity exceeds `isize::MAX` bytes.
455 /// let mut vec = Vec::with_capacity(10);
457 /// // The vector contains no items, even though it has capacity for more
458 /// assert_eq!(vec.len(), 0);
459 /// assert!(vec.capacity() >= 10);
461 /// // These are all done without reallocating...
465 /// assert_eq!(vec.len(), 10);
466 /// assert!(vec.capacity() >= 10);
468 /// // ...but this may make the vector reallocate
470 /// assert_eq!(vec.len(), 11);
471 /// assert!(vec.capacity() >= 11);
473 /// // A vector of a zero-sized type will always over-allocate, since no
474 /// // allocation is necessary
475 /// let vec_units = Vec::<()>::with_capacity(10);
476 /// assert_eq!(vec_units.capacity(), usize::MAX);
478 #[cfg(not(no_global_oom_handling))]
480 #[stable(feature = "rust1", since = "1.0.0")]
482 pub fn with_capacity(capacity: usize) -> Self {
483 Self::with_capacity_in(capacity, Global)
486 /// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
490 /// This is highly unsafe, due to the number of invariants that aren't
493 /// * `ptr` must have been allocated using the global allocator, such as via
494 /// the [`alloc::alloc`] function.
495 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
496 /// (`T` having a less strict alignment is not sufficient, the alignment really
497 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
498 /// allocated and deallocated with the same layout.)
499 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
500 /// to be the same size as the pointer was allocated with. (Because similar to
501 /// alignment, [`dealloc`] must be called with the same layout `size`.)
502 /// * `length` needs to be less than or equal to `capacity`.
503 /// * The first `length` values must be properly initialized values of type `T`.
504 /// * `capacity` needs to be the capacity that the pointer was allocated with.
505 /// * The allocated size in bytes must be no larger than `isize::MAX`.
506 /// See the safety documentation of [`pointer::offset`].
508 /// These requirements are always upheld by any `ptr` that has been allocated
509 /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
512 /// Violating these may cause problems like corrupting the allocator's
513 /// internal data structures. For example it is normally **not** safe
514 /// to build a `Vec<u8>` from a pointer to a C `char` array with length
515 /// `size_t`, doing so is only safe if the array was initially allocated by
516 /// a `Vec` or `String`.
517 /// It's also not safe to build one from a `Vec<u16>` and its length, because
518 /// the allocator cares about the alignment, and these two types have different
519 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
520 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
521 /// these issues, it is often preferable to do casting/transmuting using
522 /// [`slice::from_raw_parts`] instead.
524 /// The ownership of `ptr` is effectively transferred to the
525 /// `Vec<T>` which may then deallocate, reallocate or change the
526 /// contents of memory pointed to by the pointer at will. Ensure
527 /// that nothing else uses the pointer after calling this
530 /// [`String`]: crate::string::String
531 /// [`alloc::alloc`]: crate::alloc::alloc
532 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
540 /// let v = vec![1, 2, 3];
542 // FIXME Update this when vec_into_raw_parts is stabilized
543 /// // Prevent running `v`'s destructor so we are in complete control
544 /// // of the allocation.
545 /// let mut v = mem::ManuallyDrop::new(v);
547 /// // Pull out the various important pieces of information about `v`
548 /// let p = v.as_mut_ptr();
549 /// let len = v.len();
550 /// let cap = v.capacity();
553 /// // Overwrite memory with 4, 5, 6
554 /// for i in 0..len {
555 /// ptr::write(p.add(i), 4 + i);
558 /// // Put everything back together into a Vec
559 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
560 /// assert_eq!(rebuilt, [4, 5, 6]);
564 /// Using memory that was allocated elsewhere:
567 /// #![feature(allocator_api)]
569 /// use std::alloc::{AllocError, Allocator, Global, Layout};
572 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
574 /// let vec = unsafe {
575 /// let mem = match Global.allocate(layout) {
576 /// Ok(mem) => mem.cast::<u32>().as_ptr(),
577 /// Err(AllocError) => return,
580 /// mem.write(1_000_000);
582 /// Vec::from_raw_parts_in(mem, 1, 16, Global)
585 /// assert_eq!(vec, &[1_000_000]);
586 /// assert_eq!(vec.capacity(), 16);
590 #[stable(feature = "rust1", since = "1.0.0")]
591 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
592 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
596 impl<T, A: Allocator> Vec<T, A> {
597 /// Constructs a new, empty `Vec<T, A>`.
599 /// The vector will not allocate until elements are pushed onto it.
604 /// #![feature(allocator_api)]
606 /// use std::alloc::System;
608 /// # #[allow(unused_mut)]
609 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
612 #[unstable(feature = "allocator_api", issue = "32838")]
613 pub const fn new_in(alloc: A) -> Self {
614 Vec { buf: RawVec::new_in(alloc), len: 0 }
617 /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
618 /// with the provided allocator.
620 /// The vector will be able to hold at least `capacity` elements without
621 /// reallocating. This method is allowed to allocate for more elements than
622 /// `capacity`. If `capacity` is 0, the vector will not allocate.
624 /// It is important to note that although the returned vector has the
625 /// minimum *capacity* specified, the vector will have a zero *length*. For
626 /// an explanation of the difference between length and capacity, see
627 /// *[Capacity and reallocation]*.
629 /// If it is important to know the exact allocated capacity of a `Vec`,
630 /// always use the [`capacity`] method after construction.
632 /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
633 /// and the capacity will always be `usize::MAX`.
635 /// [Capacity and reallocation]: #capacity-and-reallocation
636 /// [`capacity`]: Vec::capacity
640 /// Panics if the new capacity exceeds `isize::MAX` bytes.
645 /// #![feature(allocator_api)]
647 /// use std::alloc::System;
649 /// let mut vec = Vec::with_capacity_in(10, System);
651 /// // The vector contains no items, even though it has capacity for more
652 /// assert_eq!(vec.len(), 0);
653 /// assert_eq!(vec.capacity(), 10);
655 /// // These are all done without reallocating...
659 /// assert_eq!(vec.len(), 10);
660 /// assert_eq!(vec.capacity(), 10);
662 /// // ...but this may make the vector reallocate
664 /// assert_eq!(vec.len(), 11);
665 /// assert!(vec.capacity() >= 11);
667 /// // A vector of a zero-sized type will always over-allocate, since no
668 /// // allocation is necessary
669 /// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
670 /// assert_eq!(vec_units.capacity(), usize::MAX);
672 #[cfg(not(no_global_oom_handling))]
674 #[unstable(feature = "allocator_api", issue = "32838")]
675 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
676 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
679 /// Creates a `Vec<T, A>` directly from a pointer, a capacity, a length,
680 /// and an allocator.
684 /// This is highly unsafe, due to the number of invariants that aren't
687 /// * `ptr` must be [*currently allocated*] via the given allocator `alloc`.
688 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
689 /// (`T` having a less strict alignment is not sufficient, the alignment really
690 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
691 /// allocated and deallocated with the same layout.)
692 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
693 /// to be the same size as the pointer was allocated with. (Because similar to
694 /// alignment, [`dealloc`] must be called with the same layout `size`.)
695 /// * `length` needs to be less than or equal to `capacity`.
696 /// * The first `length` values must be properly initialized values of type `T`.
697 /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
698 /// * The allocated size in bytes must be no larger than `isize::MAX`.
699 /// See the safety documentation of [`pointer::offset`].
701 /// These requirements are always upheld by any `ptr` that has been allocated
702 /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
705 /// Violating these may cause problems like corrupting the allocator's
706 /// internal data structures. For example it is **not** safe
707 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
708 /// It's also not safe to build one from a `Vec<u16>` and its length, because
709 /// the allocator cares about the alignment, and these two types have different
710 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
711 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
713 /// The ownership of `ptr` is effectively transferred to the
714 /// `Vec<T>` which may then deallocate, reallocate or change the
715 /// contents of memory pointed to by the pointer at will. Ensure
716 /// that nothing else uses the pointer after calling this
719 /// [`String`]: crate::string::String
720 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
721 /// [*currently allocated*]: crate::alloc::Allocator#currently-allocated-memory
722 /// [*fit*]: crate::alloc::Allocator#memory-fitting
727 /// #![feature(allocator_api)]
729 /// use std::alloc::System;
734 /// let mut v = Vec::with_capacity_in(3, System);
739 // FIXME Update this when vec_into_raw_parts is stabilized
740 /// // Prevent running `v`'s destructor so we are in complete control
741 /// // of the allocation.
742 /// let mut v = mem::ManuallyDrop::new(v);
744 /// // Pull out the various important pieces of information about `v`
745 /// let p = v.as_mut_ptr();
746 /// let len = v.len();
747 /// let cap = v.capacity();
748 /// let alloc = v.allocator();
751 /// // Overwrite memory with 4, 5, 6
752 /// for i in 0..len {
753 /// ptr::write(p.add(i), 4 + i);
756 /// // Put everything back together into a Vec
757 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
758 /// assert_eq!(rebuilt, [4, 5, 6]);
762 /// Using memory that was allocated elsewhere:
765 /// use std::alloc::{alloc, Layout};
768 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
769 /// let vec = unsafe {
770 /// let mem = alloc(layout).cast::<u32>();
771 /// if mem.is_null() {
775 /// mem.write(1_000_000);
777 /// Vec::from_raw_parts(mem, 1, 16)
780 /// assert_eq!(vec, &[1_000_000]);
781 /// assert_eq!(vec.capacity(), 16);
785 #[unstable(feature = "allocator_api", issue = "32838")]
786 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
787 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
790 /// Decomposes a `Vec<T>` into its raw components.
792 /// Returns the raw pointer to the underlying data, the length of
793 /// the vector (in elements), and the allocated capacity of the
794 /// data (in elements). These are the same arguments in the same
795 /// order as the arguments to [`from_raw_parts`].
797 /// After calling this function, the caller is responsible for the
798 /// memory previously managed by the `Vec`. The only way to do
799 /// this is to convert the raw pointer, length, and capacity back
800 /// into a `Vec` with the [`from_raw_parts`] function, allowing
801 /// the destructor to perform the cleanup.
803 /// [`from_raw_parts`]: Vec::from_raw_parts
808 /// #![feature(vec_into_raw_parts)]
809 /// let v: Vec<i32> = vec![-1, 0, 1];
811 /// let (ptr, len, cap) = v.into_raw_parts();
813 /// let rebuilt = unsafe {
814 /// // We can now make changes to the components, such as
815 /// // transmuting the raw pointer to a compatible type.
816 /// let ptr = ptr as *mut u32;
818 /// Vec::from_raw_parts(ptr, len, cap)
820 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
822 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
823 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
824 let mut me = ManuallyDrop::new(self);
825 (me.as_mut_ptr(), me.len(), me.capacity())
828 /// Decomposes a `Vec<T>` into its raw components.
830 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
831 /// the allocated capacity of the data (in elements), and the allocator. These are the same
832 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
834 /// After calling this function, the caller is responsible for the
835 /// memory previously managed by the `Vec`. The only way to do
836 /// this is to convert the raw pointer, length, and capacity back
837 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
838 /// the destructor to perform the cleanup.
840 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
845 /// #![feature(allocator_api, vec_into_raw_parts)]
847 /// use std::alloc::System;
849 /// let mut v: Vec<i32, System> = Vec::new_in(System);
854 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
856 /// let rebuilt = unsafe {
857 /// // We can now make changes to the components, such as
858 /// // transmuting the raw pointer to a compatible type.
859 /// let ptr = ptr as *mut u32;
861 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
863 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
865 #[unstable(feature = "allocator_api", issue = "32838")]
866 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
867 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
868 let mut me = ManuallyDrop::new(self);
870 let capacity = me.capacity();
871 let ptr = me.as_mut_ptr();
872 let alloc = unsafe { ptr::read(me.allocator()) };
873 (ptr, len, capacity, alloc)
876 /// Returns the total number of elements the vector can hold without
882 /// let mut vec: Vec<i32> = Vec::with_capacity(10);
884 /// assert_eq!(vec.capacity(), 10);
887 #[stable(feature = "rust1", since = "1.0.0")]
888 pub fn capacity(&self) -> usize {
892 /// Reserves capacity for at least `additional` more elements to be inserted
893 /// in the given `Vec<T>`. The collection may reserve more space to
894 /// speculatively avoid frequent reallocations. After calling `reserve`,
895 /// capacity will be greater than or equal to `self.len() + additional`.
896 /// Does nothing if capacity is already sufficient.
900 /// Panics if the new capacity exceeds `isize::MAX` bytes.
905 /// let mut vec = vec![1];
907 /// assert!(vec.capacity() >= 11);
909 #[cfg(not(no_global_oom_handling))]
910 #[stable(feature = "rust1", since = "1.0.0")]
911 pub fn reserve(&mut self, additional: usize) {
912 self.buf.reserve(self.len, additional);
915 /// Reserves the minimum capacity for at least `additional` more elements to
916 /// be inserted in the given `Vec<T>`. Unlike [`reserve`], this will not
917 /// deliberately over-allocate to speculatively avoid frequent allocations.
918 /// After calling `reserve_exact`, capacity will be greater than or equal to
919 /// `self.len() + additional`. Does nothing if the capacity is already
922 /// Note that the allocator may give the collection more space than it
923 /// requests. Therefore, capacity can not be relied upon to be precisely
924 /// minimal. Prefer [`reserve`] if future insertions are expected.
926 /// [`reserve`]: Vec::reserve
930 /// Panics if the new capacity exceeds `isize::MAX` bytes.
935 /// let mut vec = vec![1];
936 /// vec.reserve_exact(10);
937 /// assert!(vec.capacity() >= 11);
939 #[cfg(not(no_global_oom_handling))]
940 #[stable(feature = "rust1", since = "1.0.0")]
941 pub fn reserve_exact(&mut self, additional: usize) {
942 self.buf.reserve_exact(self.len, additional);
945 /// Tries to reserve capacity for at least `additional` more elements to be inserted
946 /// in the given `Vec<T>`. The collection may reserve more space to speculatively avoid
947 /// frequent reallocations. After calling `try_reserve`, capacity will be
948 /// greater than or equal to `self.len() + additional` if it returns
949 /// `Ok(())`. Does nothing if capacity is already sufficient. This method
950 /// preserves the contents even if an error occurs.
954 /// If the capacity overflows, or the allocator reports a failure, then an error
960 /// use std::collections::TryReserveError;
962 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
963 /// let mut output = Vec::new();
965 /// // Pre-reserve the memory, exiting if we can't
966 /// output.try_reserve(data.len())?;
968 /// // Now we know this can't OOM in the middle of our complex work
969 /// output.extend(data.iter().map(|&val| {
970 /// val * 2 + 5 // very complicated
975 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
977 #[stable(feature = "try_reserve", since = "1.57.0")]
978 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
979 self.buf.try_reserve(self.len, additional)
982 /// Tries to reserve the minimum capacity for at least `additional`
983 /// elements to be inserted in the given `Vec<T>`. Unlike [`try_reserve`],
984 /// this will not deliberately over-allocate to speculatively avoid frequent
985 /// allocations. After calling `try_reserve_exact`, capacity will be greater
986 /// than or equal to `self.len() + additional` if it returns `Ok(())`.
987 /// Does nothing if the capacity is already sufficient.
989 /// Note that the allocator may give the collection more space than it
990 /// requests. Therefore, capacity can not be relied upon to be precisely
991 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
993 /// [`try_reserve`]: Vec::try_reserve
997 /// If the capacity overflows, or the allocator reports a failure, then an error
1003 /// use std::collections::TryReserveError;
1005 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
1006 /// let mut output = Vec::new();
1008 /// // Pre-reserve the memory, exiting if we can't
1009 /// output.try_reserve_exact(data.len())?;
1011 /// // Now we know this can't OOM in the middle of our complex work
1012 /// output.extend(data.iter().map(|&val| {
1013 /// val * 2 + 5 // very complicated
1018 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
1020 #[stable(feature = "try_reserve", since = "1.57.0")]
1021 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1022 self.buf.try_reserve_exact(self.len, additional)
1025 /// Shrinks the capacity of the vector as much as possible.
1027 /// It will drop down as close as possible to the length but the allocator
1028 /// may still inform the vector that there is space for a few more elements.
1033 /// let mut vec = Vec::with_capacity(10);
1034 /// vec.extend([1, 2, 3]);
1035 /// assert_eq!(vec.capacity(), 10);
1036 /// vec.shrink_to_fit();
1037 /// assert!(vec.capacity() >= 3);
1039 #[cfg(not(no_global_oom_handling))]
1040 #[stable(feature = "rust1", since = "1.0.0")]
1041 pub fn shrink_to_fit(&mut self) {
1042 // The capacity is never less than the length, and there's nothing to do when
1043 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
1044 // by only calling it with a greater capacity.
1045 if self.capacity() > self.len {
1046 self.buf.shrink_to_fit(self.len);
1050 /// Shrinks the capacity of the vector with a lower bound.
1052 /// The capacity will remain at least as large as both the length
1053 /// and the supplied value.
1055 /// If the current capacity is less than the lower limit, this is a no-op.
1060 /// let mut vec = Vec::with_capacity(10);
1061 /// vec.extend([1, 2, 3]);
1062 /// assert_eq!(vec.capacity(), 10);
1063 /// vec.shrink_to(4);
1064 /// assert!(vec.capacity() >= 4);
1065 /// vec.shrink_to(0);
1066 /// assert!(vec.capacity() >= 3);
1068 #[cfg(not(no_global_oom_handling))]
1069 #[stable(feature = "shrink_to", since = "1.56.0")]
1070 pub fn shrink_to(&mut self, min_capacity: usize) {
1071 if self.capacity() > min_capacity {
1072 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
1076 /// Converts the vector into [`Box<[T]>`][owned slice].
1078 /// If the vector has excess capacity, its items will be moved into a
1079 /// newly-allocated buffer with exactly the right capacity.
1081 /// [owned slice]: Box
1086 /// let v = vec![1, 2, 3];
1088 /// let slice = v.into_boxed_slice();
1091 /// Any excess capacity is removed:
1094 /// let mut vec = Vec::with_capacity(10);
1095 /// vec.extend([1, 2, 3]);
1097 /// assert_eq!(vec.capacity(), 10);
1098 /// let slice = vec.into_boxed_slice();
1099 /// assert_eq!(slice.into_vec().capacity(), 3);
1101 #[cfg(not(no_global_oom_handling))]
1102 #[stable(feature = "rust1", since = "1.0.0")]
1103 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
1105 self.shrink_to_fit();
1106 let me = ManuallyDrop::new(self);
1107 let buf = ptr::read(&me.buf);
1109 buf.into_box(len).assume_init()
1113 /// Shortens the vector, keeping the first `len` elements and dropping
1116 /// If `len` is greater than the vector's current length, this has no
1119 /// The [`drain`] method can emulate `truncate`, but causes the excess
1120 /// elements to be returned instead of dropped.
1122 /// Note that this method has no effect on the allocated capacity
1127 /// Truncating a five element vector to two elements:
1130 /// let mut vec = vec![1, 2, 3, 4, 5];
1131 /// vec.truncate(2);
1132 /// assert_eq!(vec, [1, 2]);
1135 /// No truncation occurs when `len` is greater than the vector's current
1139 /// let mut vec = vec![1, 2, 3];
1140 /// vec.truncate(8);
1141 /// assert_eq!(vec, [1, 2, 3]);
1144 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1148 /// let mut vec = vec![1, 2, 3];
1149 /// vec.truncate(0);
1150 /// assert_eq!(vec, []);
1153 /// [`clear`]: Vec::clear
1154 /// [`drain`]: Vec::drain
1155 #[stable(feature = "rust1", since = "1.0.0")]
1156 pub fn truncate(&mut self, len: usize) {
1157 // This is safe because:
1159 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1160 // case avoids creating an invalid slice, and
1161 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1162 // such that no value will be dropped twice in case `drop_in_place`
1163 // were to panic once (if it panics twice, the program aborts).
1165 // Note: It's intentional that this is `>` and not `>=`.
1166 // Changing it to `>=` has negative performance
1167 // implications in some cases. See #78884 for more.
1171 let remaining_len = self.len - len;
1172 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1174 ptr::drop_in_place(s);
1178 /// Extracts a slice containing the entire vector.
1180 /// Equivalent to `&s[..]`.
1185 /// use std::io::{self, Write};
1186 /// let buffer = vec![1, 2, 3, 5, 8];
1187 /// io::sink().write(buffer.as_slice()).unwrap();
1190 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1191 pub fn as_slice(&self) -> &[T] {
1195 /// Extracts a mutable slice of the entire vector.
1197 /// Equivalent to `&mut s[..]`.
1202 /// use std::io::{self, Read};
1203 /// let mut buffer = vec![0; 3];
1204 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1207 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1208 pub fn as_mut_slice(&mut self) -> &mut [T] {
1212 /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
1213 /// valid for zero sized reads if the vector didn't allocate.
1215 /// The caller must ensure that the vector outlives the pointer this
1216 /// function returns, or else it will end up pointing to garbage.
1217 /// Modifying the vector may cause its buffer to be reallocated,
1218 /// which would also make any pointers to it invalid.
1220 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1221 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1222 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1227 /// let x = vec![1, 2, 4];
1228 /// let x_ptr = x.as_ptr();
1231 /// for i in 0..x.len() {
1232 /// assert_eq!(*x_ptr.add(i), 1 << i);
1237 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1238 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1240 pub fn as_ptr(&self) -> *const T {
1241 // We shadow the slice method of the same name to avoid going through
1242 // `deref`, which creates an intermediate reference.
1243 let ptr = self.buf.ptr();
1245 assume(!ptr.is_null());
1250 /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
1251 /// raw pointer valid for zero sized reads if the vector didn't allocate.
1253 /// The caller must ensure that the vector outlives the pointer this
1254 /// function returns, or else it will end up pointing to garbage.
1255 /// Modifying the vector may cause its buffer to be reallocated,
1256 /// which would also make any pointers to it invalid.
1261 /// // Allocate vector big enough for 4 elements.
1263 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1264 /// let x_ptr = x.as_mut_ptr();
1266 /// // Initialize elements via raw pointer writes, then set length.
1268 /// for i in 0..size {
1269 /// *x_ptr.add(i) = i as i32;
1271 /// x.set_len(size);
1273 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1275 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1277 pub fn as_mut_ptr(&mut self) -> *mut T {
1278 // We shadow the slice method of the same name to avoid going through
1279 // `deref_mut`, which creates an intermediate reference.
1280 let ptr = self.buf.ptr();
1282 assume(!ptr.is_null());
1287 /// Returns a reference to the underlying allocator.
1288 #[unstable(feature = "allocator_api", issue = "32838")]
1290 pub fn allocator(&self) -> &A {
1291 self.buf.allocator()
1294 /// Forces the length of the vector to `new_len`.
1296 /// This is a low-level operation that maintains none of the normal
1297 /// invariants of the type. Normally changing the length of a vector
1298 /// is done using one of the safe operations instead, such as
1299 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1301 /// [`truncate`]: Vec::truncate
1302 /// [`resize`]: Vec::resize
1303 /// [`extend`]: Extend::extend
1304 /// [`clear`]: Vec::clear
1308 /// - `new_len` must be less than or equal to [`capacity()`].
1309 /// - The elements at `old_len..new_len` must be initialized.
1311 /// [`capacity()`]: Vec::capacity
1315 /// This method can be useful for situations in which the vector
1316 /// is serving as a buffer for other code, particularly over FFI:
1319 /// # #![allow(dead_code)]
1320 /// # // This is just a minimal skeleton for the doc example;
1321 /// # // don't use this as a starting point for a real library.
1322 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1323 /// # const Z_OK: i32 = 0;
1325 /// # fn deflateGetDictionary(
1326 /// # strm: *mut std::ffi::c_void,
1327 /// # dictionary: *mut u8,
1328 /// # dictLength: *mut usize,
1331 /// # impl StreamWrapper {
1332 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1333 /// // Per the FFI method's docs, "32768 bytes is always enough".
1334 /// let mut dict = Vec::with_capacity(32_768);
1335 /// let mut dict_length = 0;
1336 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1337 /// // 1. `dict_length` elements were initialized.
1338 /// // 2. `dict_length` <= the capacity (32_768)
1339 /// // which makes `set_len` safe to call.
1341 /// // Make the FFI call...
1342 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1344 /// // ...and update the length to what was initialized.
1345 /// dict.set_len(dict_length);
1355 /// While the following example is sound, there is a memory leak since
1356 /// the inner vectors were not freed prior to the `set_len` call:
1359 /// let mut vec = vec![vec![1, 0, 0],
1363 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1364 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1370 /// Normally, here, one would use [`clear`] instead to correctly drop
1371 /// the contents and thus not leak memory.
1373 #[stable(feature = "rust1", since = "1.0.0")]
1374 pub unsafe fn set_len(&mut self, new_len: usize) {
1375 debug_assert!(new_len <= self.capacity());
1380 /// Removes an element from the vector and returns it.
1382 /// The removed element is replaced by the last element of the vector.
1384 /// This does not preserve ordering, but is *O*(1).
1385 /// If you need to preserve the element order, use [`remove`] instead.
1387 /// [`remove`]: Vec::remove
1391 /// Panics if `index` is out of bounds.
1396 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1398 /// assert_eq!(v.swap_remove(1), "bar");
1399 /// assert_eq!(v, ["foo", "qux", "baz"]);
1401 /// assert_eq!(v.swap_remove(0), "foo");
1402 /// assert_eq!(v, ["baz", "qux"]);
1405 #[stable(feature = "rust1", since = "1.0.0")]
1406 pub fn swap_remove(&mut self, index: usize) -> T {
1409 fn assert_failed(index: usize, len: usize) -> ! {
1410 panic!("swap_remove index (is {index}) should be < len (is {len})");
1413 let len = self.len();
1415 assert_failed(index, len);
1418 // We replace self[index] with the last element. Note that if the
1419 // bounds check above succeeds there must be a last element (which
1420 // can be self[index] itself).
1421 let value = ptr::read(self.as_ptr().add(index));
1422 let base_ptr = self.as_mut_ptr();
1423 ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
1424 self.set_len(len - 1);
1429 /// Inserts an element at position `index` within the vector, shifting all
1430 /// elements after it to the right.
1434 /// Panics if `index > len`.
1439 /// let mut vec = vec![1, 2, 3];
1440 /// vec.insert(1, 4);
1441 /// assert_eq!(vec, [1, 4, 2, 3]);
1442 /// vec.insert(4, 5);
1443 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1445 #[cfg(not(no_global_oom_handling))]
1446 #[stable(feature = "rust1", since = "1.0.0")]
1447 pub fn insert(&mut self, index: usize, element: T) {
1450 fn assert_failed(index: usize, len: usize) -> ! {
1451 panic!("insertion index (is {index}) should be <= len (is {len})");
1454 let len = self.len();
1456 // space for the new element
1457 if len == self.buf.capacity() {
1463 // The spot to put the new value
1465 let p = self.as_mut_ptr().add(index);
1467 // Shift everything over to make space. (Duplicating the
1468 // `index`th element into two consecutive places.)
1469 ptr::copy(p, p.add(1), len - index);
1470 } else if index == len {
1471 // No elements need shifting.
1473 assert_failed(index, len);
1475 // Write it in, overwriting the first copy of the `index`th
1477 ptr::write(p, element);
1479 self.set_len(len + 1);
1483 /// Removes and returns the element at position `index` within the vector,
1484 /// shifting all elements after it to the left.
1486 /// Note: Because this shifts over the remaining elements, it has a
1487 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1488 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1489 /// elements from the beginning of the `Vec`, consider using
1490 /// [`VecDeque::pop_front`] instead.
1492 /// [`swap_remove`]: Vec::swap_remove
1493 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1497 /// Panics if `index` is out of bounds.
1502 /// let mut v = vec![1, 2, 3];
1503 /// assert_eq!(v.remove(1), 2);
1504 /// assert_eq!(v, [1, 3]);
1506 #[stable(feature = "rust1", since = "1.0.0")]
1508 pub fn remove(&mut self, index: usize) -> T {
1512 fn assert_failed(index: usize, len: usize) -> ! {
1513 panic!("removal index (is {index}) should be < len (is {len})");
1516 let len = self.len();
1518 assert_failed(index, len);
1524 // the place we are taking from.
1525 let ptr = self.as_mut_ptr().add(index);
1526 // copy it out, unsafely having a copy of the value on
1527 // the stack and in the vector at the same time.
1528 ret = ptr::read(ptr);
1530 // Shift everything down to fill in that spot.
1531 ptr::copy(ptr.add(1), ptr, len - index - 1);
1533 self.set_len(len - 1);
1538 /// Retains only the elements specified by the predicate.
1540 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1541 /// This method operates in place, visiting each element exactly once in the
1542 /// original order, and preserves the order of the retained elements.
1547 /// let mut vec = vec![1, 2, 3, 4];
1548 /// vec.retain(|&x| x % 2 == 0);
1549 /// assert_eq!(vec, [2, 4]);
1552 /// Because the elements are visited exactly once in the original order,
1553 /// external state may be used to decide which elements to keep.
1556 /// let mut vec = vec![1, 2, 3, 4, 5];
1557 /// let keep = [false, true, true, false, true];
1558 /// let mut iter = keep.iter();
1559 /// vec.retain(|_| *iter.next().unwrap());
1560 /// assert_eq!(vec, [2, 3, 5]);
1562 #[stable(feature = "rust1", since = "1.0.0")]
1563 pub fn retain<F>(&mut self, mut f: F)
1565 F: FnMut(&T) -> bool,
1567 self.retain_mut(|elem| f(elem));
1570 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1572 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1573 /// This method operates in place, visiting each element exactly once in the
1574 /// original order, and preserves the order of the retained elements.
1579 /// let mut vec = vec![1, 2, 3, 4];
1580 /// vec.retain_mut(|x| if *x <= 3 {
1586 /// assert_eq!(vec, [2, 3, 4]);
1588 #[stable(feature = "vec_retain_mut", since = "1.61.0")]
1589 pub fn retain_mut<F>(&mut self, mut f: F)
1591 F: FnMut(&mut T) -> bool,
1593 let original_len = self.len();
1594 // Avoid double drop if the drop guard is not executed,
1595 // since we may make some holes during the process.
1596 unsafe { self.set_len(0) };
1598 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1599 // |<- processed len ->| ^- next to check
1600 // |<- deleted cnt ->|
1601 // |<- original_len ->|
1602 // Kept: Elements which predicate returns true on.
1603 // Hole: Moved or dropped element slot.
1604 // Unchecked: Unchecked valid elements.
1606 // This drop guard will be invoked when predicate or `drop` of element panicked.
1607 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1608 // In cases when predicate and `drop` never panick, it will be optimized out.
1609 struct BackshiftOnDrop<'a, T, A: Allocator> {
1610 v: &'a mut Vec<T, A>,
1611 processed_len: usize,
1613 original_len: usize,
1616 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1617 fn drop(&mut self) {
1618 if self.deleted_cnt > 0 {
1619 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1622 self.v.as_ptr().add(self.processed_len),
1623 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1624 self.original_len - self.processed_len,
1628 // SAFETY: After filling holes, all items are in contiguous memory.
1630 self.v.set_len(self.original_len - self.deleted_cnt);
1635 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1637 fn process_loop<F, T, A: Allocator, const DELETED: bool>(
1638 original_len: usize,
1640 g: &mut BackshiftOnDrop<'_, T, A>,
1642 F: FnMut(&mut T) -> bool,
1644 while g.processed_len != original_len {
1645 // SAFETY: Unchecked element must be valid.
1646 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1648 // Advance early to avoid double drop if `drop_in_place` panicked.
1649 g.processed_len += 1;
1651 // SAFETY: We never touch this element again after dropped.
1652 unsafe { ptr::drop_in_place(cur) };
1653 // We already advanced the counter.
1661 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1662 // We use copy for move, and never touch this element again.
1664 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1665 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1668 g.processed_len += 1;
1672 // Stage 1: Nothing was deleted.
1673 process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
1675 // Stage 2: Some elements were deleted.
1676 process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
1678 // All item are processed. This can be optimized to `set_len` by LLVM.
1682 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1685 /// If the vector is sorted, this removes all duplicates.
1690 /// let mut vec = vec![10, 20, 21, 30, 20];
1692 /// vec.dedup_by_key(|i| *i / 10);
1694 /// assert_eq!(vec, [10, 20, 30, 20]);
1696 #[stable(feature = "dedup_by", since = "1.16.0")]
1698 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1700 F: FnMut(&mut T) -> K,
1703 self.dedup_by(|a, b| key(a) == key(b))
1706 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1709 /// The `same_bucket` function is passed references to two elements from the vector and
1710 /// must determine if the elements compare equal. The elements are passed in opposite order
1711 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1713 /// If the vector is sorted, this removes all duplicates.
1718 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1720 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1722 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1724 #[stable(feature = "dedup_by", since = "1.16.0")]
1725 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1727 F: FnMut(&mut T, &mut T) -> bool,
1729 let len = self.len();
1734 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1735 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1736 /* Offset of the element we want to check if it is duplicate */
1739 /* Offset of the place where we want to place the non-duplicate
1740 * when we find it. */
1743 /* The Vec that would need correction if `same_bucket` panicked */
1744 vec: &'a mut Vec<T, A>,
1747 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1748 fn drop(&mut self) {
1749 /* This code gets executed when `same_bucket` panics */
1751 /* SAFETY: invariant guarantees that `read - write`
1752 * and `len - read` never overflow and that the copy is always
1755 let ptr = self.vec.as_mut_ptr();
1756 let len = self.vec.len();
1758 /* How many items were left when `same_bucket` panicked.
1759 * Basically vec[read..].len() */
1760 let items_left = len.wrapping_sub(self.read);
1762 /* Pointer to first item in vec[write..write+items_left] slice */
1763 let dropped_ptr = ptr.add(self.write);
1764 /* Pointer to first item in vec[read..] slice */
1765 let valid_ptr = ptr.add(self.read);
1767 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1768 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1769 ptr::copy(valid_ptr, dropped_ptr, items_left);
1771 /* How many items have been already dropped
1772 * Basically vec[read..write].len() */
1773 let dropped = self.read.wrapping_sub(self.write);
1775 self.vec.set_len(len - dropped);
1780 let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
1781 let ptr = gap.vec.as_mut_ptr();
1783 /* Drop items while going through Vec, it should be more efficient than
1784 * doing slice partition_dedup + truncate */
1786 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1787 * are always in-bounds and read_ptr never aliases prev_ptr */
1789 while gap.read < len {
1790 let read_ptr = ptr.add(gap.read);
1791 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1793 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1794 // Increase `gap.read` now since the drop may panic.
1796 /* We have found duplicate, drop it in-place */
1797 ptr::drop_in_place(read_ptr);
1799 let write_ptr = ptr.add(gap.write);
1801 /* Because `read_ptr` can be equal to `write_ptr`, we either
1802 * have to use `copy` or conditional `copy_nonoverlapping`.
1803 * Looks like the first option is faster. */
1804 ptr::copy(read_ptr, write_ptr, 1);
1806 /* We have filled that place, so go further */
1812 /* Technically we could let `gap` clean up with its Drop, but
1813 * when `same_bucket` is guaranteed to not panic, this bloats a little
1814 * the codegen, so we just do it manually */
1815 gap.vec.set_len(gap.write);
1820 /// Appends an element to the back of a collection.
1824 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1829 /// let mut vec = vec![1, 2];
1831 /// assert_eq!(vec, [1, 2, 3]);
1833 #[cfg(not(no_global_oom_handling))]
1835 #[stable(feature = "rust1", since = "1.0.0")]
1836 pub fn push(&mut self, value: T) {
1837 // This will panic or abort if we would allocate > isize::MAX bytes
1838 // or if the length increment would overflow for zero-sized types.
1839 if self.len == self.buf.capacity() {
1840 self.buf.reserve_for_push(self.len);
1843 let end = self.as_mut_ptr().add(self.len);
1844 ptr::write(end, value);
1849 /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
1850 /// with the element.
1852 /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
1853 /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
1855 /// [`push`]: Vec::push
1856 /// [`reserve`]: Vec::reserve
1857 /// [`try_reserve`]: Vec::try_reserve
1861 /// A manual, panic-free alternative to [`FromIterator`]:
1864 /// #![feature(vec_push_within_capacity)]
1866 /// use std::collections::TryReserveError;
1867 /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
1868 /// let mut vec = Vec::new();
1869 /// for value in iter {
1870 /// if let Err(value) = vec.push_within_capacity(value) {
1871 /// vec.try_reserve(1)?;
1872 /// // this cannot fail, the previous line either returned or added at least 1 free slot
1873 /// let _ = vec.push_within_capacity(value);
1878 /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
1881 #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
1882 pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
1883 if self.len == self.buf.capacity() {
1887 let end = self.as_mut_ptr().add(self.len);
1888 ptr::write(end, value);
1894 /// Removes the last element from a vector and returns it, or [`None`] if it
1897 /// If you'd like to pop the first element, consider using
1898 /// [`VecDeque::pop_front`] instead.
1900 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1905 /// let mut vec = vec![1, 2, 3];
1906 /// assert_eq!(vec.pop(), Some(3));
1907 /// assert_eq!(vec, [1, 2]);
1910 #[stable(feature = "rust1", since = "1.0.0")]
1911 pub fn pop(&mut self) -> Option<T> {
1917 Some(ptr::read(self.as_ptr().add(self.len())))
1922 /// Moves all the elements of `other` into `self`, leaving `other` empty.
1926 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1931 /// let mut vec = vec![1, 2, 3];
1932 /// let mut vec2 = vec![4, 5, 6];
1933 /// vec.append(&mut vec2);
1934 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1935 /// assert_eq!(vec2, []);
1937 #[cfg(not(no_global_oom_handling))]
1939 #[stable(feature = "append", since = "1.4.0")]
1940 pub fn append(&mut self, other: &mut Self) {
1942 self.append_elements(other.as_slice() as _);
1947 /// Appends elements to `self` from other buffer.
1948 #[cfg(not(no_global_oom_handling))]
1950 unsafe fn append_elements(&mut self, other: *const [T]) {
1951 let count = unsafe { (*other).len() };
1952 self.reserve(count);
1953 let len = self.len();
1954 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1958 /// Removes the specified range from the vector in bulk, returning all
1959 /// removed elements as an iterator. If the iterator is dropped before
1960 /// being fully consumed, it drops the remaining removed elements.
1962 /// The returned iterator keeps a mutable borrow on the vector to optimize
1963 /// its implementation.
1967 /// Panics if the starting point is greater than the end point or if
1968 /// the end point is greater than the length of the vector.
1972 /// If the returned iterator goes out of scope without being dropped (due to
1973 /// [`mem::forget`], for example), the vector may have lost and leaked
1974 /// elements arbitrarily, including elements outside the range.
1979 /// let mut v = vec![1, 2, 3];
1980 /// let u: Vec<_> = v.drain(1..).collect();
1981 /// assert_eq!(v, &[1]);
1982 /// assert_eq!(u, &[2, 3]);
1984 /// // A full range clears the vector, like `clear()` does
1986 /// assert_eq!(v, &[]);
1988 #[stable(feature = "drain", since = "1.6.0")]
1989 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1991 R: RangeBounds<usize>,
1995 // When the Drain is first created, it shortens the length of
1996 // the source vector to make sure no uninitialized or moved-from elements
1997 // are accessible at all if the Drain's destructor never gets to run.
1999 // Drain will ptr::read out the values to remove.
2000 // When finished, remaining tail of the vec is copied back to cover
2001 // the hole, and the vector length is restored to the new length.
2003 let len = self.len();
2004 let Range { start, end } = slice::range(range, ..len);
2007 // set self.vec length's to start, to be safe in case Drain is leaked
2008 self.set_len(start);
2009 let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
2012 tail_len: len - end,
2013 iter: range_slice.iter(),
2014 vec: NonNull::from(self),
2019 /// Clears the vector, removing all values.
2021 /// Note that this method has no effect on the allocated capacity
2027 /// let mut v = vec![1, 2, 3];
2031 /// assert!(v.is_empty());
2034 #[stable(feature = "rust1", since = "1.0.0")]
2035 pub fn clear(&mut self) {
2036 let elems: *mut [T] = self.as_mut_slice();
2039 // - `elems` comes directly from `as_mut_slice` and is therefore valid.
2040 // - Setting `self.len` before calling `drop_in_place` means that,
2041 // if an element's `Drop` impl panics, the vector's `Drop` impl will
2042 // do nothing (leaking the rest of the elements) instead of dropping
2046 ptr::drop_in_place(elems);
2050 /// Returns the number of elements in the vector, also referred to
2051 /// as its 'length'.
2056 /// let a = vec![1, 2, 3];
2057 /// assert_eq!(a.len(), 3);
2060 #[stable(feature = "rust1", since = "1.0.0")]
2061 pub fn len(&self) -> usize {
2065 /// Returns `true` if the vector contains no elements.
2070 /// let mut v = Vec::new();
2071 /// assert!(v.is_empty());
2074 /// assert!(!v.is_empty());
2076 #[stable(feature = "rust1", since = "1.0.0")]
2077 pub fn is_empty(&self) -> bool {
2081 /// Splits the collection into two at the given index.
2083 /// Returns a newly allocated vector containing the elements in the range
2084 /// `[at, len)`. After the call, the original vector will be left containing
2085 /// the elements `[0, at)` with its previous capacity unchanged.
2089 /// Panics if `at > len`.
2094 /// let mut vec = vec![1, 2, 3];
2095 /// let vec2 = vec.split_off(1);
2096 /// assert_eq!(vec, [1]);
2097 /// assert_eq!(vec2, [2, 3]);
2099 #[cfg(not(no_global_oom_handling))]
2101 #[must_use = "use `.truncate()` if you don't need the other half"]
2102 #[stable(feature = "split_off", since = "1.4.0")]
2103 pub fn split_off(&mut self, at: usize) -> Self
2109 fn assert_failed(at: usize, len: usize) -> ! {
2110 panic!("`at` split index (is {at}) should be <= len (is {len})");
2113 if at > self.len() {
2114 assert_failed(at, self.len());
2118 // the new vector can take over the original buffer and avoid the copy
2119 return mem::replace(
2121 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
2125 let other_len = self.len - at;
2126 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
2128 // Unsafely `set_len` and copy items to `other`.
2131 other.set_len(other_len);
2133 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
2138 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2140 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2141 /// difference, with each additional slot filled with the result of
2142 /// calling the closure `f`. The return values from `f` will end up
2143 /// in the `Vec` in the order they have been generated.
2145 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2147 /// This method uses a closure to create new values on every push. If
2148 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
2149 /// want to use the [`Default`] trait to generate values, you can
2150 /// pass [`Default::default`] as the second argument.
2155 /// let mut vec = vec![1, 2, 3];
2156 /// vec.resize_with(5, Default::default);
2157 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
2159 /// let mut vec = vec![];
2161 /// vec.resize_with(4, || { p *= 2; p });
2162 /// assert_eq!(vec, [2, 4, 8, 16]);
2164 #[cfg(not(no_global_oom_handling))]
2165 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2166 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
2170 let len = self.len();
2172 self.extend_trusted(iter::repeat_with(f).take(new_len - len));
2174 self.truncate(new_len);
2178 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2179 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2180 /// `'a`. If the type has only static references, or none at all, then this
2181 /// may be chosen to be `'static`.
2183 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2184 /// so the leaked allocation may include unused capacity that is not part
2185 /// of the returned slice.
2187 /// This function is mainly useful for data that lives for the remainder of
2188 /// the program's life. Dropping the returned reference will cause a memory
2196 /// let x = vec![1, 2, 3];
2197 /// let static_ref: &'static mut [usize] = x.leak();
2198 /// static_ref[0] += 1;
2199 /// assert_eq!(static_ref, &[2, 2, 3]);
2201 #[stable(feature = "vec_leak", since = "1.47.0")]
2203 pub fn leak<'a>(self) -> &'a mut [T]
2207 let mut me = ManuallyDrop::new(self);
2208 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2211 /// Returns the remaining spare capacity of the vector as a slice of
2212 /// `MaybeUninit<T>`.
2214 /// The returned slice can be used to fill the vector with data (e.g. by
2215 /// reading from a file) before marking the data as initialized using the
2216 /// [`set_len`] method.
2218 /// [`set_len`]: Vec::set_len
2223 /// // Allocate vector big enough for 10 elements.
2224 /// let mut v = Vec::with_capacity(10);
2226 /// // Fill in the first 3 elements.
2227 /// let uninit = v.spare_capacity_mut();
2228 /// uninit[0].write(0);
2229 /// uninit[1].write(1);
2230 /// uninit[2].write(2);
2232 /// // Mark the first 3 elements of the vector as being initialized.
2237 /// assert_eq!(&v, &[0, 1, 2]);
2239 #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
2241 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2243 // This method is not implemented in terms of `split_at_spare_mut`,
2244 // to prevent invalidation of pointers to the buffer.
2246 slice::from_raw_parts_mut(
2247 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2248 self.buf.capacity() - self.len,
2253 /// Returns vector content as a slice of `T`, along with the remaining spare
2254 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2256 /// The returned spare capacity slice can be used to fill the vector with data
2257 /// (e.g. by reading from a file) before marking the data as initialized using
2258 /// the [`set_len`] method.
2260 /// [`set_len`]: Vec::set_len
2262 /// Note that this is a low-level API, which should be used with care for
2263 /// optimization purposes. If you need to append data to a `Vec`
2264 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2265 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2266 /// [`resize_with`], depending on your exact needs.
2268 /// [`push`]: Vec::push
2269 /// [`extend`]: Vec::extend
2270 /// [`extend_from_slice`]: Vec::extend_from_slice
2271 /// [`extend_from_within`]: Vec::extend_from_within
2272 /// [`insert`]: Vec::insert
2273 /// [`append`]: Vec::append
2274 /// [`resize`]: Vec::resize
2275 /// [`resize_with`]: Vec::resize_with
2280 /// #![feature(vec_split_at_spare)]
2282 /// let mut v = vec![1, 1, 2];
2284 /// // Reserve additional space big enough for 10 elements.
2287 /// let (init, uninit) = v.split_at_spare_mut();
2288 /// let sum = init.iter().copied().sum::<u32>();
2290 /// // Fill in the next 4 elements.
2291 /// uninit[0].write(sum);
2292 /// uninit[1].write(sum * 2);
2293 /// uninit[2].write(sum * 3);
2294 /// uninit[3].write(sum * 4);
2296 /// // Mark the 4 elements of the vector as being initialized.
2298 /// let len = v.len();
2299 /// v.set_len(len + 4);
2302 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2304 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2306 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2308 // - len is ignored and so never changed
2309 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2313 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2315 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2316 unsafe fn split_at_spare_mut_with_len(
2318 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2319 let ptr = self.as_mut_ptr();
2321 // - `ptr` is guaranteed to be valid for `self.len` elements
2322 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2324 let spare_ptr = unsafe { ptr.add(self.len) };
2325 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2326 let spare_len = self.buf.capacity() - self.len;
2329 // - `ptr` is guaranteed to be valid for `self.len` elements
2330 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2332 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2333 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2335 (initialized, spare, &mut self.len)
2340 impl<T: Clone, A: Allocator> Vec<T, A> {
2341 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2343 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2344 /// difference, with each additional slot filled with `value`.
2345 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2347 /// This method requires `T` to implement [`Clone`],
2348 /// in order to be able to clone the passed value.
2349 /// If you need more flexibility (or want to rely on [`Default`] instead of
2350 /// [`Clone`]), use [`Vec::resize_with`].
2351 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2356 /// let mut vec = vec!["hello"];
2357 /// vec.resize(3, "world");
2358 /// assert_eq!(vec, ["hello", "world", "world"]);
2360 /// let mut vec = vec![1, 2, 3, 4];
2361 /// vec.resize(2, 0);
2362 /// assert_eq!(vec, [1, 2]);
2364 #[cfg(not(no_global_oom_handling))]
2365 #[stable(feature = "vec_resize", since = "1.5.0")]
2366 pub fn resize(&mut self, new_len: usize, value: T) {
2367 let len = self.len();
2370 self.extend_with(new_len - len, ExtendElement(value))
2372 self.truncate(new_len);
2376 /// Clones and appends all elements in a slice to the `Vec`.
2378 /// Iterates over the slice `other`, clones each element, and then appends
2379 /// it to this `Vec`. The `other` slice is traversed in-order.
2381 /// Note that this function is same as [`extend`] except that it is
2382 /// specialized to work with slices instead. If and when Rust gets
2383 /// specialization this function will likely be deprecated (but still
2389 /// let mut vec = vec![1];
2390 /// vec.extend_from_slice(&[2, 3, 4]);
2391 /// assert_eq!(vec, [1, 2, 3, 4]);
2394 /// [`extend`]: Vec::extend
2395 #[cfg(not(no_global_oom_handling))]
2396 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2397 pub fn extend_from_slice(&mut self, other: &[T]) {
2398 self.spec_extend(other.iter())
2401 /// Copies elements from `src` range to the end of the vector.
2405 /// Panics if the starting point is greater than the end point or if
2406 /// the end point is greater than the length of the vector.
2411 /// let mut vec = vec![0, 1, 2, 3, 4];
2413 /// vec.extend_from_within(2..);
2414 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2416 /// vec.extend_from_within(..2);
2417 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2419 /// vec.extend_from_within(4..8);
2420 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2422 #[cfg(not(no_global_oom_handling))]
2423 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2424 pub fn extend_from_within<R>(&mut self, src: R)
2426 R: RangeBounds<usize>,
2428 let range = slice::range(src, ..self.len());
2429 self.reserve(range.len());
2432 // - `slice::range` guarantees that the given range is valid for indexing self
2434 self.spec_extend_from_within(range);
2439 impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
2440 /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
2444 /// Panics if the length of the resulting vector would overflow a `usize`.
2446 /// This is only possible when flattening a vector of arrays of zero-sized
2447 /// types, and thus tends to be irrelevant in practice. If
2448 /// `size_of::<T>() > 0`, this will never panic.
2453 /// #![feature(slice_flatten)]
2455 /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
2456 /// assert_eq!(vec.pop(), Some([7, 8, 9]));
2458 /// let mut flattened = vec.into_flattened();
2459 /// assert_eq!(flattened.pop(), Some(6));
2461 #[unstable(feature = "slice_flatten", issue = "95629")]
2462 pub fn into_flattened(self) -> Vec<T, A> {
2463 let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
2464 let (new_len, new_cap) = if T::IS_ZST {
2465 (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
2468 // - `cap * N` cannot overflow because the allocation is already in
2469 // the address space.
2470 // - Each `[T; N]` has `N` valid elements, so there are `len * N`
2471 // valid elements in the allocation.
2472 unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
2475 // - `ptr` was allocated by `self`
2476 // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
2477 // - `new_cap` refers to the same sized allocation as `cap` because
2478 // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
2479 // - `len` <= `cap`, so `len * N` <= `cap * N`.
2480 unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
2484 // This code generalizes `extend_with_{element,default}`.
2485 trait ExtendWith<T> {
2486 fn next(&mut self) -> T;
2490 struct ExtendElement<T>(T);
2491 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2492 fn next(&mut self) -> T {
2495 fn last(self) -> T {
2500 impl<T, A: Allocator> Vec<T, A> {
2501 #[cfg(not(no_global_oom_handling))]
2502 /// Extend the vector by `n` values, using the given generator.
2503 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2507 let mut ptr = self.as_mut_ptr().add(self.len());
2508 // Use SetLenOnDrop to work around bug where compiler
2509 // might not realize the store through `ptr` through self.set_len()
2511 let mut local_len = SetLenOnDrop::new(&mut self.len);
2513 // Write all elements except the last one
2515 ptr::write(ptr, value.next());
2517 // Increment the length in every step in case next() panics
2518 local_len.increment_len(1);
2522 // We can write the last element directly without cloning needlessly
2523 ptr::write(ptr, value.last());
2524 local_len.increment_len(1);
2527 // len set by scope guard
2532 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2533 /// Removes consecutive repeated elements in the vector according to the
2534 /// [`PartialEq`] trait implementation.
2536 /// If the vector is sorted, this removes all duplicates.
2541 /// let mut vec = vec![1, 2, 2, 3, 2];
2545 /// assert_eq!(vec, [1, 2, 3, 2]);
2547 #[stable(feature = "rust1", since = "1.0.0")]
2549 pub fn dedup(&mut self) {
2550 self.dedup_by(|a, b| a == b)
2554 ////////////////////////////////////////////////////////////////////////////////
2555 // Internal methods and functions
2556 ////////////////////////////////////////////////////////////////////////////////
2559 #[cfg(not(no_global_oom_handling))]
2560 #[stable(feature = "rust1", since = "1.0.0")]
2561 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2562 <T as SpecFromElem>::from_elem(elem, n, Global)
2566 #[cfg(not(no_global_oom_handling))]
2567 #[unstable(feature = "allocator_api", issue = "32838")]
2568 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2569 <T as SpecFromElem>::from_elem(elem, n, alloc)
2572 trait ExtendFromWithinSpec {
2575 /// - `src` needs to be valid index
2576 /// - `self.capacity() - self.len()` must be `>= src.len()`
2577 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2580 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2581 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2583 // - len is increased only after initializing elements
2584 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2587 // - caller guarantees that src is a valid index
2588 let to_clone = unsafe { this.get_unchecked(src) };
2590 iter::zip(to_clone, spare)
2591 .map(|(src, dst)| dst.write(src.clone()))
2593 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2594 // - len is increased after each element to prevent leaks (see issue #82533)
2595 .for_each(|_| *len += 1);
2599 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2600 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2601 let count = src.len();
2603 let (init, spare) = self.split_at_spare_mut();
2606 // - caller guarantees that `src` is a valid index
2607 let source = unsafe { init.get_unchecked(src) };
2610 // - Both pointers are created from unique slice references (`&mut [_]`)
2611 // so they are valid and do not overlap.
2612 // - Elements are :Copy so it's OK to copy them, without doing
2613 // anything with the original values
2614 // - `count` is equal to the len of `source`, so source is valid for
2616 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2617 // is valid for `count` writes
2618 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2622 // - The elements were just initialized by `copy_nonoverlapping`
2627 ////////////////////////////////////////////////////////////////////////////////
2628 // Common trait implementations for Vec
2629 ////////////////////////////////////////////////////////////////////////////////
2631 #[stable(feature = "rust1", since = "1.0.0")]
2632 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2636 fn deref(&self) -> &[T] {
2637 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2641 #[stable(feature = "rust1", since = "1.0.0")]
2642 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2644 fn deref_mut(&mut self) -> &mut [T] {
2645 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2649 #[cfg(not(no_global_oom_handling))]
2650 trait SpecCloneFrom {
2651 fn clone_from(this: &mut Self, other: &Self);
2654 #[cfg(not(no_global_oom_handling))]
2655 impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
2656 default fn clone_from(this: &mut Self, other: &Self) {
2657 // drop anything that will not be overwritten
2658 this.truncate(other.len());
2660 // self.len <= other.len due to the truncate above, so the
2661 // slices here are always in-bounds.
2662 let (init, tail) = other.split_at(this.len());
2664 // reuse the contained values' allocations/resources.
2665 this.clone_from_slice(init);
2666 this.extend_from_slice(tail);
2670 #[cfg(not(no_global_oom_handling))]
2671 impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
2672 fn clone_from(this: &mut Self, other: &Self) {
2674 this.extend_from_slice(other);
2678 #[cfg(not(no_global_oom_handling))]
2679 #[stable(feature = "rust1", since = "1.0.0")]
2680 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2682 fn clone(&self) -> Self {
2683 let alloc = self.allocator().clone();
2684 <[T]>::to_vec_in(&**self, alloc)
2687 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2688 // required for this method definition, is not available. Instead use the
2689 // `slice::to_vec` function which is only available with cfg(test)
2690 // NB see the slice::hack module in slice.rs for more information
2692 fn clone(&self) -> Self {
2693 let alloc = self.allocator().clone();
2694 crate::slice::to_vec(&**self, alloc)
2697 fn clone_from(&mut self, other: &Self) {
2698 SpecCloneFrom::clone_from(self, other)
2702 /// The hash of a vector is the same as that of the corresponding slice,
2703 /// as required by the `core::borrow::Borrow` implementation.
2706 /// #![feature(build_hasher_simple_hash_one)]
2707 /// use std::hash::BuildHasher;
2709 /// let b = std::collections::hash_map::RandomState::new();
2710 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2711 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2712 /// assert_eq!(b.hash_one(v), b.hash_one(s));
2714 #[stable(feature = "rust1", since = "1.0.0")]
2715 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2717 fn hash<H: Hasher>(&self, state: &mut H) {
2718 Hash::hash(&**self, state)
2722 #[stable(feature = "rust1", since = "1.0.0")]
2723 #[rustc_on_unimplemented(
2724 message = "vector indices are of type `usize` or ranges of `usize`",
2725 label = "vector indices are of type `usize` or ranges of `usize`"
2727 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2728 type Output = I::Output;
2731 fn index(&self, index: I) -> &Self::Output {
2732 Index::index(&**self, index)
2736 #[stable(feature = "rust1", since = "1.0.0")]
2737 #[rustc_on_unimplemented(
2738 message = "vector indices are of type `usize` or ranges of `usize`",
2739 label = "vector indices are of type `usize` or ranges of `usize`"
2741 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2743 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2744 IndexMut::index_mut(&mut **self, index)
2748 #[cfg(not(no_global_oom_handling))]
2749 #[stable(feature = "rust1", since = "1.0.0")]
2750 impl<T> FromIterator<T> for Vec<T> {
2752 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2753 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2757 #[stable(feature = "rust1", since = "1.0.0")]
2758 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2760 type IntoIter = IntoIter<T, A>;
2762 /// Creates a consuming iterator, that is, one that moves each value out of
2763 /// the vector (from start to end). The vector cannot be used after calling
2769 /// let v = vec!["a".to_string(), "b".to_string()];
2770 /// let mut v_iter = v.into_iter();
2772 /// let first_element: Option<String> = v_iter.next();
2774 /// assert_eq!(first_element, Some("a".to_string()));
2775 /// assert_eq!(v_iter.next(), Some("b".to_string()));
2776 /// assert_eq!(v_iter.next(), None);
2779 fn into_iter(self) -> Self::IntoIter {
2781 let mut me = ManuallyDrop::new(self);
2782 let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
2783 let begin = me.as_mut_ptr();
2784 let end = if T::IS_ZST {
2785 begin.wrapping_byte_add(me.len())
2787 begin.add(me.len()) as *const T
2789 let cap = me.buf.capacity();
2791 buf: NonNull::new_unchecked(begin),
2792 phantom: PhantomData,
2802 #[stable(feature = "rust1", since = "1.0.0")]
2803 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2805 type IntoIter = slice::Iter<'a, T>;
2807 fn into_iter(self) -> Self::IntoIter {
2812 #[stable(feature = "rust1", since = "1.0.0")]
2813 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2814 type Item = &'a mut T;
2815 type IntoIter = slice::IterMut<'a, T>;
2817 fn into_iter(self) -> Self::IntoIter {
2822 #[cfg(not(no_global_oom_handling))]
2823 #[stable(feature = "rust1", since = "1.0.0")]
2824 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2826 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2827 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2831 fn extend_one(&mut self, item: T) {
2836 fn extend_reserve(&mut self, additional: usize) {
2837 self.reserve(additional);
2841 impl<T, A: Allocator> Vec<T, A> {
2842 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2843 // they have no further optimizations to apply
2844 #[cfg(not(no_global_oom_handling))]
2845 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2846 // This is the case for a general iterator.
2848 // This function should be the moral equivalent of:
2850 // for item in iterator {
2853 while let Some(element) = iterator.next() {
2854 let len = self.len();
2855 if len == self.capacity() {
2856 let (lower, _) = iterator.size_hint();
2857 self.reserve(lower.saturating_add(1));
2860 ptr::write(self.as_mut_ptr().add(len), element);
2861 // Since next() executes user code which can panic we have to bump the length
2863 // NB can't overflow since we would have had to alloc the address space
2864 self.set_len(len + 1);
2869 // specific extend for `TrustedLen` iterators, called both by the specializations
2870 // and internal places where resolving specialization makes compilation slower
2871 #[cfg(not(no_global_oom_handling))]
2872 fn extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) {
2873 let (low, high) = iterator.size_hint();
2874 if let Some(additional) = high {
2878 "TrustedLen iterator's size hint is not exact: {:?}",
2881 self.reserve(additional);
2883 let ptr = self.as_mut_ptr();
2884 let mut local_len = SetLenOnDrop::new(&mut self.len);
2885 iterator.for_each(move |element| {
2886 ptr::write(ptr.add(local_len.current_len()), element);
2887 // Since the loop executes user code which can panic we have to update
2888 // the length every step to correctly drop what we've written.
2889 // NB can't overflow since we would have had to alloc the address space
2890 local_len.increment_len(1);
2894 // Per TrustedLen contract a `None` upper bound means that the iterator length
2895 // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
2896 // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
2897 // This avoids additional codegen for a fallback code path which would eventually
2899 panic!("capacity overflow");
2903 /// Creates a splicing iterator that replaces the specified range in the vector
2904 /// with the given `replace_with` iterator and yields the removed items.
2905 /// `replace_with` does not need to be the same length as `range`.
2907 /// `range` is removed even if the iterator is not consumed until the end.
2909 /// It is unspecified how many elements are removed from the vector
2910 /// if the `Splice` value is leaked.
2912 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2914 /// This is optimal if:
2916 /// * The tail (elements in the vector after `range`) is empty,
2917 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2918 /// * or the lower bound of its `size_hint()` is exact.
2920 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2924 /// Panics if the starting point is greater than the end point or if
2925 /// the end point is greater than the length of the vector.
2930 /// let mut v = vec![1, 2, 3, 4];
2931 /// let new = [7, 8, 9];
2932 /// let u: Vec<_> = v.splice(1..3, new).collect();
2933 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
2934 /// assert_eq!(u, &[2, 3]);
2936 #[cfg(not(no_global_oom_handling))]
2938 #[stable(feature = "vec_splice", since = "1.21.0")]
2939 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2941 R: RangeBounds<usize>,
2942 I: IntoIterator<Item = T>,
2944 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2947 /// Creates an iterator which uses a closure to determine if an element should be removed.
2949 /// If the closure returns true, then the element is removed and yielded.
2950 /// If the closure returns false, the element will remain in the vector and will not be yielded
2951 /// by the iterator.
2953 /// Using this method is equivalent to the following code:
2956 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2957 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2959 /// while i < vec.len() {
2960 /// if some_predicate(&mut vec[i]) {
2961 /// let val = vec.remove(i);
2962 /// // your code here
2968 /// # assert_eq!(vec, vec![1, 4, 5]);
2971 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2972 /// because it can backshift the elements of the array in bulk.
2974 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2975 /// regardless of whether you choose to keep or remove it.
2979 /// Splitting an array into evens and odds, reusing the original allocation:
2982 /// #![feature(drain_filter)]
2983 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2985 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2986 /// let odds = numbers;
2988 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2989 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2991 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2992 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
2994 F: FnMut(&mut T) -> bool,
2996 let old_len = self.len();
2998 // Guard against us getting leaked (leak amplification)
3003 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
3007 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
3009 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
3010 /// append the entire slice at once.
3012 /// [`copy_from_slice`]: slice::copy_from_slice
3013 #[cfg(not(no_global_oom_handling))]
3014 #[stable(feature = "extend_ref", since = "1.2.0")]
3015 impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
3016 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
3017 self.spec_extend(iter.into_iter())
3021 fn extend_one(&mut self, &item: &'a T) {
3026 fn extend_reserve(&mut self, additional: usize) {
3027 self.reserve(additional);
3031 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
3032 #[stable(feature = "rust1", since = "1.0.0")]
3033 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
3035 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
3036 PartialOrd::partial_cmp(&**self, &**other)
3040 #[stable(feature = "rust1", since = "1.0.0")]
3041 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
3043 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
3044 #[stable(feature = "rust1", since = "1.0.0")]
3045 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
3047 fn cmp(&self, other: &Self) -> Ordering {
3048 Ord::cmp(&**self, &**other)
3052 #[stable(feature = "rust1", since = "1.0.0")]
3053 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
3054 fn drop(&mut self) {
3057 // use a raw slice to refer to the elements of the vector as weakest necessary type;
3058 // could avoid questions of validity in certain cases
3059 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
3061 // RawVec handles deallocation
3065 #[stable(feature = "rust1", since = "1.0.0")]
3066 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3067 impl<T> const Default for Vec<T> {
3068 /// Creates an empty `Vec<T>`.
3070 /// The vector will not allocate until elements are pushed onto it.
3071 fn default() -> Vec<T> {
3076 #[stable(feature = "rust1", since = "1.0.0")]
3077 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
3078 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3079 fmt::Debug::fmt(&**self, f)
3083 #[stable(feature = "rust1", since = "1.0.0")]
3084 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
3085 fn as_ref(&self) -> &Vec<T, A> {
3090 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3091 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
3092 fn as_mut(&mut self) -> &mut Vec<T, A> {
3097 #[stable(feature = "rust1", since = "1.0.0")]
3098 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
3099 fn as_ref(&self) -> &[T] {
3104 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3105 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
3106 fn as_mut(&mut self) -> &mut [T] {
3111 #[cfg(not(no_global_oom_handling))]
3112 #[stable(feature = "rust1", since = "1.0.0")]
3113 impl<T: Clone> From<&[T]> for Vec<T> {
3114 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3119 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
3122 fn from(s: &[T]) -> Vec<T> {
3126 fn from(s: &[T]) -> Vec<T> {
3127 crate::slice::to_vec(s, Global)
3131 #[cfg(not(no_global_oom_handling))]
3132 #[stable(feature = "vec_from_mut", since = "1.19.0")]
3133 impl<T: Clone> From<&mut [T]> for Vec<T> {
3134 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3139 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
3142 fn from(s: &mut [T]) -> Vec<T> {
3146 fn from(s: &mut [T]) -> Vec<T> {
3147 crate::slice::to_vec(s, Global)
3151 #[cfg(not(no_global_oom_handling))]
3152 #[stable(feature = "vec_from_array", since = "1.44.0")]
3153 impl<T, const N: usize> From<[T; N]> for Vec<T> {
3154 /// Allocate a `Vec<T>` and move `s`'s items into it.
3159 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
3162 fn from(s: [T; N]) -> Vec<T> {
3170 fn from(s: [T; N]) -> Vec<T> {
3171 crate::slice::into_vec(Box::new(s))
3175 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
3176 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
3178 [T]: ToOwned<Owned = Vec<T>>,
3180 /// Convert a clone-on-write slice into a vector.
3182 /// If `s` already owns a `Vec<T>`, it will be returned directly.
3183 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
3184 /// filled by cloning `s`'s items into it.
3189 /// # use std::borrow::Cow;
3190 /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
3191 /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
3192 /// assert_eq!(Vec::from(o), Vec::from(b));
3194 fn from(s: Cow<'a, [T]>) -> Vec<T> {
3199 // note: test pulls in std, which causes errors here
3201 #[stable(feature = "vec_from_box", since = "1.18.0")]
3202 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
3203 /// Convert a boxed slice into a vector by transferring ownership of
3204 /// the existing heap allocation.
3209 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
3210 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
3212 fn from(s: Box<[T], A>) -> Self {
3217 // note: test pulls in std, which causes errors here
3218 #[cfg(not(no_global_oom_handling))]
3220 #[stable(feature = "box_from_vec", since = "1.20.0")]
3221 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
3222 /// Convert a vector into a boxed slice.
3224 /// If `v` has excess capacity, its items will be moved into a
3225 /// newly-allocated buffer with exactly the right capacity.
3230 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
3233 /// Any excess capacity is removed:
3235 /// let mut vec = Vec::with_capacity(10);
3236 /// vec.extend([1, 2, 3]);
3238 /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
3240 fn from(v: Vec<T, A>) -> Self {
3241 v.into_boxed_slice()
3245 #[cfg(not(no_global_oom_handling))]
3246 #[stable(feature = "rust1", since = "1.0.0")]
3247 impl From<&str> for Vec<u8> {
3248 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
3253 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
3255 fn from(s: &str) -> Vec<u8> {
3256 From::from(s.as_bytes())
3260 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
3261 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
3262 type Error = Vec<T, A>;
3264 /// Gets the entire contents of the `Vec<T>` as an array,
3265 /// if its size exactly matches that of the requested array.
3270 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3271 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3274 /// If the length doesn't match, the input comes back in `Err`:
3276 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3277 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3280 /// If you're fine with just getting a prefix of the `Vec<T>`,
3281 /// you can call [`.truncate(N)`](Vec::truncate) first.
3283 /// let mut v = String::from("hello world").into_bytes();
3286 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3287 /// assert_eq!(a, b' ');
3288 /// assert_eq!(b, b'd');
3290 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
3295 // SAFETY: `.set_len(0)` is always sound.
3296 unsafe { vec.set_len(0) };
3298 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3299 // the alignment the array needs is the same as the items.
3300 // We checked earlier that we have sufficient items.
3301 // The items will not double-drop as the `set_len`
3302 // tells the `Vec` not to also drop them.
3303 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };