1 //! A contiguous growable array type with heap-allocated contents, written
4 //! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
5 //! `O(1)` pop (from the end).
7 //! Vectors ensure they never allocate more than `isize::MAX` bytes.
11 //! You can explicitly create a [`Vec`] with [`Vec::new`]:
14 //! let v: Vec<i32> = Vec::new();
17 //! ...or by using the [`vec!`] macro:
20 //! let v: Vec<i32> = vec![];
22 //! let v = vec![1, 2, 3, 4, 5];
24 //! let v = vec![0; 10]; // ten zeroes
27 //! You can [`push`] values onto the end of a vector (which will grow the vector
31 //! let mut v = vec![1, 2];
36 //! Popping values works in much the same way:
39 //! let mut v = vec![1, 2];
41 //! let two = v.pop();
44 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
47 //! let mut v = vec![1, 2, 3];
52 //! [`push`]: Vec::push
54 #![stable(feature = "rust1", since = "1.0.0")]
56 #[cfg(not(no_global_oom_handling))]
58 use core::cmp::Ordering;
59 use core::convert::TryFrom;
61 use core::hash::{Hash, Hasher};
62 use core::intrinsics::{arith_offset, assume};
64 #[cfg(not(no_global_oom_handling))]
65 use core::iter::FromIterator;
66 use core::marker::PhantomData;
67 use core::mem::{self, ManuallyDrop, MaybeUninit};
68 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
69 use core::ptr::{self, NonNull};
70 use core::slice::{self, SliceIndex};
72 use crate::alloc::{Allocator, Global};
73 use crate::borrow::{Cow, ToOwned};
74 use crate::boxed::Box;
75 use crate::collections::TryReserveError;
76 use crate::raw_vec::RawVec;
78 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
79 pub use self::drain_filter::DrainFilter;
83 #[cfg(not(no_global_oom_handling))]
84 #[stable(feature = "vec_splice", since = "1.21.0")]
85 pub use self::splice::Splice;
87 #[cfg(not(no_global_oom_handling))]
90 #[stable(feature = "drain", since = "1.6.0")]
91 pub use self::drain::Drain;
95 #[cfg(not(no_global_oom_handling))]
98 #[cfg(not(no_global_oom_handling))]
99 pub(crate) use self::into_iter::AsIntoIter;
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 source_iter_marker;
115 #[cfg(not(no_global_oom_handling))]
116 use self::spec_from_elem::SpecFromElem;
118 #[cfg(not(no_global_oom_handling))]
121 #[cfg(not(no_global_oom_handling))]
122 use self::set_len_on_drop::SetLenOnDrop;
124 #[cfg(not(no_global_oom_handling))]
127 #[cfg(not(no_global_oom_handling))]
128 use self::in_place_drop::InPlaceDrop;
130 #[cfg(not(no_global_oom_handling))]
133 #[cfg(not(no_global_oom_handling))]
134 use self::spec_from_iter_nested::SpecFromIterNested;
136 #[cfg(not(no_global_oom_handling))]
137 mod spec_from_iter_nested;
139 #[cfg(not(no_global_oom_handling))]
140 use self::spec_from_iter::SpecFromIter;
142 #[cfg(not(no_global_oom_handling))]
145 #[cfg(not(no_global_oom_handling))]
146 use self::spec_extend::SpecExtend;
148 #[cfg(not(no_global_oom_handling))]
151 /// A contiguous growable array type, written as `Vec<T>` and pronounced 'vector'.
156 /// let mut vec = Vec::new();
160 /// assert_eq!(vec.len(), 2);
161 /// assert_eq!(vec[0], 1);
163 /// assert_eq!(vec.pop(), Some(2));
164 /// assert_eq!(vec.len(), 1);
167 /// assert_eq!(vec[0], 7);
169 /// vec.extend([1, 2, 3].iter().copied());
172 /// println!("{}", x);
174 /// assert_eq!(vec, [7, 1, 2, 3]);
177 /// The [`vec!`] macro is provided to make initialization more convenient:
180 /// let mut vec = vec![1, 2, 3];
182 /// assert_eq!(vec, [1, 2, 3, 4]);
185 /// It can also initialize each element of a `Vec<T>` with a given value.
186 /// This may be more efficient than performing allocation and initialization
187 /// in separate steps, especially when initializing a vector of zeros:
190 /// let vec = vec![0; 5];
191 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
193 /// // The following is equivalent, but potentially slower:
194 /// let mut vec = Vec::with_capacity(5);
195 /// vec.resize(5, 0);
196 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
199 /// For more information, see
200 /// [Capacity and Reallocation](#capacity-and-reallocation).
202 /// Use a `Vec<T>` as an efficient stack:
205 /// let mut stack = Vec::new();
211 /// while let Some(top) = stack.pop() {
212 /// // Prints 3, 2, 1
213 /// println!("{}", top);
219 /// The `Vec` type allows to access values by index, because it implements the
220 /// [`Index`] trait. An example will be more explicit:
223 /// let v = vec![0, 2, 4, 6];
224 /// println!("{}", v[1]); // it will display '2'
227 /// However be careful: if you try to access an index which isn't in the `Vec`,
228 /// your software will panic! You cannot do this:
231 /// let v = vec![0, 2, 4, 6];
232 /// println!("{}", v[6]); // it will panic!
235 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
240 /// A `Vec` can be mutable. On the other hand, slices are read-only objects.
241 /// To get a [slice][prim@slice], use [`&`]. Example:
244 /// fn read_slice(slice: &[usize]) {
248 /// let v = vec![0, 1];
251 /// // ... and that's all!
252 /// // you can also do it like this:
253 /// let u: &[usize] = &v;
255 /// let u: &[_] = &v;
258 /// In Rust, it's more common to pass slices as arguments rather than vectors
259 /// when you just want to provide read access. The same goes for [`String`] and
262 /// # Capacity and reallocation
264 /// The capacity of a vector is the amount of space allocated for any future
265 /// elements that will be added onto the vector. This is not to be confused with
266 /// the *length* of a vector, which specifies the number of actual elements
267 /// within the vector. If a vector's length exceeds its capacity, its capacity
268 /// will automatically be increased, but its elements will have to be
271 /// For example, a vector with capacity 10 and length 0 would be an empty vector
272 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
273 /// vector will not change its capacity or cause reallocation to occur. However,
274 /// if the vector's length is increased to 11, it will have to reallocate, which
275 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
276 /// whenever possible to specify how big the vector is expected to get.
280 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
281 /// about its design. This ensures that it's as low-overhead as possible in
282 /// the general case, and can be correctly manipulated in primitive ways
283 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
284 /// If additional type parameters are added (e.g., to support custom allocators),
285 /// overriding their defaults may change the behavior.
287 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
288 /// triplet. No more, no less. The order of these fields is completely
289 /// unspecified, and you should use the appropriate methods to modify these.
290 /// The pointer will never be null, so this type is null-pointer-optimized.
292 /// However, the pointer might not actually point to allocated memory. In particular,
293 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
294 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
295 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
296 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
297 /// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
298 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
299 /// details are very subtle — if you intend to allocate memory using a `Vec`
300 /// and use it for something else (either to pass to unsafe code, or to build your
301 /// own memory-backed collection), be sure to deallocate this memory by using
302 /// `from_raw_parts` to recover the `Vec` and then dropping it.
304 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
305 /// (as defined by the allocator Rust is configured to use by default), and its
306 /// pointer points to [`len`] initialized, contiguous elements in order (what
307 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
308 /// `[`len`] logically uninitialized, contiguous elements.
310 /// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
311 /// visualized as below. The top part is the `Vec` struct, it contains a
312 /// pointer to the head of the allocation in the heap, length and capacity.
313 /// The bottom part is the allocation on the heap, a contiguous memory block.
317 /// +--------+--------+--------+
318 /// | 0x0123 | 2 | 4 |
319 /// +--------+--------+--------+
322 /// Heap +--------+--------+--------+--------+
323 /// | 'a' | 'b' | uninit | uninit |
324 /// +--------+--------+--------+--------+
327 /// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
328 /// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
329 /// layout (including the order of fields).
331 /// `Vec` will never perform a "small optimization" where elements are actually
332 /// stored on the stack for two reasons:
334 /// * It would make it more difficult for unsafe code to correctly manipulate
335 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
336 /// only moved, and it would be more difficult to determine if a `Vec` had
337 /// actually allocated memory.
339 /// * It would penalize the general case, incurring an additional branch
342 /// `Vec` will never automatically shrink itself, even if completely empty. This
343 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
344 /// and then filling it back up to the same [`len`] should incur no calls to
345 /// the allocator. If you wish to free up unused memory, use
346 /// [`shrink_to_fit`] or [`shrink_to`].
348 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
349 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
350 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
351 /// accurate, and can be relied on. It can even be used to manually free the memory
352 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
353 /// when not necessary.
355 /// `Vec` does not guarantee any particular growth strategy when reallocating
356 /// when full, nor when [`reserve`] is called. The current strategy is basic
357 /// and it may prove desirable to use a non-constant growth factor. Whatever
358 /// strategy is used will of course guarantee *O*(1) amortized [`push`].
360 /// `vec![x; n]`, `vec![a, b, c, d]`, and
361 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
362 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
363 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
364 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
366 /// `Vec` will not specifically overwrite any data that is removed from it,
367 /// but also won't specifically preserve it. Its uninitialized memory is
368 /// scratch space that it may use however it wants. It will generally just do
369 /// whatever is most efficient or otherwise easy to implement. Do not rely on
370 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
371 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
372 /// first, that might not actually happen because the optimizer does not consider
373 /// this a side-effect that must be preserved. There is one case which we will
374 /// not break, however: using `unsafe` code to write to the excess capacity,
375 /// and then increasing the length to match, is always valid.
377 /// Currently, `Vec` does not guarantee the order in which elements are dropped.
378 /// The order has changed in the past and may change again.
380 /// [`get`]: ../../std/vec/struct.Vec.html#method.get
381 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
382 /// [`String`]: crate::string::String
383 /// [`&str`]: type@str
384 /// [`shrink_to_fit`]: Vec::shrink_to_fit
385 /// [`shrink_to`]: Vec::shrink_to
386 /// [`capacity`]: Vec::capacity
387 /// [`mem::size_of::<T>`]: core::mem::size_of
388 /// [`len`]: Vec::len
389 /// [`push`]: Vec::push
390 /// [`insert`]: Vec::insert
391 /// [`reserve`]: Vec::reserve
392 /// [`MaybeUninit`]: core::mem::MaybeUninit
393 /// [owned slice]: Box
394 #[stable(feature = "rust1", since = "1.0.0")]
395 #[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")]
396 pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
401 ////////////////////////////////////////////////////////////////////////////////
403 ////////////////////////////////////////////////////////////////////////////////
406 /// Constructs a new, empty `Vec<T>`.
408 /// The vector will not allocate until elements are pushed onto it.
413 /// # #![allow(unused_mut)]
414 /// let mut vec: Vec<i32> = Vec::new();
417 #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
418 #[stable(feature = "rust1", since = "1.0.0")]
419 pub const fn new() -> Self {
420 Vec { buf: RawVec::NEW, len: 0 }
423 /// Constructs a new, empty `Vec<T>` with the specified capacity.
425 /// The vector will be able to hold exactly `capacity` elements without
426 /// reallocating. If `capacity` is 0, the vector will not allocate.
428 /// It is important to note that although the returned vector has the
429 /// *capacity* specified, the vector will have a zero *length*. For an
430 /// explanation of the difference between length and capacity, see
431 /// *[Capacity and reallocation]*.
433 /// [Capacity and reallocation]: #capacity-and-reallocation
437 /// Panics if the new capacity exceeds `isize::MAX` bytes.
442 /// let mut vec = Vec::with_capacity(10);
444 /// // The vector contains no items, even though it has capacity for more
445 /// assert_eq!(vec.len(), 0);
446 /// assert_eq!(vec.capacity(), 10);
448 /// // These are all done without reallocating...
452 /// assert_eq!(vec.len(), 10);
453 /// assert_eq!(vec.capacity(), 10);
455 /// // ...but this may make the vector reallocate
457 /// assert_eq!(vec.len(), 11);
458 /// assert!(vec.capacity() >= 11);
460 #[cfg(not(no_global_oom_handling))]
462 #[doc(alias = "malloc")]
463 #[stable(feature = "rust1", since = "1.0.0")]
464 pub fn with_capacity(capacity: usize) -> Self {
465 Self::with_capacity_in(capacity, Global)
468 /// Creates a `Vec<T>` directly from the raw components of another vector.
472 /// This is highly unsafe, due to the number of invariants that aren't
475 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
476 /// (at least, it's highly likely to be incorrect if it wasn't).
477 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
478 /// (`T` having a less strict alignment is not sufficient, the alignment really
479 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
480 /// allocated and deallocated with the same layout.)
481 /// * `length` needs to be less than or equal to `capacity`.
482 /// * `capacity` needs to be the capacity that the pointer was allocated with.
484 /// Violating these may cause problems like corrupting the allocator's
485 /// internal data structures. For example it is **not** safe
486 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
487 /// It's also not safe to build one from a `Vec<u16>` and its length, because
488 /// the allocator cares about the alignment, and these two types have different
489 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
490 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
492 /// The ownership of `ptr` is effectively transferred to the
493 /// `Vec<T>` which may then deallocate, reallocate or change the
494 /// contents of memory pointed to by the pointer at will. Ensure
495 /// that nothing else uses the pointer after calling this
498 /// [`String`]: crate::string::String
499 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
507 /// let v = vec![1, 2, 3];
509 // FIXME Update this when vec_into_raw_parts is stabilized
510 /// // Prevent running `v`'s destructor so we are in complete control
511 /// // of the allocation.
512 /// let mut v = mem::ManuallyDrop::new(v);
514 /// // Pull out the various important pieces of information about `v`
515 /// let p = v.as_mut_ptr();
516 /// let len = v.len();
517 /// let cap = v.capacity();
520 /// // Overwrite memory with 4, 5, 6
521 /// for i in 0..len as isize {
522 /// ptr::write(p.offset(i), 4 + i);
525 /// // Put everything back together into a Vec
526 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
527 /// assert_eq!(rebuilt, [4, 5, 6]);
531 #[stable(feature = "rust1", since = "1.0.0")]
532 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
533 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
537 impl<T, A: Allocator> Vec<T, A> {
538 /// Constructs a new, empty `Vec<T, A>`.
540 /// The vector will not allocate until elements are pushed onto it.
545 /// #![feature(allocator_api)]
547 /// use std::alloc::System;
549 /// # #[allow(unused_mut)]
550 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
553 #[unstable(feature = "allocator_api", issue = "32838")]
554 pub const fn new_in(alloc: A) -> Self {
555 Vec { buf: RawVec::new_in(alloc), len: 0 }
558 /// Constructs a new, empty `Vec<T, A>` with the specified capacity with the provided
561 /// The vector will be able to hold exactly `capacity` elements without
562 /// reallocating. If `capacity` is 0, the vector will not allocate.
564 /// It is important to note that although the returned vector has the
565 /// *capacity* specified, the vector will have a zero *length*. For an
566 /// explanation of the difference between length and capacity, see
567 /// *[Capacity and reallocation]*.
569 /// [Capacity and reallocation]: #capacity-and-reallocation
573 /// Panics if the new capacity exceeds `isize::MAX` bytes.
578 /// #![feature(allocator_api)]
580 /// use std::alloc::System;
582 /// let mut vec = Vec::with_capacity_in(10, System);
584 /// // The vector contains no items, even though it has capacity for more
585 /// assert_eq!(vec.len(), 0);
586 /// assert_eq!(vec.capacity(), 10);
588 /// // These are all done without reallocating...
592 /// assert_eq!(vec.len(), 10);
593 /// assert_eq!(vec.capacity(), 10);
595 /// // ...but this may make the vector reallocate
597 /// assert_eq!(vec.len(), 11);
598 /// assert!(vec.capacity() >= 11);
600 #[cfg(not(no_global_oom_handling))]
602 #[unstable(feature = "allocator_api", issue = "32838")]
603 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
604 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
607 /// Creates a `Vec<T, A>` directly from the raw components of another vector.
611 /// This is highly unsafe, due to the number of invariants that aren't
614 /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
615 /// (at least, it's highly likely to be incorrect if it wasn't).
616 /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
617 /// (`T` having a less strict alignment is not sufficient, the alignment really
618 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
619 /// allocated and deallocated with the same layout.)
620 /// * `length` needs to be less than or equal to `capacity`.
621 /// * `capacity` needs to be the capacity that the pointer was allocated with.
623 /// Violating these may cause problems like corrupting the allocator's
624 /// internal data structures. For example it is **not** safe
625 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
626 /// It's also not safe to build one from a `Vec<u16>` and its length, because
627 /// the allocator cares about the alignment, and these two types have different
628 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
629 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
631 /// The ownership of `ptr` is effectively transferred to the
632 /// `Vec<T>` which may then deallocate, reallocate or change the
633 /// contents of memory pointed to by the pointer at will. Ensure
634 /// that nothing else uses the pointer after calling this
637 /// [`String`]: crate::string::String
638 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
643 /// #![feature(allocator_api)]
645 /// use std::alloc::System;
650 /// let mut v = Vec::with_capacity_in(3, System);
655 // FIXME Update this when vec_into_raw_parts is stabilized
656 /// // Prevent running `v`'s destructor so we are in complete control
657 /// // of the allocation.
658 /// let mut v = mem::ManuallyDrop::new(v);
660 /// // Pull out the various important pieces of information about `v`
661 /// let p = v.as_mut_ptr();
662 /// let len = v.len();
663 /// let cap = v.capacity();
664 /// let alloc = v.allocator();
667 /// // Overwrite memory with 4, 5, 6
668 /// for i in 0..len as isize {
669 /// ptr::write(p.offset(i), 4 + i);
672 /// // Put everything back together into a Vec
673 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
674 /// assert_eq!(rebuilt, [4, 5, 6]);
678 #[unstable(feature = "allocator_api", issue = "32838")]
679 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
680 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
683 /// Decomposes a `Vec<T>` into its raw components.
685 /// Returns the raw pointer to the underlying data, the length of
686 /// the vector (in elements), and the allocated capacity of the
687 /// data (in elements). These are the same arguments in the same
688 /// order as the arguments to [`from_raw_parts`].
690 /// After calling this function, the caller is responsible for the
691 /// memory previously managed by the `Vec`. The only way to do
692 /// this is to convert the raw pointer, length, and capacity back
693 /// into a `Vec` with the [`from_raw_parts`] function, allowing
694 /// the destructor to perform the cleanup.
696 /// [`from_raw_parts`]: Vec::from_raw_parts
701 /// #![feature(vec_into_raw_parts)]
702 /// let v: Vec<i32> = vec![-1, 0, 1];
704 /// let (ptr, len, cap) = v.into_raw_parts();
706 /// let rebuilt = unsafe {
707 /// // We can now make changes to the components, such as
708 /// // transmuting the raw pointer to a compatible type.
709 /// let ptr = ptr as *mut u32;
711 /// Vec::from_raw_parts(ptr, len, cap)
713 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
715 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
716 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
717 let mut me = ManuallyDrop::new(self);
718 (me.as_mut_ptr(), me.len(), me.capacity())
721 /// Decomposes a `Vec<T>` into its raw components.
723 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
724 /// the allocated capacity of the data (in elements), and the allocator. These are the same
725 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
727 /// After calling this function, the caller is responsible for the
728 /// memory previously managed by the `Vec`. The only way to do
729 /// this is to convert the raw pointer, length, and capacity back
730 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
731 /// the destructor to perform the cleanup.
733 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
738 /// #![feature(allocator_api, vec_into_raw_parts)]
740 /// use std::alloc::System;
742 /// let mut v: Vec<i32, System> = Vec::new_in(System);
747 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
749 /// let rebuilt = unsafe {
750 /// // We can now make changes to the components, such as
751 /// // transmuting the raw pointer to a compatible type.
752 /// let ptr = ptr as *mut u32;
754 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
756 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
758 #[unstable(feature = "allocator_api", issue = "32838")]
759 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
760 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
761 let mut me = ManuallyDrop::new(self);
763 let capacity = me.capacity();
764 let ptr = me.as_mut_ptr();
765 let alloc = unsafe { ptr::read(me.allocator()) };
766 (ptr, len, capacity, alloc)
769 /// Returns the number of elements the vector can hold without
775 /// let vec: Vec<i32> = Vec::with_capacity(10);
776 /// assert_eq!(vec.capacity(), 10);
779 #[stable(feature = "rust1", since = "1.0.0")]
780 pub fn capacity(&self) -> usize {
784 /// Reserves capacity for at least `additional` more elements to be inserted
785 /// in the given `Vec<T>`. The collection may reserve more space to avoid
786 /// frequent reallocations. After calling `reserve`, capacity will be
787 /// greater than or equal to `self.len() + additional`. Does nothing if
788 /// capacity is already sufficient.
792 /// Panics if the new capacity exceeds `isize::MAX` bytes.
797 /// let mut vec = vec![1];
799 /// assert!(vec.capacity() >= 11);
801 #[cfg(not(no_global_oom_handling))]
802 #[doc(alias = "realloc")]
803 #[stable(feature = "rust1", since = "1.0.0")]
804 pub fn reserve(&mut self, additional: usize) {
805 self.buf.reserve(self.len, additional);
808 /// Reserves the minimum capacity for exactly `additional` more elements to
809 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
810 /// capacity will be greater than or equal to `self.len() + additional`.
811 /// Does nothing if the capacity is already sufficient.
813 /// Note that the allocator may give the collection more space than it
814 /// requests. Therefore, capacity can not be relied upon to be precisely
815 /// minimal. Prefer `reserve` if future insertions are expected.
819 /// Panics if the new capacity overflows `usize`.
824 /// let mut vec = vec![1];
825 /// vec.reserve_exact(10);
826 /// assert!(vec.capacity() >= 11);
828 #[cfg(not(no_global_oom_handling))]
829 #[doc(alias = "realloc")]
830 #[stable(feature = "rust1", since = "1.0.0")]
831 pub fn reserve_exact(&mut self, additional: usize) {
832 self.buf.reserve_exact(self.len, additional);
835 /// Tries to reserve capacity for at least `additional` more elements to be inserted
836 /// in the given `Vec<T>`. The collection may reserve more space to avoid
837 /// frequent reallocations. After calling `try_reserve`, capacity will be
838 /// greater than or equal to `self.len() + additional`. Does nothing if
839 /// capacity is already sufficient.
843 /// If the capacity overflows, or the allocator reports a failure, then an error
849 /// #![feature(try_reserve)]
850 /// use std::collections::TryReserveError;
852 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
853 /// let mut output = Vec::new();
855 /// // Pre-reserve the memory, exiting if we can't
856 /// output.try_reserve(data.len())?;
858 /// // Now we know this can't OOM in the middle of our complex work
859 /// output.extend(data.iter().map(|&val| {
860 /// val * 2 + 5 // very complicated
865 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
867 #[doc(alias = "realloc")]
868 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
869 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
870 self.buf.try_reserve(self.len, additional)
873 /// Tries to reserve the minimum capacity for exactly `additional`
874 /// elements to be inserted in the given `Vec<T>`. After calling
875 /// `try_reserve_exact`, capacity will be greater than or equal to
876 /// `self.len() + additional` if it returns `Ok(())`.
877 /// Does nothing if the capacity is already sufficient.
879 /// Note that the allocator may give the collection more space than it
880 /// requests. Therefore, capacity can not be relied upon to be precisely
881 /// minimal. Prefer `reserve` if future insertions are expected.
885 /// If the capacity overflows, or the allocator reports a failure, then an error
891 /// #![feature(try_reserve)]
892 /// use std::collections::TryReserveError;
894 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
895 /// let mut output = Vec::new();
897 /// // Pre-reserve the memory, exiting if we can't
898 /// output.try_reserve_exact(data.len())?;
900 /// // Now we know this can't OOM in the middle of our complex work
901 /// output.extend(data.iter().map(|&val| {
902 /// val * 2 + 5 // very complicated
907 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
909 #[doc(alias = "realloc")]
910 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
911 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
912 self.buf.try_reserve_exact(self.len, additional)
915 /// Shrinks the capacity of the vector as much as possible.
917 /// It will drop down as close as possible to the length but the allocator
918 /// may still inform the vector that there is space for a few more elements.
923 /// let mut vec = Vec::with_capacity(10);
924 /// vec.extend([1, 2, 3]);
925 /// assert_eq!(vec.capacity(), 10);
926 /// vec.shrink_to_fit();
927 /// assert!(vec.capacity() >= 3);
929 #[cfg(not(no_global_oom_handling))]
930 #[doc(alias = "realloc")]
931 #[stable(feature = "rust1", since = "1.0.0")]
932 pub fn shrink_to_fit(&mut self) {
933 // The capacity is never less than the length, and there's nothing to do when
934 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
935 // by only calling it with a greater capacity.
936 if self.capacity() > self.len {
937 self.buf.shrink_to_fit(self.len);
941 /// Shrinks the capacity of the vector with a lower bound.
943 /// The capacity will remain at least as large as both the length
944 /// and the supplied value.
946 /// If the current capacity is less than the lower limit, this is a no-op.
951 /// #![feature(shrink_to)]
952 /// let mut vec = Vec::with_capacity(10);
953 /// vec.extend([1, 2, 3]);
954 /// assert_eq!(vec.capacity(), 10);
955 /// vec.shrink_to(4);
956 /// assert!(vec.capacity() >= 4);
957 /// vec.shrink_to(0);
958 /// assert!(vec.capacity() >= 3);
960 #[cfg(not(no_global_oom_handling))]
961 #[doc(alias = "realloc")]
962 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
963 pub fn shrink_to(&mut self, min_capacity: usize) {
964 if self.capacity() > min_capacity {
965 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
969 /// Converts the vector into [`Box<[T]>`][owned slice].
971 /// Note that this will drop any excess capacity.
973 /// [owned slice]: Box
978 /// let v = vec![1, 2, 3];
980 /// let slice = v.into_boxed_slice();
983 /// Any excess capacity is removed:
986 /// let mut vec = Vec::with_capacity(10);
987 /// vec.extend([1, 2, 3]);
989 /// assert_eq!(vec.capacity(), 10);
990 /// let slice = vec.into_boxed_slice();
991 /// assert_eq!(slice.into_vec().capacity(), 3);
993 #[cfg(not(no_global_oom_handling))]
994 #[stable(feature = "rust1", since = "1.0.0")]
995 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
997 self.shrink_to_fit();
998 let me = ManuallyDrop::new(self);
999 let buf = ptr::read(&me.buf);
1001 buf.into_box(len).assume_init()
1005 /// Shortens the vector, keeping the first `len` elements and dropping
1008 /// If `len` is greater than the vector's current length, this has no
1011 /// The [`drain`] method can emulate `truncate`, but causes the excess
1012 /// elements to be returned instead of dropped.
1014 /// Note that this method has no effect on the allocated capacity
1019 /// Truncating a five element vector to two elements:
1022 /// let mut vec = vec![1, 2, 3, 4, 5];
1023 /// vec.truncate(2);
1024 /// assert_eq!(vec, [1, 2]);
1027 /// No truncation occurs when `len` is greater than the vector's current
1031 /// let mut vec = vec![1, 2, 3];
1032 /// vec.truncate(8);
1033 /// assert_eq!(vec, [1, 2, 3]);
1036 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1040 /// let mut vec = vec![1, 2, 3];
1041 /// vec.truncate(0);
1042 /// assert_eq!(vec, []);
1045 /// [`clear`]: Vec::clear
1046 /// [`drain`]: Vec::drain
1047 #[stable(feature = "rust1", since = "1.0.0")]
1048 pub fn truncate(&mut self, len: usize) {
1049 // This is safe because:
1051 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1052 // case avoids creating an invalid slice, and
1053 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1054 // such that no value will be dropped twice in case `drop_in_place`
1055 // were to panic once (if it panics twice, the program aborts).
1057 // Note: It's intentional that this is `>` and not `>=`.
1058 // Changing it to `>=` has negative performance
1059 // implications in some cases. See #78884 for more.
1063 let remaining_len = self.len - len;
1064 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1066 ptr::drop_in_place(s);
1070 /// Extracts a slice containing the entire vector.
1072 /// Equivalent to `&s[..]`.
1077 /// use std::io::{self, Write};
1078 /// let buffer = vec![1, 2, 3, 5, 8];
1079 /// io::sink().write(buffer.as_slice()).unwrap();
1082 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1083 pub fn as_slice(&self) -> &[T] {
1087 /// Extracts a mutable slice of the entire vector.
1089 /// Equivalent to `&mut s[..]`.
1094 /// use std::io::{self, Read};
1095 /// let mut buffer = vec![0; 3];
1096 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1099 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1100 pub fn as_mut_slice(&mut self) -> &mut [T] {
1104 /// Returns a raw 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.
1111 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1112 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1113 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1118 /// let x = vec![1, 2, 4];
1119 /// let x_ptr = x.as_ptr();
1122 /// for i in 0..x.len() {
1123 /// assert_eq!(*x_ptr.add(i), 1 << i);
1128 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1129 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1131 pub fn as_ptr(&self) -> *const T {
1132 // We shadow the slice method of the same name to avoid going through
1133 // `deref`, which creates an intermediate reference.
1134 let ptr = self.buf.ptr();
1136 assume(!ptr.is_null());
1141 /// Returns an unsafe mutable pointer to the vector's buffer.
1143 /// The caller must ensure that the vector outlives the pointer this
1144 /// function returns, or else it will end up pointing to garbage.
1145 /// Modifying the vector may cause its buffer to be reallocated,
1146 /// which would also make any pointers to it invalid.
1151 /// // Allocate vector big enough for 4 elements.
1153 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1154 /// let x_ptr = x.as_mut_ptr();
1156 /// // Initialize elements via raw pointer writes, then set length.
1158 /// for i in 0..size {
1159 /// *x_ptr.add(i) = i as i32;
1161 /// x.set_len(size);
1163 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1165 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1167 pub fn as_mut_ptr(&mut self) -> *mut T {
1168 // We shadow the slice method of the same name to avoid going through
1169 // `deref_mut`, which creates an intermediate reference.
1170 let ptr = self.buf.ptr();
1172 assume(!ptr.is_null());
1177 /// Returns a reference to the underlying allocator.
1178 #[unstable(feature = "allocator_api", issue = "32838")]
1180 pub fn allocator(&self) -> &A {
1181 self.buf.allocator()
1184 /// Forces the length of the vector to `new_len`.
1186 /// This is a low-level operation that maintains none of the normal
1187 /// invariants of the type. Normally changing the length of a vector
1188 /// is done using one of the safe operations instead, such as
1189 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1191 /// [`truncate`]: Vec::truncate
1192 /// [`resize`]: Vec::resize
1193 /// [`extend`]: Extend::extend
1194 /// [`clear`]: Vec::clear
1198 /// - `new_len` must be less than or equal to [`capacity()`].
1199 /// - The elements at `old_len..new_len` must be initialized.
1201 /// [`capacity()`]: Vec::capacity
1205 /// This method can be useful for situations in which the vector
1206 /// is serving as a buffer for other code, particularly over FFI:
1209 /// # #![allow(dead_code)]
1210 /// # // This is just a minimal skeleton for the doc example;
1211 /// # // don't use this as a starting point for a real library.
1212 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1213 /// # const Z_OK: i32 = 0;
1215 /// # fn deflateGetDictionary(
1216 /// # strm: *mut std::ffi::c_void,
1217 /// # dictionary: *mut u8,
1218 /// # dictLength: *mut usize,
1221 /// # impl StreamWrapper {
1222 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1223 /// // Per the FFI method's docs, "32768 bytes is always enough".
1224 /// let mut dict = Vec::with_capacity(32_768);
1225 /// let mut dict_length = 0;
1226 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1227 /// // 1. `dict_length` elements were initialized.
1228 /// // 2. `dict_length` <= the capacity (32_768)
1229 /// // which makes `set_len` safe to call.
1231 /// // Make the FFI call...
1232 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1234 /// // ...and update the length to what was initialized.
1235 /// dict.set_len(dict_length);
1245 /// While the following example is sound, there is a memory leak since
1246 /// the inner vectors were not freed prior to the `set_len` call:
1249 /// let mut vec = vec![vec![1, 0, 0],
1253 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1254 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1260 /// Normally, here, one would use [`clear`] instead to correctly drop
1261 /// the contents and thus not leak memory.
1263 #[stable(feature = "rust1", since = "1.0.0")]
1264 pub unsafe fn set_len(&mut self, new_len: usize) {
1265 debug_assert!(new_len <= self.capacity());
1270 /// Removes an element from the vector and returns it.
1272 /// The removed element is replaced by the last element of the vector.
1274 /// This does not preserve ordering, but is O(1).
1278 /// Panics if `index` is out of bounds.
1283 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1285 /// assert_eq!(v.swap_remove(1), "bar");
1286 /// assert_eq!(v, ["foo", "qux", "baz"]);
1288 /// assert_eq!(v.swap_remove(0), "foo");
1289 /// assert_eq!(v, ["baz", "qux"]);
1292 #[stable(feature = "rust1", since = "1.0.0")]
1293 pub fn swap_remove(&mut self, index: usize) -> T {
1296 fn assert_failed(index: usize, len: usize) -> ! {
1297 panic!("swap_remove index (is {}) should be < len (is {})", index, len);
1300 let len = self.len();
1302 assert_failed(index, len);
1305 // We replace self[index] with the last element. Note that if the
1306 // bounds check above succeeds there must be a last element (which
1307 // can be self[index] itself).
1308 let last = ptr::read(self.as_ptr().add(len - 1));
1309 let hole = self.as_mut_ptr().add(index);
1310 self.set_len(len - 1);
1311 ptr::replace(hole, last)
1315 /// Inserts an element at position `index` within the vector, shifting all
1316 /// elements after it to the right.
1320 /// Panics if `index > len`.
1325 /// let mut vec = vec![1, 2, 3];
1326 /// vec.insert(1, 4);
1327 /// assert_eq!(vec, [1, 4, 2, 3]);
1328 /// vec.insert(4, 5);
1329 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1331 #[cfg(not(no_global_oom_handling))]
1332 #[stable(feature = "rust1", since = "1.0.0")]
1333 pub fn insert(&mut self, index: usize, element: T) {
1336 fn assert_failed(index: usize, len: usize) -> ! {
1337 panic!("insertion index (is {}) should be <= len (is {})", index, len);
1340 let len = self.len();
1342 assert_failed(index, len);
1345 // space for the new element
1346 if len == self.buf.capacity() {
1352 // The spot to put the new value
1354 let p = self.as_mut_ptr().add(index);
1355 // Shift everything over to make space. (Duplicating the
1356 // `index`th element into two consecutive places.)
1357 ptr::copy(p, p.offset(1), len - index);
1358 // Write it in, overwriting the first copy of the `index`th
1360 ptr::write(p, element);
1362 self.set_len(len + 1);
1366 /// Removes and returns the element at position `index` within the vector,
1367 /// shifting all elements after it to the left.
1371 /// Panics if `index` is out of bounds.
1376 /// let mut v = vec![1, 2, 3];
1377 /// assert_eq!(v.remove(1), 2);
1378 /// assert_eq!(v, [1, 3]);
1380 #[stable(feature = "rust1", since = "1.0.0")]
1381 pub fn remove(&mut self, index: usize) -> T {
1384 fn assert_failed(index: usize, len: usize) -> ! {
1385 panic!("removal index (is {}) should be < len (is {})", index, len);
1388 let len = self.len();
1390 assert_failed(index, len);
1396 // the place we are taking from.
1397 let ptr = self.as_mut_ptr().add(index);
1398 // copy it out, unsafely having a copy of the value on
1399 // the stack and in the vector at the same time.
1400 ret = ptr::read(ptr);
1402 // Shift everything down to fill in that spot.
1403 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1405 self.set_len(len - 1);
1410 /// Retains only the elements specified by the predicate.
1412 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1413 /// This method operates in place, visiting each element exactly once in the
1414 /// original order, and preserves the order of the retained elements.
1419 /// let mut vec = vec![1, 2, 3, 4];
1420 /// vec.retain(|&x| x % 2 == 0);
1421 /// assert_eq!(vec, [2, 4]);
1424 /// Because the elements are visited exactly once in the original order,
1425 /// external state may be used to decide which elements to keep.
1428 /// let mut vec = vec![1, 2, 3, 4, 5];
1429 /// let keep = [false, true, true, false, true];
1430 /// let mut iter = keep.iter();
1431 /// vec.retain(|_| *iter.next().unwrap());
1432 /// assert_eq!(vec, [2, 3, 5]);
1434 #[stable(feature = "rust1", since = "1.0.0")]
1435 pub fn retain<F>(&mut self, mut f: F)
1437 F: FnMut(&T) -> bool,
1439 let original_len = self.len();
1440 // Avoid double drop if the drop guard is not executed,
1441 // since we may make some holes during the process.
1442 unsafe { self.set_len(0) };
1444 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1445 // |<- processed len ->| ^- next to check
1446 // |<- deleted cnt ->|
1447 // |<- original_len ->|
1448 // Kept: Elements which predicate returns true on.
1449 // Hole: Moved or dropped element slot.
1450 // Unchecked: Unchecked valid elements.
1452 // This drop guard will be invoked when predicate or `drop` of element panicked.
1453 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1454 // In cases when predicate and `drop` never panick, it will be optimized out.
1455 struct BackshiftOnDrop<'a, T, A: Allocator> {
1456 v: &'a mut Vec<T, A>,
1457 processed_len: usize,
1459 original_len: usize,
1462 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1463 fn drop(&mut self) {
1464 if self.deleted_cnt > 0 {
1465 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1468 self.v.as_ptr().add(self.processed_len),
1469 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1470 self.original_len - self.processed_len,
1474 // SAFETY: After filling holes, all items are in contiguous memory.
1476 self.v.set_len(self.original_len - self.deleted_cnt);
1481 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1483 while g.processed_len < original_len {
1484 // SAFETY: Unchecked element must be valid.
1485 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1487 // Advance early to avoid double drop if `drop_in_place` panicked.
1488 g.processed_len += 1;
1490 // SAFETY: We never touch this element again after dropped.
1491 unsafe { ptr::drop_in_place(cur) };
1492 // We already advanced the counter.
1495 if g.deleted_cnt > 0 {
1496 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1497 // We use copy for move, and never touch this element again.
1499 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1500 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1503 g.processed_len += 1;
1506 // All item are processed. This can be optimized to `set_len` by LLVM.
1510 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1513 /// If the vector is sorted, this removes all duplicates.
1518 /// let mut vec = vec![10, 20, 21, 30, 20];
1520 /// vec.dedup_by_key(|i| *i / 10);
1522 /// assert_eq!(vec, [10, 20, 30, 20]);
1524 #[stable(feature = "dedup_by", since = "1.16.0")]
1526 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1528 F: FnMut(&mut T) -> K,
1531 self.dedup_by(|a, b| key(a) == key(b))
1534 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1537 /// The `same_bucket` function is passed references to two elements from the vector and
1538 /// must determine if the elements compare equal. The elements are passed in opposite order
1539 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1541 /// If the vector is sorted, this removes all duplicates.
1546 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1548 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1550 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1552 #[stable(feature = "dedup_by", since = "1.16.0")]
1553 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1555 F: FnMut(&mut T, &mut T) -> bool,
1557 let len = self.len();
1562 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1563 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1564 /* Offset of the element we want to check if it is duplicate */
1567 /* Offset of the place where we want to place the non-duplicate
1568 * when we find it. */
1571 /* The Vec that would need correction if `same_bucket` panicked */
1572 vec: &'a mut Vec<T, A>,
1575 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1576 fn drop(&mut self) {
1577 /* This code gets executed when `same_bucket` panics */
1579 /* SAFETY: invariant guarantees that `read - write`
1580 * and `len - read` never overflow and that the copy is always
1583 let ptr = self.vec.as_mut_ptr();
1584 let len = self.vec.len();
1586 /* How many items were left when `same_bucket` paniced.
1587 * Basically vec[read..].len() */
1588 let items_left = len.wrapping_sub(self.read);
1590 /* Pointer to first item in vec[write..write+items_left] slice */
1591 let dropped_ptr = ptr.add(self.write);
1592 /* Pointer to first item in vec[read..] slice */
1593 let valid_ptr = ptr.add(self.read);
1595 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1596 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1597 ptr::copy(valid_ptr, dropped_ptr, items_left);
1599 /* How many items have been already dropped
1600 * Basically vec[read..write].len() */
1601 let dropped = self.read.wrapping_sub(self.write);
1603 self.vec.set_len(len - dropped);
1608 let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
1609 let ptr = gap.vec.as_mut_ptr();
1611 /* Drop items while going through Vec, it should be more efficient than
1612 * doing slice partition_dedup + truncate */
1614 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1615 * are always in-bounds and read_ptr never aliases prev_ptr */
1617 while gap.read < len {
1618 let read_ptr = ptr.add(gap.read);
1619 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1621 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1622 // Increase `gap.read` now since the drop may panic.
1624 /* We have found duplicate, drop it in-place */
1625 ptr::drop_in_place(read_ptr);
1627 let write_ptr = ptr.add(gap.write);
1629 /* Because `read_ptr` can be equal to `write_ptr`, we either
1630 * have to use `copy` or conditional `copy_nonoverlapping`.
1631 * Looks like the first option is faster. */
1632 ptr::copy(read_ptr, write_ptr, 1);
1634 /* We have filled that place, so go further */
1640 /* Technically we could let `gap` clean up with its Drop, but
1641 * when `same_bucket` is guaranteed to not panic, this bloats a little
1642 * the codegen, so we just do it manually */
1643 gap.vec.set_len(gap.write);
1648 /// Appends an element to the back of a collection.
1652 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1657 /// let mut vec = vec![1, 2];
1659 /// assert_eq!(vec, [1, 2, 3]);
1661 #[cfg(not(no_global_oom_handling))]
1663 #[stable(feature = "rust1", since = "1.0.0")]
1664 pub fn push(&mut self, value: T) {
1665 // This will panic or abort if we would allocate > isize::MAX bytes
1666 // or if the length increment would overflow for zero-sized types.
1667 if self.len == self.buf.capacity() {
1671 let end = self.as_mut_ptr().add(self.len);
1672 ptr::write(end, value);
1677 /// Removes the last element from a vector and returns it, or [`None`] if it
1683 /// let mut vec = vec![1, 2, 3];
1684 /// assert_eq!(vec.pop(), Some(3));
1685 /// assert_eq!(vec, [1, 2]);
1688 #[stable(feature = "rust1", since = "1.0.0")]
1689 pub fn pop(&mut self) -> Option<T> {
1695 Some(ptr::read(self.as_ptr().add(self.len())))
1700 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1704 /// Panics if the number of elements in the vector overflows a `usize`.
1709 /// let mut vec = vec![1, 2, 3];
1710 /// let mut vec2 = vec![4, 5, 6];
1711 /// vec.append(&mut vec2);
1712 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1713 /// assert_eq!(vec2, []);
1715 #[cfg(not(no_global_oom_handling))]
1717 #[stable(feature = "append", since = "1.4.0")]
1718 pub fn append(&mut self, other: &mut Self) {
1720 self.append_elements(other.as_slice() as _);
1725 /// Appends elements to `Self` from other buffer.
1726 #[cfg(not(no_global_oom_handling))]
1728 unsafe fn append_elements(&mut self, other: *const [T]) {
1729 let count = unsafe { (*other).len() };
1730 self.reserve(count);
1731 let len = self.len();
1732 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1736 /// Creates a draining iterator that removes the specified range in the vector
1737 /// and yields the removed items.
1739 /// When the iterator **is** dropped, all elements in the range are removed
1740 /// from the vector, even if the iterator was not fully consumed. If the
1741 /// iterator **is not** dropped (with [`mem::forget`] for example), it is
1742 /// unspecified how many elements are removed.
1746 /// Panics if the starting point is greater than the end point or if
1747 /// the end point is greater than the length of the vector.
1752 /// let mut v = vec![1, 2, 3];
1753 /// let u: Vec<_> = v.drain(1..).collect();
1754 /// assert_eq!(v, &[1]);
1755 /// assert_eq!(u, &[2, 3]);
1757 /// // A full range clears the vector
1759 /// assert_eq!(v, &[]);
1761 #[stable(feature = "drain", since = "1.6.0")]
1762 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1764 R: RangeBounds<usize>,
1768 // When the Drain is first created, it shortens the length of
1769 // the source vector to make sure no uninitialized or moved-from elements
1770 // are accessible at all if the Drain's destructor never gets to run.
1772 // Drain will ptr::read out the values to remove.
1773 // When finished, remaining tail of the vec is copied back to cover
1774 // the hole, and the vector length is restored to the new length.
1776 let len = self.len();
1777 let Range { start, end } = slice::range(range, ..len);
1780 // set self.vec length's to start, to be safe in case Drain is leaked
1781 self.set_len(start);
1782 // Use the borrow in the IterMut to indicate borrowing behavior of the
1783 // whole Drain iterator (like &mut T).
1784 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1787 tail_len: len - end,
1788 iter: range_slice.iter(),
1789 vec: NonNull::from(self),
1794 /// Clears the vector, removing all values.
1796 /// Note that this method has no effect on the allocated capacity
1802 /// let mut v = vec![1, 2, 3];
1806 /// assert!(v.is_empty());
1809 #[stable(feature = "rust1", since = "1.0.0")]
1810 pub fn clear(&mut self) {
1814 /// Returns the number of elements in the vector, also referred to
1815 /// as its 'length'.
1820 /// let a = vec![1, 2, 3];
1821 /// assert_eq!(a.len(), 3);
1823 #[doc(alias = "length")]
1825 #[stable(feature = "rust1", since = "1.0.0")]
1826 pub fn len(&self) -> usize {
1830 /// Returns `true` if the vector contains no elements.
1835 /// let mut v = Vec::new();
1836 /// assert!(v.is_empty());
1839 /// assert!(!v.is_empty());
1841 #[stable(feature = "rust1", since = "1.0.0")]
1842 pub fn is_empty(&self) -> bool {
1846 /// Splits the collection into two at the given index.
1848 /// Returns a newly allocated vector containing the elements in the range
1849 /// `[at, len)`. After the call, the original vector will be left containing
1850 /// the elements `[0, at)` with its previous capacity unchanged.
1854 /// Panics if `at > len`.
1859 /// let mut vec = vec![1, 2, 3];
1860 /// let vec2 = vec.split_off(1);
1861 /// assert_eq!(vec, [1]);
1862 /// assert_eq!(vec2, [2, 3]);
1864 #[cfg(not(no_global_oom_handling))]
1866 #[must_use = "use `.truncate()` if you don't need the other half"]
1867 #[stable(feature = "split_off", since = "1.4.0")]
1868 pub fn split_off(&mut self, at: usize) -> Self
1874 fn assert_failed(at: usize, len: usize) -> ! {
1875 panic!("`at` split index (is {}) should be <= len (is {})", at, len);
1878 if at > self.len() {
1879 assert_failed(at, self.len());
1883 // the new vector can take over the original buffer and avoid the copy
1884 return mem::replace(
1886 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
1890 let other_len = self.len - at;
1891 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
1893 // Unsafely `set_len` and copy items to `other`.
1896 other.set_len(other_len);
1898 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1903 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1905 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1906 /// difference, with each additional slot filled with the result of
1907 /// calling the closure `f`. The return values from `f` will end up
1908 /// in the `Vec` in the order they have been generated.
1910 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1912 /// This method uses a closure to create new values on every push. If
1913 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
1914 /// want to use the [`Default`] trait to generate values, you can
1915 /// pass [`Default::default`] as the second argument.
1920 /// let mut vec = vec![1, 2, 3];
1921 /// vec.resize_with(5, Default::default);
1922 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1924 /// let mut vec = vec![];
1926 /// vec.resize_with(4, || { p *= 2; p });
1927 /// assert_eq!(vec, [2, 4, 8, 16]);
1929 #[cfg(not(no_global_oom_handling))]
1930 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1931 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1935 let len = self.len();
1937 self.extend_with(new_len - len, ExtendFunc(f));
1939 self.truncate(new_len);
1943 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1944 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1945 /// `'a`. If the type has only static references, or none at all, then this
1946 /// may be chosen to be `'static`.
1948 /// This function is similar to the [`leak`][Box::leak] function on [`Box`]
1949 /// except that there is no way to recover the leaked memory.
1951 /// This function is mainly useful for data that lives for the remainder of
1952 /// the program's life. Dropping the returned reference will cause a memory
1960 /// let x = vec![1, 2, 3];
1961 /// let static_ref: &'static mut [usize] = x.leak();
1962 /// static_ref[0] += 1;
1963 /// assert_eq!(static_ref, &[2, 2, 3]);
1965 #[cfg(not(no_global_oom_handling))]
1966 #[stable(feature = "vec_leak", since = "1.47.0")]
1968 pub fn leak<'a>(self) -> &'a mut [T]
1972 Box::leak(self.into_boxed_slice())
1975 /// Returns the remaining spare capacity of the vector as a slice of
1976 /// `MaybeUninit<T>`.
1978 /// The returned slice can be used to fill the vector with data (e.g. by
1979 /// reading from a file) before marking the data as initialized using the
1980 /// [`set_len`] method.
1982 /// [`set_len`]: Vec::set_len
1987 /// #![feature(vec_spare_capacity, maybe_uninit_extra)]
1989 /// // Allocate vector big enough for 10 elements.
1990 /// let mut v = Vec::with_capacity(10);
1992 /// // Fill in the first 3 elements.
1993 /// let uninit = v.spare_capacity_mut();
1994 /// uninit[0].write(0);
1995 /// uninit[1].write(1);
1996 /// uninit[2].write(2);
1998 /// // Mark the first 3 elements of the vector as being initialized.
2003 /// assert_eq!(&v, &[0, 1, 2]);
2005 #[unstable(feature = "vec_spare_capacity", issue = "75017")]
2007 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2009 // This method is not implemented in terms of `split_at_spare_mut`,
2010 // to prevent invalidation of pointers to the buffer.
2012 slice::from_raw_parts_mut(
2013 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2014 self.buf.capacity() - self.len,
2019 /// Returns vector content as a slice of `T`, along with the remaining spare
2020 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2022 /// The returned spare capacity slice can be used to fill the vector with data
2023 /// (e.g. by reading from a file) before marking the data as initialized using
2024 /// the [`set_len`] method.
2026 /// [`set_len`]: Vec::set_len
2028 /// Note that this is a low-level API, which should be used with care for
2029 /// optimization purposes. If you need to append data to a `Vec`
2030 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2031 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2032 /// [`resize_with`], depending on your exact needs.
2034 /// [`push`]: Vec::push
2035 /// [`extend`]: Vec::extend
2036 /// [`extend_from_slice`]: Vec::extend_from_slice
2037 /// [`extend_from_within`]: Vec::extend_from_within
2038 /// [`insert`]: Vec::insert
2039 /// [`append`]: Vec::append
2040 /// [`resize`]: Vec::resize
2041 /// [`resize_with`]: Vec::resize_with
2046 /// #![feature(vec_split_at_spare, maybe_uninit_extra)]
2048 /// let mut v = vec![1, 1, 2];
2050 /// // Reserve additional space big enough for 10 elements.
2053 /// let (init, uninit) = v.split_at_spare_mut();
2054 /// let sum = init.iter().copied().sum::<u32>();
2056 /// // Fill in the next 4 elements.
2057 /// uninit[0].write(sum);
2058 /// uninit[1].write(sum * 2);
2059 /// uninit[2].write(sum * 3);
2060 /// uninit[3].write(sum * 4);
2062 /// // Mark the 4 elements of the vector as being initialized.
2064 /// let len = v.len();
2065 /// v.set_len(len + 4);
2068 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2070 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2072 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2074 // - len is ignored and so never changed
2075 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2079 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2081 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2082 unsafe fn split_at_spare_mut_with_len(
2084 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2085 let Range { start: ptr, end: spare_ptr } = self.as_mut_ptr_range();
2086 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2087 let spare_len = self.buf.capacity() - self.len;
2090 // - `ptr` is guaranteed to be valid for `len` elements
2091 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2093 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2094 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2096 (initialized, spare, &mut self.len)
2101 impl<T: Clone, A: Allocator> Vec<T, A> {
2102 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2104 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2105 /// difference, with each additional slot filled with `value`.
2106 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2108 /// This method requires `T` to implement [`Clone`],
2109 /// in order to be able to clone the passed value.
2110 /// If you need more flexibility (or want to rely on [`Default`] instead of
2111 /// [`Clone`]), use [`Vec::resize_with`].
2116 /// let mut vec = vec!["hello"];
2117 /// vec.resize(3, "world");
2118 /// assert_eq!(vec, ["hello", "world", "world"]);
2120 /// let mut vec = vec![1, 2, 3, 4];
2121 /// vec.resize(2, 0);
2122 /// assert_eq!(vec, [1, 2]);
2124 #[cfg(not(no_global_oom_handling))]
2125 #[stable(feature = "vec_resize", since = "1.5.0")]
2126 pub fn resize(&mut self, new_len: usize, value: T) {
2127 let len = self.len();
2130 self.extend_with(new_len - len, ExtendElement(value))
2132 self.truncate(new_len);
2136 /// Clones and appends all elements in a slice to the `Vec`.
2138 /// Iterates over the slice `other`, clones each element, and then appends
2139 /// it to this `Vec`. The `other` vector is traversed in-order.
2141 /// Note that this function is same as [`extend`] except that it is
2142 /// specialized to work with slices instead. If and when Rust gets
2143 /// specialization this function will likely be deprecated (but still
2149 /// let mut vec = vec![1];
2150 /// vec.extend_from_slice(&[2, 3, 4]);
2151 /// assert_eq!(vec, [1, 2, 3, 4]);
2154 /// [`extend`]: Vec::extend
2155 #[cfg(not(no_global_oom_handling))]
2156 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2157 pub fn extend_from_slice(&mut self, other: &[T]) {
2158 self.spec_extend(other.iter())
2161 /// Copies elements from `src` range to the end of the vector.
2166 /// let mut vec = vec![0, 1, 2, 3, 4];
2168 /// vec.extend_from_within(2..);
2169 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2171 /// vec.extend_from_within(..2);
2172 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2174 /// vec.extend_from_within(4..8);
2175 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2177 #[cfg(not(no_global_oom_handling))]
2178 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2179 pub fn extend_from_within<R>(&mut self, src: R)
2181 R: RangeBounds<usize>,
2183 let range = slice::range(src, ..self.len());
2184 self.reserve(range.len());
2187 // - `slice::range` guarantees that the given range is valid for indexing self
2189 self.spec_extend_from_within(range);
2194 // This code generalizes `extend_with_{element,default}`.
2195 trait ExtendWith<T> {
2196 fn next(&mut self) -> T;
2200 struct ExtendElement<T>(T);
2201 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2202 fn next(&mut self) -> T {
2205 fn last(self) -> T {
2210 struct ExtendDefault;
2211 impl<T: Default> ExtendWith<T> for ExtendDefault {
2212 fn next(&mut self) -> T {
2215 fn last(self) -> T {
2220 struct ExtendFunc<F>(F);
2221 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
2222 fn next(&mut self) -> T {
2225 fn last(mut self) -> T {
2230 impl<T, A: Allocator> Vec<T, A> {
2231 #[cfg(not(no_global_oom_handling))]
2232 /// Extend the vector by `n` values, using the given generator.
2233 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2237 let mut ptr = self.as_mut_ptr().add(self.len());
2238 // Use SetLenOnDrop to work around bug where compiler
2239 // may not realize the store through `ptr` through self.set_len()
2241 let mut local_len = SetLenOnDrop::new(&mut self.len);
2243 // Write all elements except the last one
2245 ptr::write(ptr, value.next());
2246 ptr = ptr.offset(1);
2247 // Increment the length in every step in case next() panics
2248 local_len.increment_len(1);
2252 // We can write the last element directly without cloning needlessly
2253 ptr::write(ptr, value.last());
2254 local_len.increment_len(1);
2257 // len set by scope guard
2262 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2263 /// Removes consecutive repeated elements in the vector according to the
2264 /// [`PartialEq`] trait implementation.
2266 /// If the vector is sorted, this removes all duplicates.
2271 /// let mut vec = vec![1, 2, 2, 3, 2];
2275 /// assert_eq!(vec, [1, 2, 3, 2]);
2277 #[stable(feature = "rust1", since = "1.0.0")]
2279 pub fn dedup(&mut self) {
2280 self.dedup_by(|a, b| a == b)
2284 ////////////////////////////////////////////////////////////////////////////////
2285 // Internal methods and functions
2286 ////////////////////////////////////////////////////////////////////////////////
2289 #[cfg(not(no_global_oom_handling))]
2290 #[stable(feature = "rust1", since = "1.0.0")]
2291 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2292 <T as SpecFromElem>::from_elem(elem, n, Global)
2296 #[cfg(not(no_global_oom_handling))]
2297 #[unstable(feature = "allocator_api", issue = "32838")]
2298 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2299 <T as SpecFromElem>::from_elem(elem, n, alloc)
2302 trait ExtendFromWithinSpec {
2305 /// - `src` needs to be valid index
2306 /// - `self.capacity() - self.len()` must be `>= src.len()`
2307 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2310 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2311 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2313 // - len is increased only after initializing elements
2314 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2317 // - caller guaratees that src is a valid index
2318 let to_clone = unsafe { this.get_unchecked(src) };
2320 iter::zip(to_clone, spare)
2321 .map(|(src, dst)| dst.write(src.clone()))
2323 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2324 // - len is increased after each element to prevent leaks (see issue #82533)
2325 .for_each(|_| *len += 1);
2329 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2330 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2331 let count = src.len();
2333 let (init, spare) = self.split_at_spare_mut();
2336 // - caller guaratees that `src` is a valid index
2337 let source = unsafe { init.get_unchecked(src) };
2340 // - Both pointers are created from unique slice references (`&mut [_]`)
2341 // so they are valid and do not overlap.
2342 // - Elements are :Copy so it's OK to to copy them, without doing
2343 // anything with the original values
2344 // - `count` is equal to the len of `source`, so source is valid for
2346 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2347 // is valid for `count` writes
2348 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2352 // - The elements were just initialized by `copy_nonoverlapping`
2357 ////////////////////////////////////////////////////////////////////////////////
2358 // Common trait implementations for Vec
2359 ////////////////////////////////////////////////////////////////////////////////
2361 #[stable(feature = "rust1", since = "1.0.0")]
2362 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2365 fn deref(&self) -> &[T] {
2366 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2370 #[stable(feature = "rust1", since = "1.0.0")]
2371 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2372 fn deref_mut(&mut self) -> &mut [T] {
2373 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2377 #[cfg(not(no_global_oom_handling))]
2378 #[stable(feature = "rust1", since = "1.0.0")]
2379 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2381 fn clone(&self) -> Self {
2382 let alloc = self.allocator().clone();
2383 <[T]>::to_vec_in(&**self, alloc)
2386 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2387 // required for this method definition, is not available. Instead use the
2388 // `slice::to_vec` function which is only available with cfg(test)
2389 // NB see the slice::hack module in slice.rs for more information
2391 fn clone(&self) -> Self {
2392 let alloc = self.allocator().clone();
2393 crate::slice::to_vec(&**self, alloc)
2396 fn clone_from(&mut self, other: &Self) {
2397 // drop anything that will not be overwritten
2398 self.truncate(other.len());
2400 // self.len <= other.len due to the truncate above, so the
2401 // slices here are always in-bounds.
2402 let (init, tail) = other.split_at(self.len());
2404 // reuse the contained values' allocations/resources.
2405 self.clone_from_slice(init);
2406 self.extend_from_slice(tail);
2410 #[stable(feature = "rust1", since = "1.0.0")]
2411 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2413 fn hash<H: Hasher>(&self, state: &mut H) {
2414 Hash::hash(&**self, state)
2418 #[stable(feature = "rust1", since = "1.0.0")]
2419 #[rustc_on_unimplemented(
2420 message = "vector indices are of type `usize` or ranges of `usize`",
2421 label = "vector indices are of type `usize` or ranges of `usize`"
2423 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2424 type Output = I::Output;
2427 fn index(&self, index: I) -> &Self::Output {
2428 Index::index(&**self, index)
2432 #[stable(feature = "rust1", since = "1.0.0")]
2433 #[rustc_on_unimplemented(
2434 message = "vector indices are of type `usize` or ranges of `usize`",
2435 label = "vector indices are of type `usize` or ranges of `usize`"
2437 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2439 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2440 IndexMut::index_mut(&mut **self, index)
2444 #[cfg(not(no_global_oom_handling))]
2445 #[stable(feature = "rust1", since = "1.0.0")]
2446 impl<T> FromIterator<T> for Vec<T> {
2448 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2449 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2453 #[stable(feature = "rust1", since = "1.0.0")]
2454 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2456 type IntoIter = IntoIter<T, A>;
2458 /// Creates a consuming iterator, that is, one that moves each value out of
2459 /// the vector (from start to end). The vector cannot be used after calling
2465 /// let v = vec!["a".to_string(), "b".to_string()];
2466 /// for s in v.into_iter() {
2467 /// // s has type String, not &String
2468 /// println!("{}", s);
2472 fn into_iter(self) -> IntoIter<T, A> {
2474 let mut me = ManuallyDrop::new(self);
2475 let alloc = ptr::read(me.allocator());
2476 let begin = me.as_mut_ptr();
2477 let end = if mem::size_of::<T>() == 0 {
2478 arith_offset(begin as *const i8, me.len() as isize) as *const T
2480 begin.add(me.len()) as *const T
2482 let cap = me.buf.capacity();
2484 buf: NonNull::new_unchecked(begin),
2485 phantom: PhantomData,
2495 #[stable(feature = "rust1", since = "1.0.0")]
2496 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2498 type IntoIter = slice::Iter<'a, T>;
2500 fn into_iter(self) -> slice::Iter<'a, T> {
2505 #[stable(feature = "rust1", since = "1.0.0")]
2506 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2507 type Item = &'a mut T;
2508 type IntoIter = slice::IterMut<'a, T>;
2510 fn into_iter(self) -> slice::IterMut<'a, T> {
2515 #[cfg(not(no_global_oom_handling))]
2516 #[stable(feature = "rust1", since = "1.0.0")]
2517 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2519 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2520 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2524 fn extend_one(&mut self, item: T) {
2529 fn extend_reserve(&mut self, additional: usize) {
2530 self.reserve(additional);
2534 impl<T, A: Allocator> Vec<T, A> {
2535 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2536 // they have no further optimizations to apply
2537 #[cfg(not(no_global_oom_handling))]
2538 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2539 // This is the case for a general iterator.
2541 // This function should be the moral equivalent of:
2543 // for item in iterator {
2546 while let Some(element) = iterator.next() {
2547 let len = self.len();
2548 if len == self.capacity() {
2549 let (lower, _) = iterator.size_hint();
2550 self.reserve(lower.saturating_add(1));
2553 ptr::write(self.as_mut_ptr().add(len), element);
2554 // NB can't overflow since we would have had to alloc the address space
2555 self.set_len(len + 1);
2560 /// Creates a splicing iterator that replaces the specified range in the vector
2561 /// with the given `replace_with` iterator and yields the removed items.
2562 /// `replace_with` does not need to be the same length as `range`.
2564 /// `range` is removed even if the iterator is not consumed until the end.
2566 /// It is unspecified how many elements are removed from the vector
2567 /// if the `Splice` value is leaked.
2569 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2571 /// This is optimal if:
2573 /// * The tail (elements in the vector after `range`) is empty,
2574 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2575 /// * or the lower bound of its `size_hint()` is exact.
2577 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2581 /// Panics if the starting point is greater than the end point or if
2582 /// the end point is greater than the length of the vector.
2587 /// let mut v = vec![1, 2, 3];
2588 /// let new = [7, 8];
2589 /// let u: Vec<_> = v.splice(..2, new).collect();
2590 /// assert_eq!(v, &[7, 8, 3]);
2591 /// assert_eq!(u, &[1, 2]);
2593 #[cfg(not(no_global_oom_handling))]
2595 #[stable(feature = "vec_splice", since = "1.21.0")]
2596 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2598 R: RangeBounds<usize>,
2599 I: IntoIterator<Item = T>,
2601 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2604 /// Creates an iterator which uses a closure to determine if an element should be removed.
2606 /// If the closure returns true, then the element is removed and yielded.
2607 /// If the closure returns false, the element will remain in the vector and will not be yielded
2608 /// by the iterator.
2610 /// Using this method is equivalent to the following code:
2613 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2614 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2616 /// while i < vec.len() {
2617 /// if some_predicate(&mut vec[i]) {
2618 /// let val = vec.remove(i);
2619 /// // your code here
2625 /// # assert_eq!(vec, vec![1, 4, 5]);
2628 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2629 /// because it can backshift the elements of the array in bulk.
2631 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2632 /// regardless of whether you choose to keep or remove it.
2636 /// Splitting an array into evens and odds, reusing the original allocation:
2639 /// #![feature(drain_filter)]
2640 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2642 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2643 /// let odds = numbers;
2645 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2646 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2648 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2649 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
2651 F: FnMut(&mut T) -> bool,
2653 let old_len = self.len();
2655 // Guard against us getting leaked (leak amplification)
2660 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2664 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2666 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2667 /// append the entire slice at once.
2669 /// [`copy_from_slice`]: slice::copy_from_slice
2670 #[cfg(not(no_global_oom_handling))]
2671 #[stable(feature = "extend_ref", since = "1.2.0")]
2672 impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
2673 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2674 self.spec_extend(iter.into_iter())
2678 fn extend_one(&mut self, &item: &'a T) {
2683 fn extend_reserve(&mut self, additional: usize) {
2684 self.reserve(additional);
2688 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2689 #[stable(feature = "rust1", since = "1.0.0")]
2690 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
2692 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2693 PartialOrd::partial_cmp(&**self, &**other)
2697 #[stable(feature = "rust1", since = "1.0.0")]
2698 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
2700 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2701 #[stable(feature = "rust1", since = "1.0.0")]
2702 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
2704 fn cmp(&self, other: &Self) -> Ordering {
2705 Ord::cmp(&**self, &**other)
2709 #[stable(feature = "rust1", since = "1.0.0")]
2710 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
2711 fn drop(&mut self) {
2714 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2715 // could avoid questions of validity in certain cases
2716 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
2718 // RawVec handles deallocation
2722 #[stable(feature = "rust1", since = "1.0.0")]
2723 impl<T> Default for Vec<T> {
2724 /// Creates an empty `Vec<T>`.
2725 fn default() -> Vec<T> {
2730 #[stable(feature = "rust1", since = "1.0.0")]
2731 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
2732 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2733 fmt::Debug::fmt(&**self, f)
2737 #[stable(feature = "rust1", since = "1.0.0")]
2738 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
2739 fn as_ref(&self) -> &Vec<T, A> {
2744 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2745 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
2746 fn as_mut(&mut self) -> &mut Vec<T, A> {
2751 #[stable(feature = "rust1", since = "1.0.0")]
2752 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
2753 fn as_ref(&self) -> &[T] {
2758 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2759 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
2760 fn as_mut(&mut self) -> &mut [T] {
2765 #[cfg(not(no_global_oom_handling))]
2766 #[stable(feature = "rust1", since = "1.0.0")]
2767 impl<T: Clone> From<&[T]> for Vec<T> {
2768 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2773 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
2776 fn from(s: &[T]) -> Vec<T> {
2780 fn from(s: &[T]) -> Vec<T> {
2781 crate::slice::to_vec(s, Global)
2785 #[cfg(not(no_global_oom_handling))]
2786 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2787 impl<T: Clone> From<&mut [T]> for Vec<T> {
2788 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2793 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
2796 fn from(s: &mut [T]) -> Vec<T> {
2800 fn from(s: &mut [T]) -> Vec<T> {
2801 crate::slice::to_vec(s, Global)
2805 #[stable(feature = "vec_from_array", since = "1.44.0")]
2806 impl<T, const N: usize> From<[T; N]> for Vec<T> {
2808 fn from(s: [T; N]) -> Vec<T> {
2809 <[T]>::into_vec(box s)
2811 /// Allocate a `Vec<T>` and move `s`'s items into it.
2816 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
2819 fn from(s: [T; N]) -> Vec<T> {
2820 crate::slice::into_vec(box s)
2824 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2825 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2827 [T]: ToOwned<Owned = Vec<T>>,
2829 /// Convert a clone-on-write slice into a vector.
2831 /// If `s` already owns a `Vec<T>`, it will be returned directly.
2832 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
2833 /// filled by cloning `s`'s items into it.
2838 /// # use std::borrow::Cow;
2839 /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
2840 /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
2841 /// assert_eq!(Vec::from(o), Vec::from(b));
2843 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2848 // note: test pulls in libstd, which causes errors here
2850 #[stable(feature = "vec_from_box", since = "1.18.0")]
2851 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
2852 /// Convert a boxed slice into a vector by transferring ownership of
2853 /// the existing heap allocation.
2858 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
2859 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
2861 fn from(s: Box<[T], A>) -> Self {
2866 // note: test pulls in libstd, which causes errors here
2867 #[cfg(not(no_global_oom_handling))]
2869 #[stable(feature = "box_from_vec", since = "1.20.0")]
2870 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
2871 /// Convert a vector into a boxed slice.
2873 /// If `v` has excess capacity, its items will be moved into a
2874 /// newly-allocated buffer with exactly the right capacity.
2879 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
2881 fn from(v: Vec<T, A>) -> Self {
2882 v.into_boxed_slice()
2886 #[cfg(not(no_global_oom_handling))]
2887 #[stable(feature = "rust1", since = "1.0.0")]
2888 impl From<&str> for Vec<u8> {
2889 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
2894 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
2896 fn from(s: &str) -> Vec<u8> {
2897 From::from(s.as_bytes())
2901 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
2902 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
2903 type Error = Vec<T, A>;
2905 /// Gets the entire contents of the `Vec<T>` as an array,
2906 /// if its size exactly matches that of the requested array.
2911 /// use std::convert::TryInto;
2912 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
2913 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
2916 /// If the length doesn't match, the input comes back in `Err`:
2918 /// use std::convert::TryInto;
2919 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
2920 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
2923 /// If you're fine with just getting a prefix of the `Vec<T>`,
2924 /// you can call [`.truncate(N)`](Vec::truncate) first.
2926 /// use std::convert::TryInto;
2927 /// let mut v = String::from("hello world").into_bytes();
2930 /// let [a, b]: [_; 2] = v.try_into().unwrap();
2931 /// assert_eq!(a, b' ');
2932 /// assert_eq!(b, b'd');
2934 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
2939 // SAFETY: `.set_len(0)` is always sound.
2940 unsafe { vec.set_len(0) };
2942 // SAFETY: A `Vec`'s pointer is always aligned properly, and
2943 // the alignment the array needs is the same as the items.
2944 // We checked earlier that we have sufficient items.
2945 // The items will not double-drop as the `set_len`
2946 // tells the `Vec` not to also drop them.
2947 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };