1 //! A contiguous growable array type with heap-allocated contents, written
4 //! Vectors have *O*(1) indexing, amortized *O*(1) push (to the end) and
5 //! *O*(1) pop (from the end).
7 //! Vectors ensure they never allocate more than `isize::MAX` bytes.
11 //! You can explicitly create a [`Vec`] with [`Vec::new`]:
14 //! let v: Vec<i32> = Vec::new();
17 //! ...or by using the [`vec!`] macro:
20 //! let v: Vec<i32> = vec![];
22 //! let v = vec![1, 2, 3, 4, 5];
24 //! let v = vec![0; 10]; // ten zeroes
27 //! You can [`push`] values onto the end of a vector (which will grow the vector
31 //! let mut v = vec![1, 2];
36 //! Popping values works in much the same way:
39 //! let mut v = vec![1, 2];
41 //! let two = v.pop();
44 //! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
47 //! let mut v = vec![1, 2, 3];
52 //! [`push`]: Vec::push
54 #![stable(feature = "rust1", since = "1.0.0")]
56 #[cfg(not(no_global_oom_handling))]
58 use core::cmp::Ordering;
59 use core::convert::TryFrom;
61 use core::hash::{Hash, Hasher};
62 use core::intrinsics::assume;
64 #[cfg(not(no_global_oom_handling))]
65 use core::iter::FromIterator;
66 use core::marker::PhantomData;
67 use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
68 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
69 use core::ptr::{self, NonNull};
70 use core::slice::{self, SliceIndex};
72 use crate::alloc::{Allocator, Global};
73 use crate::borrow::{Cow, ToOwned};
74 use crate::boxed::Box;
75 use crate::collections::TryReserveError;
76 use crate::raw_vec::RawVec;
78 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
79 pub use self::drain_filter::DrainFilter;
83 #[cfg(not(no_global_oom_handling))]
84 #[stable(feature = "vec_splice", since = "1.21.0")]
85 pub use self::splice::Splice;
87 #[cfg(not(no_global_oom_handling))]
90 #[stable(feature = "drain", since = "1.6.0")]
91 pub use self::drain::Drain;
95 #[cfg(not(no_global_oom_handling))]
98 #[cfg(not(no_global_oom_handling))]
99 pub(crate) use self::in_place_collect::AsVecIntoIter;
100 #[stable(feature = "rust1", since = "1.0.0")]
101 pub use self::into_iter::IntoIter;
105 #[cfg(not(no_global_oom_handling))]
106 use self::is_zero::IsZero;
110 #[cfg(not(no_global_oom_handling))]
111 mod in_place_collect;
115 #[cfg(not(no_global_oom_handling))]
116 use self::spec_from_elem::SpecFromElem;
118 #[cfg(not(no_global_oom_handling))]
121 #[cfg(not(no_global_oom_handling))]
122 use self::set_len_on_drop::SetLenOnDrop;
124 #[cfg(not(no_global_oom_handling))]
127 #[cfg(not(no_global_oom_handling))]
128 use self::in_place_drop::{InPlaceDrop, InPlaceDstBufDrop};
130 #[cfg(not(no_global_oom_handling))]
133 #[cfg(not(no_global_oom_handling))]
134 use self::spec_from_iter_nested::SpecFromIterNested;
136 #[cfg(not(no_global_oom_handling))]
137 mod spec_from_iter_nested;
139 #[cfg(not(no_global_oom_handling))]
140 use self::spec_from_iter::SpecFromIter;
142 #[cfg(not(no_global_oom_handling))]
145 #[cfg(not(no_global_oom_handling))]
146 use self::spec_extend::SpecExtend;
148 #[cfg(not(no_global_oom_handling))]
151 /// A contiguous growable array type, written as `Vec<T>`, short for 'vector'.
156 /// let mut vec = Vec::new();
160 /// assert_eq!(vec.len(), 2);
161 /// assert_eq!(vec[0], 1);
163 /// assert_eq!(vec.pop(), Some(2));
164 /// assert_eq!(vec.len(), 1);
167 /// assert_eq!(vec[0], 7);
169 /// vec.extend([1, 2, 3].iter().copied());
174 /// assert_eq!(vec, [7, 1, 2, 3]);
177 /// The [`vec!`] macro is provided for convenient initialization:
180 /// let mut vec1 = vec![1, 2, 3];
182 /// let vec2 = Vec::from([1, 2, 3, 4]);
183 /// assert_eq!(vec1, vec2);
186 /// It can also initialize each element of a `Vec<T>` with a given value.
187 /// This may be more efficient than performing allocation and initialization
188 /// in separate steps, especially when initializing a vector of zeros:
191 /// let vec = vec![0; 5];
192 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
194 /// // The following is equivalent, but potentially slower:
195 /// let mut vec = Vec::with_capacity(5);
196 /// vec.resize(5, 0);
197 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
200 /// For more information, see
201 /// [Capacity and Reallocation](#capacity-and-reallocation).
203 /// Use a `Vec<T>` as an efficient stack:
206 /// let mut stack = Vec::new();
212 /// while let Some(top) = stack.pop() {
213 /// // Prints 3, 2, 1
214 /// println!("{top}");
220 /// The `Vec` type allows to access values by index, because it implements the
221 /// [`Index`] trait. An example will be more explicit:
224 /// let v = vec![0, 2, 4, 6];
225 /// println!("{}", v[1]); // it will display '2'
228 /// However be careful: if you try to access an index which isn't in the `Vec`,
229 /// your software will panic! You cannot do this:
232 /// let v = vec![0, 2, 4, 6];
233 /// println!("{}", v[6]); // it will panic!
236 /// Use [`get`] and [`get_mut`] if you want to check whether the index is in
241 /// A `Vec` can be mutable. On the other hand, slices are read-only objects.
242 /// To get a [slice][prim@slice], use [`&`]. Example:
245 /// fn read_slice(slice: &[usize]) {
249 /// let v = vec![0, 1];
252 /// // ... and that's all!
253 /// // you can also do it like this:
254 /// let u: &[usize] = &v;
256 /// let u: &[_] = &v;
259 /// In Rust, it's more common to pass slices as arguments rather than vectors
260 /// when you just want to provide read access. The same goes for [`String`] and
263 /// # Capacity and reallocation
265 /// The capacity of a vector is the amount of space allocated for any future
266 /// elements that will be added onto the vector. This is not to be confused with
267 /// the *length* of a vector, which specifies the number of actual elements
268 /// within the vector. If a vector's length exceeds its capacity, its capacity
269 /// will automatically be increased, but its elements will have to be
272 /// For example, a vector with capacity 10 and length 0 would be an empty vector
273 /// with space for 10 more elements. Pushing 10 or fewer elements onto the
274 /// vector will not change its capacity or cause reallocation to occur. However,
275 /// if the vector's length is increased to 11, it will have to reallocate, which
276 /// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
277 /// whenever possible to specify how big the vector is expected to get.
281 /// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
282 /// about its design. This ensures that it's as low-overhead as possible in
283 /// the general case, and can be correctly manipulated in primitive ways
284 /// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
285 /// If additional type parameters are added (e.g., to support custom allocators),
286 /// overriding their defaults may change the behavior.
288 /// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
289 /// triplet. No more, no less. The order of these fields is completely
290 /// unspecified, and you should use the appropriate methods to modify these.
291 /// The pointer will never be null, so this type is null-pointer-optimized.
293 /// However, the pointer might not actually point to allocated memory. In particular,
294 /// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
295 /// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
296 /// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
297 /// types inside a `Vec`, it will not allocate space for them. *Note that in this case
298 /// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
299 /// if <code>[mem::size_of::\<T>]\() * [capacity]\() > 0</code>. In general, `Vec`'s allocation
300 /// details are very subtle --- if you intend to allocate memory using a `Vec`
301 /// and use it for something else (either to pass to unsafe code, or to build your
302 /// own memory-backed collection), be sure to deallocate this memory by using
303 /// `from_raw_parts` to recover the `Vec` and then dropping it.
305 /// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
306 /// (as defined by the allocator Rust is configured to use by default), and its
307 /// pointer points to [`len`] initialized, contiguous elements in order (what
308 /// you would see if you coerced it to a slice), followed by <code>[capacity] - [len]</code>
309 /// logically uninitialized, contiguous elements.
311 /// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
312 /// visualized as below. The top part is the `Vec` struct, it contains a
313 /// pointer to the head of the allocation in the heap, length and capacity.
314 /// The bottom part is the allocation on the heap, a contiguous memory block.
318 /// +--------+--------+--------+
319 /// | 0x0123 | 2 | 4 |
320 /// +--------+--------+--------+
323 /// Heap +--------+--------+--------+--------+
324 /// | 'a' | 'b' | uninit | uninit |
325 /// +--------+--------+--------+--------+
328 /// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
329 /// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
330 /// layout (including the order of fields).
332 /// `Vec` will never perform a "small optimization" where elements are actually
333 /// stored on the stack for two reasons:
335 /// * It would make it more difficult for unsafe code to correctly manipulate
336 /// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
337 /// only moved, and it would be more difficult to determine if a `Vec` had
338 /// actually allocated memory.
340 /// * It would penalize the general case, incurring an additional branch
343 /// `Vec` will never automatically shrink itself, even if completely empty. This
344 /// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
345 /// and then filling it back up to the same [`len`] should incur no calls to
346 /// the allocator. If you wish to free up unused memory, use
347 /// [`shrink_to_fit`] or [`shrink_to`].
349 /// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
350 /// sufficient. [`push`] and [`insert`] *will* (re)allocate if
351 /// <code>[len] == [capacity]</code>. That is, the reported capacity is completely
352 /// accurate, and can be relied on. It can even be used to manually free the memory
353 /// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
354 /// when not necessary.
356 /// `Vec` does not guarantee any particular growth strategy when reallocating
357 /// when full, nor when [`reserve`] is called. The current strategy is basic
358 /// and it may prove desirable to use a non-constant growth factor. Whatever
359 /// strategy is used will of course guarantee *O*(1) amortized [`push`].
361 /// `vec![x; n]`, `vec![a, b, c, d]`, and
362 /// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
363 /// with exactly the requested capacity. If <code>[len] == [capacity]</code>,
364 /// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
365 /// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
367 /// `Vec` will not specifically overwrite any data that is removed from it,
368 /// but also won't specifically preserve it. Its uninitialized memory is
369 /// scratch space that it may use however it wants. It will generally just do
370 /// whatever is most efficient or otherwise easy to implement. Do not rely on
371 /// removed data to be erased for security purposes. Even if you drop a `Vec`, its
372 /// buffer may simply be reused by another allocation. Even if you zero a `Vec`'s memory
373 /// first, that might not actually happen because the optimizer does not consider
374 /// this a side-effect that must be preserved. There is one case which we will
375 /// not break, however: using `unsafe` code to write to the excess capacity,
376 /// and then increasing the length to match, is always valid.
378 /// Currently, `Vec` does not guarantee the order in which elements are dropped.
379 /// The order has changed in the past and may change again.
381 /// [`get`]: ../../std/vec/struct.Vec.html#method.get
382 /// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
383 /// [`String`]: crate::string::String
384 /// [`&str`]: type@str
385 /// [`shrink_to_fit`]: Vec::shrink_to_fit
386 /// [`shrink_to`]: Vec::shrink_to
387 /// [capacity]: Vec::capacity
388 /// [`capacity`]: Vec::capacity
389 /// [mem::size_of::\<T>]: core::mem::size_of
391 /// [`len`]: Vec::len
392 /// [`push`]: Vec::push
393 /// [`insert`]: Vec::insert
394 /// [`reserve`]: Vec::reserve
395 /// [`MaybeUninit`]: core::mem::MaybeUninit
396 /// [owned slice]: Box
397 #[stable(feature = "rust1", since = "1.0.0")]
398 #[cfg_attr(not(test), rustc_diagnostic_item = "Vec")]
399 #[rustc_insignificant_dtor]
400 pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
405 ////////////////////////////////////////////////////////////////////////////////
407 ////////////////////////////////////////////////////////////////////////////////
410 /// Constructs a new, empty `Vec<T>`.
412 /// The vector will not allocate until elements are pushed onto it.
417 /// # #![allow(unused_mut)]
418 /// let mut vec: Vec<i32> = Vec::new();
421 #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
422 #[stable(feature = "rust1", since = "1.0.0")]
424 pub const fn new() -> Self {
425 Vec { buf: RawVec::NEW, len: 0 }
428 /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
430 /// The vector will be able to hold at least `capacity` elements without
431 /// reallocating. This method is allowed to allocate for more elements than
432 /// `capacity`. If `capacity` is 0, the vector will not allocate.
434 /// It is important to note that although the returned vector has the
435 /// minimum *capacity* specified, the vector will have a zero *length*. For
436 /// an explanation of the difference between length and capacity, see
437 /// *[Capacity and reallocation]*.
439 /// If it is important to know the exact allocated capacity of a `Vec`,
440 /// always use the [`capacity`] method after construction.
442 /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
443 /// and the capacity will always be `usize::MAX`.
445 /// [Capacity and reallocation]: #capacity-and-reallocation
446 /// [`capacity`]: Vec::capacity
450 /// Panics if the new capacity exceeds `isize::MAX` bytes.
455 /// let mut vec = Vec::with_capacity(10);
457 /// // The vector contains no items, even though it has capacity for more
458 /// assert_eq!(vec.len(), 0);
459 /// assert!(vec.capacity() >= 10);
461 /// // These are all done without reallocating...
465 /// assert_eq!(vec.len(), 10);
466 /// assert!(vec.capacity() >= 10);
468 /// // ...but this may make the vector reallocate
470 /// assert_eq!(vec.len(), 11);
471 /// assert!(vec.capacity() >= 11);
473 /// // A vector of a zero-sized type will always over-allocate, since no
474 /// // allocation is necessary
475 /// let vec_units = Vec::<()>::with_capacity(10);
476 /// assert_eq!(vec_units.capacity(), usize::MAX);
478 #[cfg(not(no_global_oom_handling))]
480 #[stable(feature = "rust1", since = "1.0.0")]
482 pub fn with_capacity(capacity: usize) -> Self {
483 Self::with_capacity_in(capacity, Global)
486 /// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
490 /// This is highly unsafe, due to the number of invariants that aren't
493 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
494 /// (`T` having a less strict alignment is not sufficient, the alignment really
495 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
496 /// allocated and deallocated with the same layout.)
497 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
498 /// to be the same size as the pointer was allocated with. (Because similar to
499 /// alignment, [`dealloc`] must be called with the same layout `size`.)
500 /// * `length` needs to be less than or equal to `capacity`.
501 /// * The first `length` values must be properly initialized values of type `T`.
502 /// * `capacity` needs to be the capacity that the pointer was allocated with.
503 /// * The allocated size in bytes must be no larger than `isize::MAX`.
504 /// See the safety documentation of [`pointer::offset`].
506 /// These requirements are always upheld by any `ptr` that has been allocated
507 /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
510 /// Violating these may cause problems like corrupting the allocator's
511 /// internal data structures. For example it is normally **not** safe
512 /// to build a `Vec<u8>` from a pointer to a C `char` array with length
513 /// `size_t`, doing so is only safe if the array was initially allocated by
514 /// a `Vec` or `String`.
515 /// It's also not safe to build one from a `Vec<u16>` and its length, because
516 /// the allocator cares about the alignment, and these two types have different
517 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
518 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
519 /// these issues, it is often preferable to do casting/transmuting using
520 /// [`slice::from_raw_parts`] instead.
522 /// The ownership of `ptr` is effectively transferred to the
523 /// `Vec<T>` which may then deallocate, reallocate or change the
524 /// contents of memory pointed to by the pointer at will. Ensure
525 /// that nothing else uses the pointer after calling this
528 /// [`String`]: crate::string::String
529 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
537 /// let v = vec![1, 2, 3];
539 // FIXME Update this when vec_into_raw_parts is stabilized
540 /// // Prevent running `v`'s destructor so we are in complete control
541 /// // of the allocation.
542 /// let mut v = mem::ManuallyDrop::new(v);
544 /// // Pull out the various important pieces of information about `v`
545 /// let p = v.as_mut_ptr();
546 /// let len = v.len();
547 /// let cap = v.capacity();
550 /// // Overwrite memory with 4, 5, 6
551 /// for i in 0..len {
552 /// ptr::write(p.add(i), 4 + i);
555 /// // Put everything back together into a Vec
556 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
557 /// assert_eq!(rebuilt, [4, 5, 6]);
561 /// Using memory that was allocated elsewhere:
564 /// #![feature(allocator_api)]
566 /// use std::alloc::{AllocError, Allocator, Global, Layout};
569 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
571 /// let vec = unsafe {
572 /// let mem = match Global.allocate(layout) {
573 /// Ok(mem) => mem.cast::<u32>().as_ptr(),
574 /// Err(AllocError) => return,
577 /// mem.write(1_000_000);
579 /// Vec::from_raw_parts_in(mem, 1, 16, Global)
582 /// assert_eq!(vec, &[1_000_000]);
583 /// assert_eq!(vec.capacity(), 16);
587 #[stable(feature = "rust1", since = "1.0.0")]
588 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
589 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
593 impl<T, A: Allocator> Vec<T, A> {
594 /// Constructs a new, empty `Vec<T, A>`.
596 /// The vector will not allocate until elements are pushed onto it.
601 /// #![feature(allocator_api)]
603 /// use std::alloc::System;
605 /// # #[allow(unused_mut)]
606 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
609 #[unstable(feature = "allocator_api", issue = "32838")]
610 pub const fn new_in(alloc: A) -> Self {
611 Vec { buf: RawVec::new_in(alloc), len: 0 }
614 /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
615 /// with the provided allocator.
617 /// The vector will be able to hold at least `capacity` elements without
618 /// reallocating. This method is allowed to allocate for more elements than
619 /// `capacity`. If `capacity` is 0, the vector will not allocate.
621 /// It is important to note that although the returned vector has the
622 /// minimum *capacity* specified, the vector will have a zero *length*. For
623 /// an explanation of the difference between length and capacity, see
624 /// *[Capacity and reallocation]*.
626 /// If it is important to know the exact allocated capacity of a `Vec`,
627 /// always use the [`capacity`] method after construction.
629 /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
630 /// and the capacity will always be `usize::MAX`.
632 /// [Capacity and reallocation]: #capacity-and-reallocation
633 /// [`capacity`]: Vec::capacity
637 /// Panics if the new capacity exceeds `isize::MAX` bytes.
642 /// #![feature(allocator_api)]
644 /// use std::alloc::System;
646 /// let mut vec = Vec::with_capacity_in(10, System);
648 /// // The vector contains no items, even though it has capacity for more
649 /// assert_eq!(vec.len(), 0);
650 /// assert_eq!(vec.capacity(), 10);
652 /// // These are all done without reallocating...
656 /// assert_eq!(vec.len(), 10);
657 /// assert_eq!(vec.capacity(), 10);
659 /// // ...but this may make the vector reallocate
661 /// assert_eq!(vec.len(), 11);
662 /// assert!(vec.capacity() >= 11);
664 /// // A vector of a zero-sized type will always over-allocate, since no
665 /// // allocation is necessary
666 /// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
667 /// assert_eq!(vec_units.capacity(), usize::MAX);
669 #[cfg(not(no_global_oom_handling))]
671 #[unstable(feature = "allocator_api", issue = "32838")]
672 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
673 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
676 /// Creates a `Vec<T, A>` directly from a pointer, a capacity, a length,
677 /// and an allocator.
681 /// This is highly unsafe, due to the number of invariants that aren't
684 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
685 /// (`T` having a less strict alignment is not sufficient, the alignment really
686 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
687 /// allocated and deallocated with the same layout.)
688 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
689 /// to be the same size as the pointer was allocated with. (Because similar to
690 /// alignment, [`dealloc`] must be called with the same layout `size`.)
691 /// * `length` needs to be less than or equal to `capacity`.
692 /// * The first `length` values must be properly initialized values of type `T`.
693 /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
694 /// * The allocated size in bytes must be no larger than `isize::MAX`.
695 /// See the safety documentation of [`pointer::offset`].
697 /// These requirements are always upheld by any `ptr` that has been allocated
698 /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
701 /// Violating these may cause problems like corrupting the allocator's
702 /// internal data structures. For example it is **not** safe
703 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
704 /// It's also not safe to build one from a `Vec<u16>` and its length, because
705 /// the allocator cares about the alignment, and these two types have different
706 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
707 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
709 /// The ownership of `ptr` is effectively transferred to the
710 /// `Vec<T>` which may then deallocate, reallocate or change the
711 /// contents of memory pointed to by the pointer at will. Ensure
712 /// that nothing else uses the pointer after calling this
715 /// [`String`]: crate::string::String
716 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
717 /// [*fit*]: crate::alloc::Allocator#memory-fitting
722 /// #![feature(allocator_api)]
724 /// use std::alloc::System;
729 /// let mut v = Vec::with_capacity_in(3, System);
734 // FIXME Update this when vec_into_raw_parts is stabilized
735 /// // Prevent running `v`'s destructor so we are in complete control
736 /// // of the allocation.
737 /// let mut v = mem::ManuallyDrop::new(v);
739 /// // Pull out the various important pieces of information about `v`
740 /// let p = v.as_mut_ptr();
741 /// let len = v.len();
742 /// let cap = v.capacity();
743 /// let alloc = v.allocator();
746 /// // Overwrite memory with 4, 5, 6
747 /// for i in 0..len {
748 /// ptr::write(p.add(i), 4 + i);
751 /// // Put everything back together into a Vec
752 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
753 /// assert_eq!(rebuilt, [4, 5, 6]);
757 /// Using memory that was allocated elsewhere:
760 /// use std::alloc::{alloc, Layout};
763 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
764 /// let vec = unsafe {
765 /// let mem = alloc(layout).cast::<u32>();
766 /// if mem.is_null() {
770 /// mem.write(1_000_000);
772 /// Vec::from_raw_parts(mem, 1, 16)
775 /// assert_eq!(vec, &[1_000_000]);
776 /// assert_eq!(vec.capacity(), 16);
780 #[unstable(feature = "allocator_api", issue = "32838")]
781 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
782 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
785 /// Decomposes a `Vec<T>` into its raw components.
787 /// Returns the raw pointer to the underlying data, the length of
788 /// the vector (in elements), and the allocated capacity of the
789 /// data (in elements). These are the same arguments in the same
790 /// order as the arguments to [`from_raw_parts`].
792 /// After calling this function, the caller is responsible for the
793 /// memory previously managed by the `Vec`. The only way to do
794 /// this is to convert the raw pointer, length, and capacity back
795 /// into a `Vec` with the [`from_raw_parts`] function, allowing
796 /// the destructor to perform the cleanup.
798 /// [`from_raw_parts`]: Vec::from_raw_parts
803 /// #![feature(vec_into_raw_parts)]
804 /// let v: Vec<i32> = vec![-1, 0, 1];
806 /// let (ptr, len, cap) = v.into_raw_parts();
808 /// let rebuilt = unsafe {
809 /// // We can now make changes to the components, such as
810 /// // transmuting the raw pointer to a compatible type.
811 /// let ptr = ptr as *mut u32;
813 /// Vec::from_raw_parts(ptr, len, cap)
815 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
817 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
818 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
819 let mut me = ManuallyDrop::new(self);
820 (me.as_mut_ptr(), me.len(), me.capacity())
823 /// Decomposes a `Vec<T>` into its raw components.
825 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
826 /// the allocated capacity of the data (in elements), and the allocator. These are the same
827 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
829 /// After calling this function, the caller is responsible for the
830 /// memory previously managed by the `Vec`. The only way to do
831 /// this is to convert the raw pointer, length, and capacity back
832 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
833 /// the destructor to perform the cleanup.
835 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
840 /// #![feature(allocator_api, vec_into_raw_parts)]
842 /// use std::alloc::System;
844 /// let mut v: Vec<i32, System> = Vec::new_in(System);
849 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
851 /// let rebuilt = unsafe {
852 /// // We can now make changes to the components, such as
853 /// // transmuting the raw pointer to a compatible type.
854 /// let ptr = ptr as *mut u32;
856 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
858 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
860 #[unstable(feature = "allocator_api", issue = "32838")]
861 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
862 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
863 let mut me = ManuallyDrop::new(self);
865 let capacity = me.capacity();
866 let ptr = me.as_mut_ptr();
867 let alloc = unsafe { ptr::read(me.allocator()) };
868 (ptr, len, capacity, alloc)
871 /// Returns the total number of elements the vector can hold without
877 /// let mut vec: Vec<i32> = Vec::with_capacity(10);
879 /// assert_eq!(vec.capacity(), 10);
882 #[stable(feature = "rust1", since = "1.0.0")]
883 pub fn capacity(&self) -> usize {
887 /// Reserves capacity for at least `additional` more elements to be inserted
888 /// in the given `Vec<T>`. The collection may reserve more space to
889 /// speculatively avoid frequent reallocations. After calling `reserve`,
890 /// capacity will be greater than or equal to `self.len() + additional`.
891 /// Does nothing if capacity is already sufficient.
895 /// Panics if the new capacity exceeds `isize::MAX` bytes.
900 /// let mut vec = vec![1];
902 /// assert!(vec.capacity() >= 11);
904 #[cfg(not(no_global_oom_handling))]
905 #[stable(feature = "rust1", since = "1.0.0")]
906 pub fn reserve(&mut self, additional: usize) {
907 self.buf.reserve(self.len, additional);
910 /// Reserves the minimum capacity for at least `additional` more elements to
911 /// be inserted in the given `Vec<T>`. Unlike [`reserve`], this will not
912 /// deliberately over-allocate to speculatively avoid frequent allocations.
913 /// After calling `reserve_exact`, capacity will be greater than or equal to
914 /// `self.len() + additional`. Does nothing if the capacity is already
917 /// Note that the allocator may give the collection more space than it
918 /// requests. Therefore, capacity can not be relied upon to be precisely
919 /// minimal. Prefer [`reserve`] if future insertions are expected.
921 /// [`reserve`]: Vec::reserve
925 /// Panics if the new capacity exceeds `isize::MAX` bytes.
930 /// let mut vec = vec![1];
931 /// vec.reserve_exact(10);
932 /// assert!(vec.capacity() >= 11);
934 #[cfg(not(no_global_oom_handling))]
935 #[stable(feature = "rust1", since = "1.0.0")]
936 pub fn reserve_exact(&mut self, additional: usize) {
937 self.buf.reserve_exact(self.len, additional);
940 /// Tries to reserve capacity for at least `additional` more elements to be inserted
941 /// in the given `Vec<T>`. The collection may reserve more space to speculatively avoid
942 /// frequent reallocations. After calling `try_reserve`, capacity will be
943 /// greater than or equal to `self.len() + additional` if it returns
944 /// `Ok(())`. Does nothing if capacity is already sufficient. This method
945 /// preserves the contents even if an error occurs.
949 /// If the capacity overflows, or the allocator reports a failure, then an error
955 /// use std::collections::TryReserveError;
957 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
958 /// let mut output = Vec::new();
960 /// // Pre-reserve the memory, exiting if we can't
961 /// output.try_reserve(data.len())?;
963 /// // Now we know this can't OOM in the middle of our complex work
964 /// output.extend(data.iter().map(|&val| {
965 /// val * 2 + 5 // very complicated
970 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
972 #[stable(feature = "try_reserve", since = "1.57.0")]
973 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
974 self.buf.try_reserve(self.len, additional)
977 /// Tries to reserve the minimum capacity for at least `additional`
978 /// elements to be inserted in the given `Vec<T>`. Unlike [`try_reserve`],
979 /// this will not deliberately over-allocate to speculatively avoid frequent
980 /// allocations. After calling `try_reserve_exact`, capacity will be greater
981 /// than or equal to `self.len() + additional` if it returns `Ok(())`.
982 /// Does nothing if the capacity is already sufficient.
984 /// Note that the allocator may give the collection more space than it
985 /// requests. Therefore, capacity can not be relied upon to be precisely
986 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
988 /// [`try_reserve`]: Vec::try_reserve
992 /// If the capacity overflows, or the allocator reports a failure, then an error
998 /// use std::collections::TryReserveError;
1000 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
1001 /// let mut output = Vec::new();
1003 /// // Pre-reserve the memory, exiting if we can't
1004 /// output.try_reserve_exact(data.len())?;
1006 /// // Now we know this can't OOM in the middle of our complex work
1007 /// output.extend(data.iter().map(|&val| {
1008 /// val * 2 + 5 // very complicated
1013 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
1015 #[stable(feature = "try_reserve", since = "1.57.0")]
1016 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1017 self.buf.try_reserve_exact(self.len, additional)
1020 /// Shrinks the capacity of the vector as much as possible.
1022 /// It will drop down as close as possible to the length but the allocator
1023 /// may still inform the vector that there is space for a few more elements.
1028 /// let mut vec = Vec::with_capacity(10);
1029 /// vec.extend([1, 2, 3]);
1030 /// assert_eq!(vec.capacity(), 10);
1031 /// vec.shrink_to_fit();
1032 /// assert!(vec.capacity() >= 3);
1034 #[cfg(not(no_global_oom_handling))]
1035 #[stable(feature = "rust1", since = "1.0.0")]
1036 pub fn shrink_to_fit(&mut self) {
1037 // The capacity is never less than the length, and there's nothing to do when
1038 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
1039 // by only calling it with a greater capacity.
1040 if self.capacity() > self.len {
1041 self.buf.shrink_to_fit(self.len);
1045 /// Shrinks the capacity of the vector with a lower bound.
1047 /// The capacity will remain at least as large as both the length
1048 /// and the supplied value.
1050 /// If the current capacity is less than the lower limit, this is a no-op.
1055 /// let mut vec = Vec::with_capacity(10);
1056 /// vec.extend([1, 2, 3]);
1057 /// assert_eq!(vec.capacity(), 10);
1058 /// vec.shrink_to(4);
1059 /// assert!(vec.capacity() >= 4);
1060 /// vec.shrink_to(0);
1061 /// assert!(vec.capacity() >= 3);
1063 #[cfg(not(no_global_oom_handling))]
1064 #[stable(feature = "shrink_to", since = "1.56.0")]
1065 pub fn shrink_to(&mut self, min_capacity: usize) {
1066 if self.capacity() > min_capacity {
1067 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
1071 /// Converts the vector into [`Box<[T]>`][owned slice].
1073 /// Note that this will drop any excess capacity.
1075 /// [owned slice]: Box
1080 /// let v = vec![1, 2, 3];
1082 /// let slice = v.into_boxed_slice();
1085 /// Any excess capacity is removed:
1088 /// let mut vec = Vec::with_capacity(10);
1089 /// vec.extend([1, 2, 3]);
1091 /// assert_eq!(vec.capacity(), 10);
1092 /// let slice = vec.into_boxed_slice();
1093 /// assert_eq!(slice.into_vec().capacity(), 3);
1095 #[cfg(not(no_global_oom_handling))]
1096 #[stable(feature = "rust1", since = "1.0.0")]
1097 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
1099 self.shrink_to_fit();
1100 let me = ManuallyDrop::new(self);
1101 let buf = ptr::read(&me.buf);
1103 buf.into_box(len).assume_init()
1107 /// Shortens the vector, keeping the first `len` elements and dropping
1110 /// If `len` is greater than the vector's current length, this has no
1113 /// The [`drain`] method can emulate `truncate`, but causes the excess
1114 /// elements to be returned instead of dropped.
1116 /// Note that this method has no effect on the allocated capacity
1121 /// Truncating a five element vector to two elements:
1124 /// let mut vec = vec![1, 2, 3, 4, 5];
1125 /// vec.truncate(2);
1126 /// assert_eq!(vec, [1, 2]);
1129 /// No truncation occurs when `len` is greater than the vector's current
1133 /// let mut vec = vec![1, 2, 3];
1134 /// vec.truncate(8);
1135 /// assert_eq!(vec, [1, 2, 3]);
1138 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1142 /// let mut vec = vec![1, 2, 3];
1143 /// vec.truncate(0);
1144 /// assert_eq!(vec, []);
1147 /// [`clear`]: Vec::clear
1148 /// [`drain`]: Vec::drain
1149 #[stable(feature = "rust1", since = "1.0.0")]
1150 pub fn truncate(&mut self, len: usize) {
1151 // This is safe because:
1153 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1154 // case avoids creating an invalid slice, and
1155 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1156 // such that no value will be dropped twice in case `drop_in_place`
1157 // were to panic once (if it panics twice, the program aborts).
1159 // Note: It's intentional that this is `>` and not `>=`.
1160 // Changing it to `>=` has negative performance
1161 // implications in some cases. See #78884 for more.
1165 let remaining_len = self.len - len;
1166 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1168 ptr::drop_in_place(s);
1172 /// Extracts a slice containing the entire vector.
1174 /// Equivalent to `&s[..]`.
1179 /// use std::io::{self, Write};
1180 /// let buffer = vec![1, 2, 3, 5, 8];
1181 /// io::sink().write(buffer.as_slice()).unwrap();
1184 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1185 pub fn as_slice(&self) -> &[T] {
1189 /// Extracts a mutable slice of the entire vector.
1191 /// Equivalent to `&mut s[..]`.
1196 /// use std::io::{self, Read};
1197 /// let mut buffer = vec![0; 3];
1198 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1201 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1202 pub fn as_mut_slice(&mut self) -> &mut [T] {
1206 /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
1207 /// valid for zero sized reads if the vector didn't allocate.
1209 /// The caller must ensure that the vector outlives the pointer this
1210 /// function returns, or else it will end up pointing to garbage.
1211 /// Modifying the vector may cause its buffer to be reallocated,
1212 /// which would also make any pointers to it invalid.
1214 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1215 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1216 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1221 /// let x = vec![1, 2, 4];
1222 /// let x_ptr = x.as_ptr();
1225 /// for i in 0..x.len() {
1226 /// assert_eq!(*x_ptr.add(i), 1 << i);
1231 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1232 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1234 pub fn as_ptr(&self) -> *const T {
1235 // We shadow the slice method of the same name to avoid going through
1236 // `deref`, which creates an intermediate reference.
1237 let ptr = self.buf.ptr();
1239 assume(!ptr.is_null());
1244 /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
1245 /// raw pointer valid for zero sized reads if the vector didn't allocate.
1247 /// The caller must ensure that the vector outlives the pointer this
1248 /// function returns, or else it will end up pointing to garbage.
1249 /// Modifying the vector may cause its buffer to be reallocated,
1250 /// which would also make any pointers to it invalid.
1255 /// // Allocate vector big enough for 4 elements.
1257 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1258 /// let x_ptr = x.as_mut_ptr();
1260 /// // Initialize elements via raw pointer writes, then set length.
1262 /// for i in 0..size {
1263 /// *x_ptr.add(i) = i as i32;
1265 /// x.set_len(size);
1267 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1269 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1271 pub fn as_mut_ptr(&mut self) -> *mut T {
1272 // We shadow the slice method of the same name to avoid going through
1273 // `deref_mut`, which creates an intermediate reference.
1274 let ptr = self.buf.ptr();
1276 assume(!ptr.is_null());
1281 /// Returns a reference to the underlying allocator.
1282 #[unstable(feature = "allocator_api", issue = "32838")]
1284 pub fn allocator(&self) -> &A {
1285 self.buf.allocator()
1288 /// Forces the length of the vector to `new_len`.
1290 /// This is a low-level operation that maintains none of the normal
1291 /// invariants of the type. Normally changing the length of a vector
1292 /// is done using one of the safe operations instead, such as
1293 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1295 /// [`truncate`]: Vec::truncate
1296 /// [`resize`]: Vec::resize
1297 /// [`extend`]: Extend::extend
1298 /// [`clear`]: Vec::clear
1302 /// - `new_len` must be less than or equal to [`capacity()`].
1303 /// - The elements at `old_len..new_len` must be initialized.
1305 /// [`capacity()`]: Vec::capacity
1309 /// This method can be useful for situations in which the vector
1310 /// is serving as a buffer for other code, particularly over FFI:
1313 /// # #![allow(dead_code)]
1314 /// # // This is just a minimal skeleton for the doc example;
1315 /// # // don't use this as a starting point for a real library.
1316 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1317 /// # const Z_OK: i32 = 0;
1319 /// # fn deflateGetDictionary(
1320 /// # strm: *mut std::ffi::c_void,
1321 /// # dictionary: *mut u8,
1322 /// # dictLength: *mut usize,
1325 /// # impl StreamWrapper {
1326 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1327 /// // Per the FFI method's docs, "32768 bytes is always enough".
1328 /// let mut dict = Vec::with_capacity(32_768);
1329 /// let mut dict_length = 0;
1330 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1331 /// // 1. `dict_length` elements were initialized.
1332 /// // 2. `dict_length` <= the capacity (32_768)
1333 /// // which makes `set_len` safe to call.
1335 /// // Make the FFI call...
1336 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1338 /// // ...and update the length to what was initialized.
1339 /// dict.set_len(dict_length);
1349 /// While the following example is sound, there is a memory leak since
1350 /// the inner vectors were not freed prior to the `set_len` call:
1353 /// let mut vec = vec![vec![1, 0, 0],
1357 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1358 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1364 /// Normally, here, one would use [`clear`] instead to correctly drop
1365 /// the contents and thus not leak memory.
1367 #[stable(feature = "rust1", since = "1.0.0")]
1368 pub unsafe fn set_len(&mut self, new_len: usize) {
1369 debug_assert!(new_len <= self.capacity());
1374 /// Removes an element from the vector and returns it.
1376 /// The removed element is replaced by the last element of the vector.
1378 /// This does not preserve ordering, but is *O*(1).
1379 /// If you need to preserve the element order, use [`remove`] instead.
1381 /// [`remove`]: Vec::remove
1385 /// Panics if `index` is out of bounds.
1390 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1392 /// assert_eq!(v.swap_remove(1), "bar");
1393 /// assert_eq!(v, ["foo", "qux", "baz"]);
1395 /// assert_eq!(v.swap_remove(0), "foo");
1396 /// assert_eq!(v, ["baz", "qux"]);
1399 #[stable(feature = "rust1", since = "1.0.0")]
1400 pub fn swap_remove(&mut self, index: usize) -> T {
1403 fn assert_failed(index: usize, len: usize) -> ! {
1404 panic!("swap_remove index (is {index}) should be < len (is {len})");
1407 let len = self.len();
1409 assert_failed(index, len);
1412 // We replace self[index] with the last element. Note that if the
1413 // bounds check above succeeds there must be a last element (which
1414 // can be self[index] itself).
1415 let value = ptr::read(self.as_ptr().add(index));
1416 let base_ptr = self.as_mut_ptr();
1417 ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
1418 self.set_len(len - 1);
1423 /// Inserts an element at position `index` within the vector, shifting all
1424 /// elements after it to the right.
1428 /// Panics if `index > len`.
1433 /// let mut vec = vec![1, 2, 3];
1434 /// vec.insert(1, 4);
1435 /// assert_eq!(vec, [1, 4, 2, 3]);
1436 /// vec.insert(4, 5);
1437 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1439 #[cfg(not(no_global_oom_handling))]
1440 #[stable(feature = "rust1", since = "1.0.0")]
1441 pub fn insert(&mut self, index: usize, element: T) {
1444 fn assert_failed(index: usize, len: usize) -> ! {
1445 panic!("insertion index (is {index}) should be <= len (is {len})");
1448 let len = self.len();
1450 // space for the new element
1451 if len == self.buf.capacity() {
1457 // The spot to put the new value
1459 let p = self.as_mut_ptr().add(index);
1461 // Shift everything over to make space. (Duplicating the
1462 // `index`th element into two consecutive places.)
1463 ptr::copy(p, p.add(1), len - index);
1464 } else if index == len {
1465 // No elements need shifting.
1467 assert_failed(index, len);
1469 // Write it in, overwriting the first copy of the `index`th
1471 ptr::write(p, element);
1473 self.set_len(len + 1);
1477 /// Removes and returns the element at position `index` within the vector,
1478 /// shifting all elements after it to the left.
1480 /// Note: Because this shifts over the remaining elements, it has a
1481 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1482 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1483 /// elements from the beginning of the `Vec`, consider using
1484 /// [`VecDeque::pop_front`] instead.
1486 /// [`swap_remove`]: Vec::swap_remove
1487 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1491 /// Panics if `index` is out of bounds.
1496 /// let mut v = vec![1, 2, 3];
1497 /// assert_eq!(v.remove(1), 2);
1498 /// assert_eq!(v, [1, 3]);
1500 #[stable(feature = "rust1", since = "1.0.0")]
1502 pub fn remove(&mut self, index: usize) -> T {
1506 fn assert_failed(index: usize, len: usize) -> ! {
1507 panic!("removal index (is {index}) should be < len (is {len})");
1510 let len = self.len();
1512 assert_failed(index, len);
1518 // the place we are taking from.
1519 let ptr = self.as_mut_ptr().add(index);
1520 // copy it out, unsafely having a copy of the value on
1521 // the stack and in the vector at the same time.
1522 ret = ptr::read(ptr);
1524 // Shift everything down to fill in that spot.
1525 ptr::copy(ptr.add(1), ptr, len - index - 1);
1527 self.set_len(len - 1);
1532 /// Retains only the elements specified by the predicate.
1534 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1535 /// This method operates in place, visiting each element exactly once in the
1536 /// original order, and preserves the order of the retained elements.
1541 /// let mut vec = vec![1, 2, 3, 4];
1542 /// vec.retain(|&x| x % 2 == 0);
1543 /// assert_eq!(vec, [2, 4]);
1546 /// Because the elements are visited exactly once in the original order,
1547 /// external state may be used to decide which elements to keep.
1550 /// let mut vec = vec![1, 2, 3, 4, 5];
1551 /// let keep = [false, true, true, false, true];
1552 /// let mut iter = keep.iter();
1553 /// vec.retain(|_| *iter.next().unwrap());
1554 /// assert_eq!(vec, [2, 3, 5]);
1556 #[stable(feature = "rust1", since = "1.0.0")]
1557 pub fn retain<F>(&mut self, mut f: F)
1559 F: FnMut(&T) -> bool,
1561 self.retain_mut(|elem| f(elem));
1564 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1566 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1567 /// This method operates in place, visiting each element exactly once in the
1568 /// original order, and preserves the order of the retained elements.
1573 /// let mut vec = vec![1, 2, 3, 4];
1574 /// vec.retain_mut(|x| if *x <= 3 {
1580 /// assert_eq!(vec, [2, 3, 4]);
1582 #[stable(feature = "vec_retain_mut", since = "1.61.0")]
1583 pub fn retain_mut<F>(&mut self, mut f: F)
1585 F: FnMut(&mut T) -> bool,
1587 let original_len = self.len();
1588 // Avoid double drop if the drop guard is not executed,
1589 // since we may make some holes during the process.
1590 unsafe { self.set_len(0) };
1592 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1593 // |<- processed len ->| ^- next to check
1594 // |<- deleted cnt ->|
1595 // |<- original_len ->|
1596 // Kept: Elements which predicate returns true on.
1597 // Hole: Moved or dropped element slot.
1598 // Unchecked: Unchecked valid elements.
1600 // This drop guard will be invoked when predicate or `drop` of element panicked.
1601 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1602 // In cases when predicate and `drop` never panick, it will be optimized out.
1603 struct BackshiftOnDrop<'a, T, A: Allocator> {
1604 v: &'a mut Vec<T, A>,
1605 processed_len: usize,
1607 original_len: usize,
1610 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1611 fn drop(&mut self) {
1612 if self.deleted_cnt > 0 {
1613 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1616 self.v.as_ptr().add(self.processed_len),
1617 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1618 self.original_len - self.processed_len,
1622 // SAFETY: After filling holes, all items are in contiguous memory.
1624 self.v.set_len(self.original_len - self.deleted_cnt);
1629 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1631 fn process_loop<F, T, A: Allocator, const DELETED: bool>(
1632 original_len: usize,
1634 g: &mut BackshiftOnDrop<'_, T, A>,
1636 F: FnMut(&mut T) -> bool,
1638 while g.processed_len != original_len {
1639 // SAFETY: Unchecked element must be valid.
1640 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1642 // Advance early to avoid double drop if `drop_in_place` panicked.
1643 g.processed_len += 1;
1645 // SAFETY: We never touch this element again after dropped.
1646 unsafe { ptr::drop_in_place(cur) };
1647 // We already advanced the counter.
1655 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1656 // We use copy for move, and never touch this element again.
1658 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1659 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1662 g.processed_len += 1;
1666 // Stage 1: Nothing was deleted.
1667 process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
1669 // Stage 2: Some elements were deleted.
1670 process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
1672 // All item are processed. This can be optimized to `set_len` by LLVM.
1676 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1679 /// If the vector is sorted, this removes all duplicates.
1684 /// let mut vec = vec![10, 20, 21, 30, 20];
1686 /// vec.dedup_by_key(|i| *i / 10);
1688 /// assert_eq!(vec, [10, 20, 30, 20]);
1690 #[stable(feature = "dedup_by", since = "1.16.0")]
1692 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1694 F: FnMut(&mut T) -> K,
1697 self.dedup_by(|a, b| key(a) == key(b))
1700 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1703 /// The `same_bucket` function is passed references to two elements from the vector and
1704 /// must determine if the elements compare equal. The elements are passed in opposite order
1705 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1707 /// If the vector is sorted, this removes all duplicates.
1712 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1714 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1716 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1718 #[stable(feature = "dedup_by", since = "1.16.0")]
1719 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1721 F: FnMut(&mut T, &mut T) -> bool,
1723 let len = self.len();
1728 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1729 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1730 /* Offset of the element we want to check if it is duplicate */
1733 /* Offset of the place where we want to place the non-duplicate
1734 * when we find it. */
1737 /* The Vec that would need correction if `same_bucket` panicked */
1738 vec: &'a mut Vec<T, A>,
1741 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1742 fn drop(&mut self) {
1743 /* This code gets executed when `same_bucket` panics */
1745 /* SAFETY: invariant guarantees that `read - write`
1746 * and `len - read` never overflow and that the copy is always
1749 let ptr = self.vec.as_mut_ptr();
1750 let len = self.vec.len();
1752 /* How many items were left when `same_bucket` panicked.
1753 * Basically vec[read..].len() */
1754 let items_left = len.wrapping_sub(self.read);
1756 /* Pointer to first item in vec[write..write+items_left] slice */
1757 let dropped_ptr = ptr.add(self.write);
1758 /* Pointer to first item in vec[read..] slice */
1759 let valid_ptr = ptr.add(self.read);
1761 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1762 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1763 ptr::copy(valid_ptr, dropped_ptr, items_left);
1765 /* How many items have been already dropped
1766 * Basically vec[read..write].len() */
1767 let dropped = self.read.wrapping_sub(self.write);
1769 self.vec.set_len(len - dropped);
1774 let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
1775 let ptr = gap.vec.as_mut_ptr();
1777 /* Drop items while going through Vec, it should be more efficient than
1778 * doing slice partition_dedup + truncate */
1780 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1781 * are always in-bounds and read_ptr never aliases prev_ptr */
1783 while gap.read < len {
1784 let read_ptr = ptr.add(gap.read);
1785 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1787 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1788 // Increase `gap.read` now since the drop may panic.
1790 /* We have found duplicate, drop it in-place */
1791 ptr::drop_in_place(read_ptr);
1793 let write_ptr = ptr.add(gap.write);
1795 /* Because `read_ptr` can be equal to `write_ptr`, we either
1796 * have to use `copy` or conditional `copy_nonoverlapping`.
1797 * Looks like the first option is faster. */
1798 ptr::copy(read_ptr, write_ptr, 1);
1800 /* We have filled that place, so go further */
1806 /* Technically we could let `gap` clean up with its Drop, but
1807 * when `same_bucket` is guaranteed to not panic, this bloats a little
1808 * the codegen, so we just do it manually */
1809 gap.vec.set_len(gap.write);
1814 /// Appends an element to the back of a collection.
1818 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1823 /// let mut vec = vec![1, 2];
1825 /// assert_eq!(vec, [1, 2, 3]);
1827 #[cfg(not(no_global_oom_handling))]
1829 #[stable(feature = "rust1", since = "1.0.0")]
1830 pub fn push(&mut self, value: T) {
1831 // This will panic or abort if we would allocate > isize::MAX bytes
1832 // or if the length increment would overflow for zero-sized types.
1833 if self.len == self.buf.capacity() {
1834 self.buf.reserve_for_push(self.len);
1837 let end = self.as_mut_ptr().add(self.len);
1838 ptr::write(end, value);
1843 /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
1844 /// with the element.
1846 /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
1847 /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
1849 /// [`push`]: Vec::push
1850 /// [`reserve`]: Vec::reserve
1851 /// [`try_reserve`]: Vec::try_reserve
1855 /// A manual, panic-free alternative to [`FromIterator`]:
1858 /// #![feature(vec_push_within_capacity)]
1860 /// use std::collections::TryReserveError;
1861 /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
1862 /// let mut vec = Vec::new();
1863 /// for value in iter {
1864 /// if let Err(value) = vec.push_within_capacity(value) {
1865 /// vec.try_reserve(1)?;
1866 /// // this cannot fail, the previous line either returned or added at least 1 free slot
1867 /// let _ = vec.push_within_capacity(value);
1872 /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
1875 #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
1876 pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
1877 if self.len == self.buf.capacity() {
1881 let end = self.as_mut_ptr().add(self.len);
1882 ptr::write(end, value);
1888 /// Removes the last element from a vector and returns it, or [`None`] if it
1891 /// If you'd like to pop the first element, consider using
1892 /// [`VecDeque::pop_front`] instead.
1894 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1899 /// let mut vec = vec![1, 2, 3];
1900 /// assert_eq!(vec.pop(), Some(3));
1901 /// assert_eq!(vec, [1, 2]);
1904 #[stable(feature = "rust1", since = "1.0.0")]
1905 pub fn pop(&mut self) -> Option<T> {
1911 Some(ptr::read(self.as_ptr().add(self.len())))
1916 /// Moves all the elements of `other` into `self`, leaving `other` empty.
1920 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1925 /// let mut vec = vec![1, 2, 3];
1926 /// let mut vec2 = vec![4, 5, 6];
1927 /// vec.append(&mut vec2);
1928 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1929 /// assert_eq!(vec2, []);
1931 #[cfg(not(no_global_oom_handling))]
1933 #[stable(feature = "append", since = "1.4.0")]
1934 pub fn append(&mut self, other: &mut Self) {
1936 self.append_elements(other.as_slice() as _);
1941 /// Appends elements to `self` from other buffer.
1942 #[cfg(not(no_global_oom_handling))]
1944 unsafe fn append_elements(&mut self, other: *const [T]) {
1945 let count = unsafe { (*other).len() };
1946 self.reserve(count);
1947 let len = self.len();
1948 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1952 /// Removes the specified range from the vector in bulk, returning all
1953 /// removed elements as an iterator. If the iterator is dropped before
1954 /// being fully consumed, it drops the remaining removed elements.
1956 /// The returned iterator keeps a mutable borrow on the vector to optimize
1957 /// its implementation.
1961 /// Panics if the starting point is greater than the end point or if
1962 /// the end point is greater than the length of the vector.
1966 /// If the returned iterator goes out of scope without being dropped (due to
1967 /// [`mem::forget`], for example), the vector may have lost and leaked
1968 /// elements arbitrarily, including elements outside the range.
1973 /// let mut v = vec![1, 2, 3];
1974 /// let u: Vec<_> = v.drain(1..).collect();
1975 /// assert_eq!(v, &[1]);
1976 /// assert_eq!(u, &[2, 3]);
1978 /// // A full range clears the vector, like `clear()` does
1980 /// assert_eq!(v, &[]);
1982 #[stable(feature = "drain", since = "1.6.0")]
1983 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1985 R: RangeBounds<usize>,
1989 // When the Drain is first created, it shortens the length of
1990 // the source vector to make sure no uninitialized or moved-from elements
1991 // are accessible at all if the Drain's destructor never gets to run.
1993 // Drain will ptr::read out the values to remove.
1994 // When finished, remaining tail of the vec is copied back to cover
1995 // the hole, and the vector length is restored to the new length.
1997 let len = self.len();
1998 let Range { start, end } = slice::range(range, ..len);
2001 // set self.vec length's to start, to be safe in case Drain is leaked
2002 self.set_len(start);
2003 let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
2006 tail_len: len - end,
2007 iter: range_slice.iter(),
2008 vec: NonNull::from(self),
2013 /// Clears the vector, removing all values.
2015 /// Note that this method has no effect on the allocated capacity
2021 /// let mut v = vec![1, 2, 3];
2025 /// assert!(v.is_empty());
2028 #[stable(feature = "rust1", since = "1.0.0")]
2029 pub fn clear(&mut self) {
2030 let elems: *mut [T] = self.as_mut_slice();
2033 // - `elems` comes directly from `as_mut_slice` and is therefore valid.
2034 // - Setting `self.len` before calling `drop_in_place` means that,
2035 // if an element's `Drop` impl panics, the vector's `Drop` impl will
2036 // do nothing (leaking the rest of the elements) instead of dropping
2040 ptr::drop_in_place(elems);
2044 /// Returns the number of elements in the vector, also referred to
2045 /// as its 'length'.
2050 /// let a = vec![1, 2, 3];
2051 /// assert_eq!(a.len(), 3);
2054 #[stable(feature = "rust1", since = "1.0.0")]
2055 pub fn len(&self) -> usize {
2059 /// Returns `true` if the vector contains no elements.
2064 /// let mut v = Vec::new();
2065 /// assert!(v.is_empty());
2068 /// assert!(!v.is_empty());
2070 #[stable(feature = "rust1", since = "1.0.0")]
2071 pub fn is_empty(&self) -> bool {
2075 /// Splits the collection into two at the given index.
2077 /// Returns a newly allocated vector containing the elements in the range
2078 /// `[at, len)`. After the call, the original vector will be left containing
2079 /// the elements `[0, at)` with its previous capacity unchanged.
2083 /// Panics if `at > len`.
2088 /// let mut vec = vec![1, 2, 3];
2089 /// let vec2 = vec.split_off(1);
2090 /// assert_eq!(vec, [1]);
2091 /// assert_eq!(vec2, [2, 3]);
2093 #[cfg(not(no_global_oom_handling))]
2095 #[must_use = "use `.truncate()` if you don't need the other half"]
2096 #[stable(feature = "split_off", since = "1.4.0")]
2097 pub fn split_off(&mut self, at: usize) -> Self
2103 fn assert_failed(at: usize, len: usize) -> ! {
2104 panic!("`at` split index (is {at}) should be <= len (is {len})");
2107 if at > self.len() {
2108 assert_failed(at, self.len());
2112 // the new vector can take over the original buffer and avoid the copy
2113 return mem::replace(
2115 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
2119 let other_len = self.len - at;
2120 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
2122 // Unsafely `set_len` and copy items to `other`.
2125 other.set_len(other_len);
2127 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
2132 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2134 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2135 /// difference, with each additional slot filled with the result of
2136 /// calling the closure `f`. The return values from `f` will end up
2137 /// in the `Vec` in the order they have been generated.
2139 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2141 /// This method uses a closure to create new values on every push. If
2142 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
2143 /// want to use the [`Default`] trait to generate values, you can
2144 /// pass [`Default::default`] as the second argument.
2149 /// let mut vec = vec![1, 2, 3];
2150 /// vec.resize_with(5, Default::default);
2151 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
2153 /// let mut vec = vec![];
2155 /// vec.resize_with(4, || { p *= 2; p });
2156 /// assert_eq!(vec, [2, 4, 8, 16]);
2158 #[cfg(not(no_global_oom_handling))]
2159 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2160 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
2164 let len = self.len();
2166 self.extend_with(new_len - len, ExtendFunc(f));
2168 self.truncate(new_len);
2172 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2173 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2174 /// `'a`. If the type has only static references, or none at all, then this
2175 /// may be chosen to be `'static`.
2177 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2178 /// so the leaked allocation may include unused capacity that is not part
2179 /// of the returned slice.
2181 /// This function is mainly useful for data that lives for the remainder of
2182 /// the program's life. Dropping the returned reference will cause a memory
2190 /// let x = vec![1, 2, 3];
2191 /// let static_ref: &'static mut [usize] = x.leak();
2192 /// static_ref[0] += 1;
2193 /// assert_eq!(static_ref, &[2, 2, 3]);
2195 #[stable(feature = "vec_leak", since = "1.47.0")]
2197 pub fn leak<'a>(self) -> &'a mut [T]
2201 let mut me = ManuallyDrop::new(self);
2202 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2205 /// Returns the remaining spare capacity of the vector as a slice of
2206 /// `MaybeUninit<T>`.
2208 /// The returned slice can be used to fill the vector with data (e.g. by
2209 /// reading from a file) before marking the data as initialized using the
2210 /// [`set_len`] method.
2212 /// [`set_len`]: Vec::set_len
2217 /// // Allocate vector big enough for 10 elements.
2218 /// let mut v = Vec::with_capacity(10);
2220 /// // Fill in the first 3 elements.
2221 /// let uninit = v.spare_capacity_mut();
2222 /// uninit[0].write(0);
2223 /// uninit[1].write(1);
2224 /// uninit[2].write(2);
2226 /// // Mark the first 3 elements of the vector as being initialized.
2231 /// assert_eq!(&v, &[0, 1, 2]);
2233 #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
2235 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2237 // This method is not implemented in terms of `split_at_spare_mut`,
2238 // to prevent invalidation of pointers to the buffer.
2240 slice::from_raw_parts_mut(
2241 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2242 self.buf.capacity() - self.len,
2247 /// Returns vector content as a slice of `T`, along with the remaining spare
2248 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2250 /// The returned spare capacity slice can be used to fill the vector with data
2251 /// (e.g. by reading from a file) before marking the data as initialized using
2252 /// the [`set_len`] method.
2254 /// [`set_len`]: Vec::set_len
2256 /// Note that this is a low-level API, which should be used with care for
2257 /// optimization purposes. If you need to append data to a `Vec`
2258 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2259 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2260 /// [`resize_with`], depending on your exact needs.
2262 /// [`push`]: Vec::push
2263 /// [`extend`]: Vec::extend
2264 /// [`extend_from_slice`]: Vec::extend_from_slice
2265 /// [`extend_from_within`]: Vec::extend_from_within
2266 /// [`insert`]: Vec::insert
2267 /// [`append`]: Vec::append
2268 /// [`resize`]: Vec::resize
2269 /// [`resize_with`]: Vec::resize_with
2274 /// #![feature(vec_split_at_spare)]
2276 /// let mut v = vec![1, 1, 2];
2278 /// // Reserve additional space big enough for 10 elements.
2281 /// let (init, uninit) = v.split_at_spare_mut();
2282 /// let sum = init.iter().copied().sum::<u32>();
2284 /// // Fill in the next 4 elements.
2285 /// uninit[0].write(sum);
2286 /// uninit[1].write(sum * 2);
2287 /// uninit[2].write(sum * 3);
2288 /// uninit[3].write(sum * 4);
2290 /// // Mark the 4 elements of the vector as being initialized.
2292 /// let len = v.len();
2293 /// v.set_len(len + 4);
2296 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2298 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2300 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2302 // - len is ignored and so never changed
2303 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2307 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2309 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2310 unsafe fn split_at_spare_mut_with_len(
2312 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2313 let ptr = self.as_mut_ptr();
2315 // - `ptr` is guaranteed to be valid for `self.len` elements
2316 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2318 let spare_ptr = unsafe { ptr.add(self.len) };
2319 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2320 let spare_len = self.buf.capacity() - self.len;
2323 // - `ptr` is guaranteed to be valid for `self.len` elements
2324 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2326 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2327 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2329 (initialized, spare, &mut self.len)
2334 impl<T: Clone, A: Allocator> Vec<T, A> {
2335 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2337 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2338 /// difference, with each additional slot filled with `value`.
2339 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2341 /// This method requires `T` to implement [`Clone`],
2342 /// in order to be able to clone the passed value.
2343 /// If you need more flexibility (or want to rely on [`Default`] instead of
2344 /// [`Clone`]), use [`Vec::resize_with`].
2345 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2350 /// let mut vec = vec!["hello"];
2351 /// vec.resize(3, "world");
2352 /// assert_eq!(vec, ["hello", "world", "world"]);
2354 /// let mut vec = vec![1, 2, 3, 4];
2355 /// vec.resize(2, 0);
2356 /// assert_eq!(vec, [1, 2]);
2358 #[cfg(not(no_global_oom_handling))]
2359 #[stable(feature = "vec_resize", since = "1.5.0")]
2360 pub fn resize(&mut self, new_len: usize, value: T) {
2361 let len = self.len();
2364 self.extend_with(new_len - len, ExtendElement(value))
2366 self.truncate(new_len);
2370 /// Clones and appends all elements in a slice to the `Vec`.
2372 /// Iterates over the slice `other`, clones each element, and then appends
2373 /// it to this `Vec`. The `other` slice is traversed in-order.
2375 /// Note that this function is same as [`extend`] except that it is
2376 /// specialized to work with slices instead. If and when Rust gets
2377 /// specialization this function will likely be deprecated (but still
2383 /// let mut vec = vec![1];
2384 /// vec.extend_from_slice(&[2, 3, 4]);
2385 /// assert_eq!(vec, [1, 2, 3, 4]);
2388 /// [`extend`]: Vec::extend
2389 #[cfg(not(no_global_oom_handling))]
2390 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2391 pub fn extend_from_slice(&mut self, other: &[T]) {
2392 self.spec_extend(other.iter())
2395 /// Copies elements from `src` range to the end of the vector.
2399 /// Panics if the starting point is greater than the end point or if
2400 /// the end point is greater than the length of the vector.
2405 /// let mut vec = vec![0, 1, 2, 3, 4];
2407 /// vec.extend_from_within(2..);
2408 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2410 /// vec.extend_from_within(..2);
2411 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2413 /// vec.extend_from_within(4..8);
2414 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2416 #[cfg(not(no_global_oom_handling))]
2417 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2418 pub fn extend_from_within<R>(&mut self, src: R)
2420 R: RangeBounds<usize>,
2422 let range = slice::range(src, ..self.len());
2423 self.reserve(range.len());
2426 // - `slice::range` guarantees that the given range is valid for indexing self
2428 self.spec_extend_from_within(range);
2433 impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
2434 /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
2438 /// Panics if the length of the resulting vector would overflow a `usize`.
2440 /// This is only possible when flattening a vector of arrays of zero-sized
2441 /// types, and thus tends to be irrelevant in practice. If
2442 /// `size_of::<T>() > 0`, this will never panic.
2447 /// #![feature(slice_flatten)]
2449 /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
2450 /// assert_eq!(vec.pop(), Some([7, 8, 9]));
2452 /// let mut flattened = vec.into_flattened();
2453 /// assert_eq!(flattened.pop(), Some(6));
2455 #[unstable(feature = "slice_flatten", issue = "95629")]
2456 pub fn into_flattened(self) -> Vec<T, A> {
2457 let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
2458 let (new_len, new_cap) = if T::IS_ZST {
2459 (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
2462 // - `cap * N` cannot overflow because the allocation is already in
2463 // the address space.
2464 // - Each `[T; N]` has `N` valid elements, so there are `len * N`
2465 // valid elements in the allocation.
2466 unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
2469 // - `ptr` was allocated by `self`
2470 // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
2471 // - `new_cap` refers to the same sized allocation as `cap` because
2472 // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
2473 // - `len` <= `cap`, so `len * N` <= `cap * N`.
2474 unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
2478 // This code generalizes `extend_with_{element,default}`.
2479 trait ExtendWith<T> {
2480 fn next(&mut self) -> T;
2484 struct ExtendElement<T>(T);
2485 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2486 fn next(&mut self) -> T {
2489 fn last(self) -> T {
2494 struct ExtendFunc<F>(F);
2495 impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
2496 fn next(&mut self) -> T {
2499 fn last(mut self) -> T {
2504 impl<T, A: Allocator> Vec<T, A> {
2505 #[cfg(not(no_global_oom_handling))]
2506 /// Extend the vector by `n` values, using the given generator.
2507 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2511 let mut ptr = self.as_mut_ptr().add(self.len());
2512 // Use SetLenOnDrop to work around bug where compiler
2513 // might not realize the store through `ptr` through self.set_len()
2515 let mut local_len = SetLenOnDrop::new(&mut self.len);
2517 // Write all elements except the last one
2519 ptr::write(ptr, value.next());
2521 // Increment the length in every step in case next() panics
2522 local_len.increment_len(1);
2526 // We can write the last element directly without cloning needlessly
2527 ptr::write(ptr, value.last());
2528 local_len.increment_len(1);
2531 // len set by scope guard
2536 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2537 /// Removes consecutive repeated elements in the vector according to the
2538 /// [`PartialEq`] trait implementation.
2540 /// If the vector is sorted, this removes all duplicates.
2545 /// let mut vec = vec![1, 2, 2, 3, 2];
2549 /// assert_eq!(vec, [1, 2, 3, 2]);
2551 #[stable(feature = "rust1", since = "1.0.0")]
2553 pub fn dedup(&mut self) {
2554 self.dedup_by(|a, b| a == b)
2558 ////////////////////////////////////////////////////////////////////////////////
2559 // Internal methods and functions
2560 ////////////////////////////////////////////////////////////////////////////////
2563 #[cfg(not(no_global_oom_handling))]
2564 #[stable(feature = "rust1", since = "1.0.0")]
2565 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2566 <T as SpecFromElem>::from_elem(elem, n, Global)
2570 #[cfg(not(no_global_oom_handling))]
2571 #[unstable(feature = "allocator_api", issue = "32838")]
2572 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2573 <T as SpecFromElem>::from_elem(elem, n, alloc)
2576 trait ExtendFromWithinSpec {
2579 /// - `src` needs to be valid index
2580 /// - `self.capacity() - self.len()` must be `>= src.len()`
2581 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2584 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2585 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2587 // - len is increased only after initializing elements
2588 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2591 // - caller guarantees that src is a valid index
2592 let to_clone = unsafe { this.get_unchecked(src) };
2594 iter::zip(to_clone, spare)
2595 .map(|(src, dst)| dst.write(src.clone()))
2597 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2598 // - len is increased after each element to prevent leaks (see issue #82533)
2599 .for_each(|_| *len += 1);
2603 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2604 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2605 let count = src.len();
2607 let (init, spare) = self.split_at_spare_mut();
2610 // - caller guarantees that `src` is a valid index
2611 let source = unsafe { init.get_unchecked(src) };
2614 // - Both pointers are created from unique slice references (`&mut [_]`)
2615 // so they are valid and do not overlap.
2616 // - Elements are :Copy so it's OK to copy them, without doing
2617 // anything with the original values
2618 // - `count` is equal to the len of `source`, so source is valid for
2620 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2621 // is valid for `count` writes
2622 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2626 // - The elements were just initialized by `copy_nonoverlapping`
2631 ////////////////////////////////////////////////////////////////////////////////
2632 // Common trait implementations for Vec
2633 ////////////////////////////////////////////////////////////////////////////////
2635 #[stable(feature = "rust1", since = "1.0.0")]
2636 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2640 fn deref(&self) -> &[T] {
2641 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2645 #[stable(feature = "rust1", since = "1.0.0")]
2646 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2648 fn deref_mut(&mut self) -> &mut [T] {
2649 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2653 #[cfg(not(no_global_oom_handling))]
2654 trait SpecCloneFrom {
2655 fn clone_from(this: &mut Self, other: &Self);
2658 #[cfg(not(no_global_oom_handling))]
2659 impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
2660 default fn clone_from(this: &mut Self, other: &Self) {
2661 // drop anything that will not be overwritten
2662 this.truncate(other.len());
2664 // self.len <= other.len due to the truncate above, so the
2665 // slices here are always in-bounds.
2666 let (init, tail) = other.split_at(this.len());
2668 // reuse the contained values' allocations/resources.
2669 this.clone_from_slice(init);
2670 this.extend_from_slice(tail);
2674 #[cfg(not(no_global_oom_handling))]
2675 impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
2676 fn clone_from(this: &mut Self, other: &Self) {
2678 this.extend_from_slice(other);
2682 #[cfg(not(no_global_oom_handling))]
2683 #[stable(feature = "rust1", since = "1.0.0")]
2684 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2686 fn clone(&self) -> Self {
2687 let alloc = self.allocator().clone();
2688 <[T]>::to_vec_in(&**self, alloc)
2691 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2692 // required for this method definition, is not available. Instead use the
2693 // `slice::to_vec` function which is only available with cfg(test)
2694 // NB see the slice::hack module in slice.rs for more information
2696 fn clone(&self) -> Self {
2697 let alloc = self.allocator().clone();
2698 crate::slice::to_vec(&**self, alloc)
2701 fn clone_from(&mut self, other: &Self) {
2702 SpecCloneFrom::clone_from(self, other)
2706 /// The hash of a vector is the same as that of the corresponding slice,
2707 /// as required by the `core::borrow::Borrow` implementation.
2710 /// #![feature(build_hasher_simple_hash_one)]
2711 /// use std::hash::BuildHasher;
2713 /// let b = std::collections::hash_map::RandomState::new();
2714 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2715 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2716 /// assert_eq!(b.hash_one(v), b.hash_one(s));
2718 #[stable(feature = "rust1", since = "1.0.0")]
2719 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2721 fn hash<H: Hasher>(&self, state: &mut H) {
2722 Hash::hash(&**self, state)
2726 #[stable(feature = "rust1", since = "1.0.0")]
2727 #[rustc_on_unimplemented(
2728 message = "vector indices are of type `usize` or ranges of `usize`",
2729 label = "vector indices are of type `usize` or ranges of `usize`"
2731 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2732 type Output = I::Output;
2735 fn index(&self, index: I) -> &Self::Output {
2736 Index::index(&**self, index)
2740 #[stable(feature = "rust1", since = "1.0.0")]
2741 #[rustc_on_unimplemented(
2742 message = "vector indices are of type `usize` or ranges of `usize`",
2743 label = "vector indices are of type `usize` or ranges of `usize`"
2745 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2747 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2748 IndexMut::index_mut(&mut **self, index)
2752 #[cfg(not(no_global_oom_handling))]
2753 #[stable(feature = "rust1", since = "1.0.0")]
2754 impl<T> FromIterator<T> for Vec<T> {
2756 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2757 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2761 #[stable(feature = "rust1", since = "1.0.0")]
2762 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2764 type IntoIter = IntoIter<T, A>;
2766 /// Creates a consuming iterator, that is, one that moves each value out of
2767 /// the vector (from start to end). The vector cannot be used after calling
2773 /// let v = vec!["a".to_string(), "b".to_string()];
2774 /// let mut v_iter = v.into_iter();
2776 /// let first_element: Option<String> = v_iter.next();
2778 /// assert_eq!(first_element, Some("a".to_string()));
2779 /// assert_eq!(v_iter.next(), Some("b".to_string()));
2780 /// assert_eq!(v_iter.next(), None);
2783 fn into_iter(self) -> Self::IntoIter {
2785 let mut me = ManuallyDrop::new(self);
2786 let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
2787 let begin = me.as_mut_ptr();
2788 let end = if T::IS_ZST {
2789 begin.wrapping_byte_add(me.len())
2791 begin.add(me.len()) as *const T
2793 let cap = me.buf.capacity();
2795 buf: NonNull::new_unchecked(begin),
2796 phantom: PhantomData,
2806 #[stable(feature = "rust1", since = "1.0.0")]
2807 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2809 type IntoIter = slice::Iter<'a, T>;
2811 fn into_iter(self) -> Self::IntoIter {
2816 #[stable(feature = "rust1", since = "1.0.0")]
2817 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2818 type Item = &'a mut T;
2819 type IntoIter = slice::IterMut<'a, T>;
2821 fn into_iter(self) -> Self::IntoIter {
2826 #[cfg(not(no_global_oom_handling))]
2827 #[stable(feature = "rust1", since = "1.0.0")]
2828 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2830 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2831 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2835 fn extend_one(&mut self, item: T) {
2840 fn extend_reserve(&mut self, additional: usize) {
2841 self.reserve(additional);
2845 impl<T, A: Allocator> Vec<T, A> {
2846 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2847 // they have no further optimizations to apply
2848 #[cfg(not(no_global_oom_handling))]
2849 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2850 // This is the case for a general iterator.
2852 // This function should be the moral equivalent of:
2854 // for item in iterator {
2857 while let Some(element) = iterator.next() {
2858 let len = self.len();
2859 if len == self.capacity() {
2860 let (lower, _) = iterator.size_hint();
2861 self.reserve(lower.saturating_add(1));
2864 ptr::write(self.as_mut_ptr().add(len), element);
2865 // Since next() executes user code which can panic we have to bump the length
2867 // NB can't overflow since we would have had to alloc the address space
2868 self.set_len(len + 1);
2873 /// Creates a splicing iterator that replaces the specified range in the vector
2874 /// with the given `replace_with` iterator and yields the removed items.
2875 /// `replace_with` does not need to be the same length as `range`.
2877 /// `range` is removed even if the iterator is not consumed until the end.
2879 /// It is unspecified how many elements are removed from the vector
2880 /// if the `Splice` value is leaked.
2882 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2884 /// This is optimal if:
2886 /// * The tail (elements in the vector after `range`) is empty,
2887 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2888 /// * or the lower bound of its `size_hint()` is exact.
2890 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2894 /// Panics if the starting point is greater than the end point or if
2895 /// the end point is greater than the length of the vector.
2900 /// let mut v = vec![1, 2, 3, 4];
2901 /// let new = [7, 8, 9];
2902 /// let u: Vec<_> = v.splice(1..3, new).collect();
2903 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
2904 /// assert_eq!(u, &[2, 3]);
2906 #[cfg(not(no_global_oom_handling))]
2908 #[stable(feature = "vec_splice", since = "1.21.0")]
2909 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2911 R: RangeBounds<usize>,
2912 I: IntoIterator<Item = T>,
2914 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2917 /// Creates an iterator which uses a closure to determine if an element should be removed.
2919 /// If the closure returns true, then the element is removed and yielded.
2920 /// If the closure returns false, the element will remain in the vector and will not be yielded
2921 /// by the iterator.
2923 /// Using this method is equivalent to the following code:
2926 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2927 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2929 /// while i < vec.len() {
2930 /// if some_predicate(&mut vec[i]) {
2931 /// let val = vec.remove(i);
2932 /// // your code here
2938 /// # assert_eq!(vec, vec![1, 4, 5]);
2941 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2942 /// because it can backshift the elements of the array in bulk.
2944 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2945 /// regardless of whether you choose to keep or remove it.
2949 /// Splitting an array into evens and odds, reusing the original allocation:
2952 /// #![feature(drain_filter)]
2953 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2955 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2956 /// let odds = numbers;
2958 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2959 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2961 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2962 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
2964 F: FnMut(&mut T) -> bool,
2966 let old_len = self.len();
2968 // Guard against us getting leaked (leak amplification)
2973 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
2977 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
2979 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2980 /// append the entire slice at once.
2982 /// [`copy_from_slice`]: slice::copy_from_slice
2983 #[cfg(not(no_global_oom_handling))]
2984 #[stable(feature = "extend_ref", since = "1.2.0")]
2985 impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
2986 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2987 self.spec_extend(iter.into_iter())
2991 fn extend_one(&mut self, &item: &'a T) {
2996 fn extend_reserve(&mut self, additional: usize) {
2997 self.reserve(additional);
3001 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
3002 #[stable(feature = "rust1", since = "1.0.0")]
3003 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
3005 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
3006 PartialOrd::partial_cmp(&**self, &**other)
3010 #[stable(feature = "rust1", since = "1.0.0")]
3011 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
3013 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
3014 #[stable(feature = "rust1", since = "1.0.0")]
3015 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
3017 fn cmp(&self, other: &Self) -> Ordering {
3018 Ord::cmp(&**self, &**other)
3022 #[stable(feature = "rust1", since = "1.0.0")]
3023 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
3024 fn drop(&mut self) {
3027 // use a raw slice to refer to the elements of the vector as weakest necessary type;
3028 // could avoid questions of validity in certain cases
3029 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
3031 // RawVec handles deallocation
3035 #[stable(feature = "rust1", since = "1.0.0")]
3036 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3037 impl<T> const Default for Vec<T> {
3038 /// Creates an empty `Vec<T>`.
3040 /// The vector will not allocate until elements are pushed onto it.
3041 fn default() -> Vec<T> {
3046 #[stable(feature = "rust1", since = "1.0.0")]
3047 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
3048 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3049 fmt::Debug::fmt(&**self, f)
3053 #[stable(feature = "rust1", since = "1.0.0")]
3054 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
3055 fn as_ref(&self) -> &Vec<T, A> {
3060 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3061 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
3062 fn as_mut(&mut self) -> &mut Vec<T, A> {
3067 #[stable(feature = "rust1", since = "1.0.0")]
3068 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
3069 fn as_ref(&self) -> &[T] {
3074 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3075 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
3076 fn as_mut(&mut self) -> &mut [T] {
3081 #[cfg(not(no_global_oom_handling))]
3082 #[stable(feature = "rust1", since = "1.0.0")]
3083 impl<T: Clone> From<&[T]> for Vec<T> {
3084 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3089 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
3092 fn from(s: &[T]) -> Vec<T> {
3096 fn from(s: &[T]) -> Vec<T> {
3097 crate::slice::to_vec(s, Global)
3101 #[cfg(not(no_global_oom_handling))]
3102 #[stable(feature = "vec_from_mut", since = "1.19.0")]
3103 impl<T: Clone> From<&mut [T]> for Vec<T> {
3104 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3109 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
3112 fn from(s: &mut [T]) -> Vec<T> {
3116 fn from(s: &mut [T]) -> Vec<T> {
3117 crate::slice::to_vec(s, Global)
3121 #[cfg(not(no_global_oom_handling))]
3122 #[stable(feature = "vec_from_array", since = "1.44.0")]
3123 impl<T, const N: usize> From<[T; N]> for Vec<T> {
3124 /// Allocate a `Vec<T>` and move `s`'s items into it.
3129 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
3132 fn from(s: [T; N]) -> Vec<T> {
3140 fn from(s: [T; N]) -> Vec<T> {
3141 crate::slice::into_vec(Box::new(s))
3145 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
3146 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
3148 [T]: ToOwned<Owned = Vec<T>>,
3150 /// Convert a clone-on-write slice into a vector.
3152 /// If `s` already owns a `Vec<T>`, it will be returned directly.
3153 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
3154 /// filled by cloning `s`'s items into it.
3159 /// # use std::borrow::Cow;
3160 /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
3161 /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
3162 /// assert_eq!(Vec::from(o), Vec::from(b));
3164 fn from(s: Cow<'a, [T]>) -> Vec<T> {
3169 // note: test pulls in libstd, which causes errors here
3171 #[stable(feature = "vec_from_box", since = "1.18.0")]
3172 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
3173 /// Convert a boxed slice into a vector by transferring ownership of
3174 /// the existing heap allocation.
3179 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
3180 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
3182 fn from(s: Box<[T], A>) -> Self {
3187 // note: test pulls in libstd, which causes errors here
3188 #[cfg(not(no_global_oom_handling))]
3190 #[stable(feature = "box_from_vec", since = "1.20.0")]
3191 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
3192 /// Convert a vector into a boxed slice.
3194 /// If `v` has excess capacity, its items will be moved into a
3195 /// newly-allocated buffer with exactly the right capacity.
3200 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
3202 fn from(v: Vec<T, A>) -> Self {
3203 v.into_boxed_slice()
3207 #[cfg(not(no_global_oom_handling))]
3208 #[stable(feature = "rust1", since = "1.0.0")]
3209 impl From<&str> for Vec<u8> {
3210 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
3215 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
3217 fn from(s: &str) -> Vec<u8> {
3218 From::from(s.as_bytes())
3222 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
3223 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
3224 type Error = Vec<T, A>;
3226 /// Gets the entire contents of the `Vec<T>` as an array,
3227 /// if its size exactly matches that of the requested array.
3232 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3233 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3236 /// If the length doesn't match, the input comes back in `Err`:
3238 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3239 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3242 /// If you're fine with just getting a prefix of the `Vec<T>`,
3243 /// you can call [`.truncate(N)`](Vec::truncate) first.
3245 /// let mut v = String::from("hello world").into_bytes();
3248 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3249 /// assert_eq!(a, b' ');
3250 /// assert_eq!(b, b'd');
3252 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
3257 // SAFETY: `.set_len(0)` is always sound.
3258 unsafe { vec.set_len(0) };
3260 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3261 // the alignment the array needs is the same as the items.
3262 // We checked earlier that we have sufficient items.
3263 // The items will not double-drop as the `set_len`
3264 // tells the `Vec` not to also drop them.
3265 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };