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 use core::cmp::{self, Ordering};
57 use core::convert::TryFrom;
59 use core::hash::{Hash, Hasher};
60 use core::intrinsics::{arith_offset, assume};
61 use core::iter::FromIterator;
62 use core::marker::PhantomData;
63 use core::mem::{self, ManuallyDrop, MaybeUninit};
64 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
65 use core::ptr::{self, NonNull};
66 use core::slice::{self, SliceIndex};
68 use crate::alloc::{Allocator, Global};
69 use crate::borrow::{Cow, ToOwned};
70 use crate::boxed::Box;
71 use crate::collections::TryReserveError;
72 use crate::raw_vec::RawVec;
74 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
75 pub use self::drain_filter::DrainFilter;
79 #[stable(feature = "vec_splice", since = "1.21.0")]
80 pub use self::splice::Splice;
84 #[stable(feature = "drain", since = "1.6.0")]
85 pub use self::drain::Drain;
91 pub(crate) use self::into_iter::AsIntoIter;
92 #[stable(feature = "rust1", since = "1.0.0")]
93 pub use self::into_iter::IntoIter;
97 use self::is_zero::IsZero;
101 mod source_iter_marker;
105 use self::spec_from_elem::SpecFromElem;
109 use self::set_len_on_drop::SetLenOnDrop;
113 use self::in_place_drop::InPlaceDrop;
117 use self::spec_from_iter_nested::SpecFromIterNested;
119 mod spec_from_iter_nested;
121 use self::spec_from_iter::SpecFromIter;
125 use self::spec_extend::SpecExtend;
129 /// A contiguous growable array type, written as `Vec<T>` and pronounced 'vector'.
134 /// let mut vec = Vec::new();
138 /// assert_eq!(vec.len(), 2);
139 /// assert_eq!(vec[0], 1);
141 /// assert_eq!(vec.pop(), Some(2));
142 /// assert_eq!(vec.len(), 1);
145 /// assert_eq!(vec[0], 7);
147 /// vec.extend([1, 2, 3].iter().copied());
150 /// println!("{}", x);
152 /// assert_eq!(vec, [7, 1, 2, 3]);
155 /// The [`vec!`] macro is provided to make initialization more convenient:
158 /// let mut vec = vec![1, 2, 3];
160 /// assert_eq!(vec, [1, 2, 3, 4]);
163 /// It can also initialize each element of a `Vec<T>` with a given value.
164 /// This may be more efficient than performing allocation and initialization
165 /// in separate steps, especially when initializing a vector of zeros:
168 /// let vec = vec![0; 5];
169 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
171 /// // The following is equivalent, but potentially slower:
172 /// let mut vec = Vec::with_capacity(5);
173 /// vec.resize(5, 0);
174 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
177 /// For more information, see
178 /// [Capacity and Reallocation](#capacity-and-reallocation).
180 /// Use a `Vec<T>` as an efficient stack:
183 /// let mut stack = Vec::new();
189 /// while let Some(top) = stack.pop() {
190 /// // Prints 3, 2, 1
191 /// println!("{}", top);
197 /// The `Vec` type allows to access values by index, because it implements the
198 /// [`Index`] trait. An example will be more explicit:
201 /// let v = vec![0, 2, 4, 6];
202 /// println!("{}", v[1]); // it will display '2'
205 /// However be careful: if you try to access an index which isn't in the `Vec`,
206 /// your software will panic! You cannot do this:
209 /// let v = vec![0, 2, 4, 6];
210 /// println!("{}", v[6]); // it will panic!
213 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
218 /// A `Vec` can be mutable. On the other hand, slices are read-only objects.
219 /// To get a [slice][prim@slice], use [`&`]. Example:
222 /// fn read_slice(slice: &[usize]) {
226 /// let v = vec![0, 1];
229 /// // ... and that's all!
230 /// // you can also do it like this:
231 /// let u: &[usize] = &v;
233 /// let u: &[_] = &v;
236 /// In Rust, it's more common to pass slices as arguments rather than vectors
237 /// when you just want to provide read access. The same goes for [`String`] and
240 /// # Capacity and reallocation
242 /// The capacity of a vector is the amount of space allocated for any future
243 /// elements that will be added onto the vector. This is not to be confused with
244 /// the *length* of a vector, which specifies the number of actual elements
245 /// within the vector. If a vector's length exceeds its capacity, its capacity
246 /// will automatically be increased, but its elements will have to be
249 /// For example, a vector with capacity 10 and length 0 would be an empty vector
250 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
251 /// vector will not change its capacity or cause reallocation to occur. However,
252 /// if the vector's length is increased to 11, it will have to reallocate, which
253 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
254 /// whenever possible to specify how big the vector is expected to get.
258 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
259 /// about its design. This ensures that it's as low-overhead as possible in
260 /// the general case, and can be correctly manipulated in primitive ways
261 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
262 /// If additional type parameters are added (e.g., to support custom allocators),
263 /// overriding their defaults may change the behavior.
265 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
266 /// triplet. No more, no less. The order of these fields is completely
267 /// unspecified, and you should use the appropriate methods to modify these.
268 /// The pointer will never be null, so this type is null-pointer-optimized.
270 /// However, the pointer might not actually point to allocated memory. In particular,
271 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
272 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
273 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
274 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
275 /// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
276 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
277 /// details are very subtle — if you intend to allocate memory using a `Vec`
278 /// and use it for something else (either to pass to unsafe code, or to build your
279 /// own memory-backed collection), be sure to deallocate this memory by using
280 /// `from_raw_parts` to recover the `Vec` and then dropping it.
282 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
283 /// (as defined by the allocator Rust is configured to use by default), and its
284 /// pointer points to [`len`] initialized, contiguous elements in order (what
285 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
286 /// `[`len`] logically uninitialized, contiguous elements.
288 /// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
289 /// visualized as below. The top part is the `Vec` struct, it contains a
290 /// pointer to the head of the allocation in the heap, length and capacity.
291 /// The bottom part is the allocation on the heap, a contiguous memory block.
295 /// +--------+--------+--------+
296 /// | 0x0123 | 2 | 4 |
297 /// +--------+--------+--------+
300 /// Heap +--------+--------+--------+--------+
301 /// | 'a' | 'b' | uninit | uninit |
302 /// +--------+--------+--------+--------+
305 /// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
306 /// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
307 /// layout (including the order of fields).
309 /// `Vec` will never perform a "small optimization" where elements are actually
310 /// stored on the stack for two reasons:
312 /// * It would make it more difficult for unsafe code to correctly manipulate
313 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
314 /// only moved, and it would be more difficult to determine if a `Vec` had
315 /// actually allocated memory.
317 /// * It would penalize the general case, incurring an additional branch
320 /// `Vec` will never automatically shrink itself, even if completely empty. This
321 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
322 /// and then filling it back up to the same [`len`] should incur no calls to
323 /// the allocator. If you wish to free up unused memory, use
324 /// [`shrink_to_fit`] or [`shrink_to`].
326 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
327 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
328 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
329 /// accurate, and can be relied on. It can even be used to manually free the memory
330 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
331 /// when not necessary.
333 /// `Vec` does not guarantee any particular growth strategy when reallocating
334 /// when full, nor when [`reserve`] is called. The current strategy is basic
335 /// and it may prove desirable to use a non-constant growth factor. Whatever
336 /// strategy is used will of course guarantee *O*(1) amortized [`push`].
338 /// `vec![x; n]`, `vec![a, b, c, d]`, and
339 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
340 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
341 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
342 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
344 /// `Vec` will not specifically overwrite any data that is removed from it,
345 /// but also won't specifically preserve it. Its uninitialized memory is
346 /// scratch space that it may use however it wants. It will generally just do
347 /// whatever is most efficient or otherwise easy to implement. Do not rely on
348 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
349 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
350 /// first, that might not actually happen because the optimizer does not consider
351 /// this a side-effect that must be preserved. There is one case which we will
352 /// not break, however: using `unsafe` code to write to the excess capacity,
353 /// and then increasing the length to match, is always valid.
355 /// Currently, `Vec` does not guarantee the order in which elements are dropped.
356 /// The order has changed in the past and may change again.
358 /// [`get`]: ../../std/vec/struct.Vec.html#method.get
359 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
360 /// [`String`]: crate::string::String
361 /// [`&str`]: type@str
362 /// [`shrink_to_fit`]: Vec::shrink_to_fit
363 /// [`shrink_to`]: Vec::shrink_to
364 /// [`capacity`]: Vec::capacity
365 /// [`mem::size_of::<T>`]: core::mem::size_of
366 /// [`len`]: Vec::len
367 /// [`push`]: Vec::push
368 /// [`insert`]: Vec::insert
369 /// [`reserve`]: Vec::reserve
370 /// [`MaybeUninit`]: core::mem::MaybeUninit
371 /// [owned slice]: Box
372 #[stable(feature = "rust1", since = "1.0.0")]
373 #[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")]
374 pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
379 ////////////////////////////////////////////////////////////////////////////////
381 ////////////////////////////////////////////////////////////////////////////////
384 /// Constructs a new, empty `Vec<T>`.
386 /// The vector will not allocate until elements are pushed onto it.
391 /// # #![allow(unused_mut)]
392 /// let mut vec: Vec<i32> = Vec::new();
395 #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
396 #[stable(feature = "rust1", since = "1.0.0")]
397 pub const fn new() -> Self {
398 Vec { buf: RawVec::NEW, len: 0 }
401 /// Constructs a new, empty `Vec<T>` with the specified capacity.
403 /// The vector will be able to hold exactly `capacity` elements without
404 /// reallocating. If `capacity` is 0, the vector will not allocate.
406 /// It is important to note that although the returned vector has the
407 /// *capacity* specified, the vector will have a zero *length*. For an
408 /// explanation of the difference between length and capacity, see
409 /// *[Capacity and reallocation]*.
411 /// [Capacity and reallocation]: #capacity-and-reallocation
416 /// let mut vec = Vec::with_capacity(10);
418 /// // The vector contains no items, even though it has capacity for more
419 /// assert_eq!(vec.len(), 0);
420 /// assert_eq!(vec.capacity(), 10);
422 /// // These are all done without reallocating...
426 /// assert_eq!(vec.len(), 10);
427 /// assert_eq!(vec.capacity(), 10);
429 /// // ...but this may make the vector reallocate
431 /// assert_eq!(vec.len(), 11);
432 /// assert!(vec.capacity() >= 11);
435 #[doc(alias = "malloc")]
436 #[stable(feature = "rust1", since = "1.0.0")]
437 pub fn with_capacity(capacity: usize) -> Self {
438 Self::with_capacity_in(capacity, Global)
441 /// Creates a `Vec<T>` directly from the raw components of another vector.
445 /// This is highly unsafe, due to the number of invariants that aren't
448 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
449 /// (at least, it's highly likely to be incorrect if it wasn't).
450 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
451 /// (`T` having a less strict alignment is not sufficient, the alignment really
452 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
453 /// allocated and deallocated with the same layout.)
454 /// * `length` needs to be less than or equal to `capacity`.
455 /// * `capacity` needs to be the capacity that the pointer was allocated with.
457 /// Violating these may cause problems like corrupting the allocator's
458 /// internal data structures. For example it is **not** safe
459 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
460 /// It's also not safe to build one from a `Vec<u16>` and its length, because
461 /// the allocator cares about the alignment, and these two types have different
462 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
463 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
465 /// The ownership of `ptr` is effectively transferred to the
466 /// `Vec<T>` which may then deallocate, reallocate or change the
467 /// contents of memory pointed to by the pointer at will. Ensure
468 /// that nothing else uses the pointer after calling this
471 /// [`String`]: crate::string::String
472 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
480 /// let v = vec![1, 2, 3];
482 // FIXME Update this when vec_into_raw_parts is stabilized
483 /// // Prevent running `v`'s destructor so we are in complete control
484 /// // of the allocation.
485 /// let mut v = mem::ManuallyDrop::new(v);
487 /// // Pull out the various important pieces of information about `v`
488 /// let p = v.as_mut_ptr();
489 /// let len = v.len();
490 /// let cap = v.capacity();
493 /// // Overwrite memory with 4, 5, 6
494 /// for i in 0..len as isize {
495 /// ptr::write(p.offset(i), 4 + i);
498 /// // Put everything back together into a Vec
499 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
500 /// assert_eq!(rebuilt, [4, 5, 6]);
504 #[stable(feature = "rust1", since = "1.0.0")]
505 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
506 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
510 impl<T, A: Allocator> Vec<T, A> {
511 /// Constructs a new, empty `Vec<T, A>`.
513 /// The vector will not allocate until elements are pushed onto it.
518 /// #![feature(allocator_api)]
520 /// use std::alloc::System;
522 /// # #[allow(unused_mut)]
523 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
526 #[unstable(feature = "allocator_api", issue = "32838")]
527 pub const fn new_in(alloc: A) -> Self {
528 Vec { buf: RawVec::new_in(alloc), len: 0 }
531 /// Constructs a new, empty `Vec<T, A>` with the specified capacity with the provided
534 /// The vector will be able to hold exactly `capacity` elements without
535 /// reallocating. If `capacity` is 0, the vector will not allocate.
537 /// It is important to note that although the returned vector has the
538 /// *capacity* specified, the vector will have a zero *length*. For an
539 /// explanation of the difference between length and capacity, see
540 /// *[Capacity and reallocation]*.
542 /// [Capacity and reallocation]: #capacity-and-reallocation
547 /// #![feature(allocator_api)]
549 /// use std::alloc::System;
551 /// let mut vec = Vec::with_capacity_in(10, System);
553 /// // The vector contains no items, even though it has capacity for more
554 /// assert_eq!(vec.len(), 0);
555 /// assert_eq!(vec.capacity(), 10);
557 /// // These are all done without reallocating...
561 /// assert_eq!(vec.len(), 10);
562 /// assert_eq!(vec.capacity(), 10);
564 /// // ...but this may make the vector reallocate
566 /// assert_eq!(vec.len(), 11);
567 /// assert!(vec.capacity() >= 11);
570 #[unstable(feature = "allocator_api", issue = "32838")]
571 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
572 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
575 /// Creates a `Vec<T, A>` directly from the raw components of another vector.
579 /// This is highly unsafe, due to the number of invariants that aren't
582 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
583 /// (at least, it's highly likely to be incorrect if it wasn't).
584 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
585 /// (`T` having a less strict alignment is not sufficient, the alignment really
586 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
587 /// allocated and deallocated with the same layout.)
588 /// * `length` needs to be less than or equal to `capacity`.
589 /// * `capacity` needs to be the capacity that the pointer was allocated with.
591 /// Violating these may cause problems like corrupting the allocator's
592 /// internal data structures. For example it is **not** safe
593 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
594 /// It's also not safe to build one from a `Vec<u16>` and its length, because
595 /// the allocator cares about the alignment, and these two types have different
596 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
597 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
599 /// The ownership of `ptr` is effectively transferred to the
600 /// `Vec<T>` which may then deallocate, reallocate or change the
601 /// contents of memory pointed to by the pointer at will. Ensure
602 /// that nothing else uses the pointer after calling this
605 /// [`String`]: crate::string::String
606 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
611 /// #![feature(allocator_api)]
613 /// use std::alloc::System;
618 /// let mut v = Vec::with_capacity_in(3, System);
623 // FIXME Update this when vec_into_raw_parts is stabilized
624 /// // Prevent running `v`'s destructor so we are in complete control
625 /// // of the allocation.
626 /// let mut v = mem::ManuallyDrop::new(v);
628 /// // Pull out the various important pieces of information about `v`
629 /// let p = v.as_mut_ptr();
630 /// let len = v.len();
631 /// let cap = v.capacity();
632 /// let alloc = v.allocator();
635 /// // Overwrite memory with 4, 5, 6
636 /// for i in 0..len as isize {
637 /// ptr::write(p.offset(i), 4 + i);
640 /// // Put everything back together into a Vec
641 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
642 /// assert_eq!(rebuilt, [4, 5, 6]);
646 #[unstable(feature = "allocator_api", issue = "32838")]
647 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
648 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
651 /// Decomposes a `Vec<T>` into its raw components.
653 /// Returns the raw pointer to the underlying data, the length of
654 /// the vector (in elements), and the allocated capacity of the
655 /// data (in elements). These are the same arguments in the same
656 /// order as the arguments to [`from_raw_parts`].
658 /// After calling this function, the caller is responsible for the
659 /// memory previously managed by the `Vec`. The only way to do
660 /// this is to convert the raw pointer, length, and capacity back
661 /// into a `Vec` with the [`from_raw_parts`] function, allowing
662 /// the destructor to perform the cleanup.
664 /// [`from_raw_parts`]: Vec::from_raw_parts
669 /// #![feature(vec_into_raw_parts)]
670 /// let v: Vec<i32> = vec![-1, 0, 1];
672 /// let (ptr, len, cap) = v.into_raw_parts();
674 /// let rebuilt = unsafe {
675 /// // We can now make changes to the components, such as
676 /// // transmuting the raw pointer to a compatible type.
677 /// let ptr = ptr as *mut u32;
679 /// Vec::from_raw_parts(ptr, len, cap)
681 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
683 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
684 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
685 let mut me = ManuallyDrop::new(self);
686 (me.as_mut_ptr(), me.len(), me.capacity())
689 /// Decomposes a `Vec<T>` into its raw components.
691 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
692 /// the allocated capacity of the data (in elements), and the allocator. These are the same
693 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
695 /// After calling this function, the caller is responsible for the
696 /// memory previously managed by the `Vec`. The only way to do
697 /// this is to convert the raw pointer, length, and capacity back
698 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
699 /// the destructor to perform the cleanup.
701 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
706 /// #![feature(allocator_api, vec_into_raw_parts)]
708 /// use std::alloc::System;
710 /// let mut v: Vec<i32, System> = Vec::new_in(System);
715 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
717 /// let rebuilt = unsafe {
718 /// // We can now make changes to the components, such as
719 /// // transmuting the raw pointer to a compatible type.
720 /// let ptr = ptr as *mut u32;
722 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
724 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
726 #[unstable(feature = "allocator_api", issue = "32838")]
727 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
728 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
729 let mut me = ManuallyDrop::new(self);
731 let capacity = me.capacity();
732 let ptr = me.as_mut_ptr();
733 let alloc = unsafe { ptr::read(me.allocator()) };
734 (ptr, len, capacity, alloc)
737 /// Returns the number of elements the vector can hold without
743 /// let vec: Vec<i32> = Vec::with_capacity(10);
744 /// assert_eq!(vec.capacity(), 10);
747 #[stable(feature = "rust1", since = "1.0.0")]
748 pub fn capacity(&self) -> usize {
752 /// Reserves capacity for at least `additional` more elements to be inserted
753 /// in the given `Vec<T>`. The collection may reserve more space to avoid
754 /// frequent reallocations. After calling `reserve`, capacity will be
755 /// greater than or equal to `self.len() + additional`. Does nothing if
756 /// capacity is already sufficient.
760 /// Panics if the new capacity exceeds `isize::MAX` bytes.
765 /// let mut vec = vec![1];
767 /// assert!(vec.capacity() >= 11);
769 #[doc(alias = "realloc")]
770 #[stable(feature = "rust1", since = "1.0.0")]
771 pub fn reserve(&mut self, additional: usize) {
772 self.buf.reserve(self.len, additional);
775 /// Reserves the minimum capacity for exactly `additional` more elements to
776 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
777 /// capacity will be greater than or equal to `self.len() + additional`.
778 /// Does nothing if the capacity is already sufficient.
780 /// Note that the allocator may give the collection more space than it
781 /// requests. Therefore, capacity can not be relied upon to be precisely
782 /// minimal. Prefer `reserve` if future insertions are expected.
786 /// Panics if the new capacity overflows `usize`.
791 /// let mut vec = vec![1];
792 /// vec.reserve_exact(10);
793 /// assert!(vec.capacity() >= 11);
795 #[doc(alias = "realloc")]
796 #[stable(feature = "rust1", since = "1.0.0")]
797 pub fn reserve_exact(&mut self, additional: usize) {
798 self.buf.reserve_exact(self.len, additional);
801 /// Tries to reserve capacity for at least `additional` more elements to be inserted
802 /// in the given `Vec<T>`. The collection may reserve more space to avoid
803 /// frequent reallocations. After calling `try_reserve`, capacity will be
804 /// greater than or equal to `self.len() + additional`. Does nothing if
805 /// capacity is already sufficient.
809 /// If the capacity overflows, or the allocator reports a failure, then an error
815 /// #![feature(try_reserve)]
816 /// use std::collections::TryReserveError;
818 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
819 /// let mut output = Vec::new();
821 /// // Pre-reserve the memory, exiting if we can't
822 /// output.try_reserve(data.len())?;
824 /// // Now we know this can't OOM in the middle of our complex work
825 /// output.extend(data.iter().map(|&val| {
826 /// val * 2 + 5 // very complicated
831 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
833 #[doc(alias = "realloc")]
834 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
835 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
836 self.buf.try_reserve(self.len, additional)
839 /// Tries to reserve the minimum capacity for exactly `additional`
840 /// elements to be inserted in the given `Vec<T>`. After calling
841 /// `try_reserve_exact`, capacity will be greater than or equal to
842 /// `self.len() + additional` if it returns `Ok(())`.
843 /// Does nothing if the capacity is already sufficient.
845 /// Note that the allocator may give the collection more space than it
846 /// requests. Therefore, capacity can not be relied upon to be precisely
847 /// minimal. Prefer `reserve` if future insertions are expected.
851 /// If the capacity overflows, or the allocator reports a failure, then an error
857 /// #![feature(try_reserve)]
858 /// use std::collections::TryReserveError;
860 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
861 /// let mut output = Vec::new();
863 /// // Pre-reserve the memory, exiting if we can't
864 /// output.try_reserve_exact(data.len())?;
866 /// // Now we know this can't OOM in the middle of our complex work
867 /// output.extend(data.iter().map(|&val| {
868 /// val * 2 + 5 // very complicated
873 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
875 #[doc(alias = "realloc")]
876 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
877 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
878 self.buf.try_reserve_exact(self.len, additional)
881 /// Shrinks the capacity of the vector as much as possible.
883 /// It will drop down as close as possible to the length but the allocator
884 /// may still inform the vector that there is space for a few more elements.
889 /// let mut vec = Vec::with_capacity(10);
890 /// vec.extend([1, 2, 3].iter().cloned());
891 /// assert_eq!(vec.capacity(), 10);
892 /// vec.shrink_to_fit();
893 /// assert!(vec.capacity() >= 3);
895 #[doc(alias = "realloc")]
896 #[stable(feature = "rust1", since = "1.0.0")]
897 pub fn shrink_to_fit(&mut self) {
898 // The capacity is never less than the length, and there's nothing to do when
899 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
900 // by only calling it with a greater capacity.
901 if self.capacity() > self.len {
902 self.buf.shrink_to_fit(self.len);
906 /// Shrinks the capacity of the vector with a lower bound.
908 /// The capacity will remain at least as large as both the length
909 /// and the supplied value.
911 /// If the current capacity is less than the lower limit, this is a no-op.
916 /// #![feature(shrink_to)]
917 /// let mut vec = Vec::with_capacity(10);
918 /// vec.extend([1, 2, 3].iter().cloned());
919 /// assert_eq!(vec.capacity(), 10);
920 /// vec.shrink_to(4);
921 /// assert!(vec.capacity() >= 4);
922 /// vec.shrink_to(0);
923 /// assert!(vec.capacity() >= 3);
925 #[doc(alias = "realloc")]
926 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
927 pub fn shrink_to(&mut self, min_capacity: usize) {
928 if self.capacity() > min_capacity {
929 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
933 /// Converts the vector into [`Box<[T]>`][owned slice].
935 /// Note that this will drop any excess capacity.
937 /// [owned slice]: Box
942 /// let v = vec![1, 2, 3];
944 /// let slice = v.into_boxed_slice();
947 /// Any excess capacity is removed:
950 /// let mut vec = Vec::with_capacity(10);
951 /// vec.extend([1, 2, 3].iter().cloned());
953 /// assert_eq!(vec.capacity(), 10);
954 /// let slice = vec.into_boxed_slice();
955 /// assert_eq!(slice.into_vec().capacity(), 3);
957 #[stable(feature = "rust1", since = "1.0.0")]
958 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
960 self.shrink_to_fit();
961 let me = ManuallyDrop::new(self);
962 let buf = ptr::read(&me.buf);
964 buf.into_box(len).assume_init()
968 /// Shortens the vector, keeping the first `len` elements and dropping
971 /// If `len` is greater than the vector's current length, this has no
974 /// The [`drain`] method can emulate `truncate`, but causes the excess
975 /// elements to be returned instead of dropped.
977 /// Note that this method has no effect on the allocated capacity
982 /// Truncating a five element vector to two elements:
985 /// let mut vec = vec![1, 2, 3, 4, 5];
987 /// assert_eq!(vec, [1, 2]);
990 /// No truncation occurs when `len` is greater than the vector's current
994 /// let mut vec = vec![1, 2, 3];
996 /// assert_eq!(vec, [1, 2, 3]);
999 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1003 /// let mut vec = vec![1, 2, 3];
1004 /// vec.truncate(0);
1005 /// assert_eq!(vec, []);
1008 /// [`clear`]: Vec::clear
1009 /// [`drain`]: Vec::drain
1010 #[stable(feature = "rust1", since = "1.0.0")]
1011 pub fn truncate(&mut self, len: usize) {
1012 // This is safe because:
1014 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1015 // case avoids creating an invalid slice, and
1016 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1017 // such that no value will be dropped twice in case `drop_in_place`
1018 // were to panic once (if it panics twice, the program aborts).
1020 // Note: It's intentional that this is `>` and not `>=`.
1021 // Changing it to `>=` has negative performance
1022 // implications in some cases. See #78884 for more.
1026 let remaining_len = self.len - len;
1027 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1029 ptr::drop_in_place(s);
1033 /// Extracts a slice containing the entire vector.
1035 /// Equivalent to `&s[..]`.
1040 /// use std::io::{self, Write};
1041 /// let buffer = vec![1, 2, 3, 5, 8];
1042 /// io::sink().write(buffer.as_slice()).unwrap();
1045 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1046 pub fn as_slice(&self) -> &[T] {
1050 /// Extracts a mutable slice of the entire vector.
1052 /// Equivalent to `&mut s[..]`.
1057 /// use std::io::{self, Read};
1058 /// let mut buffer = vec![0; 3];
1059 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1062 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1063 pub fn as_mut_slice(&mut self) -> &mut [T] {
1067 /// Returns a raw pointer to the vector's buffer.
1069 /// The caller must ensure that the vector outlives the pointer this
1070 /// function returns, or else it will end up pointing to garbage.
1071 /// Modifying the vector may cause its buffer to be reallocated,
1072 /// which would also make any pointers to it invalid.
1074 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1075 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1076 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1081 /// let x = vec![1, 2, 4];
1082 /// let x_ptr = x.as_ptr();
1085 /// for i in 0..x.len() {
1086 /// assert_eq!(*x_ptr.add(i), 1 << i);
1091 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1092 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1094 pub fn as_ptr(&self) -> *const T {
1095 // We shadow the slice method of the same name to avoid going through
1096 // `deref`, which creates an intermediate reference.
1097 let ptr = self.buf.ptr();
1099 assume(!ptr.is_null());
1104 /// Returns an unsafe mutable pointer to the vector's buffer.
1106 /// The caller must ensure that the vector outlives the pointer this
1107 /// function returns, or else it will end up pointing to garbage.
1108 /// Modifying the vector may cause its buffer to be reallocated,
1109 /// which would also make any pointers to it invalid.
1114 /// // Allocate vector big enough for 4 elements.
1116 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1117 /// let x_ptr = x.as_mut_ptr();
1119 /// // Initialize elements via raw pointer writes, then set length.
1121 /// for i in 0..size {
1122 /// *x_ptr.add(i) = i as i32;
1124 /// x.set_len(size);
1126 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1128 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1130 pub fn as_mut_ptr(&mut self) -> *mut T {
1131 // We shadow the slice method of the same name to avoid going through
1132 // `deref_mut`, which creates an intermediate reference.
1133 let ptr = self.buf.ptr();
1135 assume(!ptr.is_null());
1140 /// Returns a reference to the underlying allocator.
1141 #[unstable(feature = "allocator_api", issue = "32838")]
1143 pub fn allocator(&self) -> &A {
1144 self.buf.allocator()
1147 /// Forces the length of the vector to `new_len`.
1149 /// This is a low-level operation that maintains none of the normal
1150 /// invariants of the type. Normally changing the length of a vector
1151 /// is done using one of the safe operations instead, such as
1152 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1154 /// [`truncate`]: Vec::truncate
1155 /// [`resize`]: Vec::resize
1156 /// [`extend`]: Extend::extend
1157 /// [`clear`]: Vec::clear
1161 /// - `new_len` must be less than or equal to [`capacity()`].
1162 /// - The elements at `old_len..new_len` must be initialized.
1164 /// [`capacity()`]: Vec::capacity
1168 /// This method can be useful for situations in which the vector
1169 /// is serving as a buffer for other code, particularly over FFI:
1172 /// # #![allow(dead_code)]
1173 /// # // This is just a minimal skeleton for the doc example;
1174 /// # // don't use this as a starting point for a real library.
1175 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1176 /// # const Z_OK: i32 = 0;
1178 /// # fn deflateGetDictionary(
1179 /// # strm: *mut std::ffi::c_void,
1180 /// # dictionary: *mut u8,
1181 /// # dictLength: *mut usize,
1184 /// # impl StreamWrapper {
1185 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1186 /// // Per the FFI method's docs, "32768 bytes is always enough".
1187 /// let mut dict = Vec::with_capacity(32_768);
1188 /// let mut dict_length = 0;
1189 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1190 /// // 1. `dict_length` elements were initialized.
1191 /// // 2. `dict_length` <= the capacity (32_768)
1192 /// // which makes `set_len` safe to call.
1194 /// // Make the FFI call...
1195 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1197 /// // ...and update the length to what was initialized.
1198 /// dict.set_len(dict_length);
1208 /// While the following example is sound, there is a memory leak since
1209 /// the inner vectors were not freed prior to the `set_len` call:
1212 /// let mut vec = vec![vec![1, 0, 0],
1216 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1217 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1223 /// Normally, here, one would use [`clear`] instead to correctly drop
1224 /// the contents and thus not leak memory.
1226 #[stable(feature = "rust1", since = "1.0.0")]
1227 pub unsafe fn set_len(&mut self, new_len: usize) {
1228 debug_assert!(new_len <= self.capacity());
1233 /// Removes an element from the vector and returns it.
1235 /// The removed element is replaced by the last element of the vector.
1237 /// This does not preserve ordering, but is O(1).
1241 /// Panics if `index` is out of bounds.
1246 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1248 /// assert_eq!(v.swap_remove(1), "bar");
1249 /// assert_eq!(v, ["foo", "qux", "baz"]);
1251 /// assert_eq!(v.swap_remove(0), "foo");
1252 /// assert_eq!(v, ["baz", "qux"]);
1255 #[stable(feature = "rust1", since = "1.0.0")]
1256 pub fn swap_remove(&mut self, index: usize) -> T {
1259 fn assert_failed(index: usize, len: usize) -> ! {
1260 panic!("swap_remove index (is {}) should be < len (is {})", index, len);
1263 let len = self.len();
1265 assert_failed(index, len);
1268 // We replace self[index] with the last element. Note that if the
1269 // bounds check above succeeds there must be a last element (which
1270 // can be self[index] itself).
1271 let last = ptr::read(self.as_ptr().add(len - 1));
1272 let hole = self.as_mut_ptr().add(index);
1273 self.set_len(len - 1);
1274 ptr::replace(hole, last)
1278 /// Inserts an element at position `index` within the vector, shifting all
1279 /// elements after it to the right.
1283 /// Panics if `index > len`.
1288 /// let mut vec = vec![1, 2, 3];
1289 /// vec.insert(1, 4);
1290 /// assert_eq!(vec, [1, 4, 2, 3]);
1291 /// vec.insert(4, 5);
1292 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1294 #[stable(feature = "rust1", since = "1.0.0")]
1295 pub fn insert(&mut self, index: usize, element: T) {
1298 fn assert_failed(index: usize, len: usize) -> ! {
1299 panic!("insertion index (is {}) should be <= len (is {})", index, len);
1302 let len = self.len();
1304 assert_failed(index, len);
1307 // space for the new element
1308 if len == self.buf.capacity() {
1314 // The spot to put the new value
1316 let p = self.as_mut_ptr().add(index);
1317 // Shift everything over to make space. (Duplicating the
1318 // `index`th element into two consecutive places.)
1319 ptr::copy(p, p.offset(1), len - index);
1320 // Write it in, overwriting the first copy of the `index`th
1322 ptr::write(p, element);
1324 self.set_len(len + 1);
1328 /// Removes and returns the element at position `index` within the vector,
1329 /// shifting all elements after it to the left.
1333 /// Panics if `index` is out of bounds.
1338 /// let mut v = vec![1, 2, 3];
1339 /// assert_eq!(v.remove(1), 2);
1340 /// assert_eq!(v, [1, 3]);
1342 #[stable(feature = "rust1", since = "1.0.0")]
1343 pub fn remove(&mut self, index: usize) -> T {
1346 fn assert_failed(index: usize, len: usize) -> ! {
1347 panic!("removal index (is {}) should be < len (is {})", index, len);
1350 let len = self.len();
1352 assert_failed(index, len);
1358 // the place we are taking from.
1359 let ptr = self.as_mut_ptr().add(index);
1360 // copy it out, unsafely having a copy of the value on
1361 // the stack and in the vector at the same time.
1362 ret = ptr::read(ptr);
1364 // Shift everything down to fill in that spot.
1365 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1367 self.set_len(len - 1);
1372 /// Retains only the elements specified by the predicate.
1374 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1375 /// This method operates in place, visiting each element exactly once in the
1376 /// original order, and preserves the order of the retained elements.
1381 /// let mut vec = vec![1, 2, 3, 4];
1382 /// vec.retain(|&x| x % 2 == 0);
1383 /// assert_eq!(vec, [2, 4]);
1386 /// Because the elements are visited exactly once in the original order,
1387 /// external state may be used to decide which elements to keep.
1390 /// let mut vec = vec![1, 2, 3, 4, 5];
1391 /// let keep = [false, true, true, false, true];
1392 /// let mut iter = keep.iter();
1393 /// vec.retain(|_| *iter.next().unwrap());
1394 /// assert_eq!(vec, [2, 3, 5]);
1396 #[stable(feature = "rust1", since = "1.0.0")]
1397 pub fn retain<F>(&mut self, mut f: F)
1399 F: FnMut(&T) -> bool,
1401 let original_len = self.len();
1402 // Avoid double drop if the drop guard is not executed,
1403 // since we may make some holes during the process.
1404 unsafe { self.set_len(0) };
1406 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1407 // |<- processed len ->| ^- next to check
1408 // |<- deleted cnt ->|
1409 // |<- original_len ->|
1410 // Kept: Elements which predicate returns true on.
1411 // Hole: Moved or dropped element slot.
1412 // Unchecked: Unchecked valid elements.
1414 // This drop guard will be invoked when predicate or `drop` of element panicked.
1415 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1416 // In cases when predicate and `drop` never panick, it will be optimized out.
1417 struct BackshiftOnDrop<'a, T, A: Allocator> {
1418 v: &'a mut Vec<T, A>,
1419 processed_len: usize,
1421 original_len: usize,
1424 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1425 fn drop(&mut self) {
1426 if self.deleted_cnt > 0 {
1427 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1430 self.v.as_ptr().add(self.processed_len),
1431 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1432 self.original_len - self.processed_len,
1436 // SAFETY: After filling holes, all items are in contiguous memory.
1438 self.v.set_len(self.original_len - self.deleted_cnt);
1443 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1445 while g.processed_len < original_len {
1446 // SAFETY: Unchecked element must be valid.
1447 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1449 // Advance early to avoid double drop if `drop_in_place` panicked.
1450 g.processed_len += 1;
1452 // SAFETY: We never touch this element again after dropped.
1453 unsafe { ptr::drop_in_place(cur) };
1454 // We already advanced the counter.
1457 if g.deleted_cnt > 0 {
1458 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1459 // We use copy for move, and never touch this element again.
1461 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1462 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1465 g.processed_len += 1;
1468 // All item are processed. This can be optimized to `set_len` by LLVM.
1472 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1475 /// If the vector is sorted, this removes all duplicates.
1480 /// let mut vec = vec![10, 20, 21, 30, 20];
1482 /// vec.dedup_by_key(|i| *i / 10);
1484 /// assert_eq!(vec, [10, 20, 30, 20]);
1486 #[stable(feature = "dedup_by", since = "1.16.0")]
1488 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1490 F: FnMut(&mut T) -> K,
1493 self.dedup_by(|a, b| key(a) == key(b))
1496 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1499 /// The `same_bucket` function is passed references to two elements from the vector and
1500 /// must determine if the elements compare equal. The elements are passed in opposite order
1501 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1503 /// If the vector is sorted, this removes all duplicates.
1508 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1510 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1512 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1514 #[stable(feature = "dedup_by", since = "1.16.0")]
1515 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1517 F: FnMut(&mut T, &mut T) -> bool,
1519 let len = self.len();
1524 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1525 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1526 /* Offset of the element we want to check if it is duplicate */
1529 /* Offset of the place where we want to place the non-duplicate
1530 * when we find it. */
1533 /* The Vec that would need correction if `same_bucket` panicked */
1534 vec: &'a mut Vec<T, A>,
1537 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1538 fn drop(&mut self) {
1539 /* This code gets executed when `same_bucket` panics */
1541 /* SAFETY: invariant guarantees that `read - write`
1542 * and `len - read` never overflow and that the copy is always
1545 let ptr = self.vec.as_mut_ptr();
1546 let len = self.vec.len();
1548 /* How many items were left when `same_bucket` paniced.
1549 * Basically vec[read..].len() */
1550 let items_left = len.wrapping_sub(self.read);
1552 /* Pointer to first item in vec[write..write+items_left] slice */
1553 let dropped_ptr = ptr.add(self.write);
1554 /* Pointer to first item in vec[read..] slice */
1555 let valid_ptr = ptr.add(self.read);
1557 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1558 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1559 ptr::copy(valid_ptr, dropped_ptr, items_left);
1561 /* How many items have been already dropped
1562 * Basically vec[read..write].len() */
1563 let dropped = self.read.wrapping_sub(self.write);
1565 self.vec.set_len(len - dropped);
1570 let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
1571 let ptr = gap.vec.as_mut_ptr();
1573 /* Drop items while going through Vec, it should be more efficient than
1574 * doing slice partition_dedup + truncate */
1576 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1577 * are always in-bounds and read_ptr never aliases prev_ptr */
1579 while gap.read < len {
1580 let read_ptr = ptr.add(gap.read);
1581 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1583 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1584 /* We have found duplicate, drop it in-place */
1585 ptr::drop_in_place(read_ptr);
1587 let write_ptr = ptr.add(gap.write);
1589 /* Because `read_ptr` can be equal to `write_ptr`, we either
1590 * have to use `copy` or conditional `copy_nonoverlapping`.
1591 * Looks like the first option is faster. */
1592 ptr::copy(read_ptr, write_ptr, 1);
1594 /* We have filled that place, so go further */
1601 /* Technically we could let `gap` clean up with its Drop, but
1602 * when `same_bucket` is guaranteed to not panic, this bloats a little
1603 * the codegen, so we just do it manually */
1604 gap.vec.set_len(gap.write);
1609 /// Appends an element to the back of a collection.
1613 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1618 /// let mut vec = vec![1, 2];
1620 /// assert_eq!(vec, [1, 2, 3]);
1623 #[stable(feature = "rust1", since = "1.0.0")]
1624 pub fn push(&mut self, value: T) {
1625 // This will panic or abort if we would allocate > isize::MAX bytes
1626 // or if the length increment would overflow for zero-sized types.
1627 if self.len == self.buf.capacity() {
1631 let end = self.as_mut_ptr().add(self.len);
1632 ptr::write(end, value);
1637 /// Removes the last element from a vector and returns it, or [`None`] if it
1643 /// let mut vec = vec![1, 2, 3];
1644 /// assert_eq!(vec.pop(), Some(3));
1645 /// assert_eq!(vec, [1, 2]);
1648 #[stable(feature = "rust1", since = "1.0.0")]
1649 pub fn pop(&mut self) -> Option<T> {
1655 Some(ptr::read(self.as_ptr().add(self.len())))
1660 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1664 /// Panics if the number of elements in the vector overflows a `usize`.
1669 /// let mut vec = vec![1, 2, 3];
1670 /// let mut vec2 = vec![4, 5, 6];
1671 /// vec.append(&mut vec2);
1672 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1673 /// assert_eq!(vec2, []);
1676 #[stable(feature = "append", since = "1.4.0")]
1677 pub fn append(&mut self, other: &mut Self) {
1679 self.append_elements(other.as_slice() as _);
1684 /// Appends elements to `Self` from other buffer.
1686 unsafe fn append_elements(&mut self, other: *const [T]) {
1687 let count = unsafe { (*other).len() };
1688 self.reserve(count);
1689 let len = self.len();
1690 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1694 /// Creates a draining iterator that removes the specified range in the vector
1695 /// and yields the removed items.
1697 /// When the iterator **is** dropped, all elements in the range are removed
1698 /// from the vector, even if the iterator was not fully consumed. If the
1699 /// iterator **is not** dropped (with [`mem::forget`] for example), it is
1700 /// unspecified how many elements are removed.
1704 /// Panics if the starting point is greater than the end point or if
1705 /// the end point is greater than the length of the vector.
1710 /// let mut v = vec![1, 2, 3];
1711 /// let u: Vec<_> = v.drain(1..).collect();
1712 /// assert_eq!(v, &[1]);
1713 /// assert_eq!(u, &[2, 3]);
1715 /// // A full range clears the vector
1717 /// assert_eq!(v, &[]);
1719 #[stable(feature = "drain", since = "1.6.0")]
1720 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1722 R: RangeBounds<usize>,
1726 // When the Drain is first created, it shortens the length of
1727 // the source vector to make sure no uninitialized or moved-from elements
1728 // are accessible at all if the Drain's destructor never gets to run.
1730 // Drain will ptr::read out the values to remove.
1731 // When finished, remaining tail of the vec is copied back to cover
1732 // the hole, and the vector length is restored to the new length.
1734 let len = self.len();
1735 let Range { start, end } = slice::range(range, ..len);
1738 // set self.vec length's to start, to be safe in case Drain is leaked
1739 self.set_len(start);
1740 // Use the borrow in the IterMut to indicate borrowing behavior of the
1741 // whole Drain iterator (like &mut T).
1742 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1745 tail_len: len - end,
1746 iter: range_slice.iter(),
1747 vec: NonNull::from(self),
1752 /// Clears the vector, removing all values.
1754 /// Note that this method has no effect on the allocated capacity
1760 /// let mut v = vec![1, 2, 3];
1764 /// assert!(v.is_empty());
1767 #[stable(feature = "rust1", since = "1.0.0")]
1768 pub fn clear(&mut self) {
1772 /// Returns the number of elements in the vector, also referred to
1773 /// as its 'length'.
1778 /// let a = vec![1, 2, 3];
1779 /// assert_eq!(a.len(), 3);
1781 #[doc(alias = "length")]
1783 #[stable(feature = "rust1", since = "1.0.0")]
1784 pub fn len(&self) -> usize {
1788 /// Returns `true` if the vector contains no elements.
1793 /// let mut v = Vec::new();
1794 /// assert!(v.is_empty());
1797 /// assert!(!v.is_empty());
1799 #[stable(feature = "rust1", since = "1.0.0")]
1800 pub fn is_empty(&self) -> bool {
1804 /// Splits the collection into two at the given index.
1806 /// Returns a newly allocated vector containing the elements in the range
1807 /// `[at, len)`. After the call, the original vector will be left containing
1808 /// the elements `[0, at)` with its previous capacity unchanged.
1812 /// Panics if `at > len`.
1817 /// let mut vec = vec![1, 2, 3];
1818 /// let vec2 = vec.split_off(1);
1819 /// assert_eq!(vec, [1]);
1820 /// assert_eq!(vec2, [2, 3]);
1823 #[must_use = "use `.truncate()` if you don't need the other half"]
1824 #[stable(feature = "split_off", since = "1.4.0")]
1825 pub fn split_off(&mut self, at: usize) -> Self
1831 fn assert_failed(at: usize, len: usize) -> ! {
1832 panic!("`at` split index (is {}) should be <= len (is {})", at, len);
1835 if at > self.len() {
1836 assert_failed(at, self.len());
1840 // the new vector can take over the original buffer and avoid the copy
1841 return mem::replace(
1843 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
1847 let other_len = self.len - at;
1848 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
1850 // Unsafely `set_len` and copy items to `other`.
1853 other.set_len(other_len);
1855 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1860 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1862 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1863 /// difference, with each additional slot filled with the result of
1864 /// calling the closure `f`. The return values from `f` will end up
1865 /// in the `Vec` in the order they have been generated.
1867 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1869 /// This method uses a closure to create new values on every push. If
1870 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
1871 /// want to use the [`Default`] trait to generate values, you can
1872 /// pass [`Default::default`] as the second argument.
1877 /// let mut vec = vec![1, 2, 3];
1878 /// vec.resize_with(5, Default::default);
1879 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1881 /// let mut vec = vec![];
1883 /// vec.resize_with(4, || { p *= 2; p });
1884 /// assert_eq!(vec, [2, 4, 8, 16]);
1886 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1887 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1891 let len = self.len();
1893 self.extend_with(new_len - len, ExtendFunc(f));
1895 self.truncate(new_len);
1899 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1900 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1901 /// `'a`. If the type has only static references, or none at all, then this
1902 /// may be chosen to be `'static`.
1904 /// This function is similar to the [`leak`][Box::leak] function on [`Box`]
1905 /// except that there is no way to recover the leaked memory.
1907 /// This function is mainly useful for data that lives for the remainder of
1908 /// the program's life. Dropping the returned reference will cause a memory
1916 /// let x = vec![1, 2, 3];
1917 /// let static_ref: &'static mut [usize] = x.leak();
1918 /// static_ref[0] += 1;
1919 /// assert_eq!(static_ref, &[2, 2, 3]);
1921 #[stable(feature = "vec_leak", since = "1.47.0")]
1923 pub fn leak<'a>(self) -> &'a mut [T]
1927 Box::leak(self.into_boxed_slice())
1930 /// Returns the remaining spare capacity of the vector as a slice of
1931 /// `MaybeUninit<T>`.
1933 /// The returned slice can be used to fill the vector with data (e.g. by
1934 /// reading from a file) before marking the data as initialized using the
1935 /// [`set_len`] method.
1937 /// [`set_len`]: Vec::set_len
1942 /// #![feature(vec_spare_capacity, maybe_uninit_extra)]
1944 /// // Allocate vector big enough for 10 elements.
1945 /// let mut v = Vec::with_capacity(10);
1947 /// // Fill in the first 3 elements.
1948 /// let uninit = v.spare_capacity_mut();
1949 /// uninit[0].write(0);
1950 /// uninit[1].write(1);
1951 /// uninit[2].write(2);
1953 /// // Mark the first 3 elements of the vector as being initialized.
1958 /// assert_eq!(&v, &[0, 1, 2]);
1960 #[unstable(feature = "vec_spare_capacity", issue = "75017")]
1962 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
1964 // This method is not implemented in terms of `split_at_spare_mut`,
1965 // to prevent invalidation of pointers to the buffer.
1967 slice::from_raw_parts_mut(
1968 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
1969 self.buf.capacity() - self.len,
1974 /// Returns vector content as a slice of `T`, along with the remaining spare
1975 /// capacity of the vector as a slice of `MaybeUninit<T>`.
1977 /// The returned spare capacity slice can be used to fill the vector with data
1978 /// (e.g. by reading from a file) before marking the data as initialized using
1979 /// the [`set_len`] method.
1981 /// [`set_len`]: Vec::set_len
1983 /// Note that this is a low-level API, which should be used with care for
1984 /// optimization purposes. If you need to append data to a `Vec`
1985 /// you can use [`push`], [`extend`], [`extend_from_slice`],
1986 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
1987 /// [`resize_with`], depending on your exact needs.
1989 /// [`push`]: Vec::push
1990 /// [`extend`]: Vec::extend
1991 /// [`extend_from_slice`]: Vec::extend_from_slice
1992 /// [`extend_from_within`]: Vec::extend_from_within
1993 /// [`insert`]: Vec::insert
1994 /// [`append`]: Vec::append
1995 /// [`resize`]: Vec::resize
1996 /// [`resize_with`]: Vec::resize_with
2001 /// #![feature(vec_split_at_spare, maybe_uninit_extra)]
2003 /// let mut v = vec![1, 1, 2];
2005 /// // Reserve additional space big enough for 10 elements.
2008 /// let (init, uninit) = v.split_at_spare_mut();
2009 /// let sum = init.iter().copied().sum::<u32>();
2011 /// // Fill in the next 4 elements.
2012 /// uninit[0].write(sum);
2013 /// uninit[1].write(sum * 2);
2014 /// uninit[2].write(sum * 3);
2015 /// uninit[3].write(sum * 4);
2017 /// // Mark the 4 elements of the vector as being initialized.
2019 /// let len = v.len();
2020 /// v.set_len(len + 4);
2023 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2025 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2027 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2029 // - len is ignored and so never changed
2030 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2034 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2036 /// This method is used to have unique access to all vec parts at once in `extend_from_within`.
2037 unsafe fn split_at_spare_mut_with_len(
2039 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2040 let Range { start: ptr, end: spare_ptr } = self.as_mut_ptr_range();
2041 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2042 let spare_len = self.buf.capacity() - self.len;
2045 // - `ptr` is guaranteed to be valid for `len` elements
2046 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2048 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2049 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2051 (initialized, spare, &mut self.len)
2056 impl<T: Clone, A: Allocator> Vec<T, A> {
2057 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2059 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2060 /// difference, with each additional slot filled with `value`.
2061 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2063 /// This method requires `T` to implement [`Clone`],
2064 /// in order to be able to clone the passed value.
2065 /// If you need more flexibility (or want to rely on [`Default`] instead of
2066 /// [`Clone`]), use [`Vec::resize_with`].
2071 /// let mut vec = vec!["hello"];
2072 /// vec.resize(3, "world");
2073 /// assert_eq!(vec, ["hello", "world", "world"]);
2075 /// let mut vec = vec![1, 2, 3, 4];
2076 /// vec.resize(2, 0);
2077 /// assert_eq!(vec, [1, 2]);
2079 #[stable(feature = "vec_resize", since = "1.5.0")]
2080 pub fn resize(&mut self, new_len: usize, value: T) {
2081 let len = self.len();
2084 self.extend_with(new_len - len, ExtendElement(value))
2086 self.truncate(new_len);
2090 /// Clones and appends all elements in a slice to the `Vec`.
2092 /// Iterates over the slice `other`, clones each element, and then appends
2093 /// it to this `Vec`. The `other` vector is traversed in-order.
2095 /// Note that this function is same as [`extend`] except that it is
2096 /// specialized to work with slices instead. If and when Rust gets
2097 /// specialization this function will likely be deprecated (but still
2103 /// let mut vec = vec![1];
2104 /// vec.extend_from_slice(&[2, 3, 4]);
2105 /// assert_eq!(vec, [1, 2, 3, 4]);
2108 /// [`extend`]: Vec::extend
2109 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2110 pub fn extend_from_slice(&mut self, other: &[T]) {
2111 self.spec_extend(other.iter())
2114 /// Copies elements from `src` range to the end of the vector.
2119 /// #![feature(vec_extend_from_within)]
2121 /// let mut vec = vec![0, 1, 2, 3, 4];
2123 /// vec.extend_from_within(2..);
2124 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2126 /// vec.extend_from_within(..2);
2127 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2129 /// vec.extend_from_within(4..8);
2130 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2132 #[unstable(feature = "vec_extend_from_within", issue = "81656")]
2133 pub fn extend_from_within<R>(&mut self, src: R)
2135 R: RangeBounds<usize>,
2137 let range = slice::range(src, ..self.len());
2138 self.reserve(range.len());
2141 // - `slice::range` guarantees that the given range is valid for indexing self
2143 self.spec_extend_from_within(range);
2148 // This code generalizes `extend_with_{element,default}`.
2149 trait ExtendWith<T> {
2150 fn next(&mut self) -> T;
2154 struct ExtendElement<T>(T);
2155 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2156 fn next(&mut self) -> T {
2159 fn last(self) -> T {
2164 struct ExtendDefault;
2165 impl<T: Default> ExtendWith<T> for ExtendDefault {
2166 fn next(&mut self) -> T {
2169 fn last(self) -> T {
2174 struct ExtendFunc<F>(F);
2175 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
2176 fn next(&mut self) -> T {
2179 fn last(mut self) -> T {
2184 impl<T, A: Allocator> Vec<T, A> {
2185 /// Extend the vector by `n` values, using the given generator.
2186 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2190 let mut ptr = self.as_mut_ptr().add(self.len());
2191 // Use SetLenOnDrop to work around bug where compiler
2192 // may not realize the store through `ptr` through self.set_len()
2194 let mut local_len = SetLenOnDrop::new(&mut self.len);
2196 // Write all elements except the last one
2198 ptr::write(ptr, value.next());
2199 ptr = ptr.offset(1);
2200 // Increment the length in every step in case next() panics
2201 local_len.increment_len(1);
2205 // We can write the last element directly without cloning needlessly
2206 ptr::write(ptr, value.last());
2207 local_len.increment_len(1);
2210 // len set by scope guard
2215 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2216 /// Removes consecutive repeated elements in the vector according to the
2217 /// [`PartialEq`] trait implementation.
2219 /// If the vector is sorted, this removes all duplicates.
2224 /// let mut vec = vec![1, 2, 2, 3, 2];
2228 /// assert_eq!(vec, [1, 2, 3, 2]);
2230 #[stable(feature = "rust1", since = "1.0.0")]
2232 pub fn dedup(&mut self) {
2233 self.dedup_by(|a, b| a == b)
2237 ////////////////////////////////////////////////////////////////////////////////
2238 // Internal methods and functions
2239 ////////////////////////////////////////////////////////////////////////////////
2242 #[stable(feature = "rust1", since = "1.0.0")]
2243 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2244 <T as SpecFromElem>::from_elem(elem, n, Global)
2248 #[unstable(feature = "allocator_api", issue = "32838")]
2249 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2250 <T as SpecFromElem>::from_elem(elem, n, alloc)
2253 trait ExtendFromWithinSpec {
2256 /// - `src` needs to be valid index
2257 /// - `self.capacity() - self.len()` must be `>= src.len()`
2258 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2261 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2262 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2264 // - len is increased only after initializing elements
2265 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2268 // - caller guaratees that src is a valid index
2269 let to_clone = unsafe { this.get_unchecked(src) };
2274 .zip(spare.iter_mut())
2275 .map(|(src, dst)| dst.write(src))
2277 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increace len
2278 // - len is increased after each element to prevent leaks (see issue #82533)
2279 .for_each(|_| *len += 1);
2283 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2284 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2285 let count = src.len();
2287 let (init, spare) = self.split_at_spare_mut();
2290 // - caller guaratees that `src` is a valid index
2291 let source = unsafe { init.get_unchecked(src) };
2294 // - Both pointers are created from unique slice references (`&mut [_]`)
2295 // so they are valid and do not overlap.
2296 // - Elements are :Copy so it's OK to to copy them, without doing
2297 // anything with the original values
2298 // - `count` is equal to the len of `source`, so source is valid for
2300 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2301 // is valid for `count` writes
2302 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2306 // - The elements were just initialized by `copy_nonoverlapping`
2311 ////////////////////////////////////////////////////////////////////////////////
2312 // Common trait implementations for Vec
2313 ////////////////////////////////////////////////////////////////////////////////
2315 #[stable(feature = "rust1", since = "1.0.0")]
2316 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2319 fn deref(&self) -> &[T] {
2320 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2324 #[stable(feature = "rust1", since = "1.0.0")]
2325 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2326 fn deref_mut(&mut self) -> &mut [T] {
2327 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2331 #[stable(feature = "rust1", since = "1.0.0")]
2332 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2334 fn clone(&self) -> Self {
2335 let alloc = self.allocator().clone();
2336 <[T]>::to_vec_in(&**self, alloc)
2339 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2340 // required for this method definition, is not available. Instead use the
2341 // `slice::to_vec` function which is only available with cfg(test)
2342 // NB see the slice::hack module in slice.rs for more information
2344 fn clone(&self) -> Self {
2345 let alloc = self.allocator().clone();
2346 crate::slice::to_vec(&**self, alloc)
2349 fn clone_from(&mut self, other: &Self) {
2350 // drop anything that will not be overwritten
2351 self.truncate(other.len());
2353 // self.len <= other.len due to the truncate above, so the
2354 // slices here are always in-bounds.
2355 let (init, tail) = other.split_at(self.len());
2357 // reuse the contained values' allocations/resources.
2358 self.clone_from_slice(init);
2359 self.extend_from_slice(tail);
2363 #[stable(feature = "rust1", since = "1.0.0")]
2364 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2366 fn hash<H: Hasher>(&self, state: &mut H) {
2367 Hash::hash(&**self, state)
2371 #[stable(feature = "rust1", since = "1.0.0")]
2372 #[rustc_on_unimplemented(
2373 message = "vector indices are of type `usize` or ranges of `usize`",
2374 label = "vector indices are of type `usize` or ranges of `usize`"
2376 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2377 type Output = I::Output;
2380 fn index(&self, index: I) -> &Self::Output {
2381 Index::index(&**self, index)
2385 #[stable(feature = "rust1", since = "1.0.0")]
2386 #[rustc_on_unimplemented(
2387 message = "vector indices are of type `usize` or ranges of `usize`",
2388 label = "vector indices are of type `usize` or ranges of `usize`"
2390 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2392 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2393 IndexMut::index_mut(&mut **self, index)
2397 #[stable(feature = "rust1", since = "1.0.0")]
2398 impl<T> FromIterator<T> for Vec<T> {
2400 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2401 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2405 #[stable(feature = "rust1", since = "1.0.0")]
2406 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2408 type IntoIter = IntoIter<T, A>;
2410 /// Creates a consuming iterator, that is, one that moves each value out of
2411 /// the vector (from start to end). The vector cannot be used after calling
2417 /// let v = vec!["a".to_string(), "b".to_string()];
2418 /// for s in v.into_iter() {
2419 /// // s has type String, not &String
2420 /// println!("{}", s);
2424 fn into_iter(self) -> IntoIter<T, A> {
2426 let mut me = ManuallyDrop::new(self);
2427 let alloc = ptr::read(me.allocator());
2428 let begin = me.as_mut_ptr();
2429 let end = if mem::size_of::<T>() == 0 {
2430 arith_offset(begin as *const i8, me.len() as isize) as *const T
2432 begin.add(me.len()) as *const T
2434 let cap = me.buf.capacity();
2436 buf: NonNull::new_unchecked(begin),
2437 phantom: PhantomData,
2447 #[stable(feature = "rust1", since = "1.0.0")]
2448 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2450 type IntoIter = slice::Iter<'a, T>;
2452 fn into_iter(self) -> slice::Iter<'a, T> {
2457 #[stable(feature = "rust1", since = "1.0.0")]
2458 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2459 type Item = &'a mut T;
2460 type IntoIter = slice::IterMut<'a, T>;
2462 fn into_iter(self) -> slice::IterMut<'a, T> {
2467 #[stable(feature = "rust1", since = "1.0.0")]
2468 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2470 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2471 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2475 fn extend_one(&mut self, item: T) {
2480 fn extend_reserve(&mut self, additional: usize) {
2481 self.reserve(additional);
2485 impl<T, A: Allocator> Vec<T, A> {
2486 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2487 // they have no further optimizations to apply
2488 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2489 // This is the case for a general iterator.
2491 // This function should be the moral equivalent of:
2493 // for item in iterator {
2496 while let Some(element) = iterator.next() {
2497 let len = self.len();
2498 if len == self.capacity() {
2499 let (lower, _) = iterator.size_hint();
2500 self.reserve(lower.saturating_add(1));
2503 ptr::write(self.as_mut_ptr().add(len), element);
2504 // NB can't overflow since we would have had to alloc the address space
2505 self.set_len(len + 1);
2510 /// Creates a splicing iterator that replaces the specified range in the vector
2511 /// with the given `replace_with` iterator and yields the removed items.
2512 /// `replace_with` does not need to be the same length as `range`.
2514 /// `range` is removed even if the iterator is not consumed until the end.
2516 /// It is unspecified how many elements are removed from the vector
2517 /// if the `Splice` value is leaked.
2519 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2521 /// This is optimal if:
2523 /// * The tail (elements in the vector after `range`) is empty,
2524 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2525 /// * or the lower bound of its `size_hint()` is exact.
2527 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2531 /// Panics if the starting point is greater than the end point or if
2532 /// the end point is greater than the length of the vector.
2537 /// let mut v = vec![1, 2, 3];
2538 /// let new = [7, 8];
2539 /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
2540 /// assert_eq!(v, &[7, 8, 3]);
2541 /// assert_eq!(u, &[1, 2]);
2544 #[stable(feature = "vec_splice", since = "1.21.0")]
2545 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2547 R: RangeBounds<usize>,
2548 I: IntoIterator<Item = T>,
2550 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2553 /// Creates an iterator which uses a closure to determine if an element should be removed.
2555 /// If the closure returns true, then the element is removed and yielded.
2556 /// If the closure returns false, the element will remain in the vector and will not be yielded
2557 /// by the iterator.
2559 /// Using this method is equivalent to the following code:
2562 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2563 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2565 /// while i != vec.len() {
2566 /// if some_predicate(&mut vec[i]) {
2567 /// let val = vec.remove(i);
2568 /// // your code here
2574 /// # assert_eq!(vec, vec![1, 4, 5]);
2577 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2578 /// because it can backshift the elements of the array in bulk.
2580 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2581 /// regardless of whether you choose to keep or remove it.
2585 /// Splitting an array into evens and odds, reusing the original allocation:
2588 /// #![feature(drain_filter)]
2589 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2591 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2592 /// let odds = numbers;
2594 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2595 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2597 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2598 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
2600 F: FnMut(&mut T) -> bool,
2602 let old_len = self.len();
2604 // Guard against us getting leaked (leak amplification)
2609 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2613 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2615 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2616 /// append the entire slice at once.
2618 /// [`copy_from_slice`]: slice::copy_from_slice
2619 #[stable(feature = "extend_ref", since = "1.2.0")]
2620 impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
2621 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2622 self.spec_extend(iter.into_iter())
2626 fn extend_one(&mut self, &item: &'a T) {
2631 fn extend_reserve(&mut self, additional: usize) {
2632 self.reserve(additional);
2636 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2637 #[stable(feature = "rust1", since = "1.0.0")]
2638 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
2640 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2641 PartialOrd::partial_cmp(&**self, &**other)
2645 #[stable(feature = "rust1", since = "1.0.0")]
2646 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
2648 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2649 #[stable(feature = "rust1", since = "1.0.0")]
2650 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
2652 fn cmp(&self, other: &Self) -> Ordering {
2653 Ord::cmp(&**self, &**other)
2657 #[stable(feature = "rust1", since = "1.0.0")]
2658 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
2659 fn drop(&mut self) {
2662 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2663 // could avoid questions of validity in certain cases
2664 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
2666 // RawVec handles deallocation
2670 #[stable(feature = "rust1", since = "1.0.0")]
2671 impl<T> Default for Vec<T> {
2672 /// Creates an empty `Vec<T>`.
2673 fn default() -> Vec<T> {
2678 #[stable(feature = "rust1", since = "1.0.0")]
2679 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
2680 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2681 fmt::Debug::fmt(&**self, f)
2685 #[stable(feature = "rust1", since = "1.0.0")]
2686 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
2687 fn as_ref(&self) -> &Vec<T, A> {
2692 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2693 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
2694 fn as_mut(&mut self) -> &mut Vec<T, A> {
2699 #[stable(feature = "rust1", since = "1.0.0")]
2700 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
2701 fn as_ref(&self) -> &[T] {
2706 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2707 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
2708 fn as_mut(&mut self) -> &mut [T] {
2713 #[stable(feature = "rust1", since = "1.0.0")]
2714 impl<T: Clone> From<&[T]> for Vec<T> {
2716 fn from(s: &[T]) -> Vec<T> {
2720 fn from(s: &[T]) -> Vec<T> {
2721 crate::slice::to_vec(s, Global)
2725 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2726 impl<T: Clone> From<&mut [T]> for Vec<T> {
2728 fn from(s: &mut [T]) -> Vec<T> {
2732 fn from(s: &mut [T]) -> Vec<T> {
2733 crate::slice::to_vec(s, Global)
2737 #[stable(feature = "vec_from_array", since = "1.44.0")]
2738 impl<T, const N: usize> From<[T; N]> for Vec<T> {
2740 fn from(s: [T; N]) -> Vec<T> {
2741 <[T]>::into_vec(box s)
2744 fn from(s: [T; N]) -> Vec<T> {
2745 crate::slice::into_vec(box s)
2749 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2750 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2752 [T]: ToOwned<Owned = Vec<T>>,
2754 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2759 // note: test pulls in libstd, which causes errors here
2761 #[stable(feature = "vec_from_box", since = "1.18.0")]
2762 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
2763 fn from(s: Box<[T], A>) -> Self {
2765 Self { buf: RawVec::from_box(s), len }
2769 // note: test pulls in libstd, which causes errors here
2771 #[stable(feature = "box_from_vec", since = "1.20.0")]
2772 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
2773 fn from(v: Vec<T, A>) -> Self {
2774 v.into_boxed_slice()
2778 #[stable(feature = "rust1", since = "1.0.0")]
2779 impl From<&str> for Vec<u8> {
2780 fn from(s: &str) -> Vec<u8> {
2781 From::from(s.as_bytes())
2785 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
2786 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
2787 type Error = Vec<T, A>;
2789 /// Gets the entire contents of the `Vec<T>` as an array,
2790 /// if its size exactly matches that of the requested array.
2795 /// use std::convert::TryInto;
2796 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
2797 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
2800 /// If the length doesn't match, the input comes back in `Err`:
2802 /// use std::convert::TryInto;
2803 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
2804 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
2807 /// If you're fine with just getting a prefix of the `Vec<T>`,
2808 /// you can call [`.truncate(N)`](Vec::truncate) first.
2810 /// use std::convert::TryInto;
2811 /// let mut v = String::from("hello world").into_bytes();
2814 /// let [a, b]: [_; 2] = v.try_into().unwrap();
2815 /// assert_eq!(a, b' ');
2816 /// assert_eq!(b, b'd');
2818 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
2823 // SAFETY: `.set_len(0)` is always sound.
2824 unsafe { vec.set_len(0) };
2826 // SAFETY: A `Vec`'s pointer is always aligned properly, and
2827 // the alignment the array needs is the same as the items.
2828 // We checked earlier that we have sufficient items.
2829 // The items will not double-drop as the `set_len`
2830 // tells the `Vec` not to also drop them.
2831 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };