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 for convenient initialization:
180 /// let mut vec1 = vec![1, 2, 3];
182 /// let vec2 = Vec::from([1, 2, 3, 4]);
183 /// assert_eq!(vec1, vec2);
186 /// It can also initialize each element of a `Vec<T>` with a given value.
187 /// This may be more efficient than performing allocation and initialization
188 /// in separate steps, especially when initializing a vector of zeros:
191 /// let vec = vec![0; 5];
192 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
194 /// // The following is equivalent, but potentially slower:
195 /// let mut vec = Vec::with_capacity(5);
196 /// vec.resize(5, 0);
197 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
200 /// For more information, see
201 /// [Capacity and Reallocation](#capacity-and-reallocation).
203 /// Use a `Vec<T>` as an efficient stack:
206 /// let mut stack = Vec::new();
212 /// while let Some(top) = stack.pop() {
213 /// // Prints 3, 2, 1
214 /// println!("{}", top);
220 /// The `Vec` type allows to access values by index, because it implements the
221 /// [`Index`] trait. An example will be more explicit:
224 /// let v = vec![0, 2, 4, 6];
225 /// println!("{}", v[1]); // it will display '2'
228 /// However be careful: if you try to access an index which isn't in the `Vec`,
229 /// your software will panic! You cannot do this:
232 /// let v = vec![0, 2, 4, 6];
233 /// println!("{}", v[6]); // it will panic!
236 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
241 /// A `Vec` can be mutable. On the other hand, slices are read-only objects.
242 /// To get a [slice][prim@slice], use [`&`]. Example:
245 /// fn read_slice(slice: &[usize]) {
249 /// let v = vec![0, 1];
252 /// // ... and that's all!
253 /// // you can also do it like this:
254 /// let u: &[usize] = &v;
256 /// let u: &[_] = &v;
259 /// In Rust, it's more common to pass slices as arguments rather than vectors
260 /// when you just want to provide read access. The same goes for [`String`] and
263 /// # Capacity and reallocation
265 /// The capacity of a vector is the amount of space allocated for any future
266 /// elements that will be added onto the vector. This is not to be confused with
267 /// the *length* of a vector, which specifies the number of actual elements
268 /// within the vector. If a vector's length exceeds its capacity, its capacity
269 /// will automatically be increased, but its elements will have to be
272 /// For example, a vector with capacity 10 and length 0 would be an empty vector
273 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
274 /// vector will not change its capacity or cause reallocation to occur. However,
275 /// if the vector's length is increased to 11, it will have to reallocate, which
276 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
277 /// whenever possible to specify how big the vector is expected to get.
281 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
282 /// about its design. This ensures that it's as low-overhead as possible in
283 /// the general case, and can be correctly manipulated in primitive ways
284 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
285 /// If additional type parameters are added (e.g., to support custom allocators),
286 /// overriding their defaults may change the behavior.
288 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
289 /// triplet. No more, no less. The order of these fields is completely
290 /// unspecified, and you should use the appropriate methods to modify these.
291 /// The pointer will never be null, so this type is null-pointer-optimized.
293 /// However, the pointer might not actually point to allocated memory. In particular,
294 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
295 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
296 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
297 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
298 /// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
299 /// if [`mem::size_of::<T>`]`() * capacity() > 0`. In general, `Vec`'s allocation
300 /// details are very subtle — if you intend to allocate memory using a `Vec`
301 /// and use it for something else (either to pass to unsafe code, or to build your
302 /// own memory-backed collection), be sure to deallocate this memory by using
303 /// `from_raw_parts` to recover the `Vec` and then dropping it.
305 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
306 /// (as defined by the allocator Rust is configured to use by default), and its
307 /// pointer points to [`len`] initialized, contiguous elements in order (what
308 /// you would see if you coerced it to a slice), followed by [`capacity`]` -
309 /// `[`len`] logically uninitialized, contiguous elements.
311 /// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
312 /// visualized as below. The top part is the `Vec` struct, it contains a
313 /// pointer to the head of the allocation in the heap, length and capacity.
314 /// The bottom part is the allocation on the heap, a contiguous memory block.
318 /// +--------+--------+--------+
319 /// | 0x0123 | 2 | 4 |
320 /// +--------+--------+--------+
323 /// Heap +--------+--------+--------+--------+
324 /// | 'a' | 'b' | uninit | uninit |
325 /// +--------+--------+--------+--------+
328 /// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
329 /// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
330 /// layout (including the order of fields).
332 /// `Vec` will never perform a "small optimization" where elements are actually
333 /// stored on the stack for two reasons:
335 /// * It would make it more difficult for unsafe code to correctly manipulate
336 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
337 /// only moved, and it would be more difficult to determine if a `Vec` had
338 /// actually allocated memory.
340 /// * It would penalize the general case, incurring an additional branch
343 /// `Vec` will never automatically shrink itself, even if completely empty. This
344 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
345 /// and then filling it back up to the same [`len`] should incur no calls to
346 /// the allocator. If you wish to free up unused memory, use
347 /// [`shrink_to_fit`] or [`shrink_to`].
349 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
350 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
351 /// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
352 /// accurate, and can be relied on. It can even be used to manually free the memory
353 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
354 /// when not necessary.
356 /// `Vec` does not guarantee any particular growth strategy when reallocating
357 /// when full, nor when [`reserve`] is called. The current strategy is basic
358 /// and it may prove desirable to use a non-constant growth factor. Whatever
359 /// strategy is used will of course guarantee *O*(1) amortized [`push`].
361 /// `vec![x; n]`, `vec![a, b, c, d]`, and
362 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
363 /// with exactly the requested capacity. If [`len`]` == `[`capacity`],
364 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
365 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
367 /// `Vec` will not specifically overwrite any data that is removed from it,
368 /// but also won't specifically preserve it. Its uninitialized memory is
369 /// scratch space that it may use however it wants. It will generally just do
370 /// whatever is most efficient or otherwise easy to implement. Do not rely on
371 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
372 /// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
373 /// first, that might not actually happen because the optimizer does not consider
374 /// this a side-effect that must be preserved. There is one case which we will
375 /// not break, however: using `unsafe` code to write to the excess capacity,
376 /// and then increasing the length to match, is always valid.
378 /// Currently, `Vec` does not guarantee the order in which elements are dropped.
379 /// The order has changed in the past and may change again.
381 /// [`get`]: ../../std/vec/struct.Vec.html#method.get
382 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
383 /// [`String`]: crate::string::String
384 /// [`&str`]: type@str
385 /// [`shrink_to_fit`]: Vec::shrink_to_fit
386 /// [`shrink_to`]: Vec::shrink_to
387 /// [`capacity`]: Vec::capacity
388 /// [`mem::size_of::<T>`]: core::mem::size_of
389 /// [`len`]: Vec::len
390 /// [`push`]: Vec::push
391 /// [`insert`]: Vec::insert
392 /// [`reserve`]: Vec::reserve
393 /// [`MaybeUninit`]: core::mem::MaybeUninit
394 /// [owned slice]: Box
395 #[stable(feature = "rust1", since = "1.0.0")]
396 #[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")]
397 pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
402 ////////////////////////////////////////////////////////////////////////////////
404 ////////////////////////////////////////////////////////////////////////////////
407 /// Constructs a new, empty `Vec<T>`.
409 /// The vector will not allocate until elements are pushed onto it.
414 /// # #![allow(unused_mut)]
415 /// let mut vec: Vec<i32> = Vec::new();
418 #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
419 #[stable(feature = "rust1", since = "1.0.0")]
420 pub const fn new() -> Self {
421 Vec { buf: RawVec::NEW, len: 0 }
424 /// Constructs a new, empty `Vec<T>` with the specified capacity.
426 /// The vector will be able to hold exactly `capacity` elements without
427 /// reallocating. If `capacity` is 0, the vector will not allocate.
429 /// It is important to note that although the returned vector has the
430 /// *capacity* specified, the vector will have a zero *length*. For an
431 /// explanation of the difference between length and capacity, see
432 /// *[Capacity and reallocation]*.
434 /// [Capacity and reallocation]: #capacity-and-reallocation
438 /// Panics if the new capacity exceeds `isize::MAX` bytes.
443 /// let mut vec = Vec::with_capacity(10);
445 /// // The vector contains no items, even though it has capacity for more
446 /// assert_eq!(vec.len(), 0);
447 /// assert_eq!(vec.capacity(), 10);
449 /// // These are all done without reallocating...
453 /// assert_eq!(vec.len(), 10);
454 /// assert_eq!(vec.capacity(), 10);
456 /// // ...but this may make the vector reallocate
458 /// assert_eq!(vec.len(), 11);
459 /// assert!(vec.capacity() >= 11);
461 #[cfg(not(no_global_oom_handling))]
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 #[stable(feature = "rust1", since = "1.0.0")]
803 pub fn reserve(&mut self, additional: usize) {
804 self.buf.reserve(self.len, additional);
807 /// Reserves the minimum capacity for exactly `additional` more elements to
808 /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
809 /// capacity will be greater than or equal to `self.len() + additional`.
810 /// Does nothing if the capacity is already sufficient.
812 /// Note that the allocator may give the collection more space than it
813 /// requests. Therefore, capacity can not be relied upon to be precisely
814 /// minimal. Prefer [`reserve`] if future insertions are expected.
816 /// [`reserve`]: Vec::reserve
820 /// Panics if the new capacity overflows `usize`.
825 /// let mut vec = vec![1];
826 /// vec.reserve_exact(10);
827 /// assert!(vec.capacity() >= 11);
829 #[cfg(not(no_global_oom_handling))]
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 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
868 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
869 self.buf.try_reserve(self.len, additional)
872 /// Tries to reserve the minimum capacity for exactly `additional`
873 /// elements to be inserted in the given `Vec<T>`. After calling
874 /// `try_reserve_exact`, capacity will be greater than or equal to
875 /// `self.len() + additional` if it returns `Ok(())`.
876 /// Does nothing if the capacity is already sufficient.
878 /// Note that the allocator may give the collection more space than it
879 /// requests. Therefore, capacity can not be relied upon to be precisely
880 /// minimal. Prefer [`reserve`] if future insertions are expected.
882 /// [`reserve`]: Vec::reserve
886 /// If the capacity overflows, or the allocator reports a failure, then an error
892 /// #![feature(try_reserve)]
893 /// use std::collections::TryReserveError;
895 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
896 /// let mut output = Vec::new();
898 /// // Pre-reserve the memory, exiting if we can't
899 /// output.try_reserve_exact(data.len())?;
901 /// // Now we know this can't OOM in the middle of our complex work
902 /// output.extend(data.iter().map(|&val| {
903 /// val * 2 + 5 // very complicated
908 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
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 #[stable(feature = "rust1", since = "1.0.0")]
931 pub fn shrink_to_fit(&mut self) {
932 // The capacity is never less than the length, and there's nothing to do when
933 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
934 // by only calling it with a greater capacity.
935 if self.capacity() > self.len {
936 self.buf.shrink_to_fit(self.len);
940 /// Shrinks the capacity of the vector with a lower bound.
942 /// The capacity will remain at least as large as both the length
943 /// and the supplied value.
945 /// If the current capacity is less than the lower limit, this is a no-op.
950 /// let mut vec = Vec::with_capacity(10);
951 /// vec.extend([1, 2, 3]);
952 /// assert_eq!(vec.capacity(), 10);
953 /// vec.shrink_to(4);
954 /// assert!(vec.capacity() >= 4);
955 /// vec.shrink_to(0);
956 /// assert!(vec.capacity() >= 3);
958 #[cfg(not(no_global_oom_handling))]
959 #[stable(feature = "shrink_to", since = "1.56.0")]
960 pub fn shrink_to(&mut self, min_capacity: usize) {
961 if self.capacity() > min_capacity {
962 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
966 /// Converts the vector into [`Box<[T]>`][owned slice].
968 /// Note that this will drop any excess capacity.
970 /// [owned slice]: Box
975 /// let v = vec![1, 2, 3];
977 /// let slice = v.into_boxed_slice();
980 /// Any excess capacity is removed:
983 /// let mut vec = Vec::with_capacity(10);
984 /// vec.extend([1, 2, 3]);
986 /// assert_eq!(vec.capacity(), 10);
987 /// let slice = vec.into_boxed_slice();
988 /// assert_eq!(slice.into_vec().capacity(), 3);
990 #[cfg(not(no_global_oom_handling))]
991 #[stable(feature = "rust1", since = "1.0.0")]
992 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
994 self.shrink_to_fit();
995 let me = ManuallyDrop::new(self);
996 let buf = ptr::read(&me.buf);
998 buf.into_box(len).assume_init()
1002 /// Shortens the vector, keeping the first `len` elements and dropping
1005 /// If `len` is greater than the vector's current length, this has no
1008 /// The [`drain`] method can emulate `truncate`, but causes the excess
1009 /// elements to be returned instead of dropped.
1011 /// Note that this method has no effect on the allocated capacity
1016 /// Truncating a five element vector to two elements:
1019 /// let mut vec = vec![1, 2, 3, 4, 5];
1020 /// vec.truncate(2);
1021 /// assert_eq!(vec, [1, 2]);
1024 /// No truncation occurs when `len` is greater than the vector's current
1028 /// let mut vec = vec![1, 2, 3];
1029 /// vec.truncate(8);
1030 /// assert_eq!(vec, [1, 2, 3]);
1033 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1037 /// let mut vec = vec![1, 2, 3];
1038 /// vec.truncate(0);
1039 /// assert_eq!(vec, []);
1042 /// [`clear`]: Vec::clear
1043 /// [`drain`]: Vec::drain
1044 #[stable(feature = "rust1", since = "1.0.0")]
1045 pub fn truncate(&mut self, len: usize) {
1046 // This is safe because:
1048 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1049 // case avoids creating an invalid slice, and
1050 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1051 // such that no value will be dropped twice in case `drop_in_place`
1052 // were to panic once (if it panics twice, the program aborts).
1054 // Note: It's intentional that this is `>` and not `>=`.
1055 // Changing it to `>=` has negative performance
1056 // implications in some cases. See #78884 for more.
1060 let remaining_len = self.len - len;
1061 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1063 ptr::drop_in_place(s);
1067 /// Extracts a slice containing the entire vector.
1069 /// Equivalent to `&s[..]`.
1074 /// use std::io::{self, Write};
1075 /// let buffer = vec![1, 2, 3, 5, 8];
1076 /// io::sink().write(buffer.as_slice()).unwrap();
1079 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1080 pub fn as_slice(&self) -> &[T] {
1084 /// Extracts a mutable slice of the entire vector.
1086 /// Equivalent to `&mut s[..]`.
1091 /// use std::io::{self, Read};
1092 /// let mut buffer = vec![0; 3];
1093 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1096 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1097 pub fn as_mut_slice(&mut self) -> &mut [T] {
1101 /// Returns a raw pointer to the vector's buffer.
1103 /// The caller must ensure that the vector outlives the pointer this
1104 /// function returns, or else it will end up pointing to garbage.
1105 /// Modifying the vector may cause its buffer to be reallocated,
1106 /// which would also make any pointers to it invalid.
1108 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1109 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1110 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1115 /// let x = vec![1, 2, 4];
1116 /// let x_ptr = x.as_ptr();
1119 /// for i in 0..x.len() {
1120 /// assert_eq!(*x_ptr.add(i), 1 << i);
1125 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1126 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1128 pub fn as_ptr(&self) -> *const T {
1129 // We shadow the slice method of the same name to avoid going through
1130 // `deref`, which creates an intermediate reference.
1131 let ptr = self.buf.ptr();
1133 assume(!ptr.is_null());
1138 /// Returns an unsafe mutable pointer to the vector's buffer.
1140 /// The caller must ensure that the vector outlives the pointer this
1141 /// function returns, or else it will end up pointing to garbage.
1142 /// Modifying the vector may cause its buffer to be reallocated,
1143 /// which would also make any pointers to it invalid.
1148 /// // Allocate vector big enough for 4 elements.
1150 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1151 /// let x_ptr = x.as_mut_ptr();
1153 /// // Initialize elements via raw pointer writes, then set length.
1155 /// for i in 0..size {
1156 /// *x_ptr.add(i) = i as i32;
1158 /// x.set_len(size);
1160 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1162 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1164 pub fn as_mut_ptr(&mut self) -> *mut T {
1165 // We shadow the slice method of the same name to avoid going through
1166 // `deref_mut`, which creates an intermediate reference.
1167 let ptr = self.buf.ptr();
1169 assume(!ptr.is_null());
1174 /// Returns a reference to the underlying allocator.
1175 #[unstable(feature = "allocator_api", issue = "32838")]
1177 pub fn allocator(&self) -> &A {
1178 self.buf.allocator()
1181 /// Forces the length of the vector to `new_len`.
1183 /// This is a low-level operation that maintains none of the normal
1184 /// invariants of the type. Normally changing the length of a vector
1185 /// is done using one of the safe operations instead, such as
1186 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1188 /// [`truncate`]: Vec::truncate
1189 /// [`resize`]: Vec::resize
1190 /// [`extend`]: Extend::extend
1191 /// [`clear`]: Vec::clear
1195 /// - `new_len` must be less than or equal to [`capacity()`].
1196 /// - The elements at `old_len..new_len` must be initialized.
1198 /// [`capacity()`]: Vec::capacity
1202 /// This method can be useful for situations in which the vector
1203 /// is serving as a buffer for other code, particularly over FFI:
1206 /// # #![allow(dead_code)]
1207 /// # // This is just a minimal skeleton for the doc example;
1208 /// # // don't use this as a starting point for a real library.
1209 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1210 /// # const Z_OK: i32 = 0;
1212 /// # fn deflateGetDictionary(
1213 /// # strm: *mut std::ffi::c_void,
1214 /// # dictionary: *mut u8,
1215 /// # dictLength: *mut usize,
1218 /// # impl StreamWrapper {
1219 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1220 /// // Per the FFI method's docs, "32768 bytes is always enough".
1221 /// let mut dict = Vec::with_capacity(32_768);
1222 /// let mut dict_length = 0;
1223 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1224 /// // 1. `dict_length` elements were initialized.
1225 /// // 2. `dict_length` <= the capacity (32_768)
1226 /// // which makes `set_len` safe to call.
1228 /// // Make the FFI call...
1229 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1231 /// // ...and update the length to what was initialized.
1232 /// dict.set_len(dict_length);
1242 /// While the following example is sound, there is a memory leak since
1243 /// the inner vectors were not freed prior to the `set_len` call:
1246 /// let mut vec = vec![vec![1, 0, 0],
1250 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1251 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1257 /// Normally, here, one would use [`clear`] instead to correctly drop
1258 /// the contents and thus not leak memory.
1260 #[stable(feature = "rust1", since = "1.0.0")]
1261 pub unsafe fn set_len(&mut self, new_len: usize) {
1262 debug_assert!(new_len <= self.capacity());
1267 /// Removes an element from the vector and returns it.
1269 /// The removed element is replaced by the last element of the vector.
1271 /// This does not preserve ordering, but is O(1).
1275 /// Panics if `index` is out of bounds.
1280 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1282 /// assert_eq!(v.swap_remove(1), "bar");
1283 /// assert_eq!(v, ["foo", "qux", "baz"]);
1285 /// assert_eq!(v.swap_remove(0), "foo");
1286 /// assert_eq!(v, ["baz", "qux"]);
1289 #[stable(feature = "rust1", since = "1.0.0")]
1290 pub fn swap_remove(&mut self, index: usize) -> T {
1293 fn assert_failed(index: usize, len: usize) -> ! {
1294 panic!("swap_remove index (is {}) should be < len (is {})", index, len);
1297 let len = self.len();
1299 assert_failed(index, len);
1302 // We replace self[index] with the last element. Note that if the
1303 // bounds check above succeeds there must be a last element (which
1304 // can be self[index] itself).
1305 let last = ptr::read(self.as_ptr().add(len - 1));
1306 let hole = self.as_mut_ptr().add(index);
1307 self.set_len(len - 1);
1308 ptr::replace(hole, last)
1312 /// Inserts an element at position `index` within the vector, shifting all
1313 /// elements after it to the right.
1317 /// Panics if `index > len`.
1322 /// let mut vec = vec![1, 2, 3];
1323 /// vec.insert(1, 4);
1324 /// assert_eq!(vec, [1, 4, 2, 3]);
1325 /// vec.insert(4, 5);
1326 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1328 #[cfg(not(no_global_oom_handling))]
1329 #[stable(feature = "rust1", since = "1.0.0")]
1330 pub fn insert(&mut self, index: usize, element: T) {
1333 fn assert_failed(index: usize, len: usize) -> ! {
1334 panic!("insertion index (is {}) should be <= len (is {})", index, len);
1337 let len = self.len();
1339 assert_failed(index, len);
1342 // space for the new element
1343 if len == self.buf.capacity() {
1349 // The spot to put the new value
1351 let p = self.as_mut_ptr().add(index);
1352 // Shift everything over to make space. (Duplicating the
1353 // `index`th element into two consecutive places.)
1354 ptr::copy(p, p.offset(1), len - index);
1355 // Write it in, overwriting the first copy of the `index`th
1357 ptr::write(p, element);
1359 self.set_len(len + 1);
1363 /// Removes and returns the element at position `index` within the vector,
1364 /// shifting all elements after it to the left.
1366 /// Note: Because this shifts over the remaining elements, it has a
1367 /// worst-case performance of O(n). If you don't need the order of elements
1368 /// to be preserved, use [`swap_remove`] instead.
1370 /// [`swap_remove`]: Vec::swap_remove
1374 /// Panics if `index` is out of bounds.
1379 /// let mut v = vec![1, 2, 3];
1380 /// assert_eq!(v.remove(1), 2);
1381 /// assert_eq!(v, [1, 3]);
1383 #[stable(feature = "rust1", since = "1.0.0")]
1385 pub fn remove(&mut self, index: usize) -> T {
1389 fn assert_failed(index: usize, len: usize) -> ! {
1390 panic!("removal index (is {}) should be < len (is {})", index, len);
1393 let len = self.len();
1395 assert_failed(index, len);
1401 // the place we are taking from.
1402 let ptr = self.as_mut_ptr().add(index);
1403 // copy it out, unsafely having a copy of the value on
1404 // the stack and in the vector at the same time.
1405 ret = ptr::read(ptr);
1407 // Shift everything down to fill in that spot.
1408 ptr::copy(ptr.offset(1), ptr, len - index - 1);
1410 self.set_len(len - 1);
1415 /// Retains only the elements specified by the predicate.
1417 /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
1418 /// This method operates in place, visiting each element exactly once in the
1419 /// original order, and preserves the order of the retained elements.
1424 /// let mut vec = vec![1, 2, 3, 4];
1425 /// vec.retain(|&x| x % 2 == 0);
1426 /// assert_eq!(vec, [2, 4]);
1429 /// Because the elements are visited exactly once in the original order,
1430 /// external state may be used to decide which elements to keep.
1433 /// let mut vec = vec![1, 2, 3, 4, 5];
1434 /// let keep = [false, true, true, false, true];
1435 /// let mut iter = keep.iter();
1436 /// vec.retain(|_| *iter.next().unwrap());
1437 /// assert_eq!(vec, [2, 3, 5]);
1439 #[stable(feature = "rust1", since = "1.0.0")]
1440 pub fn retain<F>(&mut self, mut f: F)
1442 F: FnMut(&T) -> bool,
1444 let original_len = self.len();
1445 // Avoid double drop if the drop guard is not executed,
1446 // since we may make some holes during the process.
1447 unsafe { self.set_len(0) };
1449 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1450 // |<- processed len ->| ^- next to check
1451 // |<- deleted cnt ->|
1452 // |<- original_len ->|
1453 // Kept: Elements which predicate returns true on.
1454 // Hole: Moved or dropped element slot.
1455 // Unchecked: Unchecked valid elements.
1457 // This drop guard will be invoked when predicate or `drop` of element panicked.
1458 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1459 // In cases when predicate and `drop` never panick, it will be optimized out.
1460 struct BackshiftOnDrop<'a, T, A: Allocator> {
1461 v: &'a mut Vec<T, A>,
1462 processed_len: usize,
1464 original_len: usize,
1467 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1468 fn drop(&mut self) {
1469 if self.deleted_cnt > 0 {
1470 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1473 self.v.as_ptr().add(self.processed_len),
1474 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1475 self.original_len - self.processed_len,
1479 // SAFETY: After filling holes, all items are in contiguous memory.
1481 self.v.set_len(self.original_len - self.deleted_cnt);
1486 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1488 while g.processed_len < original_len {
1489 // SAFETY: Unchecked element must be valid.
1490 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1492 // Advance early to avoid double drop if `drop_in_place` panicked.
1493 g.processed_len += 1;
1495 // SAFETY: We never touch this element again after dropped.
1496 unsafe { ptr::drop_in_place(cur) };
1497 // We already advanced the counter.
1500 if g.deleted_cnt > 0 {
1501 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1502 // We use copy for move, and never touch this element again.
1504 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1505 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1508 g.processed_len += 1;
1511 // All item are processed. This can be optimized to `set_len` by LLVM.
1515 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1518 /// If the vector is sorted, this removes all duplicates.
1523 /// let mut vec = vec![10, 20, 21, 30, 20];
1525 /// vec.dedup_by_key(|i| *i / 10);
1527 /// assert_eq!(vec, [10, 20, 30, 20]);
1529 #[stable(feature = "dedup_by", since = "1.16.0")]
1531 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1533 F: FnMut(&mut T) -> K,
1536 self.dedup_by(|a, b| key(a) == key(b))
1539 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1542 /// The `same_bucket` function is passed references to two elements from the vector and
1543 /// must determine if the elements compare equal. The elements are passed in opposite order
1544 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1546 /// If the vector is sorted, this removes all duplicates.
1551 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1553 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1555 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1557 #[stable(feature = "dedup_by", since = "1.16.0")]
1558 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1560 F: FnMut(&mut T, &mut T) -> bool,
1562 let len = self.len();
1567 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1568 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1569 /* Offset of the element we want to check if it is duplicate */
1572 /* Offset of the place where we want to place the non-duplicate
1573 * when we find it. */
1576 /* The Vec that would need correction if `same_bucket` panicked */
1577 vec: &'a mut Vec<T, A>,
1580 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1581 fn drop(&mut self) {
1582 /* This code gets executed when `same_bucket` panics */
1584 /* SAFETY: invariant guarantees that `read - write`
1585 * and `len - read` never overflow and that the copy is always
1588 let ptr = self.vec.as_mut_ptr();
1589 let len = self.vec.len();
1591 /* How many items were left when `same_bucket` paniced.
1592 * Basically vec[read..].len() */
1593 let items_left = len.wrapping_sub(self.read);
1595 /* Pointer to first item in vec[write..write+items_left] slice */
1596 let dropped_ptr = ptr.add(self.write);
1597 /* Pointer to first item in vec[read..] slice */
1598 let valid_ptr = ptr.add(self.read);
1600 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1601 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1602 ptr::copy(valid_ptr, dropped_ptr, items_left);
1604 /* How many items have been already dropped
1605 * Basically vec[read..write].len() */
1606 let dropped = self.read.wrapping_sub(self.write);
1608 self.vec.set_len(len - dropped);
1613 let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
1614 let ptr = gap.vec.as_mut_ptr();
1616 /* Drop items while going through Vec, it should be more efficient than
1617 * doing slice partition_dedup + truncate */
1619 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1620 * are always in-bounds and read_ptr never aliases prev_ptr */
1622 while gap.read < len {
1623 let read_ptr = ptr.add(gap.read);
1624 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1626 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1627 // Increase `gap.read` now since the drop may panic.
1629 /* We have found duplicate, drop it in-place */
1630 ptr::drop_in_place(read_ptr);
1632 let write_ptr = ptr.add(gap.write);
1634 /* Because `read_ptr` can be equal to `write_ptr`, we either
1635 * have to use `copy` or conditional `copy_nonoverlapping`.
1636 * Looks like the first option is faster. */
1637 ptr::copy(read_ptr, write_ptr, 1);
1639 /* We have filled that place, so go further */
1645 /* Technically we could let `gap` clean up with its Drop, but
1646 * when `same_bucket` is guaranteed to not panic, this bloats a little
1647 * the codegen, so we just do it manually */
1648 gap.vec.set_len(gap.write);
1653 /// Appends an element to the back of a collection.
1657 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1662 /// let mut vec = vec![1, 2];
1664 /// assert_eq!(vec, [1, 2, 3]);
1666 #[cfg(not(no_global_oom_handling))]
1668 #[stable(feature = "rust1", since = "1.0.0")]
1669 pub fn push(&mut self, value: T) {
1670 // This will panic or abort if we would allocate > isize::MAX bytes
1671 // or if the length increment would overflow for zero-sized types.
1672 if self.len == self.buf.capacity() {
1676 let end = self.as_mut_ptr().add(self.len);
1677 ptr::write(end, value);
1682 /// Removes the last element from a vector and returns it, or [`None`] if it
1688 /// let mut vec = vec![1, 2, 3];
1689 /// assert_eq!(vec.pop(), Some(3));
1690 /// assert_eq!(vec, [1, 2]);
1693 #[stable(feature = "rust1", since = "1.0.0")]
1694 pub fn pop(&mut self) -> Option<T> {
1700 Some(ptr::read(self.as_ptr().add(self.len())))
1705 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1709 /// Panics if the number of elements in the vector overflows a `usize`.
1714 /// let mut vec = vec![1, 2, 3];
1715 /// let mut vec2 = vec![4, 5, 6];
1716 /// vec.append(&mut vec2);
1717 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1718 /// assert_eq!(vec2, []);
1720 #[cfg(not(no_global_oom_handling))]
1722 #[stable(feature = "append", since = "1.4.0")]
1723 pub fn append(&mut self, other: &mut Self) {
1725 self.append_elements(other.as_slice() as _);
1730 /// Appends elements to `Self` from other buffer.
1731 #[cfg(not(no_global_oom_handling))]
1733 unsafe fn append_elements(&mut self, other: *const [T]) {
1734 let count = unsafe { (*other).len() };
1735 self.reserve(count);
1736 let len = self.len();
1737 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1741 /// Creates a draining iterator that removes the specified range in the vector
1742 /// and yields the removed items.
1744 /// When the iterator **is** dropped, all elements in the range are removed
1745 /// from the vector, even if the iterator was not fully consumed. If the
1746 /// iterator **is not** dropped (with [`mem::forget`] for example), it is
1747 /// unspecified how many elements are removed.
1751 /// Panics if the starting point is greater than the end point or if
1752 /// the end point is greater than the length of the vector.
1757 /// let mut v = vec![1, 2, 3];
1758 /// let u: Vec<_> = v.drain(1..).collect();
1759 /// assert_eq!(v, &[1]);
1760 /// assert_eq!(u, &[2, 3]);
1762 /// // A full range clears the vector
1764 /// assert_eq!(v, &[]);
1766 #[stable(feature = "drain", since = "1.6.0")]
1767 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1769 R: RangeBounds<usize>,
1773 // When the Drain is first created, it shortens the length of
1774 // the source vector to make sure no uninitialized or moved-from elements
1775 // are accessible at all if the Drain's destructor never gets to run.
1777 // Drain will ptr::read out the values to remove.
1778 // When finished, remaining tail of the vec is copied back to cover
1779 // the hole, and the vector length is restored to the new length.
1781 let len = self.len();
1782 let Range { start, end } = slice::range(range, ..len);
1785 // set self.vec length's to start, to be safe in case Drain is leaked
1786 self.set_len(start);
1787 // Use the borrow in the IterMut to indicate borrowing behavior of the
1788 // whole Drain iterator (like &mut T).
1789 let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
1792 tail_len: len - end,
1793 iter: range_slice.iter(),
1794 vec: NonNull::from(self),
1799 /// Clears the vector, removing all values.
1801 /// Note that this method has no effect on the allocated capacity
1807 /// let mut v = vec![1, 2, 3];
1811 /// assert!(v.is_empty());
1814 #[stable(feature = "rust1", since = "1.0.0")]
1815 pub fn clear(&mut self) {
1819 /// Returns the number of elements in the vector, also referred to
1820 /// as its 'length'.
1825 /// let a = vec![1, 2, 3];
1826 /// assert_eq!(a.len(), 3);
1829 #[stable(feature = "rust1", since = "1.0.0")]
1830 pub fn len(&self) -> usize {
1834 /// Returns `true` if the vector contains no elements.
1839 /// let mut v = Vec::new();
1840 /// assert!(v.is_empty());
1843 /// assert!(!v.is_empty());
1845 #[stable(feature = "rust1", since = "1.0.0")]
1846 pub fn is_empty(&self) -> bool {
1850 /// Splits the collection into two at the given index.
1852 /// Returns a newly allocated vector containing the elements in the range
1853 /// `[at, len)`. After the call, the original vector will be left containing
1854 /// the elements `[0, at)` with its previous capacity unchanged.
1858 /// Panics if `at > len`.
1863 /// let mut vec = vec![1, 2, 3];
1864 /// let vec2 = vec.split_off(1);
1865 /// assert_eq!(vec, [1]);
1866 /// assert_eq!(vec2, [2, 3]);
1868 #[cfg(not(no_global_oom_handling))]
1870 #[must_use = "use `.truncate()` if you don't need the other half"]
1871 #[stable(feature = "split_off", since = "1.4.0")]
1872 pub fn split_off(&mut self, at: usize) -> Self
1878 fn assert_failed(at: usize, len: usize) -> ! {
1879 panic!("`at` split index (is {}) should be <= len (is {})", at, len);
1882 if at > self.len() {
1883 assert_failed(at, self.len());
1887 // the new vector can take over the original buffer and avoid the copy
1888 return mem::replace(
1890 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
1894 let other_len = self.len - at;
1895 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
1897 // Unsafely `set_len` and copy items to `other`.
1900 other.set_len(other_len);
1902 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
1907 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
1909 /// If `new_len` is greater than `len`, the `Vec` is extended by the
1910 /// difference, with each additional slot filled with the result of
1911 /// calling the closure `f`. The return values from `f` will end up
1912 /// in the `Vec` in the order they have been generated.
1914 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
1916 /// This method uses a closure to create new values on every push. If
1917 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
1918 /// want to use the [`Default`] trait to generate values, you can
1919 /// pass [`Default::default`] as the second argument.
1924 /// let mut vec = vec![1, 2, 3];
1925 /// vec.resize_with(5, Default::default);
1926 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
1928 /// let mut vec = vec![];
1930 /// vec.resize_with(4, || { p *= 2; p });
1931 /// assert_eq!(vec, [2, 4, 8, 16]);
1933 #[cfg(not(no_global_oom_handling))]
1934 #[stable(feature = "vec_resize_with", since = "1.33.0")]
1935 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
1939 let len = self.len();
1941 self.extend_with(new_len - len, ExtendFunc(f));
1943 self.truncate(new_len);
1947 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
1948 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
1949 /// `'a`. If the type has only static references, or none at all, then this
1950 /// may be chosen to be `'static`.
1952 /// This function is similar to the [`leak`][Box::leak] function on [`Box`]
1953 /// except that there is no way to recover the leaked memory.
1955 /// This function is mainly useful for data that lives for the remainder of
1956 /// the program's life. Dropping the returned reference will cause a memory
1964 /// let x = vec![1, 2, 3];
1965 /// let static_ref: &'static mut [usize] = x.leak();
1966 /// static_ref[0] += 1;
1967 /// assert_eq!(static_ref, &[2, 2, 3]);
1969 #[cfg(not(no_global_oom_handling))]
1970 #[stable(feature = "vec_leak", since = "1.47.0")]
1972 pub fn leak<'a>(self) -> &'a mut [T]
1976 Box::leak(self.into_boxed_slice())
1979 /// Returns the remaining spare capacity of the vector as a slice of
1980 /// `MaybeUninit<T>`.
1982 /// The returned slice can be used to fill the vector with data (e.g. by
1983 /// reading from a file) before marking the data as initialized using the
1984 /// [`set_len`] method.
1986 /// [`set_len`]: Vec::set_len
1991 /// #![feature(vec_spare_capacity, maybe_uninit_extra)]
1993 /// // Allocate vector big enough for 10 elements.
1994 /// let mut v = Vec::with_capacity(10);
1996 /// // Fill in the first 3 elements.
1997 /// let uninit = v.spare_capacity_mut();
1998 /// uninit[0].write(0);
1999 /// uninit[1].write(1);
2000 /// uninit[2].write(2);
2002 /// // Mark the first 3 elements of the vector as being initialized.
2007 /// assert_eq!(&v, &[0, 1, 2]);
2009 #[unstable(feature = "vec_spare_capacity", issue = "75017")]
2011 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2013 // This method is not implemented in terms of `split_at_spare_mut`,
2014 // to prevent invalidation of pointers to the buffer.
2016 slice::from_raw_parts_mut(
2017 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2018 self.buf.capacity() - self.len,
2023 /// Returns vector content as a slice of `T`, along with the remaining spare
2024 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2026 /// The returned spare capacity slice can be used to fill the vector with data
2027 /// (e.g. by reading from a file) before marking the data as initialized using
2028 /// the [`set_len`] method.
2030 /// [`set_len`]: Vec::set_len
2032 /// Note that this is a low-level API, which should be used with care for
2033 /// optimization purposes. If you need to append data to a `Vec`
2034 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2035 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2036 /// [`resize_with`], depending on your exact needs.
2038 /// [`push`]: Vec::push
2039 /// [`extend`]: Vec::extend
2040 /// [`extend_from_slice`]: Vec::extend_from_slice
2041 /// [`extend_from_within`]: Vec::extend_from_within
2042 /// [`insert`]: Vec::insert
2043 /// [`append`]: Vec::append
2044 /// [`resize`]: Vec::resize
2045 /// [`resize_with`]: Vec::resize_with
2050 /// #![feature(vec_split_at_spare, maybe_uninit_extra)]
2052 /// let mut v = vec![1, 1, 2];
2054 /// // Reserve additional space big enough for 10 elements.
2057 /// let (init, uninit) = v.split_at_spare_mut();
2058 /// let sum = init.iter().copied().sum::<u32>();
2060 /// // Fill in the next 4 elements.
2061 /// uninit[0].write(sum);
2062 /// uninit[1].write(sum * 2);
2063 /// uninit[2].write(sum * 3);
2064 /// uninit[3].write(sum * 4);
2066 /// // Mark the 4 elements of the vector as being initialized.
2068 /// let len = v.len();
2069 /// v.set_len(len + 4);
2072 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2074 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2076 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2078 // - len is ignored and so never changed
2079 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2083 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2085 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2086 unsafe fn split_at_spare_mut_with_len(
2088 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2089 let Range { start: ptr, end: spare_ptr } = self.as_mut_ptr_range();
2090 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2091 let spare_len = self.buf.capacity() - self.len;
2094 // - `ptr` is guaranteed to be valid for `len` elements
2095 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2097 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2098 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2100 (initialized, spare, &mut self.len)
2105 impl<T: Clone, A: Allocator> Vec<T, A> {
2106 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2108 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2109 /// difference, with each additional slot filled with `value`.
2110 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2112 /// This method requires `T` to implement [`Clone`],
2113 /// in order to be able to clone the passed value.
2114 /// If you need more flexibility (or want to rely on [`Default`] instead of
2115 /// [`Clone`]), use [`Vec::resize_with`].
2120 /// let mut vec = vec!["hello"];
2121 /// vec.resize(3, "world");
2122 /// assert_eq!(vec, ["hello", "world", "world"]);
2124 /// let mut vec = vec![1, 2, 3, 4];
2125 /// vec.resize(2, 0);
2126 /// assert_eq!(vec, [1, 2]);
2128 #[cfg(not(no_global_oom_handling))]
2129 #[stable(feature = "vec_resize", since = "1.5.0")]
2130 pub fn resize(&mut self, new_len: usize, value: T) {
2131 let len = self.len();
2134 self.extend_with(new_len - len, ExtendElement(value))
2136 self.truncate(new_len);
2140 /// Clones and appends all elements in a slice to the `Vec`.
2142 /// Iterates over the slice `other`, clones each element, and then appends
2143 /// it to this `Vec`. The `other` vector is traversed in-order.
2145 /// Note that this function is same as [`extend`] except that it is
2146 /// specialized to work with slices instead. If and when Rust gets
2147 /// specialization this function will likely be deprecated (but still
2153 /// let mut vec = vec![1];
2154 /// vec.extend_from_slice(&[2, 3, 4]);
2155 /// assert_eq!(vec, [1, 2, 3, 4]);
2158 /// [`extend`]: Vec::extend
2159 #[cfg(not(no_global_oom_handling))]
2160 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2161 pub fn extend_from_slice(&mut self, other: &[T]) {
2162 self.spec_extend(other.iter())
2165 /// Copies elements from `src` range to the end of the vector.
2170 /// let mut vec = vec![0, 1, 2, 3, 4];
2172 /// vec.extend_from_within(2..);
2173 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2175 /// vec.extend_from_within(..2);
2176 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2178 /// vec.extend_from_within(4..8);
2179 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2181 #[cfg(not(no_global_oom_handling))]
2182 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2183 pub fn extend_from_within<R>(&mut self, src: R)
2185 R: RangeBounds<usize>,
2187 let range = slice::range(src, ..self.len());
2188 self.reserve(range.len());
2191 // - `slice::range` guarantees that the given range is valid for indexing self
2193 self.spec_extend_from_within(range);
2198 // This code generalizes `extend_with_{element,default}`.
2199 trait ExtendWith<T> {
2200 fn next(&mut self) -> T;
2204 struct ExtendElement<T>(T);
2205 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2206 fn next(&mut self) -> T {
2209 fn last(self) -> T {
2214 struct ExtendDefault;
2215 impl<T: Default> ExtendWith<T> for ExtendDefault {
2216 fn next(&mut self) -> T {
2219 fn last(self) -> T {
2224 struct ExtendFunc<F>(F);
2225 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
2226 fn next(&mut self) -> T {
2229 fn last(mut self) -> T {
2234 impl<T, A: Allocator> Vec<T, A> {
2235 #[cfg(not(no_global_oom_handling))]
2236 /// Extend the vector by `n` values, using the given generator.
2237 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2241 let mut ptr = self.as_mut_ptr().add(self.len());
2242 // Use SetLenOnDrop to work around bug where compiler
2243 // might not realize the store through `ptr` through self.set_len()
2245 let mut local_len = SetLenOnDrop::new(&mut self.len);
2247 // Write all elements except the last one
2249 ptr::write(ptr, value.next());
2250 ptr = ptr.offset(1);
2251 // Increment the length in every step in case next() panics
2252 local_len.increment_len(1);
2256 // We can write the last element directly without cloning needlessly
2257 ptr::write(ptr, value.last());
2258 local_len.increment_len(1);
2261 // len set by scope guard
2266 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2267 /// Removes consecutive repeated elements in the vector according to the
2268 /// [`PartialEq`] trait implementation.
2270 /// If the vector is sorted, this removes all duplicates.
2275 /// let mut vec = vec![1, 2, 2, 3, 2];
2279 /// assert_eq!(vec, [1, 2, 3, 2]);
2281 #[stable(feature = "rust1", since = "1.0.0")]
2283 pub fn dedup(&mut self) {
2284 self.dedup_by(|a, b| a == b)
2288 ////////////////////////////////////////////////////////////////////////////////
2289 // Internal methods and functions
2290 ////////////////////////////////////////////////////////////////////////////////
2293 #[cfg(not(no_global_oom_handling))]
2294 #[stable(feature = "rust1", since = "1.0.0")]
2295 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2296 <T as SpecFromElem>::from_elem(elem, n, Global)
2300 #[cfg(not(no_global_oom_handling))]
2301 #[unstable(feature = "allocator_api", issue = "32838")]
2302 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2303 <T as SpecFromElem>::from_elem(elem, n, alloc)
2306 trait ExtendFromWithinSpec {
2309 /// - `src` needs to be valid index
2310 /// - `self.capacity() - self.len()` must be `>= src.len()`
2311 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2314 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2315 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2317 // - len is increased only after initializing elements
2318 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2321 // - caller guaratees that src is a valid index
2322 let to_clone = unsafe { this.get_unchecked(src) };
2324 iter::zip(to_clone, spare)
2325 .map(|(src, dst)| dst.write(src.clone()))
2327 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2328 // - len is increased after each element to prevent leaks (see issue #82533)
2329 .for_each(|_| *len += 1);
2333 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2334 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2335 let count = src.len();
2337 let (init, spare) = self.split_at_spare_mut();
2340 // - caller guaratees that `src` is a valid index
2341 let source = unsafe { init.get_unchecked(src) };
2344 // - Both pointers are created from unique slice references (`&mut [_]`)
2345 // so they are valid and do not overlap.
2346 // - Elements are :Copy so it's OK to to copy them, without doing
2347 // anything with the original values
2348 // - `count` is equal to the len of `source`, so source is valid for
2350 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2351 // is valid for `count` writes
2352 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2356 // - The elements were just initialized by `copy_nonoverlapping`
2361 ////////////////////////////////////////////////////////////////////////////////
2362 // Common trait implementations for Vec
2363 ////////////////////////////////////////////////////////////////////////////////
2365 #[stable(feature = "rust1", since = "1.0.0")]
2366 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2369 fn deref(&self) -> &[T] {
2370 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2374 #[stable(feature = "rust1", since = "1.0.0")]
2375 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2376 fn deref_mut(&mut self) -> &mut [T] {
2377 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2381 #[cfg(not(no_global_oom_handling))]
2382 trait SpecCloneFrom {
2383 fn clone_from(this: &mut Self, other: &Self);
2386 #[cfg(not(no_global_oom_handling))]
2387 impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
2388 default fn clone_from(this: &mut Self, other: &Self) {
2389 // drop anything that will not be overwritten
2390 this.truncate(other.len());
2392 // self.len <= other.len due to the truncate above, so the
2393 // slices here are always in-bounds.
2394 let (init, tail) = other.split_at(this.len());
2396 // reuse the contained values' allocations/resources.
2397 this.clone_from_slice(init);
2398 this.extend_from_slice(tail);
2402 #[cfg(not(no_global_oom_handling))]
2403 impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
2404 fn clone_from(this: &mut Self, other: &Self) {
2406 this.extend_from_slice(other);
2410 #[cfg(not(no_global_oom_handling))]
2411 #[stable(feature = "rust1", since = "1.0.0")]
2412 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2414 fn clone(&self) -> Self {
2415 let alloc = self.allocator().clone();
2416 <[T]>::to_vec_in(&**self, alloc)
2419 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2420 // required for this method definition, is not available. Instead use the
2421 // `slice::to_vec` function which is only available with cfg(test)
2422 // NB see the slice::hack module in slice.rs for more information
2424 fn clone(&self) -> Self {
2425 let alloc = self.allocator().clone();
2426 crate::slice::to_vec(&**self, alloc)
2429 fn clone_from(&mut self, other: &Self) {
2430 SpecCloneFrom::clone_from(self, other)
2434 /// The hash of a vector is the same as that of the corresponding slice,
2435 /// as required by the `core::borrow::Borrow` implementation.
2438 /// #![feature(build_hasher_simple_hash_one)]
2439 /// use std::hash::BuildHasher;
2441 /// let b = std::collections::hash_map::RandomState::new();
2442 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2443 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2444 /// assert_eq!(b.hash_one(v), b.hash_one(s));
2446 #[stable(feature = "rust1", since = "1.0.0")]
2447 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2449 fn hash<H: Hasher>(&self, state: &mut H) {
2450 Hash::hash(&**self, state)
2454 #[stable(feature = "rust1", since = "1.0.0")]
2455 #[rustc_on_unimplemented(
2456 message = "vector indices are of type `usize` or ranges of `usize`",
2457 label = "vector indices are of type `usize` or ranges of `usize`"
2459 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2460 type Output = I::Output;
2463 fn index(&self, index: I) -> &Self::Output {
2464 Index::index(&**self, index)
2468 #[stable(feature = "rust1", since = "1.0.0")]
2469 #[rustc_on_unimplemented(
2470 message = "vector indices are of type `usize` or ranges of `usize`",
2471 label = "vector indices are of type `usize` or ranges of `usize`"
2473 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2475 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2476 IndexMut::index_mut(&mut **self, index)
2480 #[cfg(not(no_global_oom_handling))]
2481 #[stable(feature = "rust1", since = "1.0.0")]
2482 impl<T> FromIterator<T> for Vec<T> {
2484 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2485 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2489 #[stable(feature = "rust1", since = "1.0.0")]
2490 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2492 type IntoIter = IntoIter<T, A>;
2494 /// Creates a consuming iterator, that is, one that moves each value out of
2495 /// the vector (from start to end). The vector cannot be used after calling
2501 /// let v = vec!["a".to_string(), "b".to_string()];
2502 /// for s in v.into_iter() {
2503 /// // s has type String, not &String
2504 /// println!("{}", s);
2508 fn into_iter(self) -> IntoIter<T, A> {
2510 let mut me = ManuallyDrop::new(self);
2511 let alloc = ptr::read(me.allocator());
2512 let begin = me.as_mut_ptr();
2513 let end = if mem::size_of::<T>() == 0 {
2514 arith_offset(begin as *const i8, me.len() as isize) as *const T
2516 begin.add(me.len()) as *const T
2518 let cap = me.buf.capacity();
2520 buf: NonNull::new_unchecked(begin),
2521 phantom: PhantomData,
2531 #[stable(feature = "rust1", since = "1.0.0")]
2532 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2534 type IntoIter = slice::Iter<'a, T>;
2536 fn into_iter(self) -> slice::Iter<'a, T> {
2541 #[stable(feature = "rust1", since = "1.0.0")]
2542 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2543 type Item = &'a mut T;
2544 type IntoIter = slice::IterMut<'a, T>;
2546 fn into_iter(self) -> slice::IterMut<'a, T> {
2551 #[cfg(not(no_global_oom_handling))]
2552 #[stable(feature = "rust1", since = "1.0.0")]
2553 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2555 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2556 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2560 fn extend_one(&mut self, item: T) {
2565 fn extend_reserve(&mut self, additional: usize) {
2566 self.reserve(additional);
2570 impl<T, A: Allocator> Vec<T, A> {
2571 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2572 // they have no further optimizations to apply
2573 #[cfg(not(no_global_oom_handling))]
2574 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2575 // This is the case for a general iterator.
2577 // This function should be the moral equivalent of:
2579 // for item in iterator {
2582 while let Some(element) = iterator.next() {
2583 let len = self.len();
2584 if len == self.capacity() {
2585 let (lower, _) = iterator.size_hint();
2586 self.reserve(lower.saturating_add(1));
2589 ptr::write(self.as_mut_ptr().add(len), element);
2590 // Since next() executes user code which can panic we have to bump the length
2592 // NB can't overflow since we would have had to alloc the address space
2593 self.set_len(len + 1);
2598 /// Creates a splicing iterator that replaces the specified range in the vector
2599 /// with the given `replace_with` iterator and yields the removed items.
2600 /// `replace_with` does not need to be the same length as `range`.
2602 /// `range` is removed even if the iterator is not consumed until the end.
2604 /// It is unspecified how many elements are removed from the vector
2605 /// if the `Splice` value is leaked.
2607 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2609 /// This is optimal if:
2611 /// * The tail (elements in the vector after `range`) is empty,
2612 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2613 /// * or the lower bound of its `size_hint()` is exact.
2615 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2619 /// Panics if the starting point is greater than the end point or if
2620 /// the end point is greater than the length of the vector.
2625 /// let mut v = vec![1, 2, 3];
2626 /// let new = [7, 8];
2627 /// let u: Vec<_> = v.splice(..2, new).collect();
2628 /// assert_eq!(v, &[7, 8, 3]);
2629 /// assert_eq!(u, &[1, 2]);
2631 #[cfg(not(no_global_oom_handling))]
2633 #[stable(feature = "vec_splice", since = "1.21.0")]
2634 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2636 R: RangeBounds<usize>,
2637 I: IntoIterator<Item = T>,
2639 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2642 /// Creates an iterator which uses a closure to determine if an element should be removed.
2644 /// If the closure returns true, then the element is removed and yielded.
2645 /// If the closure returns false, the element will remain in the vector and will not be yielded
2646 /// by the iterator.
2648 /// Using this method is equivalent to the following code:
2651 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2652 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2654 /// while i < vec.len() {
2655 /// if some_predicate(&mut vec[i]) {
2656 /// let val = vec.remove(i);
2657 /// // your code here
2663 /// # assert_eq!(vec, vec![1, 4, 5]);
2666 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2667 /// because it can backshift the elements of the array in bulk.
2669 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2670 /// regardless of whether you choose to keep or remove it.
2674 /// Splitting an array into evens and odds, reusing the original allocation:
2677 /// #![feature(drain_filter)]
2678 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2680 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2681 /// let odds = numbers;
2683 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2684 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2686 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2687 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
2689 F: FnMut(&mut T) -> bool,
2691 let old_len = self.len();
2693 // Guard against us getting leaked (leak amplification)
2698 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2702 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2704 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2705 /// append the entire slice at once.
2707 /// [`copy_from_slice`]: slice::copy_from_slice
2708 #[cfg(not(no_global_oom_handling))]
2709 #[stable(feature = "extend_ref", since = "1.2.0")]
2710 impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
2711 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2712 self.spec_extend(iter.into_iter())
2716 fn extend_one(&mut self, &item: &'a T) {
2721 fn extend_reserve(&mut self, additional: usize) {
2722 self.reserve(additional);
2726 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2727 #[stable(feature = "rust1", since = "1.0.0")]
2728 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
2730 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2731 PartialOrd::partial_cmp(&**self, &**other)
2735 #[stable(feature = "rust1", since = "1.0.0")]
2736 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
2738 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2739 #[stable(feature = "rust1", since = "1.0.0")]
2740 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
2742 fn cmp(&self, other: &Self) -> Ordering {
2743 Ord::cmp(&**self, &**other)
2747 #[stable(feature = "rust1", since = "1.0.0")]
2748 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
2749 fn drop(&mut self) {
2752 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2753 // could avoid questions of validity in certain cases
2754 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
2756 // RawVec handles deallocation
2760 #[stable(feature = "rust1", since = "1.0.0")]
2761 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
2762 impl<T> const Default for Vec<T> {
2763 /// Creates an empty `Vec<T>`.
2764 fn default() -> Vec<T> {
2769 #[stable(feature = "rust1", since = "1.0.0")]
2770 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
2771 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2772 fmt::Debug::fmt(&**self, f)
2776 #[stable(feature = "rust1", since = "1.0.0")]
2777 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
2778 fn as_ref(&self) -> &Vec<T, A> {
2783 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2784 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
2785 fn as_mut(&mut self) -> &mut Vec<T, A> {
2790 #[stable(feature = "rust1", since = "1.0.0")]
2791 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
2792 fn as_ref(&self) -> &[T] {
2797 #[stable(feature = "vec_as_mut", since = "1.5.0")]
2798 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
2799 fn as_mut(&mut self) -> &mut [T] {
2804 #[cfg(not(no_global_oom_handling))]
2805 #[stable(feature = "rust1", since = "1.0.0")]
2806 impl<T: Clone> From<&[T]> for Vec<T> {
2807 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2812 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
2815 fn from(s: &[T]) -> Vec<T> {
2819 fn from(s: &[T]) -> Vec<T> {
2820 crate::slice::to_vec(s, Global)
2824 #[cfg(not(no_global_oom_handling))]
2825 #[stable(feature = "vec_from_mut", since = "1.19.0")]
2826 impl<T: Clone> From<&mut [T]> for Vec<T> {
2827 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2832 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
2835 fn from(s: &mut [T]) -> Vec<T> {
2839 fn from(s: &mut [T]) -> Vec<T> {
2840 crate::slice::to_vec(s, Global)
2844 #[cfg(not(no_global_oom_handling))]
2845 #[stable(feature = "vec_from_array", since = "1.44.0")]
2846 impl<T, const N: usize> From<[T; N]> for Vec<T> {
2848 fn from(s: [T; N]) -> Vec<T> {
2849 <[T]>::into_vec(box s)
2851 /// Allocate a `Vec<T>` and move `s`'s items into it.
2856 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
2859 fn from(s: [T; N]) -> Vec<T> {
2860 crate::slice::into_vec(box s)
2864 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
2865 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
2867 [T]: ToOwned<Owned = Vec<T>>,
2869 /// Convert a clone-on-write slice into a vector.
2871 /// If `s` already owns a `Vec<T>`, it will be returned directly.
2872 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
2873 /// filled by cloning `s`'s items into it.
2878 /// # use std::borrow::Cow;
2879 /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
2880 /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
2881 /// assert_eq!(Vec::from(o), Vec::from(b));
2883 fn from(s: Cow<'a, [T]>) -> Vec<T> {
2888 // note: test pulls in libstd, which causes errors here
2890 #[stable(feature = "vec_from_box", since = "1.18.0")]
2891 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
2892 /// Convert a boxed slice into a vector by transferring ownership of
2893 /// the existing heap allocation.
2898 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
2899 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
2901 fn from(s: Box<[T], A>) -> Self {
2906 // note: test pulls in libstd, which causes errors here
2907 #[cfg(not(no_global_oom_handling))]
2909 #[stable(feature = "box_from_vec", since = "1.20.0")]
2910 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
2911 /// Convert a vector into a boxed slice.
2913 /// If `v` has excess capacity, its items will be moved into a
2914 /// newly-allocated buffer with exactly the right capacity.
2919 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
2921 fn from(v: Vec<T, A>) -> Self {
2922 v.into_boxed_slice()
2926 #[cfg(not(no_global_oom_handling))]
2927 #[stable(feature = "rust1", since = "1.0.0")]
2928 impl From<&str> for Vec<u8> {
2929 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
2934 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
2936 fn from(s: &str) -> Vec<u8> {
2937 From::from(s.as_bytes())
2941 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
2942 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
2943 type Error = Vec<T, A>;
2945 /// Gets the entire contents of the `Vec<T>` as an array,
2946 /// if its size exactly matches that of the requested array.
2951 /// use std::convert::TryInto;
2952 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
2953 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
2956 /// If the length doesn't match, the input comes back in `Err`:
2958 /// use std::convert::TryInto;
2959 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
2960 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
2963 /// If you're fine with just getting a prefix of the `Vec<T>`,
2964 /// you can call [`.truncate(N)`](Vec::truncate) first.
2966 /// use std::convert::TryInto;
2967 /// let mut v = String::from("hello world").into_bytes();
2970 /// let [a, b]: [_; 2] = v.try_into().unwrap();
2971 /// assert_eq!(a, b' ');
2972 /// assert_eq!(b, b'd');
2974 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
2979 // SAFETY: `.set_len(0)` is always sound.
2980 unsafe { vec.set_len(0) };
2982 // SAFETY: A `Vec`'s pointer is always aligned properly, and
2983 // the alignment the array needs is the same as the items.
2984 // We checked earlier that we have sufficient items.
2985 // The items will not double-drop as the `set_len`
2986 // tells the `Vec` not to also drop them.
2987 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };