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 /// If the vector has excess capacity, its items will be moved into a
1074 /// newly-allocated buffer with exactly the right capacity.
1076 /// [owned slice]: Box
1081 /// let v = vec![1, 2, 3];
1083 /// let slice = v.into_boxed_slice();
1086 /// Any excess capacity is removed:
1089 /// let mut vec = Vec::with_capacity(10);
1090 /// vec.extend([1, 2, 3]);
1092 /// assert_eq!(vec.capacity(), 10);
1093 /// let slice = vec.into_boxed_slice();
1094 /// assert_eq!(slice.into_vec().capacity(), 3);
1096 #[cfg(not(no_global_oom_handling))]
1097 #[stable(feature = "rust1", since = "1.0.0")]
1098 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
1100 self.shrink_to_fit();
1101 let me = ManuallyDrop::new(self);
1102 let buf = ptr::read(&me.buf);
1104 buf.into_box(len).assume_init()
1108 /// Shortens the vector, keeping the first `len` elements and dropping
1111 /// If `len` is greater than the vector's current length, this has no
1114 /// The [`drain`] method can emulate `truncate`, but causes the excess
1115 /// elements to be returned instead of dropped.
1117 /// Note that this method has no effect on the allocated capacity
1122 /// Truncating a five element vector to two elements:
1125 /// let mut vec = vec![1, 2, 3, 4, 5];
1126 /// vec.truncate(2);
1127 /// assert_eq!(vec, [1, 2]);
1130 /// No truncation occurs when `len` is greater than the vector's current
1134 /// let mut vec = vec![1, 2, 3];
1135 /// vec.truncate(8);
1136 /// assert_eq!(vec, [1, 2, 3]);
1139 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1143 /// let mut vec = vec![1, 2, 3];
1144 /// vec.truncate(0);
1145 /// assert_eq!(vec, []);
1148 /// [`clear`]: Vec::clear
1149 /// [`drain`]: Vec::drain
1150 #[stable(feature = "rust1", since = "1.0.0")]
1151 pub fn truncate(&mut self, len: usize) {
1152 // This is safe because:
1154 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1155 // case avoids creating an invalid slice, and
1156 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1157 // such that no value will be dropped twice in case `drop_in_place`
1158 // were to panic once (if it panics twice, the program aborts).
1160 // Note: It's intentional that this is `>` and not `>=`.
1161 // Changing it to `>=` has negative performance
1162 // implications in some cases. See #78884 for more.
1166 let remaining_len = self.len - len;
1167 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1169 ptr::drop_in_place(s);
1173 /// Extracts a slice containing the entire vector.
1175 /// Equivalent to `&s[..]`.
1180 /// use std::io::{self, Write};
1181 /// let buffer = vec![1, 2, 3, 5, 8];
1182 /// io::sink().write(buffer.as_slice()).unwrap();
1185 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1186 pub fn as_slice(&self) -> &[T] {
1190 /// Extracts a mutable slice of the entire vector.
1192 /// Equivalent to `&mut s[..]`.
1197 /// use std::io::{self, Read};
1198 /// let mut buffer = vec![0; 3];
1199 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1202 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1203 pub fn as_mut_slice(&mut self) -> &mut [T] {
1207 /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
1208 /// valid for zero sized reads if the vector didn't allocate.
1210 /// The caller must ensure that the vector outlives the pointer this
1211 /// function returns, or else it will end up pointing to garbage.
1212 /// Modifying the vector may cause its buffer to be reallocated,
1213 /// which would also make any pointers to it invalid.
1215 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1216 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1217 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1222 /// let x = vec![1, 2, 4];
1223 /// let x_ptr = x.as_ptr();
1226 /// for i in 0..x.len() {
1227 /// assert_eq!(*x_ptr.add(i), 1 << i);
1232 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1233 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1235 pub fn as_ptr(&self) -> *const T {
1236 // We shadow the slice method of the same name to avoid going through
1237 // `deref`, which creates an intermediate reference.
1238 let ptr = self.buf.ptr();
1240 assume(!ptr.is_null());
1245 /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
1246 /// raw pointer valid for zero sized reads if the vector didn't allocate.
1248 /// The caller must ensure that the vector outlives the pointer this
1249 /// function returns, or else it will end up pointing to garbage.
1250 /// Modifying the vector may cause its buffer to be reallocated,
1251 /// which would also make any pointers to it invalid.
1256 /// // Allocate vector big enough for 4 elements.
1258 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1259 /// let x_ptr = x.as_mut_ptr();
1261 /// // Initialize elements via raw pointer writes, then set length.
1263 /// for i in 0..size {
1264 /// *x_ptr.add(i) = i as i32;
1266 /// x.set_len(size);
1268 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1270 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1272 pub fn as_mut_ptr(&mut self) -> *mut T {
1273 // We shadow the slice method of the same name to avoid going through
1274 // `deref_mut`, which creates an intermediate reference.
1275 let ptr = self.buf.ptr();
1277 assume(!ptr.is_null());
1282 /// Returns a reference to the underlying allocator.
1283 #[unstable(feature = "allocator_api", issue = "32838")]
1285 pub fn allocator(&self) -> &A {
1286 self.buf.allocator()
1289 /// Forces the length of the vector to `new_len`.
1291 /// This is a low-level operation that maintains none of the normal
1292 /// invariants of the type. Normally changing the length of a vector
1293 /// is done using one of the safe operations instead, such as
1294 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1296 /// [`truncate`]: Vec::truncate
1297 /// [`resize`]: Vec::resize
1298 /// [`extend`]: Extend::extend
1299 /// [`clear`]: Vec::clear
1303 /// - `new_len` must be less than or equal to [`capacity()`].
1304 /// - The elements at `old_len..new_len` must be initialized.
1306 /// [`capacity()`]: Vec::capacity
1310 /// This method can be useful for situations in which the vector
1311 /// is serving as a buffer for other code, particularly over FFI:
1314 /// # #![allow(dead_code)]
1315 /// # // This is just a minimal skeleton for the doc example;
1316 /// # // don't use this as a starting point for a real library.
1317 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1318 /// # const Z_OK: i32 = 0;
1320 /// # fn deflateGetDictionary(
1321 /// # strm: *mut std::ffi::c_void,
1322 /// # dictionary: *mut u8,
1323 /// # dictLength: *mut usize,
1326 /// # impl StreamWrapper {
1327 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1328 /// // Per the FFI method's docs, "32768 bytes is always enough".
1329 /// let mut dict = Vec::with_capacity(32_768);
1330 /// let mut dict_length = 0;
1331 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1332 /// // 1. `dict_length` elements were initialized.
1333 /// // 2. `dict_length` <= the capacity (32_768)
1334 /// // which makes `set_len` safe to call.
1336 /// // Make the FFI call...
1337 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1339 /// // ...and update the length to what was initialized.
1340 /// dict.set_len(dict_length);
1350 /// While the following example is sound, there is a memory leak since
1351 /// the inner vectors were not freed prior to the `set_len` call:
1354 /// let mut vec = vec![vec![1, 0, 0],
1358 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1359 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1365 /// Normally, here, one would use [`clear`] instead to correctly drop
1366 /// the contents and thus not leak memory.
1368 #[stable(feature = "rust1", since = "1.0.0")]
1369 pub unsafe fn set_len(&mut self, new_len: usize) {
1370 debug_assert!(new_len <= self.capacity());
1375 /// Removes an element from the vector and returns it.
1377 /// The removed element is replaced by the last element of the vector.
1379 /// This does not preserve ordering, but is *O*(1).
1380 /// If you need to preserve the element order, use [`remove`] instead.
1382 /// [`remove`]: Vec::remove
1386 /// Panics if `index` is out of bounds.
1391 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1393 /// assert_eq!(v.swap_remove(1), "bar");
1394 /// assert_eq!(v, ["foo", "qux", "baz"]);
1396 /// assert_eq!(v.swap_remove(0), "foo");
1397 /// assert_eq!(v, ["baz", "qux"]);
1400 #[stable(feature = "rust1", since = "1.0.0")]
1401 pub fn swap_remove(&mut self, index: usize) -> T {
1404 fn assert_failed(index: usize, len: usize) -> ! {
1405 panic!("swap_remove index (is {index}) should be < len (is {len})");
1408 let len = self.len();
1410 assert_failed(index, len);
1413 // We replace self[index] with the last element. Note that if the
1414 // bounds check above succeeds there must be a last element (which
1415 // can be self[index] itself).
1416 let value = ptr::read(self.as_ptr().add(index));
1417 let base_ptr = self.as_mut_ptr();
1418 ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
1419 self.set_len(len - 1);
1424 /// Inserts an element at position `index` within the vector, shifting all
1425 /// elements after it to the right.
1429 /// Panics if `index > len`.
1434 /// let mut vec = vec![1, 2, 3];
1435 /// vec.insert(1, 4);
1436 /// assert_eq!(vec, [1, 4, 2, 3]);
1437 /// vec.insert(4, 5);
1438 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1440 #[cfg(not(no_global_oom_handling))]
1441 #[stable(feature = "rust1", since = "1.0.0")]
1442 pub fn insert(&mut self, index: usize, element: T) {
1445 fn assert_failed(index: usize, len: usize) -> ! {
1446 panic!("insertion index (is {index}) should be <= len (is {len})");
1449 let len = self.len();
1451 // space for the new element
1452 if len == self.buf.capacity() {
1458 // The spot to put the new value
1460 let p = self.as_mut_ptr().add(index);
1462 // Shift everything over to make space. (Duplicating the
1463 // `index`th element into two consecutive places.)
1464 ptr::copy(p, p.add(1), len - index);
1465 } else if index == len {
1466 // No elements need shifting.
1468 assert_failed(index, len);
1470 // Write it in, overwriting the first copy of the `index`th
1472 ptr::write(p, element);
1474 self.set_len(len + 1);
1478 /// Removes and returns the element at position `index` within the vector,
1479 /// shifting all elements after it to the left.
1481 /// Note: Because this shifts over the remaining elements, it has a
1482 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1483 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1484 /// elements from the beginning of the `Vec`, consider using
1485 /// [`VecDeque::pop_front`] instead.
1487 /// [`swap_remove`]: Vec::swap_remove
1488 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1492 /// Panics if `index` is out of bounds.
1497 /// let mut v = vec![1, 2, 3];
1498 /// assert_eq!(v.remove(1), 2);
1499 /// assert_eq!(v, [1, 3]);
1501 #[stable(feature = "rust1", since = "1.0.0")]
1503 pub fn remove(&mut self, index: usize) -> T {
1507 fn assert_failed(index: usize, len: usize) -> ! {
1508 panic!("removal index (is {index}) should be < len (is {len})");
1511 let len = self.len();
1513 assert_failed(index, len);
1519 // the place we are taking from.
1520 let ptr = self.as_mut_ptr().add(index);
1521 // copy it out, unsafely having a copy of the value on
1522 // the stack and in the vector at the same time.
1523 ret = ptr::read(ptr);
1525 // Shift everything down to fill in that spot.
1526 ptr::copy(ptr.add(1), ptr, len - index - 1);
1528 self.set_len(len - 1);
1533 /// Retains only the elements specified by the predicate.
1535 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1536 /// This method operates in place, visiting each element exactly once in the
1537 /// original order, and preserves the order of the retained elements.
1542 /// let mut vec = vec![1, 2, 3, 4];
1543 /// vec.retain(|&x| x % 2 == 0);
1544 /// assert_eq!(vec, [2, 4]);
1547 /// Because the elements are visited exactly once in the original order,
1548 /// external state may be used to decide which elements to keep.
1551 /// let mut vec = vec![1, 2, 3, 4, 5];
1552 /// let keep = [false, true, true, false, true];
1553 /// let mut iter = keep.iter();
1554 /// vec.retain(|_| *iter.next().unwrap());
1555 /// assert_eq!(vec, [2, 3, 5]);
1557 #[stable(feature = "rust1", since = "1.0.0")]
1558 pub fn retain<F>(&mut self, mut f: F)
1560 F: FnMut(&T) -> bool,
1562 self.retain_mut(|elem| f(elem));
1565 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1567 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1568 /// This method operates in place, visiting each element exactly once in the
1569 /// original order, and preserves the order of the retained elements.
1574 /// let mut vec = vec![1, 2, 3, 4];
1575 /// vec.retain_mut(|x| if *x <= 3 {
1581 /// assert_eq!(vec, [2, 3, 4]);
1583 #[stable(feature = "vec_retain_mut", since = "1.61.0")]
1584 pub fn retain_mut<F>(&mut self, mut f: F)
1586 F: FnMut(&mut T) -> bool,
1588 let original_len = self.len();
1589 // Avoid double drop if the drop guard is not executed,
1590 // since we may make some holes during the process.
1591 unsafe { self.set_len(0) };
1593 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1594 // |<- processed len ->| ^- next to check
1595 // |<- deleted cnt ->|
1596 // |<- original_len ->|
1597 // Kept: Elements which predicate returns true on.
1598 // Hole: Moved or dropped element slot.
1599 // Unchecked: Unchecked valid elements.
1601 // This drop guard will be invoked when predicate or `drop` of element panicked.
1602 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1603 // In cases when predicate and `drop` never panick, it will be optimized out.
1604 struct BackshiftOnDrop<'a, T, A: Allocator> {
1605 v: &'a mut Vec<T, A>,
1606 processed_len: usize,
1608 original_len: usize,
1611 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1612 fn drop(&mut self) {
1613 if self.deleted_cnt > 0 {
1614 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1617 self.v.as_ptr().add(self.processed_len),
1618 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1619 self.original_len - self.processed_len,
1623 // SAFETY: After filling holes, all items are in contiguous memory.
1625 self.v.set_len(self.original_len - self.deleted_cnt);
1630 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1632 fn process_loop<F, T, A: Allocator, const DELETED: bool>(
1633 original_len: usize,
1635 g: &mut BackshiftOnDrop<'_, T, A>,
1637 F: FnMut(&mut T) -> bool,
1639 while g.processed_len != original_len {
1640 // SAFETY: Unchecked element must be valid.
1641 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1643 // Advance early to avoid double drop if `drop_in_place` panicked.
1644 g.processed_len += 1;
1646 // SAFETY: We never touch this element again after dropped.
1647 unsafe { ptr::drop_in_place(cur) };
1648 // We already advanced the counter.
1656 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1657 // We use copy for move, and never touch this element again.
1659 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1660 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1663 g.processed_len += 1;
1667 // Stage 1: Nothing was deleted.
1668 process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
1670 // Stage 2: Some elements were deleted.
1671 process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
1673 // All item are processed. This can be optimized to `set_len` by LLVM.
1677 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1680 /// If the vector is sorted, this removes all duplicates.
1685 /// let mut vec = vec![10, 20, 21, 30, 20];
1687 /// vec.dedup_by_key(|i| *i / 10);
1689 /// assert_eq!(vec, [10, 20, 30, 20]);
1691 #[stable(feature = "dedup_by", since = "1.16.0")]
1693 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1695 F: FnMut(&mut T) -> K,
1698 self.dedup_by(|a, b| key(a) == key(b))
1701 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1704 /// The `same_bucket` function is passed references to two elements from the vector and
1705 /// must determine if the elements compare equal. The elements are passed in opposite order
1706 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1708 /// If the vector is sorted, this removes all duplicates.
1713 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1715 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1717 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1719 #[stable(feature = "dedup_by", since = "1.16.0")]
1720 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1722 F: FnMut(&mut T, &mut T) -> bool,
1724 let len = self.len();
1729 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1730 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1731 /* Offset of the element we want to check if it is duplicate */
1734 /* Offset of the place where we want to place the non-duplicate
1735 * when we find it. */
1738 /* The Vec that would need correction if `same_bucket` panicked */
1739 vec: &'a mut Vec<T, A>,
1742 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1743 fn drop(&mut self) {
1744 /* This code gets executed when `same_bucket` panics */
1746 /* SAFETY: invariant guarantees that `read - write`
1747 * and `len - read` never overflow and that the copy is always
1750 let ptr = self.vec.as_mut_ptr();
1751 let len = self.vec.len();
1753 /* How many items were left when `same_bucket` panicked.
1754 * Basically vec[read..].len() */
1755 let items_left = len.wrapping_sub(self.read);
1757 /* Pointer to first item in vec[write..write+items_left] slice */
1758 let dropped_ptr = ptr.add(self.write);
1759 /* Pointer to first item in vec[read..] slice */
1760 let valid_ptr = ptr.add(self.read);
1762 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1763 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1764 ptr::copy(valid_ptr, dropped_ptr, items_left);
1766 /* How many items have been already dropped
1767 * Basically vec[read..write].len() */
1768 let dropped = self.read.wrapping_sub(self.write);
1770 self.vec.set_len(len - dropped);
1775 let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
1776 let ptr = gap.vec.as_mut_ptr();
1778 /* Drop items while going through Vec, it should be more efficient than
1779 * doing slice partition_dedup + truncate */
1781 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1782 * are always in-bounds and read_ptr never aliases prev_ptr */
1784 while gap.read < len {
1785 let read_ptr = ptr.add(gap.read);
1786 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1788 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1789 // Increase `gap.read` now since the drop may panic.
1791 /* We have found duplicate, drop it in-place */
1792 ptr::drop_in_place(read_ptr);
1794 let write_ptr = ptr.add(gap.write);
1796 /* Because `read_ptr` can be equal to `write_ptr`, we either
1797 * have to use `copy` or conditional `copy_nonoverlapping`.
1798 * Looks like the first option is faster. */
1799 ptr::copy(read_ptr, write_ptr, 1);
1801 /* We have filled that place, so go further */
1807 /* Technically we could let `gap` clean up with its Drop, but
1808 * when `same_bucket` is guaranteed to not panic, this bloats a little
1809 * the codegen, so we just do it manually */
1810 gap.vec.set_len(gap.write);
1815 /// Appends an element to the back of a collection.
1819 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1824 /// let mut vec = vec![1, 2];
1826 /// assert_eq!(vec, [1, 2, 3]);
1828 #[cfg(not(no_global_oom_handling))]
1830 #[stable(feature = "rust1", since = "1.0.0")]
1831 pub fn push(&mut self, value: T) {
1832 // This will panic or abort if we would allocate > isize::MAX bytes
1833 // or if the length increment would overflow for zero-sized types.
1834 if self.len == self.buf.capacity() {
1835 self.buf.reserve_for_push(self.len);
1838 let end = self.as_mut_ptr().add(self.len);
1839 ptr::write(end, value);
1844 /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
1845 /// with the element.
1847 /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
1848 /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
1850 /// [`push`]: Vec::push
1851 /// [`reserve`]: Vec::reserve
1852 /// [`try_reserve`]: Vec::try_reserve
1856 /// A manual, panic-free alternative to [`FromIterator`]:
1859 /// #![feature(vec_push_within_capacity)]
1861 /// use std::collections::TryReserveError;
1862 /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
1863 /// let mut vec = Vec::new();
1864 /// for value in iter {
1865 /// if let Err(value) = vec.push_within_capacity(value) {
1866 /// vec.try_reserve(1)?;
1867 /// // this cannot fail, the previous line either returned or added at least 1 free slot
1868 /// let _ = vec.push_within_capacity(value);
1873 /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
1876 #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
1877 pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
1878 if self.len == self.buf.capacity() {
1882 let end = self.as_mut_ptr().add(self.len);
1883 ptr::write(end, value);
1889 /// Removes the last element from a vector and returns it, or [`None`] if it
1892 /// If you'd like to pop the first element, consider using
1893 /// [`VecDeque::pop_front`] instead.
1895 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1900 /// let mut vec = vec![1, 2, 3];
1901 /// assert_eq!(vec.pop(), Some(3));
1902 /// assert_eq!(vec, [1, 2]);
1905 #[stable(feature = "rust1", since = "1.0.0")]
1906 pub fn pop(&mut self) -> Option<T> {
1912 Some(ptr::read(self.as_ptr().add(self.len())))
1917 /// Moves all the elements of `other` into `self`, leaving `other` empty.
1921 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1926 /// let mut vec = vec![1, 2, 3];
1927 /// let mut vec2 = vec![4, 5, 6];
1928 /// vec.append(&mut vec2);
1929 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1930 /// assert_eq!(vec2, []);
1932 #[cfg(not(no_global_oom_handling))]
1934 #[stable(feature = "append", since = "1.4.0")]
1935 pub fn append(&mut self, other: &mut Self) {
1937 self.append_elements(other.as_slice() as _);
1942 /// Appends elements to `self` from other buffer.
1943 #[cfg(not(no_global_oom_handling))]
1945 unsafe fn append_elements(&mut self, other: *const [T]) {
1946 let count = unsafe { (*other).len() };
1947 self.reserve(count);
1948 let len = self.len();
1949 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1953 /// Removes the specified range from the vector in bulk, returning all
1954 /// removed elements as an iterator. If the iterator is dropped before
1955 /// being fully consumed, it drops the remaining removed elements.
1957 /// The returned iterator keeps a mutable borrow on the vector to optimize
1958 /// its implementation.
1962 /// Panics if the starting point is greater than the end point or if
1963 /// the end point is greater than the length of the vector.
1967 /// If the returned iterator goes out of scope without being dropped (due to
1968 /// [`mem::forget`], for example), the vector may have lost and leaked
1969 /// elements arbitrarily, including elements outside the range.
1974 /// let mut v = vec![1, 2, 3];
1975 /// let u: Vec<_> = v.drain(1..).collect();
1976 /// assert_eq!(v, &[1]);
1977 /// assert_eq!(u, &[2, 3]);
1979 /// // A full range clears the vector, like `clear()` does
1981 /// assert_eq!(v, &[]);
1983 #[stable(feature = "drain", since = "1.6.0")]
1984 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1986 R: RangeBounds<usize>,
1990 // When the Drain is first created, it shortens the length of
1991 // the source vector to make sure no uninitialized or moved-from elements
1992 // are accessible at all if the Drain's destructor never gets to run.
1994 // Drain will ptr::read out the values to remove.
1995 // When finished, remaining tail of the vec is copied back to cover
1996 // the hole, and the vector length is restored to the new length.
1998 let len = self.len();
1999 let Range { start, end } = slice::range(range, ..len);
2002 // set self.vec length's to start, to be safe in case Drain is leaked
2003 self.set_len(start);
2004 let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
2007 tail_len: len - end,
2008 iter: range_slice.iter(),
2009 vec: NonNull::from(self),
2014 /// Clears the vector, removing all values.
2016 /// Note that this method has no effect on the allocated capacity
2022 /// let mut v = vec![1, 2, 3];
2026 /// assert!(v.is_empty());
2029 #[stable(feature = "rust1", since = "1.0.0")]
2030 pub fn clear(&mut self) {
2031 let elems: *mut [T] = self.as_mut_slice();
2034 // - `elems` comes directly from `as_mut_slice` and is therefore valid.
2035 // - Setting `self.len` before calling `drop_in_place` means that,
2036 // if an element's `Drop` impl panics, the vector's `Drop` impl will
2037 // do nothing (leaking the rest of the elements) instead of dropping
2041 ptr::drop_in_place(elems);
2045 /// Returns the number of elements in the vector, also referred to
2046 /// as its 'length'.
2051 /// let a = vec![1, 2, 3];
2052 /// assert_eq!(a.len(), 3);
2055 #[stable(feature = "rust1", since = "1.0.0")]
2056 pub fn len(&self) -> usize {
2060 /// Returns `true` if the vector contains no elements.
2065 /// let mut v = Vec::new();
2066 /// assert!(v.is_empty());
2069 /// assert!(!v.is_empty());
2071 #[stable(feature = "rust1", since = "1.0.0")]
2072 pub fn is_empty(&self) -> bool {
2076 /// Splits the collection into two at the given index.
2078 /// Returns a newly allocated vector containing the elements in the range
2079 /// `[at, len)`. After the call, the original vector will be left containing
2080 /// the elements `[0, at)` with its previous capacity unchanged.
2084 /// Panics if `at > len`.
2089 /// let mut vec = vec![1, 2, 3];
2090 /// let vec2 = vec.split_off(1);
2091 /// assert_eq!(vec, [1]);
2092 /// assert_eq!(vec2, [2, 3]);
2094 #[cfg(not(no_global_oom_handling))]
2096 #[must_use = "use `.truncate()` if you don't need the other half"]
2097 #[stable(feature = "split_off", since = "1.4.0")]
2098 pub fn split_off(&mut self, at: usize) -> Self
2104 fn assert_failed(at: usize, len: usize) -> ! {
2105 panic!("`at` split index (is {at}) should be <= len (is {len})");
2108 if at > self.len() {
2109 assert_failed(at, self.len());
2113 // the new vector can take over the original buffer and avoid the copy
2114 return mem::replace(
2116 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
2120 let other_len = self.len - at;
2121 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
2123 // Unsafely `set_len` and copy items to `other`.
2126 other.set_len(other_len);
2128 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
2133 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2135 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2136 /// difference, with each additional slot filled with the result of
2137 /// calling the closure `f`. The return values from `f` will end up
2138 /// in the `Vec` in the order they have been generated.
2140 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2142 /// This method uses a closure to create new values on every push. If
2143 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
2144 /// want to use the [`Default`] trait to generate values, you can
2145 /// pass [`Default::default`] as the second argument.
2150 /// let mut vec = vec![1, 2, 3];
2151 /// vec.resize_with(5, Default::default);
2152 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
2154 /// let mut vec = vec![];
2156 /// vec.resize_with(4, || { p *= 2; p });
2157 /// assert_eq!(vec, [2, 4, 8, 16]);
2159 #[cfg(not(no_global_oom_handling))]
2160 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2161 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
2165 let len = self.len();
2167 self.extend_trusted(iter::repeat_with(f).take(new_len - len));
2169 self.truncate(new_len);
2173 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2174 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2175 /// `'a`. If the type has only static references, or none at all, then this
2176 /// may be chosen to be `'static`.
2178 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2179 /// so the leaked allocation may include unused capacity that is not part
2180 /// of the returned slice.
2182 /// This function is mainly useful for data that lives for the remainder of
2183 /// the program's life. Dropping the returned reference will cause a memory
2191 /// let x = vec![1, 2, 3];
2192 /// let static_ref: &'static mut [usize] = x.leak();
2193 /// static_ref[0] += 1;
2194 /// assert_eq!(static_ref, &[2, 2, 3]);
2196 #[stable(feature = "vec_leak", since = "1.47.0")]
2198 pub fn leak<'a>(self) -> &'a mut [T]
2202 let mut me = ManuallyDrop::new(self);
2203 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2206 /// Returns the remaining spare capacity of the vector as a slice of
2207 /// `MaybeUninit<T>`.
2209 /// The returned slice can be used to fill the vector with data (e.g. by
2210 /// reading from a file) before marking the data as initialized using the
2211 /// [`set_len`] method.
2213 /// [`set_len`]: Vec::set_len
2218 /// // Allocate vector big enough for 10 elements.
2219 /// let mut v = Vec::with_capacity(10);
2221 /// // Fill in the first 3 elements.
2222 /// let uninit = v.spare_capacity_mut();
2223 /// uninit[0].write(0);
2224 /// uninit[1].write(1);
2225 /// uninit[2].write(2);
2227 /// // Mark the first 3 elements of the vector as being initialized.
2232 /// assert_eq!(&v, &[0, 1, 2]);
2234 #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
2236 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2238 // This method is not implemented in terms of `split_at_spare_mut`,
2239 // to prevent invalidation of pointers to the buffer.
2241 slice::from_raw_parts_mut(
2242 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2243 self.buf.capacity() - self.len,
2248 /// Returns vector content as a slice of `T`, along with the remaining spare
2249 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2251 /// The returned spare capacity slice can be used to fill the vector with data
2252 /// (e.g. by reading from a file) before marking the data as initialized using
2253 /// the [`set_len`] method.
2255 /// [`set_len`]: Vec::set_len
2257 /// Note that this is a low-level API, which should be used with care for
2258 /// optimization purposes. If you need to append data to a `Vec`
2259 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2260 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2261 /// [`resize_with`], depending on your exact needs.
2263 /// [`push`]: Vec::push
2264 /// [`extend`]: Vec::extend
2265 /// [`extend_from_slice`]: Vec::extend_from_slice
2266 /// [`extend_from_within`]: Vec::extend_from_within
2267 /// [`insert`]: Vec::insert
2268 /// [`append`]: Vec::append
2269 /// [`resize`]: Vec::resize
2270 /// [`resize_with`]: Vec::resize_with
2275 /// #![feature(vec_split_at_spare)]
2277 /// let mut v = vec![1, 1, 2];
2279 /// // Reserve additional space big enough for 10 elements.
2282 /// let (init, uninit) = v.split_at_spare_mut();
2283 /// let sum = init.iter().copied().sum::<u32>();
2285 /// // Fill in the next 4 elements.
2286 /// uninit[0].write(sum);
2287 /// uninit[1].write(sum * 2);
2288 /// uninit[2].write(sum * 3);
2289 /// uninit[3].write(sum * 4);
2291 /// // Mark the 4 elements of the vector as being initialized.
2293 /// let len = v.len();
2294 /// v.set_len(len + 4);
2297 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2299 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2301 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2303 // - len is ignored and so never changed
2304 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2308 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2310 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2311 unsafe fn split_at_spare_mut_with_len(
2313 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2314 let ptr = self.as_mut_ptr();
2316 // - `ptr` is guaranteed to be valid for `self.len` elements
2317 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2319 let spare_ptr = unsafe { ptr.add(self.len) };
2320 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2321 let spare_len = self.buf.capacity() - self.len;
2324 // - `ptr` is guaranteed to be valid for `self.len` elements
2325 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2327 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2328 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2330 (initialized, spare, &mut self.len)
2335 impl<T: Clone, A: Allocator> Vec<T, A> {
2336 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2338 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2339 /// difference, with each additional slot filled with `value`.
2340 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2342 /// This method requires `T` to implement [`Clone`],
2343 /// in order to be able to clone the passed value.
2344 /// If you need more flexibility (or want to rely on [`Default`] instead of
2345 /// [`Clone`]), use [`Vec::resize_with`].
2346 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2351 /// let mut vec = vec!["hello"];
2352 /// vec.resize(3, "world");
2353 /// assert_eq!(vec, ["hello", "world", "world"]);
2355 /// let mut vec = vec![1, 2, 3, 4];
2356 /// vec.resize(2, 0);
2357 /// assert_eq!(vec, [1, 2]);
2359 #[cfg(not(no_global_oom_handling))]
2360 #[stable(feature = "vec_resize", since = "1.5.0")]
2361 pub fn resize(&mut self, new_len: usize, value: T) {
2362 let len = self.len();
2365 self.extend_with(new_len - len, ExtendElement(value))
2367 self.truncate(new_len);
2371 /// Clones and appends all elements in a slice to the `Vec`.
2373 /// Iterates over the slice `other`, clones each element, and then appends
2374 /// it to this `Vec`. The `other` slice is traversed in-order.
2376 /// Note that this function is same as [`extend`] except that it is
2377 /// specialized to work with slices instead. If and when Rust gets
2378 /// specialization this function will likely be deprecated (but still
2384 /// let mut vec = vec![1];
2385 /// vec.extend_from_slice(&[2, 3, 4]);
2386 /// assert_eq!(vec, [1, 2, 3, 4]);
2389 /// [`extend`]: Vec::extend
2390 #[cfg(not(no_global_oom_handling))]
2391 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2392 pub fn extend_from_slice(&mut self, other: &[T]) {
2393 self.spec_extend(other.iter())
2396 /// Copies elements from `src` range to the end of the vector.
2400 /// Panics if the starting point is greater than the end point or if
2401 /// the end point is greater than the length of the vector.
2406 /// let mut vec = vec![0, 1, 2, 3, 4];
2408 /// vec.extend_from_within(2..);
2409 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2411 /// vec.extend_from_within(..2);
2412 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2414 /// vec.extend_from_within(4..8);
2415 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2417 #[cfg(not(no_global_oom_handling))]
2418 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2419 pub fn extend_from_within<R>(&mut self, src: R)
2421 R: RangeBounds<usize>,
2423 let range = slice::range(src, ..self.len());
2424 self.reserve(range.len());
2427 // - `slice::range` guarantees that the given range is valid for indexing self
2429 self.spec_extend_from_within(range);
2434 impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
2435 /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
2439 /// Panics if the length of the resulting vector would overflow a `usize`.
2441 /// This is only possible when flattening a vector of arrays of zero-sized
2442 /// types, and thus tends to be irrelevant in practice. If
2443 /// `size_of::<T>() > 0`, this will never panic.
2448 /// #![feature(slice_flatten)]
2450 /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
2451 /// assert_eq!(vec.pop(), Some([7, 8, 9]));
2453 /// let mut flattened = vec.into_flattened();
2454 /// assert_eq!(flattened.pop(), Some(6));
2456 #[unstable(feature = "slice_flatten", issue = "95629")]
2457 pub fn into_flattened(self) -> Vec<T, A> {
2458 let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
2459 let (new_len, new_cap) = if T::IS_ZST {
2460 (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
2463 // - `cap * N` cannot overflow because the allocation is already in
2464 // the address space.
2465 // - Each `[T; N]` has `N` valid elements, so there are `len * N`
2466 // valid elements in the allocation.
2467 unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
2470 // - `ptr` was allocated by `self`
2471 // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
2472 // - `new_cap` refers to the same sized allocation as `cap` because
2473 // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
2474 // - `len` <= `cap`, so `len * N` <= `cap * N`.
2475 unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
2479 // This code generalizes `extend_with_{element,default}`.
2480 trait ExtendWith<T> {
2481 fn next(&mut self) -> T;
2485 struct ExtendElement<T>(T);
2486 impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2487 fn next(&mut self) -> T {
2490 fn last(self) -> T {
2495 impl<T, A: Allocator> Vec<T, A> {
2496 #[cfg(not(no_global_oom_handling))]
2497 /// Extend the vector by `n` values, using the given generator.
2498 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2502 let mut ptr = self.as_mut_ptr().add(self.len());
2503 // Use SetLenOnDrop to work around bug where compiler
2504 // might not realize the store through `ptr` through self.set_len()
2506 let mut local_len = SetLenOnDrop::new(&mut self.len);
2508 // Write all elements except the last one
2510 ptr::write(ptr, value.next());
2512 // Increment the length in every step in case next() panics
2513 local_len.increment_len(1);
2517 // We can write the last element directly without cloning needlessly
2518 ptr::write(ptr, value.last());
2519 local_len.increment_len(1);
2522 // len set by scope guard
2527 impl<T: PartialEq, A: Allocator> Vec<T, A> {
2528 /// Removes consecutive repeated elements in the vector according to the
2529 /// [`PartialEq`] trait implementation.
2531 /// If the vector is sorted, this removes all duplicates.
2536 /// let mut vec = vec![1, 2, 2, 3, 2];
2540 /// assert_eq!(vec, [1, 2, 3, 2]);
2542 #[stable(feature = "rust1", since = "1.0.0")]
2544 pub fn dedup(&mut self) {
2545 self.dedup_by(|a, b| a == b)
2549 ////////////////////////////////////////////////////////////////////////////////
2550 // Internal methods and functions
2551 ////////////////////////////////////////////////////////////////////////////////
2554 #[cfg(not(no_global_oom_handling))]
2555 #[stable(feature = "rust1", since = "1.0.0")]
2556 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2557 <T as SpecFromElem>::from_elem(elem, n, Global)
2561 #[cfg(not(no_global_oom_handling))]
2562 #[unstable(feature = "allocator_api", issue = "32838")]
2563 pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2564 <T as SpecFromElem>::from_elem(elem, n, alloc)
2567 trait ExtendFromWithinSpec {
2570 /// - `src` needs to be valid index
2571 /// - `self.capacity() - self.len()` must be `>= src.len()`
2572 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2575 impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2576 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2578 // - len is increased only after initializing elements
2579 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2582 // - caller guarantees that src is a valid index
2583 let to_clone = unsafe { this.get_unchecked(src) };
2585 iter::zip(to_clone, spare)
2586 .map(|(src, dst)| dst.write(src.clone()))
2588 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2589 // - len is increased after each element to prevent leaks (see issue #82533)
2590 .for_each(|_| *len += 1);
2594 impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2595 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2596 let count = src.len();
2598 let (init, spare) = self.split_at_spare_mut();
2601 // - caller guarantees that `src` is a valid index
2602 let source = unsafe { init.get_unchecked(src) };
2605 // - Both pointers are created from unique slice references (`&mut [_]`)
2606 // so they are valid and do not overlap.
2607 // - Elements are :Copy so it's OK to copy them, without doing
2608 // anything with the original values
2609 // - `count` is equal to the len of `source`, so source is valid for
2611 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2612 // is valid for `count` writes
2613 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2617 // - The elements were just initialized by `copy_nonoverlapping`
2622 ////////////////////////////////////////////////////////////////////////////////
2623 // Common trait implementations for Vec
2624 ////////////////////////////////////////////////////////////////////////////////
2626 #[stable(feature = "rust1", since = "1.0.0")]
2627 impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2631 fn deref(&self) -> &[T] {
2632 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2636 #[stable(feature = "rust1", since = "1.0.0")]
2637 impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2639 fn deref_mut(&mut self) -> &mut [T] {
2640 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2644 #[cfg(not(no_global_oom_handling))]
2645 trait SpecCloneFrom {
2646 fn clone_from(this: &mut Self, other: &Self);
2649 #[cfg(not(no_global_oom_handling))]
2650 impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
2651 default fn clone_from(this: &mut Self, other: &Self) {
2652 // drop anything that will not be overwritten
2653 this.truncate(other.len());
2655 // self.len <= other.len due to the truncate above, so the
2656 // slices here are always in-bounds.
2657 let (init, tail) = other.split_at(this.len());
2659 // reuse the contained values' allocations/resources.
2660 this.clone_from_slice(init);
2661 this.extend_from_slice(tail);
2665 #[cfg(not(no_global_oom_handling))]
2666 impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
2667 fn clone_from(this: &mut Self, other: &Self) {
2669 this.extend_from_slice(other);
2673 #[cfg(not(no_global_oom_handling))]
2674 #[stable(feature = "rust1", since = "1.0.0")]
2675 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2677 fn clone(&self) -> Self {
2678 let alloc = self.allocator().clone();
2679 <[T]>::to_vec_in(&**self, alloc)
2682 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2683 // required for this method definition, is not available. Instead use the
2684 // `slice::to_vec` function which is only available with cfg(test)
2685 // NB see the slice::hack module in slice.rs for more information
2687 fn clone(&self) -> Self {
2688 let alloc = self.allocator().clone();
2689 crate::slice::to_vec(&**self, alloc)
2692 fn clone_from(&mut self, other: &Self) {
2693 SpecCloneFrom::clone_from(self, other)
2697 /// The hash of a vector is the same as that of the corresponding slice,
2698 /// as required by the `core::borrow::Borrow` implementation.
2701 /// #![feature(build_hasher_simple_hash_one)]
2702 /// use std::hash::BuildHasher;
2704 /// let b = std::collections::hash_map::RandomState::new();
2705 /// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2706 /// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2707 /// assert_eq!(b.hash_one(v), b.hash_one(s));
2709 #[stable(feature = "rust1", since = "1.0.0")]
2710 impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2712 fn hash<H: Hasher>(&self, state: &mut H) {
2713 Hash::hash(&**self, state)
2717 #[stable(feature = "rust1", since = "1.0.0")]
2718 #[rustc_on_unimplemented(
2719 message = "vector indices are of type `usize` or ranges of `usize`",
2720 label = "vector indices are of type `usize` or ranges of `usize`"
2722 impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2723 type Output = I::Output;
2726 fn index(&self, index: I) -> &Self::Output {
2727 Index::index(&**self, index)
2731 #[stable(feature = "rust1", since = "1.0.0")]
2732 #[rustc_on_unimplemented(
2733 message = "vector indices are of type `usize` or ranges of `usize`",
2734 label = "vector indices are of type `usize` or ranges of `usize`"
2736 impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2738 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2739 IndexMut::index_mut(&mut **self, index)
2743 #[cfg(not(no_global_oom_handling))]
2744 #[stable(feature = "rust1", since = "1.0.0")]
2745 impl<T> FromIterator<T> for Vec<T> {
2747 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2748 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2752 #[stable(feature = "rust1", since = "1.0.0")]
2753 impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2755 type IntoIter = IntoIter<T, A>;
2757 /// Creates a consuming iterator, that is, one that moves each value out of
2758 /// the vector (from start to end). The vector cannot be used after calling
2764 /// let v = vec!["a".to_string(), "b".to_string()];
2765 /// let mut v_iter = v.into_iter();
2767 /// let first_element: Option<String> = v_iter.next();
2769 /// assert_eq!(first_element, Some("a".to_string()));
2770 /// assert_eq!(v_iter.next(), Some("b".to_string()));
2771 /// assert_eq!(v_iter.next(), None);
2774 fn into_iter(self) -> Self::IntoIter {
2776 let mut me = ManuallyDrop::new(self);
2777 let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
2778 let begin = me.as_mut_ptr();
2779 let end = if T::IS_ZST {
2780 begin.wrapping_byte_add(me.len())
2782 begin.add(me.len()) as *const T
2784 let cap = me.buf.capacity();
2786 buf: NonNull::new_unchecked(begin),
2787 phantom: PhantomData,
2797 #[stable(feature = "rust1", since = "1.0.0")]
2798 impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2800 type IntoIter = slice::Iter<'a, T>;
2802 fn into_iter(self) -> Self::IntoIter {
2807 #[stable(feature = "rust1", since = "1.0.0")]
2808 impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2809 type Item = &'a mut T;
2810 type IntoIter = slice::IterMut<'a, T>;
2812 fn into_iter(self) -> Self::IntoIter {
2817 #[cfg(not(no_global_oom_handling))]
2818 #[stable(feature = "rust1", since = "1.0.0")]
2819 impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2821 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2822 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
2826 fn extend_one(&mut self, item: T) {
2831 fn extend_reserve(&mut self, additional: usize) {
2832 self.reserve(additional);
2836 impl<T, A: Allocator> Vec<T, A> {
2837 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
2838 // they have no further optimizations to apply
2839 #[cfg(not(no_global_oom_handling))]
2840 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
2841 // This is the case for a general iterator.
2843 // This function should be the moral equivalent of:
2845 // for item in iterator {
2848 while let Some(element) = iterator.next() {
2849 let len = self.len();
2850 if len == self.capacity() {
2851 let (lower, _) = iterator.size_hint();
2852 self.reserve(lower.saturating_add(1));
2855 ptr::write(self.as_mut_ptr().add(len), element);
2856 // Since next() executes user code which can panic we have to bump the length
2858 // NB can't overflow since we would have had to alloc the address space
2859 self.set_len(len + 1);
2864 // specific extend for `TrustedLen` iterators, called both by the specializations
2865 // and internal places where resolving specialization makes compilation slower
2866 #[cfg(not(no_global_oom_handling))]
2867 fn extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) {
2868 let (low, high) = iterator.size_hint();
2869 if let Some(additional) = high {
2873 "TrustedLen iterator's size hint is not exact: {:?}",
2876 self.reserve(additional);
2878 let ptr = self.as_mut_ptr();
2879 let mut local_len = SetLenOnDrop::new(&mut self.len);
2880 iterator.for_each(move |element| {
2881 ptr::write(ptr.add(local_len.current_len()), element);
2882 // Since the loop executes user code which can panic we have to update
2883 // the length every step to correctly drop what we've written.
2884 // NB can't overflow since we would have had to alloc the address space
2885 local_len.increment_len(1);
2889 // Per TrustedLen contract a `None` upper bound means that the iterator length
2890 // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
2891 // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
2892 // This avoids additional codegen for a fallback code path which would eventually
2894 panic!("capacity overflow");
2898 /// Creates a splicing iterator that replaces the specified range in the vector
2899 /// with the given `replace_with` iterator and yields the removed items.
2900 /// `replace_with` does not need to be the same length as `range`.
2902 /// `range` is removed even if the iterator is not consumed until the end.
2904 /// It is unspecified how many elements are removed from the vector
2905 /// if the `Splice` value is leaked.
2907 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2909 /// This is optimal if:
2911 /// * The tail (elements in the vector after `range`) is empty,
2912 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2913 /// * or the lower bound of its `size_hint()` is exact.
2915 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2919 /// Panics if the starting point is greater than the end point or if
2920 /// the end point is greater than the length of the vector.
2925 /// let mut v = vec![1, 2, 3, 4];
2926 /// let new = [7, 8, 9];
2927 /// let u: Vec<_> = v.splice(1..3, new).collect();
2928 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
2929 /// assert_eq!(u, &[2, 3]);
2931 #[cfg(not(no_global_oom_handling))]
2933 #[stable(feature = "vec_splice", since = "1.21.0")]
2934 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2936 R: RangeBounds<usize>,
2937 I: IntoIterator<Item = T>,
2939 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
2942 /// Creates an iterator which uses a closure to determine if an element should be removed.
2944 /// If the closure returns true, then the element is removed and yielded.
2945 /// If the closure returns false, the element will remain in the vector and will not be yielded
2946 /// by the iterator.
2948 /// Using this method is equivalent to the following code:
2951 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
2952 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
2954 /// while i < vec.len() {
2955 /// if some_predicate(&mut vec[i]) {
2956 /// let val = vec.remove(i);
2957 /// // your code here
2963 /// # assert_eq!(vec, vec![1, 4, 5]);
2966 /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
2967 /// because it can backshift the elements of the array in bulk.
2969 /// Note that `drain_filter` also lets you mutate every element in the filter closure,
2970 /// regardless of whether you choose to keep or remove it.
2974 /// Splitting an array into evens and odds, reusing the original allocation:
2977 /// #![feature(drain_filter)]
2978 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
2980 /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
2981 /// let odds = numbers;
2983 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
2984 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
2986 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
2987 pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
2989 F: FnMut(&mut T) -> bool,
2991 let old_len = self.len();
2993 // Guard against us getting leaked (leak amplification)
2998 DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
3002 /// Extend implementation that copies elements out of references before pushing them onto the Vec.
3004 /// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
3005 /// append the entire slice at once.
3007 /// [`copy_from_slice`]: slice::copy_from_slice
3008 #[cfg(not(no_global_oom_handling))]
3009 #[stable(feature = "extend_ref", since = "1.2.0")]
3010 impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
3011 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
3012 self.spec_extend(iter.into_iter())
3016 fn extend_one(&mut self, &item: &'a T) {
3021 fn extend_reserve(&mut self, additional: usize) {
3022 self.reserve(additional);
3026 /// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
3027 #[stable(feature = "rust1", since = "1.0.0")]
3028 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
3030 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
3031 PartialOrd::partial_cmp(&**self, &**other)
3035 #[stable(feature = "rust1", since = "1.0.0")]
3036 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
3038 /// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
3039 #[stable(feature = "rust1", since = "1.0.0")]
3040 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
3042 fn cmp(&self, other: &Self) -> Ordering {
3043 Ord::cmp(&**self, &**other)
3047 #[stable(feature = "rust1", since = "1.0.0")]
3048 unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
3049 fn drop(&mut self) {
3052 // use a raw slice to refer to the elements of the vector as weakest necessary type;
3053 // could avoid questions of validity in certain cases
3054 ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
3056 // RawVec handles deallocation
3060 #[stable(feature = "rust1", since = "1.0.0")]
3061 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3062 impl<T> const Default for Vec<T> {
3063 /// Creates an empty `Vec<T>`.
3065 /// The vector will not allocate until elements are pushed onto it.
3066 fn default() -> Vec<T> {
3071 #[stable(feature = "rust1", since = "1.0.0")]
3072 impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
3073 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3074 fmt::Debug::fmt(&**self, f)
3078 #[stable(feature = "rust1", since = "1.0.0")]
3079 impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
3080 fn as_ref(&self) -> &Vec<T, A> {
3085 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3086 impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
3087 fn as_mut(&mut self) -> &mut Vec<T, A> {
3092 #[stable(feature = "rust1", since = "1.0.0")]
3093 impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
3094 fn as_ref(&self) -> &[T] {
3099 #[stable(feature = "vec_as_mut", since = "1.5.0")]
3100 impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
3101 fn as_mut(&mut self) -> &mut [T] {
3106 #[cfg(not(no_global_oom_handling))]
3107 #[stable(feature = "rust1", since = "1.0.0")]
3108 impl<T: Clone> From<&[T]> for Vec<T> {
3109 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3114 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
3117 fn from(s: &[T]) -> Vec<T> {
3121 fn from(s: &[T]) -> Vec<T> {
3122 crate::slice::to_vec(s, Global)
3126 #[cfg(not(no_global_oom_handling))]
3127 #[stable(feature = "vec_from_mut", since = "1.19.0")]
3128 impl<T: Clone> From<&mut [T]> for Vec<T> {
3129 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3134 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
3137 fn from(s: &mut [T]) -> Vec<T> {
3141 fn from(s: &mut [T]) -> Vec<T> {
3142 crate::slice::to_vec(s, Global)
3146 #[cfg(not(no_global_oom_handling))]
3147 #[stable(feature = "vec_from_array", since = "1.44.0")]
3148 impl<T, const N: usize> From<[T; N]> for Vec<T> {
3149 /// Allocate a `Vec<T>` and move `s`'s items into it.
3154 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
3157 fn from(s: [T; N]) -> Vec<T> {
3165 fn from(s: [T; N]) -> Vec<T> {
3166 crate::slice::into_vec(Box::new(s))
3170 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
3171 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
3173 [T]: ToOwned<Owned = Vec<T>>,
3175 /// Convert a clone-on-write slice into a vector.
3177 /// If `s` already owns a `Vec<T>`, it will be returned directly.
3178 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
3179 /// filled by cloning `s`'s items into it.
3184 /// # use std::borrow::Cow;
3185 /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
3186 /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
3187 /// assert_eq!(Vec::from(o), Vec::from(b));
3189 fn from(s: Cow<'a, [T]>) -> Vec<T> {
3194 // note: test pulls in libstd, which causes errors here
3196 #[stable(feature = "vec_from_box", since = "1.18.0")]
3197 impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
3198 /// Convert a boxed slice into a vector by transferring ownership of
3199 /// the existing heap allocation.
3204 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
3205 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
3207 fn from(s: Box<[T], A>) -> Self {
3212 // note: test pulls in libstd, which causes errors here
3213 #[cfg(not(no_global_oom_handling))]
3215 #[stable(feature = "box_from_vec", since = "1.20.0")]
3216 impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
3217 /// Convert a vector into a boxed slice.
3219 /// If `v` has excess capacity, its items will be moved into a
3220 /// newly-allocated buffer with exactly the right capacity.
3225 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
3228 /// Any excess capacity is removed:
3230 /// let mut vec = Vec::with_capacity(10);
3231 /// vec.extend([1, 2, 3]);
3233 /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
3235 fn from(v: Vec<T, A>) -> Self {
3236 v.into_boxed_slice()
3240 #[cfg(not(no_global_oom_handling))]
3241 #[stable(feature = "rust1", since = "1.0.0")]
3242 impl From<&str> for Vec<u8> {
3243 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
3248 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
3250 fn from(s: &str) -> Vec<u8> {
3251 From::from(s.as_bytes())
3255 #[stable(feature = "array_try_from_vec", since = "1.48.0")]
3256 impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
3257 type Error = Vec<T, A>;
3259 /// Gets the entire contents of the `Vec<T>` as an array,
3260 /// if its size exactly matches that of the requested array.
3265 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3266 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3269 /// If the length doesn't match, the input comes back in `Err`:
3271 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3272 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3275 /// If you're fine with just getting a prefix of the `Vec<T>`,
3276 /// you can call [`.truncate(N)`](Vec::truncate) first.
3278 /// let mut v = String::from("hello world").into_bytes();
3281 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3282 /// assert_eq!(a, b' ');
3283 /// assert_eq!(b, b'd');
3285 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
3290 // SAFETY: `.set_len(0)` is always sound.
3291 unsafe { vec.set_len(0) };
3293 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3294 // the alignment the array needs is the same as the items.
3295 // We checked earlier that we have sufficient items.
3296 // The items will not double-drop as the `set_len`
3297 // tells the `Vec` not to also drop them.
3298 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };