1//! A contiguous growable array type with heap-allocated contents, written
2//! `Vec<T>`.
3//!
4//! Vectors have *O*(1) indexing, amortized *O*(1) push (to the end) and
5//! *O*(1) pop (from the end).
6//!
7//! Vectors ensure they never allocate more than `isize::MAX` bytes.
8//!
9//! # Examples
10//!
11//! You can explicitly create a [`Vec`] with [`Vec::new`]:
12//!
13//! ```
14//! let v: Vec<i32> = Vec::new();
15//! ```
16//!
17//! ...or by using the [`vec!`] macro:
18//!
19//! ```
20//! let v: Vec<i32> = vec![];
21//!
22//! let v = vec![1, 2, 3, 4, 5];
23//!
24//! let v = vec![0; 10]; // ten zeroes
25//! ```
26//!
27//! You can [`push`] values onto the end of a vector (which will grow the vector
28//! as needed):
29//!
30//! ```
31//! let mut v = vec![1, 2];
32//!
33//! v.push(3);
34//! ```
35//!
36//! Popping values works in much the same way:
37//!
38//! ```
39//! let mut v = vec![1, 2];
40//!
41//! let two = v.pop();
42//! ```
43//!
44//! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
45//!
46//! ```
47//! let mut v = vec![1, 2, 3];
48//! let three = v[2];
49//! v[1] = v[1] + 5;
50//! ```
51//!
52//! [`push`]: Vec::push
53
54#![stable(feature = "rust1", since = "1.0.0")]
55
56#[cfg(not(no_global_oom_handling))]
57use core::cmp;
58use core::cmp::Ordering;
59use core::fmt;
60use core::hash::{Hash, Hasher};
61#[cfg(not(no_global_oom_handling))]
62use core::iter;
63use core::marker::PhantomData;
64use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
65use core::ops::{self, Index, IndexMut, Range, RangeBounds};
66use core::ptr::{self, NonNull};
67use core::slice::{self, SliceIndex};
68
69use crate::alloc::{Allocator, Global};
70use crate::borrow::{Cow, ToOwned};
71use crate::boxed::Box;
72use crate::collections::TryReserveError;
73use crate::raw_vec::RawVec;
74
75#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
76pub use self::extract_if::ExtractIf;
77
78mod extract_if;
79
80#[cfg(not(no_global_oom_handling))]
81#[stable(feature = "vec_splice", since = "1.21.0")]
82pub use self::splice::Splice;
83
84#[cfg(not(no_global_oom_handling))]
85mod splice;
86
87#[stable(feature = "drain", since = "1.6.0")]
88pub use self::drain::Drain;
89
90mod drain;
91
92#[cfg(not(no_global_oom_handling))]
93mod cow;
94
95#[cfg(not(no_global_oom_handling))]
96pub(crate) use self::in_place_collect::AsVecIntoIter;
97#[stable(feature = "rust1", since = "1.0.0")]
98pub use self::into_iter::IntoIter;
99
100mod into_iter;
101
102#[cfg(not(no_global_oom_handling))]
103use self::is_zero::IsZero;
104
105#[cfg(not(no_global_oom_handling))]
106mod is_zero;
107
108#[cfg(not(no_global_oom_handling))]
109mod in_place_collect;
110
111mod partial_eq;
112
113#[cfg(not(no_global_oom_handling))]
114use self::spec_from_elem::SpecFromElem;
115
116#[cfg(not(no_global_oom_handling))]
117mod spec_from_elem;
118
119#[cfg(not(no_global_oom_handling))]
120use self::set_len_on_drop::SetLenOnDrop;
121
122#[cfg(not(no_global_oom_handling))]
123mod set_len_on_drop;
124
125#[cfg(not(no_global_oom_handling))]
126use self::in_place_drop::{InPlaceDrop, InPlaceDstDataSrcBufDrop};
127
128#[cfg(not(no_global_oom_handling))]
129mod in_place_drop;
130
131#[cfg(not(no_global_oom_handling))]
132use self::spec_from_iter_nested::SpecFromIterNested;
133
134#[cfg(not(no_global_oom_handling))]
135mod spec_from_iter_nested;
136
137#[cfg(not(no_global_oom_handling))]
138use self::spec_from_iter::SpecFromIter;
139
140#[cfg(not(no_global_oom_handling))]
141mod spec_from_iter;
142
143#[cfg(not(no_global_oom_handling))]
144use self::spec_extend::SpecExtend;
145
146#[cfg(not(no_global_oom_handling))]
147mod spec_extend;
148
149/// A contiguous growable array type, written as `Vec<T>`, short for 'vector'.
150///
151/// # Examples
152///
153/// ```
154/// let mut vec = Vec::new();
155/// vec.push(1);
156/// vec.push(2);
157///
158/// assert_eq!(vec.len(), 2);
159/// assert_eq!(vec[0], 1);
160///
161/// assert_eq!(vec.pop(), Some(2));
162/// assert_eq!(vec.len(), 1);
163///
164/// vec[0] = 7;
165/// assert_eq!(vec[0], 7);
166///
167/// vec.extend([1, 2, 3]);
168///
169/// for x in &vec {
170/// println!("{x}");
171/// }
172/// assert_eq!(vec, [7, 1, 2, 3]);
173/// ```
174///
175/// The [`vec!`] macro is provided for convenient initialization:
176///
177/// ```
178/// let mut vec1 = vec![1, 2, 3];
179/// vec1.push(4);
180/// let vec2 = Vec::from([1, 2, 3, 4]);
181/// assert_eq!(vec1, vec2);
182/// ```
183///
184/// It can also initialize each element of a `Vec<T>` with a given value.
185/// This may be more efficient than performing allocation and initialization
186/// in separate steps, especially when initializing a vector of zeros:
187///
188/// ```
189/// let vec = vec![0; 5];
190/// assert_eq!(vec, [0, 0, 0, 0, 0]);
191///
192/// // The following is equivalent, but potentially slower:
193/// let mut vec = Vec::with_capacity(5);
194/// vec.resize(5, 0);
195/// assert_eq!(vec, [0, 0, 0, 0, 0]);
196/// ```
197///
198/// For more information, see
199/// [Capacity and Reallocation](#capacity-and-reallocation).
200///
201/// Use a `Vec<T>` as an efficient stack:
202///
203/// ```
204/// let mut stack = Vec::new();
205///
206/// stack.push(1);
207/// stack.push(2);
208/// stack.push(3);
209///
210/// while let Some(top) = stack.pop() {
211/// // Prints 3, 2, 1
212/// println!("{top}");
213/// }
214/// ```
215///
216/// # Indexing
217///
218/// The `Vec` type allows access to values by index, because it implements the
219/// [`Index`] trait. An example will be more explicit:
220///
221/// ```
222/// let v = vec![0, 2, 4, 6];
223/// println!("{}", v[1]); // it will display '2'
224/// ```
225///
226/// However be careful: if you try to access an index which isn't in the `Vec`,
227/// your software will panic! You cannot do this:
228///
229/// ```should_panic
230/// let v = vec![0, 2, 4, 6];
231/// println!("{}", v[6]); // it will panic!
232/// ```
233///
234/// Use [`get`] and [`get_mut`] if you want to check whether the index is in
235/// the `Vec`.
236///
237/// # Slicing
238///
239/// A `Vec` can be mutable. On the other hand, slices are read-only objects.
240/// To get a [slice][prim@slice], use [`&`]. Example:
241///
242/// ```
243/// fn read_slice(slice: &[usize]) {
244/// // ...
245/// }
246///
247/// let v = vec![0, 1];
248/// read_slice(&v);
249///
250/// // ... and that's all!
251/// // you can also do it like this:
252/// let u: &[usize] = &v;
253/// // or like this:
254/// let u: &[_] = &v;
255/// ```
256///
257/// In Rust, it's more common to pass slices as arguments rather than vectors
258/// when you just want to provide read access. The same goes for [`String`] and
259/// [`&str`].
260///
261/// # Capacity and reallocation
262///
263/// The capacity of a vector is the amount of space allocated for any future
264/// elements that will be added onto the vector. This is not to be confused with
265/// the *length* of a vector, which specifies the number of actual elements
266/// within the vector. If a vector's length exceeds its capacity, its capacity
267/// will automatically be increased, but its elements will have to be
268/// reallocated.
269///
270/// For example, a vector with capacity 10 and length 0 would be an empty vector
271/// with space for 10 more elements. Pushing 10 or fewer elements onto the
272/// vector will not change its capacity or cause reallocation to occur. However,
273/// if the vector's length is increased to 11, it will have to reallocate, which
274/// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
275/// whenever possible to specify how big the vector is expected to get.
276///
277/// # Guarantees
278///
279/// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
280/// about its design. This ensures that it's as low-overhead as possible in
281/// the general case, and can be correctly manipulated in primitive ways
282/// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
283/// If additional type parameters are added (e.g., to support custom allocators),
284/// overriding their defaults may change the behavior.
285///
286/// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
287/// triplet. No more, no less. The order of these fields is completely
288/// unspecified, and you should use the appropriate methods to modify these.
289/// The pointer will never be null, so this type is null-pointer-optimized.
290///
291/// However, the pointer might not actually point to allocated memory. In particular,
292/// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
293/// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
294/// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
295/// types inside a `Vec`, it will not allocate space for them. *Note that in this case
296/// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
297/// if <code>[mem::size_of::\<T>]\() * [capacity]\() > 0</code>. In general, `Vec`'s allocation
298/// details are very subtle --- if you intend to allocate memory using a `Vec`
299/// and use it for something else (either to pass to unsafe code, or to build your
300/// own memory-backed collection), be sure to deallocate this memory by using
301/// `from_raw_parts` to recover the `Vec` and then dropping it.
302///
303/// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
304/// (as defined by the allocator Rust is configured to use by default), and its
305/// pointer points to [`len`] initialized, contiguous elements in order (what
306/// you would see if you coerced it to a slice), followed by <code>[capacity] - [len]</code>
307/// logically uninitialized, contiguous elements.
308///
309/// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
310/// visualized as below. The top part is the `Vec` struct, it contains a
311/// pointer to the head of the allocation in the heap, length and capacity.
312/// The bottom part is the allocation on the heap, a contiguous memory block.
313///
314/// ```text
315/// ptr len capacity
316/// +--------+--------+--------+
317/// | 0x0123 | 2 | 4 |
318/// +--------+--------+--------+
319/// |
320/// v
321/// Heap +--------+--------+--------+--------+
322/// | 'a' | 'b' | uninit | uninit |
323/// +--------+--------+--------+--------+
324/// ```
325///
326/// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
327/// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
328/// layout (including the order of fields).
329///
330/// `Vec` will never perform a "small optimization" where elements are actually
331/// stored on the stack for two reasons:
332///
333/// * It would make it more difficult for unsafe code to correctly manipulate
334/// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
335/// only moved, and it would be more difficult to determine if a `Vec` had
336/// actually allocated memory.
337///
338/// * It would penalize the general case, incurring an additional branch
339/// on every access.
340///
341/// `Vec` will never automatically shrink itself, even if completely empty. This
342/// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
343/// and then filling it back up to the same [`len`] should incur no calls to
344/// the allocator. If you wish to free up unused memory, use
345/// [`shrink_to_fit`] or [`shrink_to`].
346///
347/// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
348/// sufficient. [`push`] and [`insert`] *will* (re)allocate if
349/// <code>[len] == [capacity]</code>. That is, the reported capacity is completely
350/// accurate, and can be relied on. It can even be used to manually free the memory
351/// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
352/// when not necessary.
353///
354/// `Vec` does not guarantee any particular growth strategy when reallocating
355/// when full, nor when [`reserve`] is called. The current strategy is basic
356/// and it may prove desirable to use a non-constant growth factor. Whatever
357/// strategy is used will of course guarantee *O*(1) amortized [`push`].
358///
359/// `vec![x; n]`, `vec![a, b, c, d]`, and
360/// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
361/// with at least the requested capacity. If <code>[len] == [capacity]</code>,
362/// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
363/// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
364///
365/// `Vec` will not specifically overwrite any data that is removed from it,
366/// but also won't specifically preserve it. Its uninitialized memory is
367/// scratch space that it may use however it wants. It will generally just do
368/// whatever is most efficient or otherwise easy to implement. Do not rely on
369/// removed data to be erased for security purposes. Even if you drop a `Vec`, its
370/// buffer may simply be reused by another allocation. Even if you zero a `Vec`'s memory
371/// first, that might not actually happen because the optimizer does not consider
372/// this a side-effect that must be preserved. There is one case which we will
373/// not break, however: using `unsafe` code to write to the excess capacity,
374/// and then increasing the length to match, is always valid.
375///
376/// Currently, `Vec` does not guarantee the order in which elements are dropped.
377/// The order has changed in the past and may change again.
378///
379/// [`get`]: slice::get
380/// [`get_mut`]: slice::get_mut
381/// [`String`]: crate::string::String
382/// [`&str`]: type@str
383/// [`shrink_to_fit`]: Vec::shrink_to_fit
384/// [`shrink_to`]: Vec::shrink_to
385/// [capacity]: Vec::capacity
386/// [`capacity`]: Vec::capacity
387/// [mem::size_of::\<T>]: core::mem::size_of
388/// [len]: Vec::len
389/// [`len`]: Vec::len
390/// [`push`]: Vec::push
391/// [`insert`]: Vec::insert
392/// [`reserve`]: Vec::reserve
393/// [`MaybeUninit`]: core::mem::MaybeUninit
394/// [owned slice]: Box
395#[stable(feature = "rust1", since = "1.0.0")]
396#[cfg_attr(not(test), rustc_diagnostic_item = "Vec")]
397#[rustc_insignificant_dtor]
398pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
399 buf: RawVec<T, A>,
400 len: usize,
401}
402
403////////////////////////////////////////////////////////////////////////////////
404// Inherent methods
405////////////////////////////////////////////////////////////////////////////////
406
407impl<T> Vec<T> {
408 /// Constructs a new, empty `Vec<T>`.
409 ///
410 /// The vector will not allocate until elements are pushed onto it.
411 ///
412 /// # Examples
413 ///
414 /// ```
415 /// # #![allow(unused_mut)]
416 /// let mut vec: Vec<i32> = Vec::new();
417 /// ```
418 #[inline]
419 #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
420 #[stable(feature = "rust1", since = "1.0.0")]
421 #[must_use]
422 pub const fn new() -> Self {
423 Vec { buf: RawVec::NEW, len: 0 }
424 }
425
426 /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
427 ///
428 /// The vector will be able to hold at least `capacity` elements without
429 /// reallocating. This method is allowed to allocate for more elements than
430 /// `capacity`. If `capacity` is 0, the vector will not allocate.
431 ///
432 /// It is important to note that although the returned vector has the
433 /// minimum *capacity* specified, the vector will have a zero *length*. For
434 /// an explanation of the difference between length and capacity, see
435 /// *[Capacity and reallocation]*.
436 ///
437 /// If it is important to know the exact allocated capacity of a `Vec`,
438 /// always use the [`capacity`] method after construction.
439 ///
440 /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
441 /// and the capacity will always be `usize::MAX`.
442 ///
443 /// [Capacity and reallocation]: #capacity-and-reallocation
444 /// [`capacity`]: Vec::capacity
445 ///
446 /// # Panics
447 ///
448 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
449 ///
450 /// # Examples
451 ///
452 /// ```
453 /// let mut vec = Vec::with_capacity(10);
454 ///
455 /// // The vector contains no items, even though it has capacity for more
456 /// assert_eq!(vec.len(), 0);
457 /// assert!(vec.capacity() >= 10);
458 ///
459 /// // These are all done without reallocating...
460 /// for i in 0..10 {
461 /// vec.push(i);
462 /// }
463 /// assert_eq!(vec.len(), 10);
464 /// assert!(vec.capacity() >= 10);
465 ///
466 /// // ...but this may make the vector reallocate
467 /// vec.push(11);
468 /// assert_eq!(vec.len(), 11);
469 /// assert!(vec.capacity() >= 11);
470 ///
471 /// // A vector of a zero-sized type will always over-allocate, since no
472 /// // allocation is necessary
473 /// let vec_units = Vec::<()>::with_capacity(10);
474 /// assert_eq!(vec_units.capacity(), usize::MAX);
475 /// ```
476 #[cfg(not(no_global_oom_handling))]
477 #[inline]
478 #[stable(feature = "rust1", since = "1.0.0")]
479 #[must_use]
480 pub fn with_capacity(capacity: usize) -> Self {
481 Self::with_capacity_in(capacity, Global)
482 }
483
484 /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
485 ///
486 /// The vector will be able to hold at least `capacity` elements without
487 /// reallocating. This method is allowed to allocate for more elements than
488 /// `capacity`. If `capacity` is 0, the vector will not allocate.
489 ///
490 /// # Errors
491 ///
492 /// Returns an error if the capacity exceeds `isize::MAX` _bytes_,
493 /// or if the allocator reports allocation failure.
494 #[inline]
495 #[unstable(feature = "try_with_capacity", issue = "91913")]
496 pub fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError> {
497 Self::try_with_capacity_in(capacity, Global)
498 }
499
500 /// Creates a `Vec<T>` directly from a pointer, a length, and a capacity.
501 ///
502 /// # Safety
503 ///
504 /// This is highly unsafe, due to the number of invariants that aren't
505 /// checked:
506 ///
507 /// * `ptr` must have been allocated using the global allocator, such as via
508 /// the [`alloc::alloc`] function.
509 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
510 /// (`T` having a less strict alignment is not sufficient, the alignment really
511 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
512 /// allocated and deallocated with the same layout.)
513 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
514 /// to be the same size as the pointer was allocated with. (Because similar to
515 /// alignment, [`dealloc`] must be called with the same layout `size`.)
516 /// * `length` needs to be less than or equal to `capacity`.
517 /// * The first `length` values must be properly initialized values of type `T`.
518 /// * `capacity` needs to be the capacity that the pointer was allocated with.
519 /// * The allocated size in bytes must be no larger than `isize::MAX`.
520 /// See the safety documentation of [`pointer::offset`].
521 ///
522 /// These requirements are always upheld by any `ptr` that has been allocated
523 /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
524 /// upheld.
525 ///
526 /// Violating these may cause problems like corrupting the allocator's
527 /// internal data structures. For example it is normally **not** safe
528 /// to build a `Vec<u8>` from a pointer to a C `char` array with length
529 /// `size_t`, doing so is only safe if the array was initially allocated by
530 /// a `Vec` or `String`.
531 /// It's also not safe to build one from a `Vec<u16>` and its length, because
532 /// the allocator cares about the alignment, and these two types have different
533 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
534 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
535 /// these issues, it is often preferable to do casting/transmuting using
536 /// [`slice::from_raw_parts`] instead.
537 ///
538 /// The ownership of `ptr` is effectively transferred to the
539 /// `Vec<T>` which may then deallocate, reallocate or change the
540 /// contents of memory pointed to by the pointer at will. Ensure
541 /// that nothing else uses the pointer after calling this
542 /// function.
543 ///
544 /// [`String`]: crate::string::String
545 /// [`alloc::alloc`]: crate::alloc::alloc
546 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
547 ///
548 /// # Examples
549 ///
550 /// ```
551 /// use std::ptr;
552 /// use std::mem;
553 ///
554 /// let v = vec![1, 2, 3];
555 ///
556 // FIXME Update this when vec_into_raw_parts is stabilized
557 /// // Prevent running `v`'s destructor so we are in complete control
558 /// // of the allocation.
559 /// let mut v = mem::ManuallyDrop::new(v);
560 ///
561 /// // Pull out the various important pieces of information about `v`
562 /// let p = v.as_mut_ptr();
563 /// let len = v.len();
564 /// let cap = v.capacity();
565 ///
566 /// unsafe {
567 /// // Overwrite memory with 4, 5, 6
568 /// for i in 0..len {
569 /// ptr::write(p.add(i), 4 + i);
570 /// }
571 ///
572 /// // Put everything back together into a Vec
573 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
574 /// assert_eq!(rebuilt, [4, 5, 6]);
575 /// }
576 /// ```
577 ///
578 /// Using memory that was allocated elsewhere:
579 ///
580 /// ```rust
581 /// use std::alloc::{alloc, Layout};
582 ///
583 /// fn main() {
584 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
585 ///
586 /// let vec = unsafe {
587 /// let mem = alloc(layout).cast::<u32>();
588 /// if mem.is_null() {
589 /// return;
590 /// }
591 ///
592 /// mem.write(1_000_000);
593 ///
594 /// Vec::from_raw_parts(mem, 1, 16)
595 /// };
596 ///
597 /// assert_eq!(vec, &[1_000_000]);
598 /// assert_eq!(vec.capacity(), 16);
599 /// }
600 /// ```
601 #[inline]
602 #[stable(feature = "rust1", since = "1.0.0")]
603 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
604 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
605 }
606
607 /// A convenience method for hoisting the non-null precondition out of [`Vec::from_raw_parts`].
608 ///
609 /// # Safety
610 ///
611 /// See [`Vec::from_raw_parts`].
612 #[inline]
613 #[cfg(not(no_global_oom_handling))] // required by tests/run-make/alloc-no-oom-handling
614 pub(crate) unsafe fn from_nonnull(ptr: NonNull<T>, length: usize, capacity: usize) -> Self {
615 unsafe { Self::from_nonnull_in(ptr, length, capacity, Global) }
616 }
617}
618
619impl<T, A: Allocator> Vec<T, A> {
620 /// Constructs a new, empty `Vec<T, A>`.
621 ///
622 /// The vector will not allocate until elements are pushed onto it.
623 ///
624 /// # Examples
625 ///
626 /// ```
627 /// #![feature(allocator_api)]
628 ///
629 /// use std::alloc::System;
630 ///
631 /// # #[allow(unused_mut)]
632 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
633 /// ```
634 #[inline]
635 #[unstable(feature = "allocator_api", issue = "32838")]
636 pub const fn new_in(alloc: A) -> Self {
637 Vec { buf: RawVec::new_in(alloc), len: 0 }
638 }
639
640 /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
641 /// with the provided allocator.
642 ///
643 /// The vector will be able to hold at least `capacity` elements without
644 /// reallocating. This method is allowed to allocate for more elements than
645 /// `capacity`. If `capacity` is 0, the vector will not allocate.
646 ///
647 /// It is important to note that although the returned vector has the
648 /// minimum *capacity* specified, the vector will have a zero *length*. For
649 /// an explanation of the difference between length and capacity, see
650 /// *[Capacity and reallocation]*.
651 ///
652 /// If it is important to know the exact allocated capacity of a `Vec`,
653 /// always use the [`capacity`] method after construction.
654 ///
655 /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
656 /// and the capacity will always be `usize::MAX`.
657 ///
658 /// [Capacity and reallocation]: #capacity-and-reallocation
659 /// [`capacity`]: Vec::capacity
660 ///
661 /// # Panics
662 ///
663 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
664 ///
665 /// # Examples
666 ///
667 /// ```
668 /// #![feature(allocator_api)]
669 ///
670 /// use std::alloc::System;
671 ///
672 /// let mut vec = Vec::with_capacity_in(10, System);
673 ///
674 /// // The vector contains no items, even though it has capacity for more
675 /// assert_eq!(vec.len(), 0);
676 /// assert!(vec.capacity() >= 10);
677 ///
678 /// // These are all done without reallocating...
679 /// for i in 0..10 {
680 /// vec.push(i);
681 /// }
682 /// assert_eq!(vec.len(), 10);
683 /// assert!(vec.capacity() >= 10);
684 ///
685 /// // ...but this may make the vector reallocate
686 /// vec.push(11);
687 /// assert_eq!(vec.len(), 11);
688 /// assert!(vec.capacity() >= 11);
689 ///
690 /// // A vector of a zero-sized type will always over-allocate, since no
691 /// // allocation is necessary
692 /// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
693 /// assert_eq!(vec_units.capacity(), usize::MAX);
694 /// ```
695 #[cfg(not(no_global_oom_handling))]
696 #[inline]
697 #[unstable(feature = "allocator_api", issue = "32838")]
698 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
699 Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
700 }
701
702 /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
703 /// with the provided allocator.
704 ///
705 /// The vector will be able to hold at least `capacity` elements without
706 /// reallocating. This method is allowed to allocate for more elements than
707 /// `capacity`. If `capacity` is 0, the vector will not allocate.
708 ///
709 /// # Errors
710 ///
711 /// Returns an error if the capacity exceeds `isize::MAX` _bytes_,
712 /// or if the allocator reports allocation failure.
713 #[inline]
714 #[unstable(feature = "allocator_api", issue = "32838")]
715 // #[unstable(feature = "try_with_capacity", issue = "91913")]
716 pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
717 Ok(Vec { buf: RawVec::try_with_capacity_in(capacity, alloc)?, len: 0 })
718 }
719
720 /// Creates a `Vec<T, A>` directly from a pointer, a length, a capacity,
721 /// and an allocator.
722 ///
723 /// # Safety
724 ///
725 /// This is highly unsafe, due to the number of invariants that aren't
726 /// checked:
727 ///
728 /// * `ptr` must be [*currently allocated*] via the given allocator `alloc`.
729 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
730 /// (`T` having a less strict alignment is not sufficient, the alignment really
731 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
732 /// allocated and deallocated with the same layout.)
733 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
734 /// to be the same size as the pointer was allocated with. (Because similar to
735 /// alignment, [`dealloc`] must be called with the same layout `size`.)
736 /// * `length` needs to be less than or equal to `capacity`.
737 /// * The first `length` values must be properly initialized values of type `T`.
738 /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
739 /// * The allocated size in bytes must be no larger than `isize::MAX`.
740 /// See the safety documentation of [`pointer::offset`].
741 ///
742 /// These requirements are always upheld by any `ptr` that has been allocated
743 /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
744 /// upheld.
745 ///
746 /// Violating these may cause problems like corrupting the allocator's
747 /// internal data structures. For example it is **not** safe
748 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
749 /// It's also not safe to build one from a `Vec<u16>` and its length, because
750 /// the allocator cares about the alignment, and these two types have different
751 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
752 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
753 ///
754 /// The ownership of `ptr` is effectively transferred to the
755 /// `Vec<T>` which may then deallocate, reallocate or change the
756 /// contents of memory pointed to by the pointer at will. Ensure
757 /// that nothing else uses the pointer after calling this
758 /// function.
759 ///
760 /// [`String`]: crate::string::String
761 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
762 /// [*currently allocated*]: crate::alloc::Allocator#currently-allocated-memory
763 /// [*fit*]: crate::alloc::Allocator#memory-fitting
764 ///
765 /// # Examples
766 ///
767 /// ```
768 /// #![feature(allocator_api)]
769 ///
770 /// use std::alloc::System;
771 ///
772 /// use std::ptr;
773 /// use std::mem;
774 ///
775 /// let mut v = Vec::with_capacity_in(3, System);
776 /// v.push(1);
777 /// v.push(2);
778 /// v.push(3);
779 ///
780 // FIXME Update this when vec_into_raw_parts is stabilized
781 /// // Prevent running `v`'s destructor so we are in complete control
782 /// // of the allocation.
783 /// let mut v = mem::ManuallyDrop::new(v);
784 ///
785 /// // Pull out the various important pieces of information about `v`
786 /// let p = v.as_mut_ptr();
787 /// let len = v.len();
788 /// let cap = v.capacity();
789 /// let alloc = v.allocator();
790 ///
791 /// unsafe {
792 /// // Overwrite memory with 4, 5, 6
793 /// for i in 0..len {
794 /// ptr::write(p.add(i), 4 + i);
795 /// }
796 ///
797 /// // Put everything back together into a Vec
798 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
799 /// assert_eq!(rebuilt, [4, 5, 6]);
800 /// }
801 /// ```
802 ///
803 /// Using memory that was allocated elsewhere:
804 ///
805 /// ```rust
806 /// #![feature(allocator_api)]
807 ///
808 /// use std::alloc::{AllocError, Allocator, Global, Layout};
809 ///
810 /// fn main() {
811 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
812 ///
813 /// let vec = unsafe {
814 /// let mem = match Global.allocate(layout) {
815 /// Ok(mem) => mem.cast::<u32>().as_ptr(),
816 /// Err(AllocError) => return,
817 /// };
818 ///
819 /// mem.write(1_000_000);
820 ///
821 /// Vec::from_raw_parts_in(mem, 1, 16, Global)
822 /// };
823 ///
824 /// assert_eq!(vec, &[1_000_000]);
825 /// assert_eq!(vec.capacity(), 16);
826 /// }
827 /// ```
828 #[inline]
829 #[unstable(feature = "allocator_api", issue = "32838")]
830 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
831 unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
832 }
833
834 /// A convenience method for hoisting the non-null precondition out of [`Vec::from_raw_parts_in`].
835 ///
836 /// # Safety
837 ///
838 /// See [`Vec::from_raw_parts_in`].
839 #[inline]
840 #[cfg(not(no_global_oom_handling))] // required by tests/run-make/alloc-no-oom-handling
841 pub(crate) unsafe fn from_nonnull_in(
842 ptr: NonNull<T>,
843 length: usize,
844 capacity: usize,
845 alloc: A,
846 ) -> Self {
847 unsafe { Vec { buf: RawVec::from_nonnull_in(ptr, capacity, alloc), len: length } }
848 }
849
850 /// Decomposes a `Vec<T>` into its raw components: `(pointer, length, capacity)`.
851 ///
852 /// Returns the raw pointer to the underlying data, the length of
853 /// the vector (in elements), and the allocated capacity of the
854 /// data (in elements). These are the same arguments in the same
855 /// order as the arguments to [`from_raw_parts`].
856 ///
857 /// After calling this function, the caller is responsible for the
858 /// memory previously managed by the `Vec`. The only way to do
859 /// this is to convert the raw pointer, length, and capacity back
860 /// into a `Vec` with the [`from_raw_parts`] function, allowing
861 /// the destructor to perform the cleanup.
862 ///
863 /// [`from_raw_parts`]: Vec::from_raw_parts
864 ///
865 /// # Examples
866 ///
867 /// ```
868 /// #![feature(vec_into_raw_parts)]
869 /// let v: Vec<i32> = vec![-1, 0, 1];
870 ///
871 /// let (ptr, len, cap) = v.into_raw_parts();
872 ///
873 /// let rebuilt = unsafe {
874 /// // We can now make changes to the components, such as
875 /// // transmuting the raw pointer to a compatible type.
876 /// let ptr = ptr as *mut u32;
877 ///
878 /// Vec::from_raw_parts(ptr, len, cap)
879 /// };
880 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
881 /// ```
882 #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
883 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
884 let mut me = ManuallyDrop::new(self);
885 (me.as_mut_ptr(), me.len(), me.capacity())
886 }
887
888 /// Decomposes a `Vec<T>` into its raw components: `(pointer, length, capacity, allocator)`.
889 ///
890 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
891 /// the allocated capacity of the data (in elements), and the allocator. These are the same
892 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
893 ///
894 /// After calling this function, the caller is responsible for the
895 /// memory previously managed by the `Vec`. The only way to do
896 /// this is to convert the raw pointer, length, and capacity back
897 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
898 /// the destructor to perform the cleanup.
899 ///
900 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
901 ///
902 /// # Examples
903 ///
904 /// ```
905 /// #![feature(allocator_api, vec_into_raw_parts)]
906 ///
907 /// use std::alloc::System;
908 ///
909 /// let mut v: Vec<i32, System> = Vec::new_in(System);
910 /// v.push(-1);
911 /// v.push(0);
912 /// v.push(1);
913 ///
914 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
915 ///
916 /// let rebuilt = unsafe {
917 /// // We can now make changes to the components, such as
918 /// // transmuting the raw pointer to a compatible type.
919 /// let ptr = ptr as *mut u32;
920 ///
921 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
922 /// };
923 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
924 /// ```
925 #[unstable(feature = "allocator_api", issue = "32838")]
926 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
927 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
928 let mut me = ManuallyDrop::new(self);
929 let len = me.len();
930 let capacity = me.capacity();
931 let ptr = me.as_mut_ptr();
932 let alloc = unsafe { ptr::read(me.allocator()) };
933 (ptr, len, capacity, alloc)
934 }
935
936 /// Returns the total number of elements the vector can hold without
937 /// reallocating.
938 ///
939 /// # Examples
940 ///
941 /// ```
942 /// let mut vec: Vec<i32> = Vec::with_capacity(10);
943 /// vec.push(42);
944 /// assert!(vec.capacity() >= 10);
945 /// ```
946 #[inline]
947 #[stable(feature = "rust1", since = "1.0.0")]
948 pub fn capacity(&self) -> usize {
949 self.buf.capacity()
950 }
951
952 /// Reserves capacity for at least `additional` more elements to be inserted
953 /// in the given `Vec<T>`. The collection may reserve more space to
954 /// speculatively avoid frequent reallocations. After calling `reserve`,
955 /// capacity will be greater than or equal to `self.len() + additional`.
956 /// Does nothing if capacity is already sufficient.
957 ///
958 /// # Panics
959 ///
960 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
961 ///
962 /// # Examples
963 ///
964 /// ```
965 /// let mut vec = vec![1];
966 /// vec.reserve(10);
967 /// assert!(vec.capacity() >= 11);
968 /// ```
969 #[cfg(not(no_global_oom_handling))]
970 #[stable(feature = "rust1", since = "1.0.0")]
971 pub fn reserve(&mut self, additional: usize) {
972 self.buf.reserve(self.len, additional);
973 }
974
975 /// Reserves the minimum capacity for at least `additional` more elements to
976 /// be inserted in the given `Vec<T>`. Unlike [`reserve`], this will not
977 /// deliberately over-allocate to speculatively avoid frequent allocations.
978 /// After calling `reserve_exact`, capacity will be greater than or equal to
979 /// `self.len() + additional`. Does nothing if the capacity is already
980 /// sufficient.
981 ///
982 /// Note that the allocator may give the collection more space than it
983 /// requests. Therefore, capacity can not be relied upon to be precisely
984 /// minimal. Prefer [`reserve`] if future insertions are expected.
985 ///
986 /// [`reserve`]: Vec::reserve
987 ///
988 /// # Panics
989 ///
990 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
991 ///
992 /// # Examples
993 ///
994 /// ```
995 /// let mut vec = vec![1];
996 /// vec.reserve_exact(10);
997 /// assert!(vec.capacity() >= 11);
998 /// ```
999 #[cfg(not(no_global_oom_handling))]
1000 #[stable(feature = "rust1", since = "1.0.0")]
1001 pub fn reserve_exact(&mut self, additional: usize) {
1002 self.buf.reserve_exact(self.len, additional);
1003 }
1004
1005 /// Tries to reserve capacity for at least `additional` more elements to be inserted
1006 /// in the given `Vec<T>`. The collection may reserve more space to speculatively avoid
1007 /// frequent reallocations. After calling `try_reserve`, capacity will be
1008 /// greater than or equal to `self.len() + additional` if it returns
1009 /// `Ok(())`. Does nothing if capacity is already sufficient. This method
1010 /// preserves the contents even if an error occurs.
1011 ///
1012 /// # Errors
1013 ///
1014 /// If the capacity overflows, or the allocator reports a failure, then an error
1015 /// is returned.
1016 ///
1017 /// # Examples
1018 ///
1019 /// ```
1020 /// use std::collections::TryReserveError;
1021 ///
1022 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
1023 /// let mut output = Vec::new();
1024 ///
1025 /// // Pre-reserve the memory, exiting if we can't
1026 /// output.try_reserve(data.len())?;
1027 ///
1028 /// // Now we know this can't OOM in the middle of our complex work
1029 /// output.extend(data.iter().map(|&val| {
1030 /// val * 2 + 5 // very complicated
1031 /// }));
1032 ///
1033 /// Ok(output)
1034 /// }
1035 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
1036 /// ```
1037 #[stable(feature = "try_reserve", since = "1.57.0")]
1038 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
1039 self.buf.try_reserve(self.len, additional)
1040 }
1041
1042 /// Tries to reserve the minimum capacity for at least `additional`
1043 /// elements to be inserted in the given `Vec<T>`. Unlike [`try_reserve`],
1044 /// this will not deliberately over-allocate to speculatively avoid frequent
1045 /// allocations. After calling `try_reserve_exact`, capacity will be greater
1046 /// than or equal to `self.len() + additional` if it returns `Ok(())`.
1047 /// Does nothing if the capacity is already sufficient.
1048 ///
1049 /// Note that the allocator may give the collection more space than it
1050 /// requests. Therefore, capacity can not be relied upon to be precisely
1051 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
1052 ///
1053 /// [`try_reserve`]: Vec::try_reserve
1054 ///
1055 /// # Errors
1056 ///
1057 /// If the capacity overflows, or the allocator reports a failure, then an error
1058 /// is returned.
1059 ///
1060 /// # Examples
1061 ///
1062 /// ```
1063 /// use std::collections::TryReserveError;
1064 ///
1065 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
1066 /// let mut output = Vec::new();
1067 ///
1068 /// // Pre-reserve the memory, exiting if we can't
1069 /// output.try_reserve_exact(data.len())?;
1070 ///
1071 /// // Now we know this can't OOM in the middle of our complex work
1072 /// output.extend(data.iter().map(|&val| {
1073 /// val * 2 + 5 // very complicated
1074 /// }));
1075 ///
1076 /// Ok(output)
1077 /// }
1078 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
1079 /// ```
1080 #[stable(feature = "try_reserve", since = "1.57.0")]
1081 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
1082 self.buf.try_reserve_exact(self.len, additional)
1083 }
1084
1085 /// Shrinks the capacity of the vector as much as possible.
1086 ///
1087 /// The behavior of this method depends on the allocator, which may either shrink the vector
1088 /// in-place or reallocate. The resulting vector might still have some excess capacity, just as
1089 /// is the case for [`with_capacity`]. See [`Allocator::shrink`] for more details.
1090 ///
1091 /// [`with_capacity`]: Vec::with_capacity
1092 ///
1093 /// # Examples
1094 ///
1095 /// ```
1096 /// let mut vec = Vec::with_capacity(10);
1097 /// vec.extend([1, 2, 3]);
1098 /// assert!(vec.capacity() >= 10);
1099 /// vec.shrink_to_fit();
1100 /// assert!(vec.capacity() >= 3);
1101 /// ```
1102 #[cfg(not(no_global_oom_handling))]
1103 #[stable(feature = "rust1", since = "1.0.0")]
1104 pub fn shrink_to_fit(&mut self) {
1105 // The capacity is never less than the length, and there's nothing to do when
1106 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
1107 // by only calling it with a greater capacity.
1108 if self.capacity() > self.len {
1109 self.buf.shrink_to_fit(self.len);
1110 }
1111 }
1112
1113 /// Shrinks the capacity of the vector with a lower bound.
1114 ///
1115 /// The capacity will remain at least as large as both the length
1116 /// and the supplied value.
1117 ///
1118 /// If the current capacity is less than the lower limit, this is a no-op.
1119 ///
1120 /// # Examples
1121 ///
1122 /// ```
1123 /// let mut vec = Vec::with_capacity(10);
1124 /// vec.extend([1, 2, 3]);
1125 /// assert!(vec.capacity() >= 10);
1126 /// vec.shrink_to(4);
1127 /// assert!(vec.capacity() >= 4);
1128 /// vec.shrink_to(0);
1129 /// assert!(vec.capacity() >= 3);
1130 /// ```
1131 #[cfg(not(no_global_oom_handling))]
1132 #[stable(feature = "shrink_to", since = "1.56.0")]
1133 pub fn shrink_to(&mut self, min_capacity: usize) {
1134 if self.capacity() > min_capacity {
1135 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
1136 }
1137 }
1138
1139 /// Converts the vector into [`Box<[T]>`][owned slice].
1140 ///
1141 /// Before doing the conversion, this method discards excess capacity like [`shrink_to_fit`].
1142 ///
1143 /// [owned slice]: Box
1144 /// [`shrink_to_fit`]: Vec::shrink_to_fit
1145 ///
1146 /// # Examples
1147 ///
1148 /// ```
1149 /// let v = vec![1, 2, 3];
1150 ///
1151 /// let slice = v.into_boxed_slice();
1152 /// ```
1153 ///
1154 /// Any excess capacity is removed:
1155 ///
1156 /// ```
1157 /// let mut vec = Vec::with_capacity(10);
1158 /// vec.extend([1, 2, 3]);
1159 ///
1160 /// assert!(vec.capacity() >= 10);
1161 /// let slice = vec.into_boxed_slice();
1162 /// assert_eq!(slice.into_vec().capacity(), 3);
1163 /// ```
1164 #[cfg(not(no_global_oom_handling))]
1165 #[stable(feature = "rust1", since = "1.0.0")]
1166 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
1167 unsafe {
1168 self.shrink_to_fit();
1169 let me = ManuallyDrop::new(self);
1170 let buf = ptr::read(&me.buf);
1171 let len = me.len();
1172 buf.into_box(len).assume_init()
1173 }
1174 }
1175
1176 /// Shortens the vector, keeping the first `len` elements and dropping
1177 /// the rest.
1178 ///
1179 /// If `len` is greater or equal to the vector's current length, this has
1180 /// no effect.
1181 ///
1182 /// The [`drain`] method can emulate `truncate`, but causes the excess
1183 /// elements to be returned instead of dropped.
1184 ///
1185 /// Note that this method has no effect on the allocated capacity
1186 /// of the vector.
1187 ///
1188 /// # Examples
1189 ///
1190 /// Truncating a five element vector to two elements:
1191 ///
1192 /// ```
1193 /// let mut vec = vec![1, 2, 3, 4, 5];
1194 /// vec.truncate(2);
1195 /// assert_eq!(vec, [1, 2]);
1196 /// ```
1197 ///
1198 /// No truncation occurs when `len` is greater than the vector's current
1199 /// length:
1200 ///
1201 /// ```
1202 /// let mut vec = vec![1, 2, 3];
1203 /// vec.truncate(8);
1204 /// assert_eq!(vec, [1, 2, 3]);
1205 /// ```
1206 ///
1207 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1208 /// method.
1209 ///
1210 /// ```
1211 /// let mut vec = vec![1, 2, 3];
1212 /// vec.truncate(0);
1213 /// assert_eq!(vec, []);
1214 /// ```
1215 ///
1216 /// [`clear`]: Vec::clear
1217 /// [`drain`]: Vec::drain
1218 #[stable(feature = "rust1", since = "1.0.0")]
1219 pub fn truncate(&mut self, len: usize) {
1220 // This is safe because:
1221 //
1222 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1223 // case avoids creating an invalid slice, and
1224 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1225 // such that no value will be dropped twice in case `drop_in_place`
1226 // were to panic once (if it panics twice, the program aborts).
1227 unsafe {
1228 // Note: It's intentional that this is `>` and not `>=`.
1229 // Changing it to `>=` has negative performance
1230 // implications in some cases. See #78884 for more.
1231 if len > self.len {
1232 return;
1233 }
1234 let remaining_len = self.len - len;
1235 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1236 self.len = len;
1237 ptr::drop_in_place(s);
1238 }
1239 }
1240
1241 /// Extracts a slice containing the entire vector.
1242 ///
1243 /// Equivalent to `&s[..]`.
1244 ///
1245 /// # Examples
1246 ///
1247 /// ```
1248 /// use std::io::{self, Write};
1249 /// let buffer = vec![1, 2, 3, 5, 8];
1250 /// io::sink().write(buffer.as_slice()).unwrap();
1251 /// ```
1252 #[inline]
1253 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1254 pub fn as_slice(&self) -> &[T] {
1255 self
1256 }
1257
1258 /// Extracts a mutable slice of the entire vector.
1259 ///
1260 /// Equivalent to `&mut s[..]`.
1261 ///
1262 /// # Examples
1263 ///
1264 /// ```
1265 /// use std::io::{self, Read};
1266 /// let mut buffer = vec![0; 3];
1267 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1268 /// ```
1269 #[inline]
1270 #[stable(feature = "vec_as_slice", since = "1.7.0")]
1271 pub fn as_mut_slice(&mut self) -> &mut [T] {
1272 self
1273 }
1274
1275 /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
1276 /// valid for zero sized reads if the vector didn't allocate.
1277 ///
1278 /// The caller must ensure that the vector outlives the pointer this
1279 /// function returns, or else it will end up pointing to garbage.
1280 /// Modifying the vector may cause its buffer to be reallocated,
1281 /// which would also make any pointers to it invalid.
1282 ///
1283 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1284 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1285 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1286 ///
1287 /// This method guarantees that for the purpose of the aliasing model, this method
1288 /// does not materialize a reference to the underlying slice, and thus the returned pointer
1289 /// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
1290 /// Note that calling other methods that materialize mutable references to the slice,
1291 /// or mutable references to specific elements you are planning on accessing through this pointer,
1292 /// as well as writing to those elements, may still invalidate this pointer.
1293 /// See the second example below for how this guarantee can be used.
1294 ///
1295 ///
1296 /// # Examples
1297 ///
1298 /// ```
1299 /// let x = vec![1, 2, 4];
1300 /// let x_ptr = x.as_ptr();
1301 ///
1302 /// unsafe {
1303 /// for i in 0..x.len() {
1304 /// assert_eq!(*x_ptr.add(i), 1 << i);
1305 /// }
1306 /// }
1307 /// ```
1308 ///
1309 /// Due to the aliasing guarantee, the following code is legal:
1310 ///
1311 /// ```rust
1312 /// unsafe {
1313 /// let mut v = vec![0, 1, 2];
1314 /// let ptr1 = v.as_ptr();
1315 /// let _ = ptr1.read();
1316 /// let ptr2 = v.as_mut_ptr().offset(2);
1317 /// ptr2.write(2);
1318 /// // Notably, the write to `ptr2` did *not* invalidate `ptr1`
1319 /// // because it mutated a different element:
1320 /// let _ = ptr1.read();
1321 /// }
1322 /// ```
1323 ///
1324 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1325 /// [`as_ptr`]: Vec::as_ptr
1326 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1327 #[rustc_never_returns_null_ptr]
1328 #[inline]
1329 pub fn as_ptr(&self) -> *const T {
1330 // We shadow the slice method of the same name to avoid going through
1331 // `deref`, which creates an intermediate reference.
1332 self.buf.ptr()
1333 }
1334
1335 /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
1336 /// raw pointer valid for zero sized reads if the vector didn't allocate.
1337 ///
1338 /// The caller must ensure that the vector outlives the pointer this
1339 /// function returns, or else it will end up pointing to garbage.
1340 /// Modifying the vector may cause its buffer to be reallocated,
1341 /// which would also make any pointers to it invalid.
1342 ///
1343 /// This method guarantees that for the purpose of the aliasing model, this method
1344 /// does not materialize a reference to the underlying slice, and thus the returned pointer
1345 /// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
1346 /// Note that calling other methods that materialize references to the slice,
1347 /// or references to specific elements you are planning on accessing through this pointer,
1348 /// may still invalidate this pointer.
1349 /// See the second example below for how this guarantee can be used.
1350 ///
1351 ///
1352 /// # Examples
1353 ///
1354 /// ```
1355 /// // Allocate vector big enough for 4 elements.
1356 /// let size = 4;
1357 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1358 /// let x_ptr = x.as_mut_ptr();
1359 ///
1360 /// // Initialize elements via raw pointer writes, then set length.
1361 /// unsafe {
1362 /// for i in 0..size {
1363 /// *x_ptr.add(i) = i as i32;
1364 /// }
1365 /// x.set_len(size);
1366 /// }
1367 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1368 /// ```
1369 ///
1370 /// Due to the aliasing guarantee, the following code is legal:
1371 ///
1372 /// ```rust
1373 /// unsafe {
1374 /// let mut v = vec![0];
1375 /// let ptr1 = v.as_mut_ptr();
1376 /// ptr1.write(1);
1377 /// let ptr2 = v.as_mut_ptr();
1378 /// ptr2.write(2);
1379 /// // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
1380 /// ptr1.write(3);
1381 /// }
1382 /// ```
1383 ///
1384 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1385 /// [`as_ptr`]: Vec::as_ptr
1386 #[stable(feature = "vec_as_ptr", since = "1.37.0")]
1387 #[rustc_never_returns_null_ptr]
1388 #[inline]
1389 pub fn as_mut_ptr(&mut self) -> *mut T {
1390 // We shadow the slice method of the same name to avoid going through
1391 // `deref_mut`, which creates an intermediate reference.
1392 self.buf.ptr()
1393 }
1394
1395 /// Returns a reference to the underlying allocator.
1396 #[unstable(feature = "allocator_api", issue = "32838")]
1397 #[inline]
1398 pub fn allocator(&self) -> &A {
1399 self.buf.allocator()
1400 }
1401
1402 /// Forces the length of the vector to `new_len`.
1403 ///
1404 /// This is a low-level operation that maintains none of the normal
1405 /// invariants of the type. Normally changing the length of a vector
1406 /// is done using one of the safe operations instead, such as
1407 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1408 ///
1409 /// [`truncate`]: Vec::truncate
1410 /// [`resize`]: Vec::resize
1411 /// [`extend`]: Extend::extend
1412 /// [`clear`]: Vec::clear
1413 ///
1414 /// # Safety
1415 ///
1416 /// - `new_len` must be less than or equal to [`capacity()`].
1417 /// - The elements at `old_len..new_len` must be initialized.
1418 ///
1419 /// [`capacity()`]: Vec::capacity
1420 ///
1421 /// # Examples
1422 ///
1423 /// This method can be useful for situations in which the vector
1424 /// is serving as a buffer for other code, particularly over FFI:
1425 ///
1426 /// ```no_run
1427 /// # #![allow(dead_code)]
1428 /// # // This is just a minimal skeleton for the doc example;
1429 /// # // don't use this as a starting point for a real library.
1430 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1431 /// # const Z_OK: i32 = 0;
1432 /// # extern "C" {
1433 /// # fn deflateGetDictionary(
1434 /// # strm: *mut std::ffi::c_void,
1435 /// # dictionary: *mut u8,
1436 /// # dictLength: *mut usize,
1437 /// # ) -> i32;
1438 /// # }
1439 /// # impl StreamWrapper {
1440 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1441 /// // Per the FFI method's docs, "32768 bytes is always enough".
1442 /// let mut dict = Vec::with_capacity(32_768);
1443 /// let mut dict_length = 0;
1444 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1445 /// // 1. `dict_length` elements were initialized.
1446 /// // 2. `dict_length` <= the capacity (32_768)
1447 /// // which makes `set_len` safe to call.
1448 /// unsafe {
1449 /// // Make the FFI call...
1450 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1451 /// if r == Z_OK {
1452 /// // ...and update the length to what was initialized.
1453 /// dict.set_len(dict_length);
1454 /// Some(dict)
1455 /// } else {
1456 /// None
1457 /// }
1458 /// }
1459 /// }
1460 /// # }
1461 /// ```
1462 ///
1463 /// While the following example is sound, there is a memory leak since
1464 /// the inner vectors were not freed prior to the `set_len` call:
1465 ///
1466 /// ```
1467 /// let mut vec = vec![vec![1, 0, 0],
1468 /// vec![0, 1, 0],
1469 /// vec![0, 0, 1]];
1470 /// // SAFETY:
1471 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1472 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1473 /// unsafe {
1474 /// vec.set_len(0);
1475 /// }
1476 /// ```
1477 ///
1478 /// Normally, here, one would use [`clear`] instead to correctly drop
1479 /// the contents and thus not leak memory.
1480 #[inline]
1481 #[stable(feature = "rust1", since = "1.0.0")]
1482 pub unsafe fn set_len(&mut self, new_len: usize) {
1483 debug_assert!(new_len <= self.capacity());
1484
1485 self.len = new_len;
1486 }
1487
1488 /// Removes an element from the vector and returns it.
1489 ///
1490 /// The removed element is replaced by the last element of the vector.
1491 ///
1492 /// This does not preserve ordering of the remaining elements, but is *O*(1).
1493 /// If you need to preserve the element order, use [`remove`] instead.
1494 ///
1495 /// [`remove`]: Vec::remove
1496 ///
1497 /// # Panics
1498 ///
1499 /// Panics if `index` is out of bounds.
1500 ///
1501 /// # Examples
1502 ///
1503 /// ```
1504 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1505 ///
1506 /// assert_eq!(v.swap_remove(1), "bar");
1507 /// assert_eq!(v, ["foo", "qux", "baz"]);
1508 ///
1509 /// assert_eq!(v.swap_remove(0), "foo");
1510 /// assert_eq!(v, ["baz", "qux"]);
1511 /// ```
1512 #[inline]
1513 #[stable(feature = "rust1", since = "1.0.0")]
1514 pub fn swap_remove(&mut self, index: usize) -> T {
1515 #[cold]
1516 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
1517 #[track_caller]
1518 fn assert_failed(index: usize, len: usize) -> ! {
1519 panic!("swap_remove index (is {index}) should be < len (is {len})");
1520 }
1521
1522 let len = self.len();
1523 if index >= len {
1524 assert_failed(index, len);
1525 }
1526 unsafe {
1527 // We replace self[index] with the last element. Note that if the
1528 // bounds check above succeeds there must be a last element (which
1529 // can be self[index] itself).
1530 let value = ptr::read(self.as_ptr().add(index));
1531 let base_ptr = self.as_mut_ptr();
1532 ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
1533 self.set_len(len - 1);
1534 value
1535 }
1536 }
1537
1538 /// Inserts an element at position `index` within the vector, shifting all
1539 /// elements after it to the right.
1540 ///
1541 /// # Panics
1542 ///
1543 /// Panics if `index > len`.
1544 ///
1545 /// # Examples
1546 ///
1547 /// ```
1548 /// let mut vec = vec![1, 2, 3];
1549 /// vec.insert(1, 4);
1550 /// assert_eq!(vec, [1, 4, 2, 3]);
1551 /// vec.insert(4, 5);
1552 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1553 /// ```
1554 ///
1555 /// # Time complexity
1556 ///
1557 /// Takes *O*([`Vec::len`]) time. All items after the insertion index must be
1558 /// shifted to the right. In the worst case, all elements are shifted when
1559 /// the insertion index is 0.
1560 #[cfg(not(no_global_oom_handling))]
1561 #[stable(feature = "rust1", since = "1.0.0")]
1562 pub fn insert(&mut self, index: usize, element: T) {
1563 #[cold]
1564 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
1565 #[track_caller]
1566 fn assert_failed(index: usize, len: usize) -> ! {
1567 panic!("insertion index (is {index}) should be <= len (is {len})");
1568 }
1569
1570 let len = self.len();
1571 if index > len {
1572 assert_failed(index, len);
1573 }
1574
1575 // space for the new element
1576 if len == self.buf.capacity() {
1577 self.buf.grow_one();
1578 }
1579
1580 unsafe {
1581 // infallible
1582 // The spot to put the new value
1583 {
1584 let p = self.as_mut_ptr().add(index);
1585 if index < len {
1586 // Shift everything over to make space. (Duplicating the
1587 // `index`th element into two consecutive places.)
1588 ptr::copy(p, p.add(1), len - index);
1589 }
1590 // Write it in, overwriting the first copy of the `index`th
1591 // element.
1592 ptr::write(p, element);
1593 }
1594 self.set_len(len + 1);
1595 }
1596 }
1597
1598 /// Removes and returns the element at position `index` within the vector,
1599 /// shifting all elements after it to the left.
1600 ///
1601 /// Note: Because this shifts over the remaining elements, it has a
1602 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1603 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1604 /// elements from the beginning of the `Vec`, consider using
1605 /// [`VecDeque::pop_front`] instead.
1606 ///
1607 /// [`swap_remove`]: Vec::swap_remove
1608 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
1609 ///
1610 /// # Panics
1611 ///
1612 /// Panics if `index` is out of bounds.
1613 ///
1614 /// # Examples
1615 ///
1616 /// ```
1617 /// let mut v = vec![1, 2, 3];
1618 /// assert_eq!(v.remove(1), 2);
1619 /// assert_eq!(v, [1, 3]);
1620 /// ```
1621 #[stable(feature = "rust1", since = "1.0.0")]
1622 #[track_caller]
1623 #[rustc_confusables("delete", "take")]
1624 pub fn remove(&mut self, index: usize) -> T {
1625 #[cold]
1626 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
1627 #[track_caller]
1628 fn assert_failed(index: usize, len: usize) -> ! {
1629 panic!("removal index (is {index}) should be < len (is {len})");
1630 }
1631
1632 let len = self.len();
1633 if index >= len {
1634 assert_failed(index, len);
1635 }
1636 unsafe {
1637 // infallible
1638 let ret;
1639 {
1640 // the place we are taking from.
1641 let ptr = self.as_mut_ptr().add(index);
1642 // copy it out, unsafely having a copy of the value on
1643 // the stack and in the vector at the same time.
1644 ret = ptr::read(ptr);
1645
1646 // Shift everything down to fill in that spot.
1647 ptr::copy(ptr.add(1), ptr, len - index - 1);
1648 }
1649 self.set_len(len - 1);
1650 ret
1651 }
1652 }
1653
1654 /// Retains only the elements specified by the predicate.
1655 ///
1656 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1657 /// This method operates in place, visiting each element exactly once in the
1658 /// original order, and preserves the order of the retained elements.
1659 ///
1660 /// # Examples
1661 ///
1662 /// ```
1663 /// let mut vec = vec![1, 2, 3, 4];
1664 /// vec.retain(|&x| x % 2 == 0);
1665 /// assert_eq!(vec, [2, 4]);
1666 /// ```
1667 ///
1668 /// Because the elements are visited exactly once in the original order,
1669 /// external state may be used to decide which elements to keep.
1670 ///
1671 /// ```
1672 /// let mut vec = vec![1, 2, 3, 4, 5];
1673 /// let keep = [false, true, true, false, true];
1674 /// let mut iter = keep.iter();
1675 /// vec.retain(|_| *iter.next().unwrap());
1676 /// assert_eq!(vec, [2, 3, 5]);
1677 /// ```
1678 #[stable(feature = "rust1", since = "1.0.0")]
1679 pub fn retain<F>(&mut self, mut f: F)
1680 where
1681 F: FnMut(&T) -> bool,
1682 {
1683 self.retain_mut(|elem| f(elem));
1684 }
1685
1686 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1687 ///
1688 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1689 /// This method operates in place, visiting each element exactly once in the
1690 /// original order, and preserves the order of the retained elements.
1691 ///
1692 /// # Examples
1693 ///
1694 /// ```
1695 /// let mut vec = vec![1, 2, 3, 4];
1696 /// vec.retain_mut(|x| if *x <= 3 {
1697 /// *x += 1;
1698 /// true
1699 /// } else {
1700 /// false
1701 /// });
1702 /// assert_eq!(vec, [2, 3, 4]);
1703 /// ```
1704 #[stable(feature = "vec_retain_mut", since = "1.61.0")]
1705 pub fn retain_mut<F>(&mut self, mut f: F)
1706 where
1707 F: FnMut(&mut T) -> bool,
1708 {
1709 let original_len = self.len();
1710 // Avoid double drop if the drop guard is not executed,
1711 // since we may make some holes during the process.
1712 unsafe { self.set_len(0) };
1713
1714 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1715 // |<- processed len ->| ^- next to check
1716 // |<- deleted cnt ->|
1717 // |<- original_len ->|
1718 // Kept: Elements which predicate returns true on.
1719 // Hole: Moved or dropped element slot.
1720 // Unchecked: Unchecked valid elements.
1721 //
1722 // This drop guard will be invoked when predicate or `drop` of element panicked.
1723 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1724 // In cases when predicate and `drop` never panick, it will be optimized out.
1725 struct BackshiftOnDrop<'a, T, A: Allocator> {
1726 v: &'a mut Vec<T, A>,
1727 processed_len: usize,
1728 deleted_cnt: usize,
1729 original_len: usize,
1730 }
1731
1732 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1733 fn drop(&mut self) {
1734 if self.deleted_cnt > 0 {
1735 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1736 unsafe {
1737 ptr::copy(
1738 self.v.as_ptr().add(self.processed_len),
1739 self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
1740 self.original_len - self.processed_len,
1741 );
1742 }
1743 }
1744 // SAFETY: After filling holes, all items are in contiguous memory.
1745 unsafe {
1746 self.v.set_len(self.original_len - self.deleted_cnt);
1747 }
1748 }
1749 }
1750
1751 let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
1752
1753 fn process_loop<F, T, A: Allocator, const DELETED: bool>(
1754 original_len: usize,
1755 f: &mut F,
1756 g: &mut BackshiftOnDrop<'_, T, A>,
1757 ) where
1758 F: FnMut(&mut T) -> bool,
1759 {
1760 while g.processed_len != original_len {
1761 // SAFETY: Unchecked element must be valid.
1762 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1763 if !f(cur) {
1764 // Advance early to avoid double drop if `drop_in_place` panicked.
1765 g.processed_len += 1;
1766 g.deleted_cnt += 1;
1767 // SAFETY: We never touch this element again after dropped.
1768 unsafe { ptr::drop_in_place(cur) };
1769 // We already advanced the counter.
1770 if DELETED {
1771 continue;
1772 } else {
1773 break;
1774 }
1775 }
1776 if DELETED {
1777 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1778 // We use copy for move, and never touch this element again.
1779 unsafe {
1780 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1781 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1782 }
1783 }
1784 g.processed_len += 1;
1785 }
1786 }
1787
1788 // Stage 1: Nothing was deleted.
1789 process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
1790
1791 // Stage 2: Some elements were deleted.
1792 process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
1793
1794 // All item are processed. This can be optimized to `set_len` by LLVM.
1795 drop(g);
1796 }
1797
1798 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1799 /// key.
1800 ///
1801 /// If the vector is sorted, this removes all duplicates.
1802 ///
1803 /// # Examples
1804 ///
1805 /// ```
1806 /// let mut vec = vec![10, 20, 21, 30, 20];
1807 ///
1808 /// vec.dedup_by_key(|i| *i / 10);
1809 ///
1810 /// assert_eq!(vec, [10, 20, 30, 20]);
1811 /// ```
1812 #[stable(feature = "dedup_by", since = "1.16.0")]
1813 #[inline]
1814 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1815 where
1816 F: FnMut(&mut T) -> K,
1817 K: PartialEq,
1818 {
1819 self.dedup_by(|a, b| key(a) == key(b))
1820 }
1821
1822 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1823 /// relation.
1824 ///
1825 /// The `same_bucket` function is passed references to two elements from the vector and
1826 /// must determine if the elements compare equal. The elements are passed in opposite order
1827 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1828 ///
1829 /// If the vector is sorted, this removes all duplicates.
1830 ///
1831 /// # Examples
1832 ///
1833 /// ```
1834 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1835 ///
1836 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1837 ///
1838 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1839 /// ```
1840 #[stable(feature = "dedup_by", since = "1.16.0")]
1841 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1842 where
1843 F: FnMut(&mut T, &mut T) -> bool,
1844 {
1845 let len = self.len();
1846 if len <= 1 {
1847 return;
1848 }
1849
1850 // Check if we ever want to remove anything.
1851 // This allows to use copy_non_overlapping in next cycle.
1852 // And avoids any memory writes if we don't need to remove anything.
1853 let mut first_duplicate_idx: usize = 1;
1854 let start = self.as_mut_ptr();
1855 while first_duplicate_idx != len {
1856 let found_duplicate = unsafe {
1857 // SAFETY: first_duplicate always in range [1..len)
1858 // Note that we start iteration from 1 so we never overflow.
1859 let prev = start.add(first_duplicate_idx.wrapping_sub(1));
1860 let current = start.add(first_duplicate_idx);
1861 // We explicitly say in docs that references are reversed.
1862 same_bucket(&mut *current, &mut *prev)
1863 };
1864 if found_duplicate {
1865 break;
1866 }
1867 first_duplicate_idx += 1;
1868 }
1869 // Don't need to remove anything.
1870 // We cannot get bigger than len.
1871 if first_duplicate_idx == len {
1872 return;
1873 }
1874
1875 /* INVARIANT: vec.len() > read > write > write-1 >= 0 */
1876 struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
1877 /* Offset of the element we want to check if it is duplicate */
1878 read: usize,
1879
1880 /* Offset of the place where we want to place the non-duplicate
1881 * when we find it. */
1882 write: usize,
1883
1884 /* The Vec that would need correction if `same_bucket` panicked */
1885 vec: &'a mut Vec<T, A>,
1886 }
1887
1888 impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
1889 fn drop(&mut self) {
1890 /* This code gets executed when `same_bucket` panics */
1891
1892 /* SAFETY: invariant guarantees that `read - write`
1893 * and `len - read` never overflow and that the copy is always
1894 * in-bounds. */
1895 unsafe {
1896 let ptr = self.vec.as_mut_ptr();
1897 let len = self.vec.len();
1898
1899 /* How many items were left when `same_bucket` panicked.
1900 * Basically vec[read..].len() */
1901 let items_left = len.wrapping_sub(self.read);
1902
1903 /* Pointer to first item in vec[write..write+items_left] slice */
1904 let dropped_ptr = ptr.add(self.write);
1905 /* Pointer to first item in vec[read..] slice */
1906 let valid_ptr = ptr.add(self.read);
1907
1908 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1909 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1910 ptr::copy(valid_ptr, dropped_ptr, items_left);
1911
1912 /* How many items have been already dropped
1913 * Basically vec[read..write].len() */
1914 let dropped = self.read.wrapping_sub(self.write);
1915
1916 self.vec.set_len(len - dropped);
1917 }
1918 }
1919 }
1920
1921 /* Drop items while going through Vec, it should be more efficient than
1922 * doing slice partition_dedup + truncate */
1923
1924 // Construct gap first and then drop item to avoid memory corruption if `T::drop` panics.
1925 let mut gap =
1926 FillGapOnDrop { read: first_duplicate_idx + 1, write: first_duplicate_idx, vec: self };
1927 unsafe {
1928 // SAFETY: we checked that first_duplicate_idx in bounds before.
1929 // If drop panics, `gap` would remove this item without drop.
1930 ptr::drop_in_place(start.add(first_duplicate_idx));
1931 }
1932
1933 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1934 * are always in-bounds and read_ptr never aliases prev_ptr */
1935 unsafe {
1936 while gap.read < len {
1937 let read_ptr = start.add(gap.read);
1938 let prev_ptr = start.add(gap.write.wrapping_sub(1));
1939
1940 // We explicitly say in docs that references are reversed.
1941 let found_duplicate = same_bucket(&mut *read_ptr, &mut *prev_ptr);
1942 if found_duplicate {
1943 // Increase `gap.read` now since the drop may panic.
1944 gap.read += 1;
1945 /* We have found duplicate, drop it in-place */
1946 ptr::drop_in_place(read_ptr);
1947 } else {
1948 let write_ptr = start.add(gap.write);
1949
1950 /* read_ptr cannot be equal to write_ptr because at this point
1951 * we guaranteed to skip at least one element (before loop starts).
1952 */
1953 ptr::copy_nonoverlapping(read_ptr, write_ptr, 1);
1954
1955 /* We have filled that place, so go further */
1956 gap.write += 1;
1957 gap.read += 1;
1958 }
1959 }
1960
1961 /* Technically we could let `gap` clean up with its Drop, but
1962 * when `same_bucket` is guaranteed to not panic, this bloats a little
1963 * the codegen, so we just do it manually */
1964 gap.vec.set_len(gap.write);
1965 mem::forget(gap);
1966 }
1967 }
1968
1969 /// Appends an element to the back of a collection.
1970 ///
1971 /// # Panics
1972 ///
1973 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
1974 ///
1975 /// # Examples
1976 ///
1977 /// ```
1978 /// let mut vec = vec![1, 2];
1979 /// vec.push(3);
1980 /// assert_eq!(vec, [1, 2, 3]);
1981 /// ```
1982 ///
1983 /// # Time complexity
1984 ///
1985 /// Takes amortized *O*(1) time. If the vector's length would exceed its
1986 /// capacity after the push, *O*(*capacity*) time is taken to copy the
1987 /// vector's elements to a larger allocation. This expensive operation is
1988 /// offset by the *capacity* *O*(1) insertions it allows.
1989 #[cfg(not(no_global_oom_handling))]
1990 #[inline]
1991 #[stable(feature = "rust1", since = "1.0.0")]
1992 #[rustc_confusables("push_back", "put", "append")]
1993 pub fn push(&mut self, value: T) {
1994 // Inform codegen that the length does not change across grow_one().
1995 let len = self.len;
1996 // This will panic or abort if we would allocate > isize::MAX bytes
1997 // or if the length increment would overflow for zero-sized types.
1998 if len == self.buf.capacity() {
1999 self.buf.grow_one();
2000 }
2001 unsafe {
2002 let end = self.as_mut_ptr().add(len);
2003 ptr::write(end, value);
2004 self.len = len + 1;
2005 }
2006 }
2007
2008 /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
2009 /// with the element.
2010 ///
2011 /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
2012 /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
2013 ///
2014 /// [`push`]: Vec::push
2015 /// [`reserve`]: Vec::reserve
2016 /// [`try_reserve`]: Vec::try_reserve
2017 ///
2018 /// # Examples
2019 ///
2020 /// A manual, panic-free alternative to [`FromIterator`]:
2021 ///
2022 /// ```
2023 /// #![feature(vec_push_within_capacity)]
2024 ///
2025 /// use std::collections::TryReserveError;
2026 /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
2027 /// let mut vec = Vec::new();
2028 /// for value in iter {
2029 /// if let Err(value) = vec.push_within_capacity(value) {
2030 /// vec.try_reserve(1)?;
2031 /// // this cannot fail, the previous line either returned or added at least 1 free slot
2032 /// let _ = vec.push_within_capacity(value);
2033 /// }
2034 /// }
2035 /// Ok(vec)
2036 /// }
2037 /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
2038 /// ```
2039 ///
2040 /// # Time complexity
2041 ///
2042 /// Takes *O*(1) time.
2043 #[inline]
2044 #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
2045 pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
2046 if self.len == self.buf.capacity() {
2047 return Err(value);
2048 }
2049 unsafe {
2050 let end = self.as_mut_ptr().add(self.len);
2051 ptr::write(end, value);
2052 self.len += 1;
2053 }
2054 Ok(())
2055 }
2056
2057 /// Removes the last element from a vector and returns it, or [`None`] if it
2058 /// is empty.
2059 ///
2060 /// If you'd like to pop the first element, consider using
2061 /// [`VecDeque::pop_front`] instead.
2062 ///
2063 /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
2064 ///
2065 /// # Examples
2066 ///
2067 /// ```
2068 /// let mut vec = vec![1, 2, 3];
2069 /// assert_eq!(vec.pop(), Some(3));
2070 /// assert_eq!(vec, [1, 2]);
2071 /// ```
2072 ///
2073 /// # Time complexity
2074 ///
2075 /// Takes *O*(1) time.
2076 #[inline]
2077 #[stable(feature = "rust1", since = "1.0.0")]
2078 pub fn pop(&mut self) -> Option<T> {
2079 if self.len == 0 {
2080 None
2081 } else {
2082 unsafe {
2083 self.len -= 1;
2084 core::hint::assert_unchecked(self.len < self.capacity());
2085 Some(ptr::read(self.as_ptr().add(self.len())))
2086 }
2087 }
2088 }
2089
2090 /// Removes and returns the last element in a vector if the predicate
2091 /// returns `true`, or [`None`] if the predicate returns false or the vector
2092 /// is empty.
2093 ///
2094 /// # Examples
2095 ///
2096 /// ```
2097 /// #![feature(vec_pop_if)]
2098 ///
2099 /// let mut vec = vec![1, 2, 3, 4];
2100 /// let pred = |x: &mut i32| *x % 2 == 0;
2101 ///
2102 /// assert_eq!(vec.pop_if(pred), Some(4));
2103 /// assert_eq!(vec, [1, 2, 3]);
2104 /// assert_eq!(vec.pop_if(pred), None);
2105 /// ```
2106 #[unstable(feature = "vec_pop_if", issue = "122741")]
2107 pub fn pop_if<F>(&mut self, f: F) -> Option<T>
2108 where
2109 F: FnOnce(&mut T) -> bool,
2110 {
2111 let last = self.last_mut()?;
2112 if f(last) { self.pop() } else { None }
2113 }
2114
2115 /// Moves all the elements of `other` into `self`, leaving `other` empty.
2116 ///
2117 /// # Panics
2118 ///
2119 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
2120 ///
2121 /// # Examples
2122 ///
2123 /// ```
2124 /// let mut vec = vec![1, 2, 3];
2125 /// let mut vec2 = vec![4, 5, 6];
2126 /// vec.append(&mut vec2);
2127 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
2128 /// assert_eq!(vec2, []);
2129 /// ```
2130 #[cfg(not(no_global_oom_handling))]
2131 #[inline]
2132 #[stable(feature = "append", since = "1.4.0")]
2133 pub fn append(&mut self, other: &mut Self) {
2134 unsafe {
2135 self.append_elements(other.as_slice() as _);
2136 other.set_len(0);
2137 }
2138 }
2139
2140 /// Appends elements to `self` from other buffer.
2141 #[cfg(not(no_global_oom_handling))]
2142 #[inline]
2143 unsafe fn append_elements(&mut self, other: *const [T]) {
2144 let count = unsafe { (*other).len() };
2145 self.reserve(count);
2146 let len = self.len();
2147 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
2148 self.len += count;
2149 }
2150
2151 /// Removes the specified range from the vector in bulk, returning all
2152 /// removed elements as an iterator. If the iterator is dropped before
2153 /// being fully consumed, it drops the remaining removed elements.
2154 ///
2155 /// The returned iterator keeps a mutable borrow on the vector to optimize
2156 /// its implementation.
2157 ///
2158 /// # Panics
2159 ///
2160 /// Panics if the starting point is greater than the end point or if
2161 /// the end point is greater than the length of the vector.
2162 ///
2163 /// # Leaking
2164 ///
2165 /// If the returned iterator goes out of scope without being dropped (due to
2166 /// [`mem::forget`], for example), the vector may have lost and leaked
2167 /// elements arbitrarily, including elements outside the range.
2168 ///
2169 /// # Examples
2170 ///
2171 /// ```
2172 /// let mut v = vec![1, 2, 3];
2173 /// let u: Vec<_> = v.drain(1..).collect();
2174 /// assert_eq!(v, &[1]);
2175 /// assert_eq!(u, &[2, 3]);
2176 ///
2177 /// // A full range clears the vector, like `clear()` does
2178 /// v.drain(..);
2179 /// assert_eq!(v, &[]);
2180 /// ```
2181 #[stable(feature = "drain", since = "1.6.0")]
2182 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
2183 where
2184 R: RangeBounds<usize>,
2185 {
2186 // Memory safety
2187 //
2188 // When the Drain is first created, it shortens the length of
2189 // the source vector to make sure no uninitialized or moved-from elements
2190 // are accessible at all if the Drain's destructor never gets to run.
2191 //
2192 // Drain will ptr::read out the values to remove.
2193 // When finished, remaining tail of the vec is copied back to cover
2194 // the hole, and the vector length is restored to the new length.
2195 //
2196 let len = self.len();
2197 let Range { start, end } = slice::range(range, ..len);
2198
2199 unsafe {
2200 // set self.vec length's to start, to be safe in case Drain is leaked
2201 self.set_len(start);
2202 let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
2203 Drain {
2204 tail_start: end,
2205 tail_len: len - end,
2206 iter: range_slice.iter(),
2207 vec: NonNull::from(self),
2208 }
2209 }
2210 }
2211
2212 /// Clears the vector, removing all values.
2213 ///
2214 /// Note that this method has no effect on the allocated capacity
2215 /// of the vector.
2216 ///
2217 /// # Examples
2218 ///
2219 /// ```
2220 /// let mut v = vec![1, 2, 3];
2221 ///
2222 /// v.clear();
2223 ///
2224 /// assert!(v.is_empty());
2225 /// ```
2226 #[inline]
2227 #[stable(feature = "rust1", since = "1.0.0")]
2228 pub fn clear(&mut self) {
2229 let elems: *mut [T] = self.as_mut_slice();
2230
2231 // SAFETY:
2232 // - `elems` comes directly from `as_mut_slice` and is therefore valid.
2233 // - Setting `self.len` before calling `drop_in_place` means that,
2234 // if an element's `Drop` impl panics, the vector's `Drop` impl will
2235 // do nothing (leaking the rest of the elements) instead of dropping
2236 // some twice.
2237 unsafe {
2238 self.len = 0;
2239 ptr::drop_in_place(elems);
2240 }
2241 }
2242
2243 /// Returns the number of elements in the vector, also referred to
2244 /// as its 'length'.
2245 ///
2246 /// # Examples
2247 ///
2248 /// ```
2249 /// let a = vec![1, 2, 3];
2250 /// assert_eq!(a.len(), 3);
2251 /// ```
2252 #[inline]
2253 #[stable(feature = "rust1", since = "1.0.0")]
2254 #[rustc_confusables("length", "size")]
2255 pub fn len(&self) -> usize {
2256 self.len
2257 }
2258
2259 /// Returns `true` if the vector contains no elements.
2260 ///
2261 /// # Examples
2262 ///
2263 /// ```
2264 /// let mut v = Vec::new();
2265 /// assert!(v.is_empty());
2266 ///
2267 /// v.push(1);
2268 /// assert!(!v.is_empty());
2269 /// ```
2270 #[stable(feature = "rust1", since = "1.0.0")]
2271 pub fn is_empty(&self) -> bool {
2272 self.len() == 0
2273 }
2274
2275 /// Splits the collection into two at the given index.
2276 ///
2277 /// Returns a newly allocated vector containing the elements in the range
2278 /// `[at, len)`. After the call, the original vector will be left containing
2279 /// the elements `[0, at)` with its previous capacity unchanged.
2280 ///
2281 /// - If you want to take ownership of the entire contents and capacity of
2282 /// the vector, see [`mem::take`] or [`mem::replace`].
2283 /// - If you don't need the returned vector at all, see [`Vec::truncate`].
2284 /// - If you want to take ownership of an arbitrary subslice, or you don't
2285 /// necessarily want to store the removed items in a vector, see [`Vec::drain`].
2286 ///
2287 /// # Panics
2288 ///
2289 /// Panics if `at > len`.
2290 ///
2291 /// # Examples
2292 ///
2293 /// ```
2294 /// let mut vec = vec![1, 2, 3];
2295 /// let vec2 = vec.split_off(1);
2296 /// assert_eq!(vec, [1]);
2297 /// assert_eq!(vec2, [2, 3]);
2298 /// ```
2299 #[cfg(not(no_global_oom_handling))]
2300 #[inline]
2301 #[must_use = "use `.truncate()` if you don't need the other half"]
2302 #[stable(feature = "split_off", since = "1.4.0")]
2303 pub fn split_off(&mut self, at: usize) -> Self
2304 where
2305 A: Clone,
2306 {
2307 #[cold]
2308 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
2309 #[track_caller]
2310 fn assert_failed(at: usize, len: usize) -> ! {
2311 panic!("`at` split index (is {at}) should be <= len (is {len})");
2312 }
2313
2314 if at > self.len() {
2315 assert_failed(at, self.len());
2316 }
2317
2318 let other_len = self.len - at;
2319 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
2320
2321 // Unsafely `set_len` and copy items to `other`.
2322 unsafe {
2323 self.set_len(at);
2324 other.set_len(other_len);
2325
2326 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
2327 }
2328 other
2329 }
2330
2331 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2332 ///
2333 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2334 /// difference, with each additional slot filled with the result of
2335 /// calling the closure `f`. The return values from `f` will end up
2336 /// in the `Vec` in the order they have been generated.
2337 ///
2338 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2339 ///
2340 /// This method uses a closure to create new values on every push. If
2341 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
2342 /// want to use the [`Default`] trait to generate values, you can
2343 /// pass [`Default::default`] as the second argument.
2344 ///
2345 /// # Examples
2346 ///
2347 /// ```
2348 /// let mut vec = vec![1, 2, 3];
2349 /// vec.resize_with(5, Default::default);
2350 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
2351 ///
2352 /// let mut vec = vec![];
2353 /// let mut p = 1;
2354 /// vec.resize_with(4, || { p *= 2; p });
2355 /// assert_eq!(vec, [2, 4, 8, 16]);
2356 /// ```
2357 #[cfg(not(no_global_oom_handling))]
2358 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2359 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
2360 where
2361 F: FnMut() -> T,
2362 {
2363 let len = self.len();
2364 if new_len > len {
2365 self.extend_trusted(iter::repeat_with(f).take(new_len - len));
2366 } else {
2367 self.truncate(new_len);
2368 }
2369 }
2370
2371 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2372 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2373 /// `'a`. If the type has only static references, or none at all, then this
2374 /// may be chosen to be `'static`.
2375 ///
2376 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2377 /// so the leaked allocation may include unused capacity that is not part
2378 /// of the returned slice.
2379 ///
2380 /// This function is mainly useful for data that lives for the remainder of
2381 /// the program's life. Dropping the returned reference will cause a memory
2382 /// leak.
2383 ///
2384 /// # Examples
2385 ///
2386 /// Simple usage:
2387 ///
2388 /// ```
2389 /// let x = vec![1, 2, 3];
2390 /// let static_ref: &'static mut [usize] = x.leak();
2391 /// static_ref[0] += 1;
2392 /// assert_eq!(static_ref, &[2, 2, 3]);
2393 /// ```
2394 #[stable(feature = "vec_leak", since = "1.47.0")]
2395 #[inline]
2396 pub fn leak<'a>(self) -> &'a mut [T]
2397 where
2398 A: 'a,
2399 {
2400 let mut me = ManuallyDrop::new(self);
2401 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2402 }
2403
2404 /// Returns the remaining spare capacity of the vector as a slice of
2405 /// `MaybeUninit<T>`.
2406 ///
2407 /// The returned slice can be used to fill the vector with data (e.g. by
2408 /// reading from a file) before marking the data as initialized using the
2409 /// [`set_len`] method.
2410 ///
2411 /// [`set_len`]: Vec::set_len
2412 ///
2413 /// # Examples
2414 ///
2415 /// ```
2416 /// // Allocate vector big enough for 10 elements.
2417 /// let mut v = Vec::with_capacity(10);
2418 ///
2419 /// // Fill in the first 3 elements.
2420 /// let uninit = v.spare_capacity_mut();
2421 /// uninit[0].write(0);
2422 /// uninit[1].write(1);
2423 /// uninit[2].write(2);
2424 ///
2425 /// // Mark the first 3 elements of the vector as being initialized.
2426 /// unsafe {
2427 /// v.set_len(3);
2428 /// }
2429 ///
2430 /// assert_eq!(&v, &[0, 1, 2]);
2431 /// ```
2432 #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
2433 #[inline]
2434 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2435 // Note:
2436 // This method is not implemented in terms of `split_at_spare_mut`,
2437 // to prevent invalidation of pointers to the buffer.
2438 unsafe {
2439 slice::from_raw_parts_mut(
2440 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2441 self.buf.capacity() - self.len,
2442 )
2443 }
2444 }
2445
2446 /// Returns vector content as a slice of `T`, along with the remaining spare
2447 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2448 ///
2449 /// The returned spare capacity slice can be used to fill the vector with data
2450 /// (e.g. by reading from a file) before marking the data as initialized using
2451 /// the [`set_len`] method.
2452 ///
2453 /// [`set_len`]: Vec::set_len
2454 ///
2455 /// Note that this is a low-level API, which should be used with care for
2456 /// optimization purposes. If you need to append data to a `Vec`
2457 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2458 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2459 /// [`resize_with`], depending on your exact needs.
2460 ///
2461 /// [`push`]: Vec::push
2462 /// [`extend`]: Vec::extend
2463 /// [`extend_from_slice`]: Vec::extend_from_slice
2464 /// [`extend_from_within`]: Vec::extend_from_within
2465 /// [`insert`]: Vec::insert
2466 /// [`append`]: Vec::append
2467 /// [`resize`]: Vec::resize
2468 /// [`resize_with`]: Vec::resize_with
2469 ///
2470 /// # Examples
2471 ///
2472 /// ```
2473 /// #![feature(vec_split_at_spare)]
2474 ///
2475 /// let mut v = vec![1, 1, 2];
2476 ///
2477 /// // Reserve additional space big enough for 10 elements.
2478 /// v.reserve(10);
2479 ///
2480 /// let (init, uninit) = v.split_at_spare_mut();
2481 /// let sum = init.iter().copied().sum::<u32>();
2482 ///
2483 /// // Fill in the next 4 elements.
2484 /// uninit[0].write(sum);
2485 /// uninit[1].write(sum * 2);
2486 /// uninit[2].write(sum * 3);
2487 /// uninit[3].write(sum * 4);
2488 ///
2489 /// // Mark the 4 elements of the vector as being initialized.
2490 /// unsafe {
2491 /// let len = v.len();
2492 /// v.set_len(len + 4);
2493 /// }
2494 ///
2495 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2496 /// ```
2497 #[unstable(feature = "vec_split_at_spare", issue = "81944")]
2498 #[inline]
2499 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2500 // SAFETY:
2501 // - len is ignored and so never changed
2502 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2503 (init, spare)
2504 }
2505
2506 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2507 ///
2508 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2509 unsafe fn split_at_spare_mut_with_len(
2510 &mut self,
2511 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2512 let ptr = self.as_mut_ptr();
2513 // SAFETY:
2514 // - `ptr` is guaranteed to be valid for `self.len` elements
2515 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2516 // uninitialized
2517 let spare_ptr = unsafe { ptr.add(self.len) };
2518 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2519 let spare_len = self.buf.capacity() - self.len;
2520
2521 // SAFETY:
2522 // - `ptr` is guaranteed to be valid for `self.len` elements
2523 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2524 unsafe {
2525 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2526 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2527
2528 (initialized, spare, &mut self.len)
2529 }
2530 }
2531}
2532
2533impl<T: Clone, A: Allocator> Vec<T, A> {
2534 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2535 ///
2536 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2537 /// difference, with each additional slot filled with `value`.
2538 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2539 ///
2540 /// This method requires `T` to implement [`Clone`],
2541 /// in order to be able to clone the passed value.
2542 /// If you need more flexibility (or want to rely on [`Default`] instead of
2543 /// [`Clone`]), use [`Vec::resize_with`].
2544 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2545 ///
2546 /// # Examples
2547 ///
2548 /// ```
2549 /// let mut vec = vec!["hello"];
2550 /// vec.resize(3, "world");
2551 /// assert_eq!(vec, ["hello", "world", "world"]);
2552 ///
2553 /// let mut vec = vec![1, 2, 3, 4];
2554 /// vec.resize(2, 0);
2555 /// assert_eq!(vec, [1, 2]);
2556 /// ```
2557 #[cfg(not(no_global_oom_handling))]
2558 #[stable(feature = "vec_resize", since = "1.5.0")]
2559 pub fn resize(&mut self, new_len: usize, value: T) {
2560 let len = self.len();
2561
2562 if new_len > len {
2563 self.extend_with(new_len - len, value)
2564 } else {
2565 self.truncate(new_len);
2566 }
2567 }
2568
2569 /// Clones and appends all elements in a slice to the `Vec`.
2570 ///
2571 /// Iterates over the slice `other`, clones each element, and then appends
2572 /// it to this `Vec`. The `other` slice is traversed in-order.
2573 ///
2574 /// Note that this function is same as [`extend`] except that it is
2575 /// specialized to work with slices instead. If and when Rust gets
2576 /// specialization this function will likely be deprecated (but still
2577 /// available).
2578 ///
2579 /// # Examples
2580 ///
2581 /// ```
2582 /// let mut vec = vec![1];
2583 /// vec.extend_from_slice(&[2, 3, 4]);
2584 /// assert_eq!(vec, [1, 2, 3, 4]);
2585 /// ```
2586 ///
2587 /// [`extend`]: Vec::extend
2588 #[cfg(not(no_global_oom_handling))]
2589 #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
2590 pub fn extend_from_slice(&mut self, other: &[T]) {
2591 self.spec_extend(other.iter())
2592 }
2593
2594 /// Copies elements from `src` range to the end of the vector.
2595 ///
2596 /// # Panics
2597 ///
2598 /// Panics if the starting point is greater than the end point or if
2599 /// the end point is greater than the length of the vector.
2600 ///
2601 /// # Examples
2602 ///
2603 /// ```
2604 /// let mut vec = vec![0, 1, 2, 3, 4];
2605 ///
2606 /// vec.extend_from_within(2..);
2607 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2608 ///
2609 /// vec.extend_from_within(..2);
2610 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2611 ///
2612 /// vec.extend_from_within(4..8);
2613 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2614 /// ```
2615 #[cfg(not(no_global_oom_handling))]
2616 #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
2617 pub fn extend_from_within<R>(&mut self, src: R)
2618 where
2619 R: RangeBounds<usize>,
2620 {
2621 let range = slice::range(src, ..self.len());
2622 self.reserve(range.len());
2623
2624 // SAFETY:
2625 // - `slice::range` guarantees that the given range is valid for indexing self
2626 unsafe {
2627 self.spec_extend_from_within(range);
2628 }
2629 }
2630}
2631
2632impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
2633 /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
2634 ///
2635 /// # Panics
2636 ///
2637 /// Panics if the length of the resulting vector would overflow a `usize`.
2638 ///
2639 /// This is only possible when flattening a vector of arrays of zero-sized
2640 /// types, and thus tends to be irrelevant in practice. If
2641 /// `size_of::<T>() > 0`, this will never panic.
2642 ///
2643 /// # Examples
2644 ///
2645 /// ```
2646 /// #![feature(slice_flatten)]
2647 ///
2648 /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
2649 /// assert_eq!(vec.pop(), Some([7, 8, 9]));
2650 ///
2651 /// let mut flattened = vec.into_flattened();
2652 /// assert_eq!(flattened.pop(), Some(6));
2653 /// ```
2654 #[unstable(feature = "slice_flatten", issue = "95629")]
2655 pub fn into_flattened(self) -> Vec<T, A> {
2656 let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
2657 let (new_len, new_cap) = if T::IS_ZST {
2658 (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
2659 } else {
2660 // SAFETY:
2661 // - `cap * N` cannot overflow because the allocation is already in
2662 // the address space.
2663 // - Each `[T; N]` has `N` valid elements, so there are `len * N`
2664 // valid elements in the allocation.
2665 unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
2666 };
2667 // SAFETY:
2668 // - `ptr` was allocated by `self`
2669 // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
2670 // - `new_cap` refers to the same sized allocation as `cap` because
2671 // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
2672 // - `len` <= `cap`, so `len * N` <= `cap * N`.
2673 unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
2674 }
2675}
2676
2677impl<T: Clone, A: Allocator> Vec<T, A> {
2678 #[cfg(not(no_global_oom_handling))]
2679 /// Extend the vector by `n` clones of value.
2680 fn extend_with(&mut self, n: usize, value: T) {
2681 self.reserve(n);
2682
2683 unsafe {
2684 let mut ptr = self.as_mut_ptr().add(self.len());
2685 // Use SetLenOnDrop to work around bug where compiler
2686 // might not realize the store through `ptr` through self.set_len()
2687 // don't alias.
2688 let mut local_len = SetLenOnDrop::new(&mut self.len);
2689
2690 // Write all elements except the last one
2691 for _ in 1..n {
2692 ptr::write(ptr, value.clone());
2693 ptr = ptr.add(1);
2694 // Increment the length in every step in case clone() panics
2695 local_len.increment_len(1);
2696 }
2697
2698 if n > 0 {
2699 // We can write the last element directly without cloning needlessly
2700 ptr::write(ptr, value);
2701 local_len.increment_len(1);
2702 }
2703
2704 // len set by scope guard
2705 }
2706 }
2707}
2708
2709impl<T: PartialEq, A: Allocator> Vec<T, A> {
2710 /// Removes consecutive repeated elements in the vector according to the
2711 /// [`PartialEq`] trait implementation.
2712 ///
2713 /// If the vector is sorted, this removes all duplicates.
2714 ///
2715 /// # Examples
2716 ///
2717 /// ```
2718 /// let mut vec = vec![1, 2, 2, 3, 2];
2719 ///
2720 /// vec.dedup();
2721 ///
2722 /// assert_eq!(vec, [1, 2, 3, 2]);
2723 /// ```
2724 #[stable(feature = "rust1", since = "1.0.0")]
2725 #[inline]
2726 pub fn dedup(&mut self) {
2727 self.dedup_by(|a: &mut T, b: &mut T| a == b)
2728 }
2729}
2730
2731////////////////////////////////////////////////////////////////////////////////
2732// Internal methods and functions
2733////////////////////////////////////////////////////////////////////////////////
2734
2735#[doc(hidden)]
2736#[cfg(not(no_global_oom_handling))]
2737#[stable(feature = "rust1", since = "1.0.0")]
2738pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
2739 <T as SpecFromElem>::from_elem(elem, n, alloc:Global)
2740}
2741
2742#[doc(hidden)]
2743#[cfg(not(no_global_oom_handling))]
2744#[unstable(feature = "allocator_api", issue = "32838")]
2745pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
2746 <T as SpecFromElem>::from_elem(elem, n, alloc)
2747}
2748
2749#[cfg(not(no_global_oom_handling))]
2750trait ExtendFromWithinSpec {
2751 /// # Safety
2752 ///
2753 /// - `src` needs to be valid index
2754 /// - `self.capacity() - self.len()` must be `>= src.len()`
2755 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
2756}
2757
2758#[cfg(not(no_global_oom_handling))]
2759impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2760 default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2761 // SAFETY:
2762 // - len is increased only after initializing elements
2763 let (this: &mut [T], spare: &mut [MaybeUninit], len: &mut usize) = unsafe { self.split_at_spare_mut_with_len() };
2764
2765 // SAFETY:
2766 // - caller guarantees that src is a valid index
2767 let to_clone: &[T] = unsafe { this.get_unchecked(index:src) };
2768
2769 iterimpl Iterator::zip(a:to_clone, b:spare)
2770 .map(|(src: &T, dst: &mut MaybeUninit)| dst.write(val:src.clone()))
2771 // Note:
2772 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2773 // - len is increased after each element to prevent leaks (see issue #82533)
2774 .for_each(|_| *len += 1);
2775 }
2776}
2777
2778#[cfg(not(no_global_oom_handling))]
2779impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
2780 unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
2781 let count = src.len();
2782 {
2783 let (init, spare) = self.split_at_spare_mut();
2784
2785 // SAFETY:
2786 // - caller guarantees that `src` is a valid index
2787 let source = unsafe { init.get_unchecked(src) };
2788
2789 // SAFETY:
2790 // - Both pointers are created from unique slice references (`&mut [_]`)
2791 // so they are valid and do not overlap.
2792 // - Elements are :Copy so it's OK to copy them, without doing
2793 // anything with the original values
2794 // - `count` is equal to the len of `source`, so source is valid for
2795 // `count` reads
2796 // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
2797 // is valid for `count` writes
2798 unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
2799 }
2800
2801 // SAFETY:
2802 // - The elements were just initialized by `copy_nonoverlapping`
2803 self.len += count;
2804 }
2805}
2806
2807////////////////////////////////////////////////////////////////////////////////
2808// Common trait implementations for Vec
2809////////////////////////////////////////////////////////////////////////////////
2810
2811#[stable(feature = "rust1", since = "1.0.0")]
2812impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2813 type Target = [T];
2814
2815 #[inline]
2816 fn deref(&self) -> &[T] {
2817 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2818 }
2819}
2820
2821#[stable(feature = "rust1", since = "1.0.0")]
2822impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2823 #[inline]
2824 fn deref_mut(&mut self) -> &mut [T] {
2825 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2826 }
2827}
2828
2829#[unstable(feature = "deref_pure_trait", issue = "87121")]
2830unsafe impl<T, A: Allocator> ops::DerefPure for Vec<T, A> {}
2831
2832#[cfg(not(no_global_oom_handling))]
2833#[stable(feature = "rust1", since = "1.0.0")]
2834impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2835 #[cfg(not(test))]
2836 fn clone(&self) -> Self {
2837 let alloc = self.allocator().clone();
2838 <[T]>::to_vec_in(&**self, alloc)
2839 }
2840
2841 // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
2842 // required for this method definition, is not available. Instead use the
2843 // `slice::to_vec` function which is only available with cfg(test)
2844 // NB see the slice::hack module in slice.rs for more information
2845 #[cfg(test)]
2846 fn clone(&self) -> Self {
2847 let alloc = self.allocator().clone();
2848 crate::slice::to_vec(&**self, alloc)
2849 }
2850
2851 /// Overwrites the contents of `self` with a clone of the contents of `source`.
2852 ///
2853 /// This method is preferred over simply assigning `source.clone()` to `self`,
2854 /// as it avoids reallocation if possible. Additionally, if the element type
2855 /// `T` overrides `clone_from()`, this will reuse the resources of `self`'s
2856 /// elements as well.
2857 ///
2858 /// # Examples
2859 ///
2860 /// ```
2861 /// let x = vec![5, 6, 7];
2862 /// let mut y = vec![8, 9, 10];
2863 /// let yp: *const i32 = y.as_ptr();
2864 ///
2865 /// y.clone_from(&x);
2866 ///
2867 /// // The value is the same
2868 /// assert_eq!(x, y);
2869 ///
2870 /// // And no reallocation occurred
2871 /// assert_eq!(yp, y.as_ptr());
2872 /// ```
2873 fn clone_from(&mut self, source: &Self) {
2874 crate::slice::SpecCloneIntoVec::clone_into(source.as_slice(), self);
2875 }
2876}
2877
2878/// The hash of a vector is the same as that of the corresponding slice,
2879/// as required by the `core::borrow::Borrow` implementation.
2880///
2881/// ```
2882/// use std::hash::BuildHasher;
2883///
2884/// let b = std::hash::RandomState::new();
2885/// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2886/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2887/// assert_eq!(b.hash_one(v), b.hash_one(s));
2888/// ```
2889#[stable(feature = "rust1", since = "1.0.0")]
2890impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2891 #[inline]
2892 fn hash<H: Hasher>(&self, state: &mut H) {
2893 Hash::hash(&**self, state)
2894 }
2895}
2896
2897#[stable(feature = "rust1", since = "1.0.0")]
2898#[rustc_on_unimplemented(
2899 message = "vector indices are of type `usize` or ranges of `usize`",
2900 label = "vector indices are of type `usize` or ranges of `usize`"
2901)]
2902impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2903 type Output = I::Output;
2904
2905 #[inline]
2906 fn index(&self, index: I) -> &Self::Output {
2907 Index::index(&**self, index)
2908 }
2909}
2910
2911#[stable(feature = "rust1", since = "1.0.0")]
2912#[rustc_on_unimplemented(
2913 message = "vector indices are of type `usize` or ranges of `usize`",
2914 label = "vector indices are of type `usize` or ranges of `usize`"
2915)]
2916impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2917 #[inline]
2918 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2919 IndexMut::index_mut(&mut **self, index)
2920 }
2921}
2922
2923/// Collects an iterator into a Vec, commonly called via [`Iterator::collect()`]
2924///
2925/// # Allocation behavior
2926///
2927/// In general `Vec` does not guarantee any particular growth or allocation strategy.
2928/// That also applies to this trait impl.
2929///
2930/// **Note:** This section covers implementation details and is therefore exempt from
2931/// stability guarantees.
2932///
2933/// Vec may use any or none of the following strategies,
2934/// depending on the supplied iterator:
2935///
2936/// * preallocate based on [`Iterator::size_hint()`]
2937/// * and panic if the number of items is outside the provided lower/upper bounds
2938/// * use an amortized growth strategy similar to `pushing` one item at a time
2939/// * perform the iteration in-place on the original allocation backing the iterator
2940///
2941/// The last case warrants some attention. It is an optimization that in many cases reduces peak memory
2942/// consumption and improves cache locality. But when big, short-lived allocations are created,
2943/// only a small fraction of their items get collected, no further use is made of the spare capacity
2944/// and the resulting `Vec` is moved into a longer-lived structure, then this can lead to the large
2945/// allocations having their lifetimes unnecessarily extended which can result in increased memory
2946/// footprint.
2947///
2948/// In cases where this is an issue, the excess capacity can be discarded with [`Vec::shrink_to()`],
2949/// [`Vec::shrink_to_fit()`] or by collecting into [`Box<[T]>`][owned slice] instead, which additionally reduces
2950/// the size of the long-lived struct.
2951///
2952/// [owned slice]: Box
2953///
2954/// ```rust
2955/// # use std::sync::Mutex;
2956/// static LONG_LIVED: Mutex<Vec<Vec<u16>>> = Mutex::new(Vec::new());
2957///
2958/// for i in 0..10 {
2959/// let big_temporary: Vec<u16> = (0..1024).collect();
2960/// // discard most items
2961/// let mut result: Vec<_> = big_temporary.into_iter().filter(|i| i % 100 == 0).collect();
2962/// // without this a lot of unused capacity might be moved into the global
2963/// result.shrink_to_fit();
2964/// LONG_LIVED.lock().unwrap().push(result);
2965/// }
2966/// ```
2967#[cfg(not(no_global_oom_handling))]
2968#[stable(feature = "rust1", since = "1.0.0")]
2969impl<T> FromIterator<T> for Vec<T> {
2970 #[inline]
2971 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2972 <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
2973 }
2974}
2975
2976#[stable(feature = "rust1", since = "1.0.0")]
2977impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2978 type Item = T;
2979 type IntoIter = IntoIter<T, A>;
2980
2981 /// Creates a consuming iterator, that is, one that moves each value out of
2982 /// the vector (from start to end). The vector cannot be used after calling
2983 /// this.
2984 ///
2985 /// # Examples
2986 ///
2987 /// ```
2988 /// let v = vec!["a".to_string(), "b".to_string()];
2989 /// let mut v_iter = v.into_iter();
2990 ///
2991 /// let first_element: Option<String> = v_iter.next();
2992 ///
2993 /// assert_eq!(first_element, Some("a".to_string()));
2994 /// assert_eq!(v_iter.next(), Some("b".to_string()));
2995 /// assert_eq!(v_iter.next(), None);
2996 /// ```
2997 #[inline]
2998 fn into_iter(self) -> Self::IntoIter {
2999 unsafe {
3000 let me = ManuallyDrop::new(self);
3001 let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
3002 let buf = me.buf.non_null();
3003 let begin = buf.as_ptr();
3004 let end = if T::IS_ZST {
3005 begin.wrapping_byte_add(me.len())
3006 } else {
3007 begin.add(me.len()) as *const T
3008 };
3009 let cap = me.buf.capacity();
3010 IntoIter { buf, phantom: PhantomData, cap, alloc, ptr: buf, end }
3011 }
3012 }
3013}
3014
3015#[stable(feature = "rust1", since = "1.0.0")]
3016impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
3017 type Item = &'a T;
3018 type IntoIter = slice::Iter<'a, T>;
3019
3020 fn into_iter(self) -> Self::IntoIter {
3021 self.iter()
3022 }
3023}
3024
3025#[stable(feature = "rust1", since = "1.0.0")]
3026impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
3027 type Item = &'a mut T;
3028 type IntoIter = slice::IterMut<'a, T>;
3029
3030 fn into_iter(self) -> Self::IntoIter {
3031 self.iter_mut()
3032 }
3033}
3034
3035#[cfg(not(no_global_oom_handling))]
3036#[stable(feature = "rust1", since = "1.0.0")]
3037impl<T, A: Allocator> Extend<T> for Vec<T, A> {
3038 #[inline]
3039 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
3040 <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
3041 }
3042
3043 #[inline]
3044 fn extend_one(&mut self, item: T) {
3045 self.push(item);
3046 }
3047
3048 #[inline]
3049 fn extend_reserve(&mut self, additional: usize) {
3050 self.reserve(additional);
3051 }
3052}
3053
3054impl<T, A: Allocator> Vec<T, A> {
3055 // leaf method to which various SpecFrom/SpecExtend implementations delegate when
3056 // they have no further optimizations to apply
3057 #[cfg(not(no_global_oom_handling))]
3058 fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
3059 // This is the case for a general iterator.
3060 //
3061 // This function should be the moral equivalent of:
3062 //
3063 // for item in iterator {
3064 // self.push(item);
3065 // }
3066 while let Some(element) = iterator.next() {
3067 let len = self.len();
3068 if len == self.capacity() {
3069 let (lower, _) = iterator.size_hint();
3070 self.reserve(lower.saturating_add(1));
3071 }
3072 unsafe {
3073 ptr::write(self.as_mut_ptr().add(len), element);
3074 // Since next() executes user code which can panic we have to bump the length
3075 // after each step.
3076 // NB can't overflow since we would have had to alloc the address space
3077 self.set_len(len + 1);
3078 }
3079 }
3080 }
3081
3082 // specific extend for `TrustedLen` iterators, called both by the specializations
3083 // and internal places where resolving specialization makes compilation slower
3084 #[cfg(not(no_global_oom_handling))]
3085 fn extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) {
3086 let (low, high) = iterator.size_hint();
3087 if let Some(additional) = high {
3088 debug_assert_eq!(
3089 low,
3090 additional,
3091 "TrustedLen iterator's size hint is not exact: {:?}",
3092 (low, high)
3093 );
3094 self.reserve(additional);
3095 unsafe {
3096 let ptr = self.as_mut_ptr();
3097 let mut local_len = SetLenOnDrop::new(&mut self.len);
3098 iterator.for_each(move |element| {
3099 ptr::write(ptr.add(local_len.current_len()), element);
3100 // Since the loop executes user code which can panic we have to update
3101 // the length every step to correctly drop what we've written.
3102 // NB can't overflow since we would have had to alloc the address space
3103 local_len.increment_len(1);
3104 });
3105 }
3106 } else {
3107 // Per TrustedLen contract a `None` upper bound means that the iterator length
3108 // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
3109 // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
3110 // This avoids additional codegen for a fallback code path which would eventually
3111 // panic anyway.
3112 panic!("capacity overflow");
3113 }
3114 }
3115
3116 /// Creates a splicing iterator that replaces the specified range in the vector
3117 /// with the given `replace_with` iterator and yields the removed items.
3118 /// `replace_with` does not need to be the same length as `range`.
3119 ///
3120 /// `range` is removed even if the iterator is not consumed until the end.
3121 ///
3122 /// It is unspecified how many elements are removed from the vector
3123 /// if the `Splice` value is leaked.
3124 ///
3125 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
3126 ///
3127 /// This is optimal if:
3128 ///
3129 /// * The tail (elements in the vector after `range`) is empty,
3130 /// * or `replace_with` yields fewer or equal elements than `range`’s length
3131 /// * or the lower bound of its `size_hint()` is exact.
3132 ///
3133 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
3134 ///
3135 /// # Panics
3136 ///
3137 /// Panics if the starting point is greater than the end point or if
3138 /// the end point is greater than the length of the vector.
3139 ///
3140 /// # Examples
3141 ///
3142 /// ```
3143 /// let mut v = vec![1, 2, 3, 4];
3144 /// let new = [7, 8, 9];
3145 /// let u: Vec<_> = v.splice(1..3, new).collect();
3146 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
3147 /// assert_eq!(u, &[2, 3]);
3148 /// ```
3149 #[cfg(not(no_global_oom_handling))]
3150 #[inline]
3151 #[stable(feature = "vec_splice", since = "1.21.0")]
3152 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
3153 where
3154 R: RangeBounds<usize>,
3155 I: IntoIterator<Item = T>,
3156 {
3157 Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
3158 }
3159
3160 /// Creates an iterator which uses a closure to determine if an element should be removed.
3161 ///
3162 /// If the closure returns true, then the element is removed and yielded.
3163 /// If the closure returns false, the element will remain in the vector and will not be yielded
3164 /// by the iterator.
3165 ///
3166 /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
3167 /// or the iteration short-circuits, then the remaining elements will be retained.
3168 /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
3169 ///
3170 /// [`retain`]: Vec::retain
3171 ///
3172 /// Using this method is equivalent to the following code:
3173 ///
3174 /// ```
3175 /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
3176 /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
3177 /// let mut i = 0;
3178 /// while i < vec.len() {
3179 /// if some_predicate(&mut vec[i]) {
3180 /// let val = vec.remove(i);
3181 /// // your code here
3182 /// } else {
3183 /// i += 1;
3184 /// }
3185 /// }
3186 ///
3187 /// # assert_eq!(vec, vec![1, 4, 5]);
3188 /// ```
3189 ///
3190 /// But `extract_if` is easier to use. `extract_if` is also more efficient,
3191 /// because it can backshift the elements of the array in bulk.
3192 ///
3193 /// Note that `extract_if` also lets you mutate every element in the filter closure,
3194 /// regardless of whether you choose to keep or remove it.
3195 ///
3196 /// # Examples
3197 ///
3198 /// Splitting an array into evens and odds, reusing the original allocation:
3199 ///
3200 /// ```
3201 /// #![feature(extract_if)]
3202 /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
3203 ///
3204 /// let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
3205 /// let odds = numbers;
3206 ///
3207 /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
3208 /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
3209 /// ```
3210 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
3211 pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A>
3212 where
3213 F: FnMut(&mut T) -> bool,
3214 {
3215 let old_len = self.len();
3216
3217 // Guard against us getting leaked (leak amplification)
3218 unsafe {
3219 self.set_len(0);
3220 }
3221
3222 ExtractIf { vec: self, idx: 0, del: 0, old_len, pred: filter }
3223 }
3224}
3225
3226/// Extend implementation that copies elements out of references before pushing them onto the Vec.
3227///
3228/// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
3229/// append the entire slice at once.
3230///
3231/// [`copy_from_slice`]: slice::copy_from_slice
3232#[cfg(not(no_global_oom_handling))]
3233#[stable(feature = "extend_ref", since = "1.2.0")]
3234impl<'a, T: Copy + 'a, A: Allocator> Extend<&'a T> for Vec<T, A> {
3235 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
3236 self.spec_extend(iter.into_iter())
3237 }
3238
3239 #[inline]
3240 fn extend_one(&mut self, &item: T: &'a T) {
3241 self.push(item);
3242 }
3243
3244 #[inline]
3245 fn extend_reserve(&mut self, additional: usize) {
3246 self.reserve(additional);
3247 }
3248}
3249
3250/// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
3251#[stable(feature = "rust1", since = "1.0.0")]
3252impl<T, A1, A2> PartialOrd<Vec<T, A2>> for Vec<T, A1>
3253where
3254 T: PartialOrd,
3255 A1: Allocator,
3256 A2: Allocator,
3257{
3258 #[inline]
3259 fn partial_cmp(&self, other: &Vec<T, A2>) -> Option<Ordering> {
3260 PartialOrd::partial_cmp(&**self, &**other)
3261 }
3262}
3263
3264#[stable(feature = "rust1", since = "1.0.0")]
3265impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
3266
3267/// Implements ordering of vectors, [lexicographically](Ord#lexicographical-comparison).
3268#[stable(feature = "rust1", since = "1.0.0")]
3269impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
3270 #[inline]
3271 fn cmp(&self, other: &Self) -> Ordering {
3272 Ord::cmp(&**self, &**other)
3273 }
3274}
3275
3276#[stable(feature = "rust1", since = "1.0.0")]
3277unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
3278 fn drop(&mut self) {
3279 unsafe {
3280 // use drop for [T]
3281 // use a raw slice to refer to the elements of the vector as weakest necessary type;
3282 // could avoid questions of validity in certain cases
3283 ptr::drop_in_place(to_drop:ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
3284 }
3285 // RawVec handles deallocation
3286 }
3287}
3288
3289#[stable(feature = "rust1", since = "1.0.0")]
3290impl<T> Default for Vec<T> {
3291 /// Creates an empty `Vec<T>`.
3292 ///
3293 /// The vector will not allocate until elements are pushed onto it.
3294 fn default() -> Vec<T> {
3295 Vec::new()
3296 }
3297}
3298
3299#[stable(feature = "rust1", since = "1.0.0")]
3300impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
3301 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3302 fmt::Debug::fmt(&**self, f)
3303 }
3304}
3305
3306#[stable(feature = "rust1", since = "1.0.0")]
3307impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
3308 fn as_ref(&self) -> &Vec<T, A> {
3309 self
3310 }
3311}
3312
3313#[stable(feature = "vec_as_mut", since = "1.5.0")]
3314impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
3315 fn as_mut(&mut self) -> &mut Vec<T, A> {
3316 self
3317 }
3318}
3319
3320#[stable(feature = "rust1", since = "1.0.0")]
3321impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
3322 fn as_ref(&self) -> &[T] {
3323 self
3324 }
3325}
3326
3327#[stable(feature = "vec_as_mut", since = "1.5.0")]
3328impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
3329 fn as_mut(&mut self) -> &mut [T] {
3330 self
3331 }
3332}
3333
3334#[cfg(not(no_global_oom_handling))]
3335#[stable(feature = "rust1", since = "1.0.0")]
3336impl<T: Clone> From<&[T]> for Vec<T> {
3337 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3338 ///
3339 /// # Examples
3340 ///
3341 /// ```
3342 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
3343 /// ```
3344 #[cfg(not(test))]
3345 fn from(s: &[T]) -> Vec<T> {
3346 s.to_vec()
3347 }
3348 #[cfg(test)]
3349 fn from(s: &[T]) -> Vec<T> {
3350 crate::slice::to_vec(s, Global)
3351 }
3352}
3353
3354#[cfg(not(no_global_oom_handling))]
3355#[stable(feature = "vec_from_mut", since = "1.19.0")]
3356impl<T: Clone> From<&mut [T]> for Vec<T> {
3357 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3358 ///
3359 /// # Examples
3360 ///
3361 /// ```
3362 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
3363 /// ```
3364 #[cfg(not(test))]
3365 fn from(s: &mut [T]) -> Vec<T> {
3366 s.to_vec()
3367 }
3368 #[cfg(test)]
3369 fn from(s: &mut [T]) -> Vec<T> {
3370 crate::slice::to_vec(s, Global)
3371 }
3372}
3373
3374#[cfg(not(no_global_oom_handling))]
3375#[stable(feature = "vec_from_array_ref", since = "1.74.0")]
3376impl<T: Clone, const N: usize> From<&[T; N]> for Vec<T> {
3377 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3378 ///
3379 /// # Examples
3380 ///
3381 /// ```
3382 /// assert_eq!(Vec::from(&[1, 2, 3]), vec![1, 2, 3]);
3383 /// ```
3384 fn from(s: &[T; N]) -> Vec<T> {
3385 Self::from(s.as_slice())
3386 }
3387}
3388
3389#[cfg(not(no_global_oom_handling))]
3390#[stable(feature = "vec_from_array_ref", since = "1.74.0")]
3391impl<T: Clone, const N: usize> From<&mut [T; N]> for Vec<T> {
3392 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
3393 ///
3394 /// # Examples
3395 ///
3396 /// ```
3397 /// assert_eq!(Vec::from(&mut [1, 2, 3]), vec![1, 2, 3]);
3398 /// ```
3399 fn from(s: &mut [T; N]) -> Vec<T> {
3400 Self::from(s.as_mut_slice())
3401 }
3402}
3403
3404#[cfg(not(no_global_oom_handling))]
3405#[stable(feature = "vec_from_array", since = "1.44.0")]
3406impl<T, const N: usize> From<[T; N]> for Vec<T> {
3407 /// Allocate a `Vec<T>` and move `s`'s items into it.
3408 ///
3409 /// # Examples
3410 ///
3411 /// ```
3412 /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
3413 /// ```
3414 #[cfg(not(test))]
3415 fn from(s: [T; N]) -> Vec<T> {
3416 <[T]>::into_vec(self:Box::new(s))
3417 }
3418
3419 #[cfg(test)]
3420 fn from(s: [T; N]) -> Vec<T> {
3421 crate::slice::into_vec(Box::new(s))
3422 }
3423}
3424
3425#[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
3426impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
3427where
3428 [T]: ToOwned<Owned = Vec<T>>,
3429{
3430 /// Convert a clone-on-write slice into a vector.
3431 ///
3432 /// If `s` already owns a `Vec<T>`, it will be returned directly.
3433 /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
3434 /// filled by cloning `s`'s items into it.
3435 ///
3436 /// # Examples
3437 ///
3438 /// ```
3439 /// # use std::borrow::Cow;
3440 /// let o: Cow<'_, [i32]> = Cow::Owned(vec![1, 2, 3]);
3441 /// let b: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);
3442 /// assert_eq!(Vec::from(o), Vec::from(b));
3443 /// ```
3444 fn from(s: Cow<'a, [T]>) -> Vec<T> {
3445 s.into_owned()
3446 }
3447}
3448
3449// note: test pulls in std, which causes errors here
3450#[cfg(not(test))]
3451#[stable(feature = "vec_from_box", since = "1.18.0")]
3452impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
3453 /// Convert a boxed slice into a vector by transferring ownership of
3454 /// the existing heap allocation.
3455 ///
3456 /// # Examples
3457 ///
3458 /// ```
3459 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
3460 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
3461 /// ```
3462 fn from(s: Box<[T], A>) -> Self {
3463 s.into_vec()
3464 }
3465}
3466
3467// note: test pulls in std, which causes errors here
3468#[cfg(not(no_global_oom_handling))]
3469#[cfg(not(test))]
3470#[stable(feature = "box_from_vec", since = "1.20.0")]
3471impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
3472 /// Convert a vector into a boxed slice.
3473 ///
3474 /// Before doing the conversion, this method discards excess capacity like [`Vec::shrink_to_fit`].
3475 ///
3476 /// [owned slice]: Box
3477 /// [`Vec::shrink_to_fit`]: Vec::shrink_to_fit
3478 ///
3479 /// # Examples
3480 ///
3481 /// ```
3482 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
3483 /// ```
3484 ///
3485 /// Any excess capacity is removed:
3486 /// ```
3487 /// let mut vec = Vec::with_capacity(10);
3488 /// vec.extend([1, 2, 3]);
3489 ///
3490 /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
3491 /// ```
3492 fn from(v: Vec<T, A>) -> Self {
3493 v.into_boxed_slice()
3494 }
3495}
3496
3497#[cfg(not(no_global_oom_handling))]
3498#[stable(feature = "rust1", since = "1.0.0")]
3499impl From<&str> for Vec<u8> {
3500 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
3501 ///
3502 /// # Examples
3503 ///
3504 /// ```
3505 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
3506 /// ```
3507 fn from(s: &str) -> Vec<u8> {
3508 From::from(s.as_bytes())
3509 }
3510}
3511
3512#[stable(feature = "array_try_from_vec", since = "1.48.0")]
3513impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
3514 type Error = Vec<T, A>;
3515
3516 /// Gets the entire contents of the `Vec<T>` as an array,
3517 /// if its size exactly matches that of the requested array.
3518 ///
3519 /// # Examples
3520 ///
3521 /// ```
3522 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3523 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3524 /// ```
3525 ///
3526 /// If the length doesn't match, the input comes back in `Err`:
3527 /// ```
3528 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3529 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3530 /// ```
3531 ///
3532 /// If you're fine with just getting a prefix of the `Vec<T>`,
3533 /// you can call [`.truncate(N)`](Vec::truncate) first.
3534 /// ```
3535 /// let mut v = String::from("hello world").into_bytes();
3536 /// v.sort();
3537 /// v.truncate(2);
3538 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3539 /// assert_eq!(a, b' ');
3540 /// assert_eq!(b, b'd');
3541 /// ```
3542 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
3543 if vec.len() != N {
3544 return Err(vec);
3545 }
3546
3547 // SAFETY: `.set_len(0)` is always sound.
3548 unsafe { vec.set_len(0) };
3549
3550 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3551 // the alignment the array needs is the same as the items.
3552 // We checked earlier that we have sufficient items.
3553 // The items will not double-drop as the `set_len`
3554 // tells the `Vec` not to also drop them.
3555 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };
3556 Ok(array)
3557 }
3558}
3559