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#[cfg(not(no_global_oom_handling))]
55use core::cmp;
56use core::cmp::Ordering;
57use core::convert::TryFrom;
58use core::fmt;
59use core::hash::{Hash, Hasher};
60#[cfg(not(no_global_oom_handling))]
61use core::iter;
62#[cfg(not(no_global_oom_handling))]
63use core::iter::FromIterator;
64use core::marker::PhantomData;
65use core::mem::{self, size_of, ManuallyDrop, MaybeUninit};
66use core::ops::{self, Bound, Index, IndexMut, RangeBounds};
67use core::ptr::{self, NonNull};
68use core::slice::{self, SliceIndex};
69
70#[cfg(feature = "std")]
71use std::io;
72
73use super::{
74 alloc::{Allocator, Global},
75 assume,
76 boxed::Box,
77 raw_vec::{RawVec, TryReserveError},
78};
79
80#[cfg(not(no_global_oom_handling))]
81pub use self::splice::Splice;
82
83#[cfg(not(no_global_oom_handling))]
84mod splice;
85
86pub use self::drain::Drain;
87
88mod drain;
89
90pub use self::into_iter::IntoIter;
91
92mod into_iter;
93
94mod partial_eq;
95
96#[cfg(not(no_global_oom_handling))]
97mod set_len_on_drop;
98
99#[cfg(not(no_global_oom_handling))]
100use self::set_len_on_drop::SetLenOnDrop;
101
102/// A contiguous growable array type, written as `Vec<T>`, short for 'vector'.
103///
104/// # Examples
105///
106/// ```
107/// let mut vec = Vec::new();
108/// vec.push(1);
109/// vec.push(2);
110///
111/// assert_eq!(vec.len(), 2);
112/// assert_eq!(vec[0], 1);
113///
114/// assert_eq!(vec.pop(), Some(2));
115/// assert_eq!(vec.len(), 1);
116///
117/// vec[0] = 7;
118/// assert_eq!(vec[0], 7);
119///
120/// vec.extend([1, 2, 3].iter().copied());
121///
122/// for x in &vec {
123/// println!("{x}");
124/// }
125/// assert_eq!(vec, [7, 1, 2, 3]);
126/// ```
127///
128/// The [`vec!`] macro is provided for convenient initialization:
129///
130/// ```
131/// let mut vec1 = vec![1, 2, 3];
132/// vec1.push(4);
133/// let vec2 = Vec::from([1, 2, 3, 4]);
134/// assert_eq!(vec1, vec2);
135/// ```
136///
137/// It can also initialize each element of a `Vec<T>` with a given value.
138/// This may be more efficient than performing allocation and initialization
139/// in separate steps, especially when initializing a vector of zeros:
140///
141/// ```
142/// let vec = vec![0; 5];
143/// assert_eq!(vec, [0, 0, 0, 0, 0]);
144///
145/// // The following is equivalent, but potentially slower:
146/// let mut vec = Vec::with_capacity(5);
147/// vec.resize(5, 0);
148/// assert_eq!(vec, [0, 0, 0, 0, 0]);
149/// ```
150///
151/// For more information, see
152/// [Capacity and Reallocation](#capacity-and-reallocation).
153///
154/// Use a `Vec<T>` as an efficient stack:
155///
156/// ```
157/// let mut stack = Vec::new();
158///
159/// stack.push(1);
160/// stack.push(2);
161/// stack.push(3);
162///
163/// while let Some(top) = stack.pop() {
164/// // Prints 3, 2, 1
165/// println!("{top}");
166/// }
167/// ```
168///
169/// # Indexing
170///
171/// The `Vec` type allows to access values by index, because it implements the
172/// [`Index`] trait. An example will be more explicit:
173///
174/// ```
175/// let v = vec![0, 2, 4, 6];
176/// println!("{}", v[1]); // it will display '2'
177/// ```
178///
179/// However be careful: if you try to access an index which isn't in the `Vec`,
180/// your software will panic! You cannot do this:
181///
182/// ```should_panic
183/// let v = vec![0, 2, 4, 6];
184/// println!("{}", v[6]); // it will panic!
185/// ```
186///
187/// Use [`get`] and [`get_mut`] if you want to check whether the index is in
188/// the `Vec`.
189///
190/// # Slicing
191///
192/// A `Vec` can be mutable. On the other hand, slices are read-only objects.
193/// To get a [slice][prim@slice], use [`&`]. Example:
194///
195/// ```
196/// fn read_slice(slice: &[usize]) {
197/// // ...
198/// }
199///
200/// let v = vec![0, 1];
201/// read_slice(&v);
202///
203/// // ... and that's all!
204/// // you can also do it like this:
205/// let u: &[usize] = &v;
206/// // or like this:
207/// let u: &[_] = &v;
208/// ```
209///
210/// In Rust, it's more common to pass slices as arguments rather than vectors
211/// when you just want to provide read access. The same goes for [`String`] and
212/// [`&str`].
213///
214/// # Capacity and reallocation
215///
216/// The capacity of a vector is the amount of space allocated for any future
217/// elements that will be added onto the vector. This is not to be confused with
218/// the *length* of a vector, which specifies the number of actual elements
219/// within the vector. If a vector's length exceeds its capacity, its capacity
220/// will automatically be increased, but its elements will have to be
221/// reallocated.
222///
223/// For example, a vector with capacity 10 and length 0 would be an empty vector
224/// with space for 10 more elements. Pushing 10 or fewer elements onto the
225/// vector will not change its capacity or cause reallocation to occur. However,
226/// if the vector's length is increased to 11, it will have to reallocate, which
227/// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
228/// whenever possible to specify how big the vector is expected to get.
229///
230/// # Guarantees
231///
232/// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
233/// about its design. This ensures that it's as low-overhead as possible in
234/// the general case, and can be correctly manipulated in primitive ways
235/// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
236/// If additional type parameters are added (e.g., to support custom allocators),
237/// overriding their defaults may change the behavior.
238///
239/// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
240/// triplet. No more, no less. The order of these fields is completely
241/// unspecified, and you should use the appropriate methods to modify these.
242/// The pointer will never be null, so this type is null-pointer-optimized.
243///
244/// However, the pointer might not actually point to allocated memory. In particular,
245/// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
246/// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
247/// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
248/// types inside a `Vec`, it will not allocate space for them. *Note that in this case
249/// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
250/// if <code>[mem::size_of::\<T>]\() * [capacity]\() > 0</code>. In general, `Vec`'s allocation
251/// details are very subtle --- if you intend to allocate memory using a `Vec`
252/// and use it for something else (either to pass to unsafe code, or to build your
253/// own memory-backed collection), be sure to deallocate this memory by using
254/// `from_raw_parts` to recover the `Vec` and then dropping it.
255///
256/// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
257/// (as defined by the allocator Rust is configured to use by default), and its
258/// pointer points to [`len`] initialized, contiguous elements in order (what
259/// you would see if you coerced it to a slice), followed by <code>[capacity] - [len]</code>
260/// logically uninitialized, contiguous elements.
261///
262/// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
263/// visualized as below. The top part is the `Vec` struct, it contains a
264/// pointer to the head of the allocation in the heap, length and capacity.
265/// The bottom part is the allocation on the heap, a contiguous memory block.
266///
267/// ```text
268/// ptr len capacity
269/// +--------+--------+--------+
270/// | 0x0123 | 2 | 4 |
271/// +--------+--------+--------+
272/// |
273/// v
274/// Heap +--------+--------+--------+--------+
275/// | 'a' | 'b' | uninit | uninit |
276/// +--------+--------+--------+--------+
277/// ```
278///
279/// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
280/// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
281/// layout (including the order of fields).
282///
283/// `Vec` will never perform a "small optimization" where elements are actually
284/// stored on the stack for two reasons:
285///
286/// * It would make it more difficult for unsafe code to correctly manipulate
287/// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
288/// only moved, and it would be more difficult to determine if a `Vec` had
289/// actually allocated memory.
290///
291/// * It would penalize the general case, incurring an additional branch
292/// on every access.
293///
294/// `Vec` will never automatically shrink itself, even if completely empty. This
295/// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
296/// and then filling it back up to the same [`len`] should incur no calls to
297/// the allocator. If you wish to free up unused memory, use
298/// [`shrink_to_fit`] or [`shrink_to`].
299///
300/// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
301/// sufficient. [`push`] and [`insert`] *will* (re)allocate if
302/// <code>[len] == [capacity]</code>. That is, the reported capacity is completely
303/// accurate, and can be relied on. It can even be used to manually free the memory
304/// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
305/// when not necessary.
306///
307/// `Vec` does not guarantee any particular growth strategy when reallocating
308/// when full, nor when [`reserve`] is called. The current strategy is basic
309/// and it may prove desirable to use a non-constant growth factor. Whatever
310/// strategy is used will of course guarantee *O*(1) amortized [`push`].
311///
312/// `vec![x; n]`, `vec![a, b, c, d]`, and
313/// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
314/// with exactly the requested capacity. If <code>[len] == [capacity]</code>,
315/// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
316/// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
317///
318/// `Vec` will not specifically overwrite any data that is removed from it,
319/// but also won't specifically preserve it. Its uninitialized memory is
320/// scratch space that it may use however it wants. It will generally just do
321/// whatever is most efficient or otherwise easy to implement. Do not rely on
322/// removed data to be erased for security purposes. Even if you drop a `Vec`, its
323/// buffer may simply be reused by another allocation. Even if you zero a `Vec`'s memory
324/// first, that might not actually happen because the optimizer does not consider
325/// this a side-effect that must be preserved. There is one case which we will
326/// not break, however: using `unsafe` code to write to the excess capacity,
327/// and then increasing the length to match, is always valid.
328///
329/// Currently, `Vec` does not guarantee the order in which elements are dropped.
330/// The order has changed in the past and may change again.
331///
332/// [`get`]: ../../std/vec/struct.Vec.html#method.get
333/// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
334/// [`String`]: alloc_crate::string::String
335/// [`&str`]: type@str
336/// [`shrink_to_fit`]: Vec::shrink_to_fit
337/// [`shrink_to`]: Vec::shrink_to
338/// [capacity]: Vec::capacity
339/// [`capacity`]: Vec::capacity
340/// [mem::size_of::\<T>]: core::mem::size_of
341/// [len]: Vec::len
342/// [`len`]: Vec::len
343/// [`push`]: Vec::push
344/// [`insert`]: Vec::insert
345/// [`reserve`]: Vec::reserve
346/// [`MaybeUninit`]: core::mem::MaybeUninit
347/// [owned slice]: Box
348pub struct Vec<T, A: Allocator = Global> {
349 buf: RawVec<T, A>,
350 len: usize,
351}
352
353////////////////////////////////////////////////////////////////////////////////
354// Inherent methods
355////////////////////////////////////////////////////////////////////////////////
356
357impl<T> Vec<T> {
358 /// Constructs a new, empty `Vec<T>`.
359 ///
360 /// The vector will not allocate until elements are pushed onto it.
361 ///
362 /// # Examples
363 ///
364 /// ```
365 /// # #![allow(unused_mut)]
366 /// let mut vec: Vec<i32> = Vec::new();
367 /// ```
368 #[inline(always)]
369 #[must_use]
370 pub const fn new() -> Self {
371 Vec {
372 buf: RawVec::new(),
373 len: 0,
374 }
375 }
376
377 /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
378 ///
379 /// The vector will be able to hold at least `capacity` elements without
380 /// reallocating. This method is allowed to allocate for more elements than
381 /// `capacity`. If `capacity` is 0, the vector will not allocate.
382 ///
383 /// It is important to note that although the returned vector has the
384 /// minimum *capacity* specified, the vector will have a zero *length*. For
385 /// an explanation of the difference between length and capacity, see
386 /// *[Capacity and reallocation]*.
387 ///
388 /// If it is important to know the exact allocated capacity of a `Vec`,
389 /// always use the [`capacity`] method after construction.
390 ///
391 /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
392 /// and the capacity will always be `usize::MAX`.
393 ///
394 /// [Capacity and reallocation]: #capacity-and-reallocation
395 /// [`capacity`]: Vec::capacity
396 ///
397 /// # Panics
398 ///
399 /// Panics if the new capacity exceeds `isize::MAX` bytes.
400 ///
401 /// # Examples
402 ///
403 /// ```
404 /// let mut vec = Vec::with_capacity(10);
405 ///
406 /// // The vector contains no items, even though it has capacity for more
407 /// assert_eq!(vec.len(), 0);
408 /// assert!(vec.capacity() >= 10);
409 ///
410 /// // These are all done without reallocating...
411 /// for i in 0..10 {
412 /// vec.push(i);
413 /// }
414 /// assert_eq!(vec.len(), 10);
415 /// assert!(vec.capacity() >= 10);
416 ///
417 /// // ...but this may make the vector reallocate
418 /// vec.push(11);
419 /// assert_eq!(vec.len(), 11);
420 /// assert!(vec.capacity() >= 11);
421 ///
422 /// // A vector of a zero-sized type will always over-allocate, since no
423 /// // allocation is necessary
424 /// let vec_units = Vec::<()>::with_capacity(10);
425 /// assert_eq!(vec_units.capacity(), usize::MAX);
426 /// ```
427 #[cfg(not(no_global_oom_handling))]
428 #[inline(always)]
429 #[must_use]
430 pub fn with_capacity(capacity: usize) -> Self {
431 Self::with_capacity_in(capacity, Global)
432 }
433
434 /// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
435 ///
436 /// # Safety
437 ///
438 /// This is highly unsafe, due to the number of invariants that aren't
439 /// checked:
440 ///
441 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
442 /// (`T` having a less strict alignment is not sufficient, the alignment really
443 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
444 /// allocated and deallocated with the same layout.)
445 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
446 /// to be the same size as the pointer was allocated with. (Because similar to
447 /// alignment, [`dealloc`] must be called with the same layout `size`.)
448 /// * `length` needs to be less than or equal to `capacity`.
449 /// * The first `length` values must be properly initialized values of type `T`.
450 /// * `capacity` needs to be the capacity that the pointer was allocated with.
451 /// * The allocated size in bytes must be no larger than `isize::MAX`.
452 /// See the safety documentation of [`pointer::offset`](https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.offset).
453 ///
454 /// These requirements are always upheld by any `ptr` that has been allocated
455 /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
456 /// upheld.
457 ///
458 /// Violating these may cause problems like corrupting the allocator's
459 /// internal data structures. For example it is normally **not** safe
460 /// to build a `Vec<u8>` from a pointer to a C `char` array with length
461 /// `size_t`, doing so is only safe if the array was initially allocated by
462 /// a `Vec` or `String`.
463 /// It's also not safe to build one from a `Vec<u16>` and its length, because
464 /// the allocator cares about the alignment, and these two types have different
465 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
466 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
467 /// these issues, it is often preferable to do casting/transmuting using
468 /// [`slice::from_raw_parts`] instead.
469 ///
470 /// The ownership of `ptr` is effectively transferred to the
471 /// `Vec<T>` which may then deallocate, reallocate or change the
472 /// contents of memory pointed to by the pointer at will. Ensure
473 /// that nothing else uses the pointer after calling this
474 /// function.
475 ///
476 /// [`String`]: alloc_crate::string::String
477 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
478 ///
479 /// # Examples
480 ///
481 /// ```
482 /// use std::ptr;
483 /// use std::mem;
484 ///
485 /// let v = vec![1, 2, 3];
486 ///
487 // FIXME Update this when vec_into_raw_parts is stabilized
488 /// // Prevent running `v`'s destructor so we are in complete control
489 /// // of the allocation.
490 /// let mut v = mem::ManuallyDrop::new(v);
491 ///
492 /// // Pull out the various important pieces of information about `v`
493 /// let p = v.as_mut_ptr();
494 /// let len = v.len();
495 /// let cap = v.capacity();
496 ///
497 /// unsafe {
498 /// // Overwrite memory with 4, 5, 6
499 /// for i in 0..len {
500 /// ptr::write(p.add(i), 4 + i);
501 /// }
502 ///
503 /// // Put everything back together into a Vec
504 /// let rebuilt = Vec::from_raw_parts(p, len, cap);
505 /// assert_eq!(rebuilt, [4, 5, 6]);
506 /// }
507 /// ```
508 ///
509 /// Using memory that was allocated elsewhere:
510 ///
511 /// ```rust
512 /// #![feature(allocator_api)]
513 ///
514 /// use std::alloc::{AllocError, Allocator, Global, Layout};
515 ///
516 /// fn main() {
517 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
518 ///
519 /// let vec = unsafe {
520 /// let mem = match Global.allocate(layout) {
521 /// Ok(mem) => mem.cast::<u32>().as_ptr(),
522 /// Err(AllocError) => return,
523 /// };
524 ///
525 /// mem.write(1_000_000);
526 ///
527 /// Vec::from_raw_parts_in(mem, 1, 16, Global)
528 /// };
529 ///
530 /// assert_eq!(vec, &[1_000_000]);
531 /// assert_eq!(vec.capacity(), 16);
532 /// }
533 /// ```
534 #[inline(always)]
535 pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
536 unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
537 }
538}
539
540impl<T, A: Allocator> Vec<T, A> {
541 /// Constructs a new, empty `Vec<T, A>`.
542 ///
543 /// The vector will not allocate until elements are pushed onto it.
544 ///
545 /// # Examples
546 ///
547 /// ```
548 /// use std::alloc::System;
549 ///
550 /// # #[allow(unused_mut)]
551 /// let mut vec: Vec<i32, _> = Vec::new_in(System);
552 /// ```
553 #[inline(always)]
554 pub const fn new_in(alloc: A) -> Self {
555 Vec {
556 buf: RawVec::new_in(alloc),
557 len: 0,
558 }
559 }
560
561 /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
562 /// with the provided allocator.
563 ///
564 /// The vector will be able to hold at least `capacity` elements without
565 /// reallocating. This method is allowed to allocate for more elements than
566 /// `capacity`. If `capacity` is 0, the vector will not allocate.
567 ///
568 /// It is important to note that although the returned vector has the
569 /// minimum *capacity* specified, the vector will have a zero *length*. For
570 /// an explanation of the difference between length and capacity, see
571 /// *[Capacity and reallocation]*.
572 ///
573 /// If it is important to know the exact allocated capacity of a `Vec`,
574 /// always use the [`capacity`] method after construction.
575 ///
576 /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
577 /// and the capacity will always be `usize::MAX`.
578 ///
579 /// [Capacity and reallocation]: #capacity-and-reallocation
580 /// [`capacity`]: Vec::capacity
581 ///
582 /// # Panics
583 ///
584 /// Panics if the new capacity exceeds `isize::MAX` bytes.
585 ///
586 /// # Examples
587 ///
588 /// ```
589 /// use std::alloc::System;
590 ///
591 /// let mut vec = Vec::with_capacity_in(10, System);
592 ///
593 /// // The vector contains no items, even though it has capacity for more
594 /// assert_eq!(vec.len(), 0);
595 /// assert_eq!(vec.capacity(), 10);
596 ///
597 /// // These are all done without reallocating...
598 /// for i in 0..10 {
599 /// vec.push(i);
600 /// }
601 /// assert_eq!(vec.len(), 10);
602 /// assert_eq!(vec.capacity(), 10);
603 ///
604 /// // ...but this may make the vector reallocate
605 /// vec.push(11);
606 /// assert_eq!(vec.len(), 11);
607 /// assert!(vec.capacity() >= 11);
608 ///
609 /// // A vector of a zero-sized type will always over-allocate, since no
610 /// // allocation is necessary
611 /// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
612 /// assert_eq!(vec_units.capacity(), usize::MAX);
613 /// ```
614 #[cfg(not(no_global_oom_handling))]
615 #[inline(always)]
616 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
617 Vec {
618 buf: RawVec::with_capacity_in(capacity, alloc),
619 len: 0,
620 }
621 }
622
623 /// Creates a `Vec<T, A>` directly from a pointer, a capacity, a length,
624 /// and an allocator.
625 ///
626 /// # Safety
627 ///
628 /// This is highly unsafe, due to the number of invariants that aren't
629 /// checked:
630 ///
631 /// * `T` needs to have the same alignment as what `ptr` was allocated with.
632 /// (`T` having a less strict alignment is not sufficient, the alignment really
633 /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
634 /// allocated and deallocated with the same layout.)
635 /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
636 /// to be the same size as the pointer was allocated with. (Because similar to
637 /// alignment, [`dealloc`] must be called with the same layout `size`.)
638 /// * `length` needs to be less than or equal to `capacity`.
639 /// * The first `length` values must be properly initialized values of type `T`.
640 /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
641 /// * The allocated size in bytes must be no larger than `isize::MAX`.
642 /// See the safety documentation of [`pointer::offset`](https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.offset).
643 ///
644 /// These requirements are always upheld by any `ptr` that has been allocated
645 /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
646 /// upheld.
647 ///
648 /// Violating these may cause problems like corrupting the allocator's
649 /// internal data structures. For example it is **not** safe
650 /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
651 /// It's also not safe to build one from a `Vec<u16>` and its length, because
652 /// the allocator cares about the alignment, and these two types have different
653 /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
654 /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
655 ///
656 /// The ownership of `ptr` is effectively transferred to the
657 /// `Vec<T>` which may then deallocate, reallocate or change the
658 /// contents of memory pointed to by the pointer at will. Ensure
659 /// that nothing else uses the pointer after calling this
660 /// function.
661 ///
662 /// [`String`]: alloc_crate::string::String
663 /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
664 /// [*fit*]: crate::alloc::Allocator#memory-fitting
665 ///
666 /// # Examples
667 ///
668 /// ```
669 /// use std::alloc::System;
670 ///
671 /// use std::ptr;
672 /// use std::mem;
673 ///
674 ///
675 /// # use allocator_api2::vec::Vec;
676 /// let mut v = Vec::with_capacity_in(3, System);
677 /// v.push(1);
678 /// v.push(2);
679 /// v.push(3);
680 ///
681 // FIXME Update this when vec_into_raw_parts is stabilized
682 /// // Prevent running `v`'s destructor so we are in complete control
683 /// // of the allocation.
684 /// let mut v = mem::ManuallyDrop::new(v);
685 ///
686 /// // Pull out the various important pieces of information about `v`
687 /// let p = v.as_mut_ptr();
688 /// let len = v.len();
689 /// let cap = v.capacity();
690 /// let alloc = v.allocator();
691 ///
692 /// unsafe {
693 /// // Overwrite memory with 4, 5, 6
694 /// for i in 0..len {
695 /// ptr::write(p.add(i), 4 + i);
696 /// }
697 ///
698 /// // Put everything back together into a Vec
699 /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
700 /// assert_eq!(rebuilt, [4, 5, 6]);
701 /// }
702 /// ```
703 ///
704 /// Using memory that was allocated elsewhere:
705 ///
706 /// ```rust
707 /// use std::alloc::{alloc, Layout};
708 ///
709 /// fn main() {
710 /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
711 /// let vec = unsafe {
712 /// let mem = alloc(layout).cast::<u32>();
713 /// if mem.is_null() {
714 /// return;
715 /// }
716 ///
717 /// mem.write(1_000_000);
718 ///
719 /// Vec::from_raw_parts(mem, 1, 16)
720 /// };
721 ///
722 /// assert_eq!(vec, &[1_000_000]);
723 /// assert_eq!(vec.capacity(), 16);
724 /// }
725 /// ```
726 #[inline(always)]
727 pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
728 unsafe {
729 Vec {
730 buf: RawVec::from_raw_parts_in(ptr, capacity, alloc),
731 len: length,
732 }
733 }
734 }
735
736 /// Decomposes a `Vec<T>` into its raw components.
737 ///
738 /// Returns the raw pointer to the underlying data, the length of
739 /// the vector (in elements), and the allocated capacity of the
740 /// data (in elements). These are the same arguments in the same
741 /// order as the arguments to [`from_raw_parts`].
742 ///
743 /// After calling this function, the caller is responsible for the
744 /// memory previously managed by the `Vec`. The only way to do
745 /// this is to convert the raw pointer, length, and capacity back
746 /// into a `Vec` with the [`from_raw_parts`] function, allowing
747 /// the destructor to perform the cleanup.
748 ///
749 /// [`from_raw_parts`]: Vec::from_raw_parts
750 ///
751 /// # Examples
752 ///
753 /// ```
754 /// #![feature(vec_into_raw_parts)]
755 /// let v: Vec<i32> = vec![-1, 0, 1];
756 ///
757 /// let (ptr, len, cap) = v.into_raw_parts();
758 ///
759 /// let rebuilt = unsafe {
760 /// // We can now make changes to the components, such as
761 /// // transmuting the raw pointer to a compatible type.
762 /// let ptr = ptr as *mut u32;
763 ///
764 /// Vec::from_raw_parts(ptr, len, cap)
765 /// };
766 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
767 /// ```
768 pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
769 let mut me = ManuallyDrop::new(self);
770 (me.as_mut_ptr(), me.len(), me.capacity())
771 }
772
773 /// Decomposes a `Vec<T>` into its raw components.
774 ///
775 /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
776 /// the allocated capacity of the data (in elements), and the allocator. These are the same
777 /// arguments in the same order as the arguments to [`from_raw_parts_in`].
778 ///
779 /// After calling this function, the caller is responsible for the
780 /// memory previously managed by the `Vec`. The only way to do
781 /// this is to convert the raw pointer, length, and capacity back
782 /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
783 /// the destructor to perform the cleanup.
784 ///
785 /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
786 ///
787 /// # Examples
788 ///
789 /// ```
790 /// #![feature(allocator_api, vec_into_raw_parts)]
791 ///
792 /// use std::alloc::System;
793 ///
794 /// let mut v: Vec<i32, System> = Vec::new_in(System);
795 /// v.push(-1);
796 /// v.push(0);
797 /// v.push(1);
798 ///
799 /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
800 ///
801 /// let rebuilt = unsafe {
802 /// // We can now make changes to the components, such as
803 /// // transmuting the raw pointer to a compatible type.
804 /// let ptr = ptr as *mut u32;
805 ///
806 /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
807 /// };
808 /// assert_eq!(rebuilt, [4294967295, 0, 1]);
809 /// ```
810 // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
811 pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
812 let mut me = ManuallyDrop::new(self);
813 let len = me.len();
814 let capacity = me.capacity();
815 let ptr = me.as_mut_ptr();
816 let alloc = unsafe { ptr::read(me.allocator()) };
817 (ptr, len, capacity, alloc)
818 }
819
820 /// Returns the total number of elements the vector can hold without
821 /// reallocating.
822 ///
823 /// # Examples
824 ///
825 /// ```
826 /// let mut vec: Vec<i32> = Vec::with_capacity(10);
827 /// vec.push(42);
828 /// assert_eq!(vec.capacity(), 10);
829 /// ```
830 #[inline(always)]
831 pub fn capacity(&self) -> usize {
832 self.buf.capacity()
833 }
834
835 /// Reserves capacity for at least `additional` more elements to be inserted
836 /// in the given `Vec<T>`. The collection may reserve more space to
837 /// speculatively avoid frequent reallocations. After calling `reserve`,
838 /// capacity will be greater than or equal to `self.len() + additional`.
839 /// Does nothing if capacity is already sufficient.
840 ///
841 /// # Panics
842 ///
843 /// Panics if the new capacity exceeds `isize::MAX` bytes.
844 ///
845 /// # Examples
846 ///
847 /// ```
848 /// let mut vec = vec![1];
849 /// vec.reserve(10);
850 /// assert!(vec.capacity() >= 11);
851 /// ```
852 #[cfg(not(no_global_oom_handling))]
853 #[inline(always)]
854 pub fn reserve(&mut self, additional: usize) {
855 self.buf.reserve(self.len, additional);
856 }
857
858 /// Reserves the minimum capacity for at least `additional` more elements to
859 /// be inserted in the given `Vec<T>`. Unlike [`reserve`], this will not
860 /// deliberately over-allocate to speculatively avoid frequent allocations.
861 /// After calling `reserve_exact`, capacity will be greater than or equal to
862 /// `self.len() + additional`. Does nothing if the capacity is already
863 /// sufficient.
864 ///
865 /// Note that the allocator may give the collection more space than it
866 /// requests. Therefore, capacity can not be relied upon to be precisely
867 /// minimal. Prefer [`reserve`] if future insertions are expected.
868 ///
869 /// [`reserve`]: Vec::reserve
870 ///
871 /// # Panics
872 ///
873 /// Panics if the new capacity exceeds `isize::MAX` bytes.
874 ///
875 /// # Examples
876 ///
877 /// ```
878 /// let mut vec = vec![1];
879 /// vec.reserve_exact(10);
880 /// assert!(vec.capacity() >= 11);
881 /// ```
882 #[cfg(not(no_global_oom_handling))]
883 #[inline(always)]
884 pub fn reserve_exact(&mut self, additional: usize) {
885 self.buf.reserve_exact(self.len, additional);
886 }
887
888 /// Tries to reserve capacity for at least `additional` more elements to be inserted
889 /// in the given `Vec<T>`. The collection may reserve more space to speculatively avoid
890 /// frequent reallocations. After calling `try_reserve`, capacity will be
891 /// greater than or equal to `self.len() + additional` if it returns
892 /// `Ok(())`. Does nothing if capacity is already sufficient. This method
893 /// preserves the contents even if an error occurs.
894 ///
895 /// # Errors
896 ///
897 /// If the capacity overflows, or the allocator reports a failure, then an error
898 /// is returned.
899 ///
900 /// # Examples
901 ///
902 /// ```
903 /// use allocator_api2::collections::TryReserveError;
904 ///
905 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
906 /// let mut output = Vec::new();
907 ///
908 /// // Pre-reserve the memory, exiting if we can't
909 /// output.try_reserve(data.len())?;
910 ///
911 /// // Now we know this can't OOM in the middle of our complex work
912 /// output.extend(data.iter().map(|&val| {
913 /// val * 2 + 5 // very complicated
914 /// }));
915 ///
916 /// Ok(output)
917 /// }
918 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
919 /// ```
920 #[inline(always)]
921 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
922 self.buf.try_reserve(self.len, additional)
923 }
924
925 /// Tries to reserve the minimum capacity for at least `additional`
926 /// elements to be inserted in the given `Vec<T>`. Unlike [`try_reserve`],
927 /// this will not deliberately over-allocate to speculatively avoid frequent
928 /// allocations. After calling `try_reserve_exact`, capacity will be greater
929 /// than or equal to `self.len() + additional` if it returns `Ok(())`.
930 /// Does nothing if the capacity is already sufficient.
931 ///
932 /// Note that the allocator may give the collection more space than it
933 /// requests. Therefore, capacity can not be relied upon to be precisely
934 /// minimal. Prefer [`try_reserve`] if future insertions are expected.
935 ///
936 /// [`try_reserve`]: Vec::try_reserve
937 ///
938 /// # Errors
939 ///
940 /// If the capacity overflows, or the allocator reports a failure, then an error
941 /// is returned.
942 ///
943 /// # Examples
944 ///
945 /// ```
946 /// use allocator_api2::collections::TryReserveError;
947 ///
948 /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
949 /// let mut output = Vec::new();
950 ///
951 /// // Pre-reserve the memory, exiting if we can't
952 /// output.try_reserve_exact(data.len())?;
953 ///
954 /// // Now we know this can't OOM in the middle of our complex work
955 /// output.extend(data.iter().map(|&val| {
956 /// val * 2 + 5 // very complicated
957 /// }));
958 ///
959 /// Ok(output)
960 /// }
961 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
962 /// ```
963 #[inline(always)]
964 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
965 self.buf.try_reserve_exact(self.len, additional)
966 }
967
968 /// Shrinks the capacity of the vector as much as possible.
969 ///
970 /// It will drop down as close as possible to the length but the allocator
971 /// may still inform the vector that there is space for a few more elements.
972 ///
973 /// # Examples
974 ///
975 /// ```
976 /// let mut vec = Vec::with_capacity(10);
977 /// vec.extend([1, 2, 3]);
978 /// assert_eq!(vec.capacity(), 10);
979 /// vec.shrink_to_fit();
980 /// assert!(vec.capacity() >= 3);
981 /// ```
982 #[cfg(not(no_global_oom_handling))]
983 #[inline(always)]
984 pub fn shrink_to_fit(&mut self) {
985 // The capacity is never less than the length, and there's nothing to do when
986 // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
987 // by only calling it with a greater capacity.
988 if self.capacity() > self.len {
989 self.buf.shrink_to_fit(self.len);
990 }
991 }
992
993 /// Shrinks the capacity of the vector with a lower bound.
994 ///
995 /// The capacity will remain at least as large as both the length
996 /// and the supplied value.
997 ///
998 /// If the current capacity is less than the lower limit, this is a no-op.
999 ///
1000 /// # Examples
1001 ///
1002 /// ```
1003 /// let mut vec = Vec::with_capacity(10);
1004 /// vec.extend([1, 2, 3]);
1005 /// assert_eq!(vec.capacity(), 10);
1006 /// vec.shrink_to(4);
1007 /// assert!(vec.capacity() >= 4);
1008 /// vec.shrink_to(0);
1009 /// assert!(vec.capacity() >= 3);
1010 /// ```
1011 #[cfg(not(no_global_oom_handling))]
1012 #[inline(always)]
1013 pub fn shrink_to(&mut self, min_capacity: usize) {
1014 if self.capacity() > min_capacity {
1015 self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
1016 }
1017 }
1018
1019 /// Converts the vector into [`Box<[T]>`][owned slice].
1020 ///
1021 /// If the vector has excess capacity, its items will be moved into a
1022 /// newly-allocated buffer with exactly the right capacity.
1023 ///
1024 /// [owned slice]: Box
1025 ///
1026 /// # Examples
1027 ///
1028 /// ```
1029 /// let v = vec![1, 2, 3];
1030 ///
1031 /// let slice = v.into_boxed_slice();
1032 /// ```
1033 ///
1034 /// Any excess capacity is removed:
1035 ///
1036 /// ```
1037 /// let mut vec = Vec::with_capacity(10);
1038 /// vec.extend([1, 2, 3]);
1039 ///
1040 /// assert_eq!(vec.capacity(), 10);
1041 /// let slice = vec.into_boxed_slice();
1042 /// assert_eq!(slice.into_vec().capacity(), 3);
1043 /// ```
1044 #[cfg(not(no_global_oom_handling))]
1045 #[inline(always)]
1046 pub fn into_boxed_slice(mut self) -> Box<[T], A> {
1047 unsafe {
1048 self.shrink_to_fit();
1049 let me = ManuallyDrop::new(self);
1050 let buf = ptr::read(&me.buf);
1051 let len = me.len();
1052 Box::<[mem::MaybeUninit<T>], A>::assume_init(buf.into_box(len))
1053 }
1054 }
1055
1056 /// Shortens the vector, keeping the first `len` elements and dropping
1057 /// the rest.
1058 ///
1059 /// If `len` is greater than the vector's current length, this has no
1060 /// effect.
1061 ///
1062 /// The [`drain`] method can emulate `truncate`, but causes the excess
1063 /// elements to be returned instead of dropped.
1064 ///
1065 /// Note that this method has no effect on the allocated capacity
1066 /// of the vector.
1067 ///
1068 /// # Examples
1069 ///
1070 /// Truncating a five element vector to two elements:
1071 ///
1072 /// ```
1073 /// let mut vec = vec![1, 2, 3, 4, 5];
1074 /// vec.truncate(2);
1075 /// assert_eq!(vec, [1, 2]);
1076 /// ```
1077 ///
1078 /// No truncation occurs when `len` is greater than the vector's current
1079 /// length:
1080 ///
1081 /// ```
1082 /// let mut vec = vec![1, 2, 3];
1083 /// vec.truncate(8);
1084 /// assert_eq!(vec, [1, 2, 3]);
1085 /// ```
1086 ///
1087 /// Truncating when `len == 0` is equivalent to calling the [`clear`]
1088 /// method.
1089 ///
1090 /// ```
1091 /// let mut vec = vec![1, 2, 3];
1092 /// vec.truncate(0);
1093 /// assert_eq!(vec, []);
1094 /// ```
1095 ///
1096 /// [`clear`]: Vec::clear
1097 /// [`drain`]: Vec::drain
1098 #[inline(always)]
1099 pub fn truncate(&mut self, len: usize) {
1100 // This is safe because:
1101 //
1102 // * the slice passed to `drop_in_place` is valid; the `len > self.len`
1103 // case avoids creating an invalid slice, and
1104 // * the `len` of the vector is shrunk before calling `drop_in_place`,
1105 // such that no value will be dropped twice in case `drop_in_place`
1106 // were to panic once (if it panics twice, the program aborts).
1107 unsafe {
1108 // Note: It's intentional that this is `>` and not `>=`.
1109 // Changing it to `>=` has negative performance
1110 // implications in some cases. See #78884 for more.
1111 if len > self.len {
1112 return;
1113 }
1114 let remaining_len = self.len - len;
1115 let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
1116 self.len = len;
1117 ptr::drop_in_place(s);
1118 }
1119 }
1120
1121 /// Extracts a slice containing the entire vector.
1122 ///
1123 /// Equivalent to `&s[..]`.
1124 ///
1125 /// # Examples
1126 ///
1127 /// ```
1128 /// use std::io::{self, Write};
1129 /// let buffer = vec![1, 2, 3, 5, 8];
1130 /// io::sink().write(buffer.as_slice()).unwrap();
1131 /// ```
1132 #[inline(always)]
1133 pub fn as_slice(&self) -> &[T] {
1134 self
1135 }
1136
1137 /// Extracts a mutable slice of the entire vector.
1138 ///
1139 /// Equivalent to `&mut s[..]`.
1140 ///
1141 /// # Examples
1142 ///
1143 /// ```
1144 /// use std::io::{self, Read};
1145 /// let mut buffer = vec![0; 3];
1146 /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
1147 /// ```
1148 #[inline(always)]
1149 pub fn as_mut_slice(&mut self) -> &mut [T] {
1150 self
1151 }
1152
1153 /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
1154 /// valid for zero sized reads if the vector didn't allocate.
1155 ///
1156 /// The caller must ensure that the vector outlives the pointer this
1157 /// function returns, or else it will end up pointing to garbage.
1158 /// Modifying the vector may cause its buffer to be reallocated,
1159 /// which would also make any pointers to it invalid.
1160 ///
1161 /// The caller must also ensure that the memory the pointer (non-transitively) points to
1162 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
1163 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
1164 ///
1165 /// # Examples
1166 ///
1167 /// ```
1168 /// let x = vec![1, 2, 4];
1169 /// let x_ptr = x.as_ptr();
1170 ///
1171 /// unsafe {
1172 /// for i in 0..x.len() {
1173 /// assert_eq!(*x_ptr.add(i), 1 << i);
1174 /// }
1175 /// }
1176 /// ```
1177 ///
1178 /// [`as_mut_ptr`]: Vec::as_mut_ptr
1179 #[inline(always)]
1180 pub fn as_ptr(&self) -> *const T {
1181 // We shadow the slice method of the same name to avoid going through
1182 // `deref`, which creates an intermediate reference.
1183 let ptr = self.buf.ptr();
1184 unsafe {
1185 assume(!ptr.is_null());
1186 }
1187 ptr
1188 }
1189
1190 /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
1191 /// raw pointer valid for zero sized reads if the vector didn't allocate.
1192 ///
1193 /// The caller must ensure that the vector outlives the pointer this
1194 /// function returns, or else it will end up pointing to garbage.
1195 /// Modifying the vector may cause its buffer to be reallocated,
1196 /// which would also make any pointers to it invalid.
1197 ///
1198 /// # Examples
1199 ///
1200 /// ```
1201 /// // Allocate vector big enough for 4 elements.
1202 /// let size = 4;
1203 /// let mut x: Vec<i32> = Vec::with_capacity(size);
1204 /// let x_ptr = x.as_mut_ptr();
1205 ///
1206 /// // Initialize elements via raw pointer writes, then set length.
1207 /// unsafe {
1208 /// for i in 0..size {
1209 /// *x_ptr.add(i) = i as i32;
1210 /// }
1211 /// x.set_len(size);
1212 /// }
1213 /// assert_eq!(&*x, &[0, 1, 2, 3]);
1214 /// ```
1215 #[inline(always)]
1216 pub fn as_mut_ptr(&mut self) -> *mut T {
1217 // We shadow the slice method of the same name to avoid going through
1218 // `deref_mut`, which creates an intermediate reference.
1219 let ptr = self.buf.ptr();
1220 unsafe {
1221 assume(!ptr.is_null());
1222 }
1223 ptr
1224 }
1225
1226 /// Returns a reference to the underlying allocator.
1227 #[inline(always)]
1228 pub fn allocator(&self) -> &A {
1229 self.buf.allocator()
1230 }
1231
1232 /// Forces the length of the vector to `new_len`.
1233 ///
1234 /// This is a low-level operation that maintains none of the normal
1235 /// invariants of the type. Normally changing the length of a vector
1236 /// is done using one of the safe operations instead, such as
1237 /// [`truncate`], [`resize`], [`extend`], or [`clear`].
1238 ///
1239 /// [`truncate`]: Vec::truncate
1240 /// [`resize`]: Vec::resize
1241 /// [`extend`]: Extend::extend
1242 /// [`clear`]: Vec::clear
1243 ///
1244 /// # Safety
1245 ///
1246 /// - `new_len` must be less than or equal to [`capacity()`].
1247 /// - The elements at `old_len..new_len` must be initialized.
1248 ///
1249 /// [`capacity()`]: Vec::capacity
1250 ///
1251 /// # Examples
1252 ///
1253 /// This method can be useful for situations in which the vector
1254 /// is serving as a buffer for other code, particularly over FFI:
1255 ///
1256 /// ```no_run
1257 /// # #![allow(dead_code)]
1258 /// # // This is just a minimal skeleton for the doc example;
1259 /// # // don't use this as a starting point for a real library.
1260 /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
1261 /// # const Z_OK: i32 = 0;
1262 /// # extern "C" {
1263 /// # fn deflateGetDictionary(
1264 /// # strm: *mut std::ffi::c_void,
1265 /// # dictionary: *mut u8,
1266 /// # dictLength: *mut usize,
1267 /// # ) -> i32;
1268 /// # }
1269 /// # impl StreamWrapper {
1270 /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
1271 /// // Per the FFI method's docs, "32768 bytes is always enough".
1272 /// let mut dict = Vec::with_capacity(32_768);
1273 /// let mut dict_length = 0;
1274 /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
1275 /// // 1. `dict_length` elements were initialized.
1276 /// // 2. `dict_length` <= the capacity (32_768)
1277 /// // which makes `set_len` safe to call.
1278 /// unsafe {
1279 /// // Make the FFI call...
1280 /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
1281 /// if r == Z_OK {
1282 /// // ...and update the length to what was initialized.
1283 /// dict.set_len(dict_length);
1284 /// Some(dict)
1285 /// } else {
1286 /// None
1287 /// }
1288 /// }
1289 /// }
1290 /// # }
1291 /// ```
1292 ///
1293 /// While the following example is sound, there is a memory leak since
1294 /// the inner vectors were not freed prior to the `set_len` call:
1295 ///
1296 /// ```
1297 /// let mut vec = vec![vec![1, 0, 0],
1298 /// vec![0, 1, 0],
1299 /// vec![0, 0, 1]];
1300 /// // SAFETY:
1301 /// // 1. `old_len..0` is empty so no elements need to be initialized.
1302 /// // 2. `0 <= capacity` always holds whatever `capacity` is.
1303 /// unsafe {
1304 /// vec.set_len(0);
1305 /// }
1306 /// ```
1307 ///
1308 /// Normally, here, one would use [`clear`] instead to correctly drop
1309 /// the contents and thus not leak memory.
1310 #[inline(always)]
1311 pub unsafe fn set_len(&mut self, new_len: usize) {
1312 debug_assert!(new_len <= self.capacity());
1313
1314 self.len = new_len;
1315 }
1316
1317 /// Removes an element from the vector and returns it.
1318 ///
1319 /// The removed element is replaced by the last element of the vector.
1320 ///
1321 /// This does not preserve ordering, but is *O*(1).
1322 /// If you need to preserve the element order, use [`remove`] instead.
1323 ///
1324 /// [`remove`]: Vec::remove
1325 ///
1326 /// # Panics
1327 ///
1328 /// Panics if `index` is out of bounds.
1329 ///
1330 /// # Examples
1331 ///
1332 /// ```
1333 /// let mut v = vec!["foo", "bar", "baz", "qux"];
1334 ///
1335 /// assert_eq!(v.swap_remove(1), "bar");
1336 /// assert_eq!(v, ["foo", "qux", "baz"]);
1337 ///
1338 /// assert_eq!(v.swap_remove(0), "foo");
1339 /// assert_eq!(v, ["baz", "qux"]);
1340 /// ```
1341 #[inline(always)]
1342 pub fn swap_remove(&mut self, index: usize) -> T {
1343 #[cold]
1344 #[inline(never)]
1345 fn assert_failed(index: usize, len: usize) -> ! {
1346 panic!(
1347 "swap_remove index (is {}) should be < len (is {})",
1348 index, len
1349 );
1350 }
1351
1352 let len = self.len();
1353 if index >= len {
1354 assert_failed(index, len);
1355 }
1356 unsafe {
1357 // We replace self[index] with the last element. Note that if the
1358 // bounds check above succeeds there must be a last element (which
1359 // can be self[index] itself).
1360 let value = ptr::read(self.as_ptr().add(index));
1361 let base_ptr = self.as_mut_ptr();
1362 ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
1363 self.set_len(len - 1);
1364 value
1365 }
1366 }
1367
1368 /// Inserts an element at position `index` within the vector, shifting all
1369 /// elements after it to the right.
1370 ///
1371 /// # Panics
1372 ///
1373 /// Panics if `index > len`.
1374 ///
1375 /// # Examples
1376 ///
1377 /// ```
1378 /// let mut vec = vec![1, 2, 3];
1379 /// vec.insert(1, 4);
1380 /// assert_eq!(vec, [1, 4, 2, 3]);
1381 /// vec.insert(4, 5);
1382 /// assert_eq!(vec, [1, 4, 2, 3, 5]);
1383 /// ```
1384 #[cfg(not(no_global_oom_handling))]
1385 pub fn insert(&mut self, index: usize, element: T) {
1386 #[cold]
1387 #[inline(never)]
1388 fn assert_failed(index: usize, len: usize) -> ! {
1389 panic!(
1390 "insertion index (is {}) should be <= len (is {})",
1391 index, len
1392 );
1393 }
1394
1395 let len = self.len();
1396
1397 // space for the new element
1398 if len == self.buf.capacity() {
1399 self.reserve(1);
1400 }
1401
1402 unsafe {
1403 // infallible
1404 // The spot to put the new value
1405 {
1406 let p = self.as_mut_ptr().add(index);
1407 match cmp::Ord::cmp(&index, &len) {
1408 Ordering::Less => {
1409 // Shift everything over to make space. (Duplicating the
1410 // `index`th element into two consecutive places.)
1411 ptr::copy(p, p.add(1), len - index);
1412 }
1413 Ordering::Equal => {
1414 // No elements need shifting.
1415 }
1416 Ordering::Greater => {
1417 assert_failed(index, len);
1418 }
1419 }
1420 // Write it in, overwriting the first copy of the `index`th
1421 // element.
1422 ptr::write(p, element);
1423 }
1424 self.set_len(len + 1);
1425 }
1426 }
1427
1428 /// Removes and returns the element at position `index` within the vector,
1429 /// shifting all elements after it to the left.
1430 ///
1431 /// Note: Because this shifts over the remaining elements, it has a
1432 /// worst-case performance of *O*(*n*). If you don't need the order of elements
1433 /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
1434 /// elements from the beginning of the `Vec`, consider using
1435 /// [`VecDeque::pop_front`] instead.
1436 ///
1437 /// [`swap_remove`]: Vec::swap_remove
1438 /// [`VecDeque::pop_front`]: alloc_crate::collections::VecDeque::pop_front
1439 ///
1440 /// # Panics
1441 ///
1442 /// Panics if `index` is out of bounds.
1443 ///
1444 /// # Examples
1445 ///
1446 /// ```
1447 /// let mut v = vec![1, 2, 3];
1448 /// assert_eq!(v.remove(1), 2);
1449 /// assert_eq!(v, [1, 3]);
1450 /// ```
1451 #[track_caller]
1452 #[inline(always)]
1453 pub fn remove(&mut self, index: usize) -> T {
1454 #[cold]
1455 #[inline(never)]
1456 #[track_caller]
1457 fn assert_failed(index: usize, len: usize) -> ! {
1458 panic!("removal index (is {}) should be < len (is {})", index, len);
1459 }
1460
1461 let len = self.len();
1462 if index >= len {
1463 assert_failed(index, len);
1464 }
1465 unsafe {
1466 // infallible
1467 let ret;
1468 {
1469 // the place we are taking from.
1470 let ptr = self.as_mut_ptr().add(index);
1471 // copy it out, unsafely having a copy of the value on
1472 // the stack and in the vector at the same time.
1473 ret = ptr::read(ptr);
1474
1475 // Shift everything down to fill in that spot.
1476 ptr::copy(ptr.add(1), ptr, len - index - 1);
1477 }
1478 self.set_len(len - 1);
1479 ret
1480 }
1481 }
1482
1483 /// Retains only the elements specified by the predicate.
1484 ///
1485 /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
1486 /// This method operates in place, visiting each element exactly once in the
1487 /// original order, and preserves the order of the retained elements.
1488 ///
1489 /// # Examples
1490 ///
1491 /// ```
1492 /// let mut vec = vec![1, 2, 3, 4];
1493 /// vec.retain(|&x| x % 2 == 0);
1494 /// assert_eq!(vec, [2, 4]);
1495 /// ```
1496 ///
1497 /// Because the elements are visited exactly once in the original order,
1498 /// external state may be used to decide which elements to keep.
1499 ///
1500 /// ```
1501 /// let mut vec = vec![1, 2, 3, 4, 5];
1502 /// let keep = [false, true, true, false, true];
1503 /// let mut iter = keep.iter();
1504 /// vec.retain(|_| *iter.next().unwrap());
1505 /// assert_eq!(vec, [2, 3, 5]);
1506 /// ```
1507 #[inline(always)]
1508 pub fn retain<F>(&mut self, mut f: F)
1509 where
1510 F: FnMut(&T) -> bool,
1511 {
1512 self.retain_mut(|elem| f(elem));
1513 }
1514
1515 /// Retains only the elements specified by the predicate, passing a mutable reference to it.
1516 ///
1517 /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
1518 /// This method operates in place, visiting each element exactly once in the
1519 /// original order, and preserves the order of the retained elements.
1520 ///
1521 /// # Examples
1522 ///
1523 /// ```
1524 /// let mut vec = vec![1, 2, 3, 4];
1525 /// vec.retain_mut(|x| if *x <= 3 {
1526 /// *x += 1;
1527 /// true
1528 /// } else {
1529 /// false
1530 /// });
1531 /// assert_eq!(vec, [2, 3, 4]);
1532 /// ```
1533 #[inline]
1534 pub fn retain_mut<F>(&mut self, mut f: F)
1535 where
1536 F: FnMut(&mut T) -> bool,
1537 {
1538 let original_len = self.len();
1539 // Avoid double drop if the drop guard is not executed,
1540 // since we may make some holes during the process.
1541 unsafe { self.set_len(0) };
1542
1543 // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
1544 // |<- processed len ->| ^- next to check
1545 // |<- deleted cnt ->|
1546 // |<- original_len ->|
1547 // Kept: Elements which predicate returns true on.
1548 // Hole: Moved or dropped element slot.
1549 // Unchecked: Unchecked valid elements.
1550 //
1551 // This drop guard will be invoked when predicate or `drop` of element panicked.
1552 // It shifts unchecked elements to cover holes and `set_len` to the correct length.
1553 // In cases when predicate and `drop` never panick, it will be optimized out.
1554 struct BackshiftOnDrop<'a, T, A: Allocator> {
1555 v: &'a mut Vec<T, A>,
1556 processed_len: usize,
1557 deleted_cnt: usize,
1558 original_len: usize,
1559 }
1560
1561 impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
1562 fn drop(&mut self) {
1563 if self.deleted_cnt > 0 {
1564 // SAFETY: Trailing unchecked items must be valid since we never touch them.
1565 unsafe {
1566 ptr::copy(
1567 self.v.as_ptr().add(self.processed_len),
1568 self.v
1569 .as_mut_ptr()
1570 .add(self.processed_len - self.deleted_cnt),
1571 self.original_len - self.processed_len,
1572 );
1573 }
1574 }
1575 // SAFETY: After filling holes, all items are in contiguous memory.
1576 unsafe {
1577 self.v.set_len(self.original_len - self.deleted_cnt);
1578 }
1579 }
1580 }
1581
1582 let mut g = BackshiftOnDrop {
1583 v: self,
1584 processed_len: 0,
1585 deleted_cnt: 0,
1586 original_len,
1587 };
1588
1589 fn process_loop<F, T, A: Allocator, const DELETED: bool>(
1590 original_len: usize,
1591 f: &mut F,
1592 g: &mut BackshiftOnDrop<'_, T, A>,
1593 ) where
1594 F: FnMut(&mut T) -> bool,
1595 {
1596 while g.processed_len != original_len {
1597 // SAFETY: Unchecked element must be valid.
1598 let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
1599 if !f(cur) {
1600 // Advance early to avoid double drop if `drop_in_place` panicked.
1601 g.processed_len += 1;
1602 g.deleted_cnt += 1;
1603 // SAFETY: We never touch this element again after dropped.
1604 unsafe { ptr::drop_in_place(cur) };
1605 // We already advanced the counter.
1606 if DELETED {
1607 continue;
1608 } else {
1609 break;
1610 }
1611 }
1612 if DELETED {
1613 // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
1614 // We use copy for move, and never touch this element again.
1615 unsafe {
1616 let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
1617 ptr::copy_nonoverlapping(cur, hole_slot, 1);
1618 }
1619 }
1620 g.processed_len += 1;
1621 }
1622 }
1623
1624 // Stage 1: Nothing was deleted.
1625 process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
1626
1627 // Stage 2: Some elements were deleted.
1628 process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
1629
1630 // All item are processed. This can be optimized to `set_len` by LLVM.
1631 drop(g);
1632 }
1633
1634 /// Removes all but the first of consecutive elements in the vector that resolve to the same
1635 /// key.
1636 ///
1637 /// If the vector is sorted, this removes all duplicates.
1638 ///
1639 /// # Examples
1640 ///
1641 /// ```
1642 /// let mut vec = vec![10, 20, 21, 30, 20];
1643 ///
1644 /// vec.dedup_by_key(|i| *i / 10);
1645 ///
1646 /// assert_eq!(vec, [10, 20, 30, 20]);
1647 /// ```
1648 #[inline(always)]
1649 pub fn dedup_by_key<F, K>(&mut self, mut key: F)
1650 where
1651 F: FnMut(&mut T) -> K,
1652 K: PartialEq,
1653 {
1654 self.dedup_by(|a, b| key(a) == key(b))
1655 }
1656
1657 /// Removes all but the first of consecutive elements in the vector satisfying a given equality
1658 /// relation.
1659 ///
1660 /// The `same_bucket` function is passed references to two elements from the vector and
1661 /// must determine if the elements compare equal. The elements are passed in opposite order
1662 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
1663 ///
1664 /// If the vector is sorted, this removes all duplicates.
1665 ///
1666 /// # Examples
1667 ///
1668 /// ```
1669 /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
1670 ///
1671 /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
1672 ///
1673 /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
1674 /// ```
1675 #[inline]
1676 pub fn dedup_by<F>(&mut self, mut same_bucket: F)
1677 where
1678 F: FnMut(&mut T, &mut T) -> bool,
1679 {
1680 let len = self.len();
1681 if len <= 1 {
1682 return;
1683 }
1684
1685 /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
1686 struct FillGapOnDrop<'a, T, A: Allocator> {
1687 /* Offset of the element we want to check if it is duplicate */
1688 read: usize,
1689
1690 /* Offset of the place where we want to place the non-duplicate
1691 * when we find it. */
1692 write: usize,
1693
1694 /* The Vec that would need correction if `same_bucket` panicked */
1695 vec: &'a mut Vec<T, A>,
1696 }
1697
1698 impl<'a, T, A: Allocator> Drop for FillGapOnDrop<'a, T, A> {
1699 fn drop(&mut self) {
1700 /* This code gets executed when `same_bucket` panics */
1701
1702 /* SAFETY: invariant guarantees that `read - write`
1703 * and `len - read` never overflow and that the copy is always
1704 * in-bounds. */
1705 unsafe {
1706 let ptr = self.vec.as_mut_ptr();
1707 let len = self.vec.len();
1708
1709 /* How many items were left when `same_bucket` panicked.
1710 * Basically vec[read..].len() */
1711 let items_left = len.wrapping_sub(self.read);
1712
1713 /* Pointer to first item in vec[write..write+items_left] slice */
1714 let dropped_ptr = ptr.add(self.write);
1715 /* Pointer to first item in vec[read..] slice */
1716 let valid_ptr = ptr.add(self.read);
1717
1718 /* Copy `vec[read..]` to `vec[write..write+items_left]`.
1719 * The slices can overlap, so `copy_nonoverlapping` cannot be used */
1720 ptr::copy(valid_ptr, dropped_ptr, items_left);
1721
1722 /* How many items have been already dropped
1723 * Basically vec[read..write].len() */
1724 let dropped = self.read.wrapping_sub(self.write);
1725
1726 self.vec.set_len(len - dropped);
1727 }
1728 }
1729 }
1730
1731 let mut gap = FillGapOnDrop {
1732 read: 1,
1733 write: 1,
1734 vec: self,
1735 };
1736 let ptr = gap.vec.as_mut_ptr();
1737
1738 /* Drop items while going through Vec, it should be more efficient than
1739 * doing slice partition_dedup + truncate */
1740
1741 /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
1742 * are always in-bounds and read_ptr never aliases prev_ptr */
1743 unsafe {
1744 while gap.read < len {
1745 let read_ptr = ptr.add(gap.read);
1746 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
1747
1748 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
1749 // Increase `gap.read` now since the drop may panic.
1750 gap.read += 1;
1751 /* We have found duplicate, drop it in-place */
1752 ptr::drop_in_place(read_ptr);
1753 } else {
1754 let write_ptr = ptr.add(gap.write);
1755
1756 /* Because `read_ptr` can be equal to `write_ptr`, we either
1757 * have to use `copy` or conditional `copy_nonoverlapping`.
1758 * Looks like the first option is faster. */
1759 ptr::copy(read_ptr, write_ptr, 1);
1760
1761 /* We have filled that place, so go further */
1762 gap.write += 1;
1763 gap.read += 1;
1764 }
1765 }
1766
1767 /* Technically we could let `gap` clean up with its Drop, but
1768 * when `same_bucket` is guaranteed to not panic, this bloats a little
1769 * the codegen, so we just do it manually */
1770 gap.vec.set_len(gap.write);
1771 mem::forget(gap);
1772 }
1773 }
1774
1775 /// Appends an element to the back of a collection.
1776 ///
1777 /// # Panics
1778 ///
1779 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1780 ///
1781 /// # Examples
1782 ///
1783 /// ```
1784 /// let mut vec = vec![1, 2];
1785 /// vec.push(3);
1786 /// assert_eq!(vec, [1, 2, 3]);
1787 /// ```
1788 #[cfg(not(no_global_oom_handling))]
1789 #[inline(always)]
1790 pub fn push(&mut self, value: T) {
1791 // This will panic or abort if we would allocate > isize::MAX bytes
1792 // or if the length increment would overflow for zero-sized types.
1793 if self.len == self.buf.capacity() {
1794 self.buf.reserve_for_push(self.len);
1795 }
1796 unsafe {
1797 let end = self.as_mut_ptr().add(self.len);
1798 ptr::write(end, value);
1799 self.len += 1;
1800 }
1801 }
1802
1803 /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
1804 /// with the element.
1805 ///
1806 /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
1807 /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
1808 ///
1809 /// [`push`]: Vec::push
1810 /// [`reserve`]: Vec::reserve
1811 /// [`try_reserve`]: Vec::try_reserve
1812 ///
1813 /// # Examples
1814 ///
1815 /// A manual, panic-free alternative to [`FromIterator`]:
1816 ///
1817 /// ```
1818 /// #![feature(vec_push_within_capacity)]
1819 ///
1820 /// use std::collections::TryReserveError;
1821 /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
1822 /// let mut vec = Vec::new();
1823 /// for value in iter {
1824 /// if let Err(value) = vec.push_within_capacity(value) {
1825 /// vec.try_reserve(1)?;
1826 /// // this cannot fail, the previous line either returned or added at least 1 free slot
1827 /// let _ = vec.push_within_capacity(value);
1828 /// }
1829 /// }
1830 /// Ok(vec)
1831 /// }
1832 /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
1833 /// ```
1834 #[inline(always)]
1835 pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
1836 if self.len == self.buf.capacity() {
1837 return Err(value);
1838 }
1839 unsafe {
1840 let end = self.as_mut_ptr().add(self.len);
1841 ptr::write(end, value);
1842 self.len += 1;
1843 }
1844 Ok(())
1845 }
1846
1847 /// Removes the last element from a vector and returns it, or [`None`] if it
1848 /// is empty.
1849 ///
1850 /// If you'd like to pop the first element, consider using
1851 /// [`VecDeque::pop_front`] instead.
1852 ///
1853 /// [`VecDeque::pop_front`]: alloc_crate::collections::VecDeque::pop_front
1854 ///
1855 /// # Examples
1856 ///
1857 /// ```
1858 /// let mut vec = vec![1, 2, 3];
1859 /// assert_eq!(vec.pop(), Some(3));
1860 /// assert_eq!(vec, [1, 2]);
1861 /// ```
1862 #[inline(always)]
1863 pub fn pop(&mut self) -> Option<T> {
1864 if self.len == 0 {
1865 None
1866 } else {
1867 unsafe {
1868 self.len -= 1;
1869 Some(ptr::read(self.as_ptr().add(self.len())))
1870 }
1871 }
1872 }
1873
1874 /// Moves all the elements of `other` into `self`, leaving `other` empty.
1875 ///
1876 /// # Panics
1877 ///
1878 /// Panics if the new capacity exceeds `isize::MAX` bytes.
1879 ///
1880 /// # Examples
1881 ///
1882 /// ```
1883 /// let mut vec = vec![1, 2, 3];
1884 /// let mut vec2 = vec![4, 5, 6];
1885 /// vec.append(&mut vec2);
1886 /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
1887 /// assert_eq!(vec2, []);
1888 /// ```
1889 #[cfg(not(no_global_oom_handling))]
1890 #[inline(always)]
1891 pub fn append(&mut self, other: &mut Self) {
1892 unsafe {
1893 self.append_elements(other.as_slice() as _);
1894 other.set_len(0);
1895 }
1896 }
1897
1898 /// Appends elements to `self` from other buffer.
1899 #[cfg(not(no_global_oom_handling))]
1900 #[inline(always)]
1901 unsafe fn append_elements(&mut self, other: *const [T]) {
1902 let count = unsafe { (*other).len() };
1903 self.reserve(count);
1904 let len = self.len();
1905 unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
1906 self.len += count;
1907 }
1908
1909 /// Removes the specified range from the vector in bulk, returning all
1910 /// removed elements as an iterator. If the iterator is dropped before
1911 /// being fully consumed, it drops the remaining removed elements.
1912 ///
1913 /// The returned iterator keeps a mutable borrow on the vector to optimize
1914 /// its implementation.
1915 ///
1916 /// # Panics
1917 ///
1918 /// Panics if the starting point is greater than the end point or if
1919 /// the end point is greater than the length of the vector.
1920 ///
1921 /// # Leaking
1922 ///
1923 /// If the returned iterator goes out of scope without being dropped (due to
1924 /// [`mem::forget`], for example), the vector may have lost and leaked
1925 /// elements arbitrarily, including elements outside the range.
1926 ///
1927 /// # Examples
1928 ///
1929 /// ```
1930 /// let mut v = vec![1, 2, 3];
1931 /// let u: Vec<_> = v.drain(1..).collect();
1932 /// assert_eq!(v, &[1]);
1933 /// assert_eq!(u, &[2, 3]);
1934 ///
1935 /// // A full range clears the vector, like `clear()` does
1936 /// v.drain(..);
1937 /// assert_eq!(v, &[]);
1938 /// ```
1939 #[inline(always)]
1940 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1941 where
1942 R: RangeBounds<usize>,
1943 {
1944 // Memory safety
1945 //
1946 // When the Drain is first created, it shortens the length of
1947 // the source vector to make sure no uninitialized or moved-from elements
1948 // are accessible at all if the Drain's destructor never gets to run.
1949 //
1950 // Drain will ptr::read out the values to remove.
1951 // When finished, remaining tail of the vec is copied back to cover
1952 // the hole, and the vector length is restored to the new length.
1953 //
1954 let len = self.len();
1955
1956 // Replaced by code below
1957 // let Range { start, end } = slice::range(range, ..len);
1958
1959 // Panics if range is out of bounds
1960 let _ = &self.as_slice()[(range.start_bound().cloned(), range.end_bound().cloned())];
1961
1962 let start = match range.start_bound() {
1963 Bound::Included(&n) => n,
1964 Bound::Excluded(&n) => n + 1,
1965 Bound::Unbounded => 0,
1966 };
1967 let end = match range.end_bound() {
1968 Bound::Included(&n) => n + 1,
1969 Bound::Excluded(&n) => n,
1970 Bound::Unbounded => len,
1971 };
1972
1973 unsafe {
1974 // set self.vec length's to start, to be safe in case Drain is leaked
1975 self.set_len(start);
1976 let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
1977 Drain {
1978 tail_start: end,
1979 tail_len: len - end,
1980 iter: range_slice.iter(),
1981 vec: NonNull::from(self),
1982 }
1983 }
1984 }
1985
1986 /// Clears the vector, removing all values.
1987 ///
1988 /// Note that this method has no effect on the allocated capacity
1989 /// of the vector.
1990 ///
1991 /// # Examples
1992 ///
1993 /// ```
1994 /// let mut v = vec![1, 2, 3];
1995 ///
1996 /// v.clear();
1997 ///
1998 /// assert!(v.is_empty());
1999 /// ```
2000 #[inline(always)]
2001 pub fn clear(&mut self) {
2002 let elems: *mut [T] = self.as_mut_slice();
2003
2004 // SAFETY:
2005 // - `elems` comes directly from `as_mut_slice` and is therefore valid.
2006 // - Setting `self.len` before calling `drop_in_place` means that,
2007 // if an element's `Drop` impl panics, the vector's `Drop` impl will
2008 // do nothing (leaking the rest of the elements) instead of dropping
2009 // some twice.
2010 unsafe {
2011 self.len = 0;
2012 ptr::drop_in_place(elems);
2013 }
2014 }
2015
2016 /// Returns the number of elements in the vector, also referred to
2017 /// as its 'length'.
2018 ///
2019 /// # Examples
2020 ///
2021 /// ```
2022 /// let a = vec![1, 2, 3];
2023 /// assert_eq!(a.len(), 3);
2024 /// ```
2025 #[inline(always)]
2026 pub fn len(&self) -> usize {
2027 self.len
2028 }
2029
2030 /// Returns `true` if the vector contains no elements.
2031 ///
2032 /// # Examples
2033 ///
2034 /// ```
2035 /// let mut v = Vec::new();
2036 /// assert!(v.is_empty());
2037 ///
2038 /// v.push(1);
2039 /// assert!(!v.is_empty());
2040 /// ```
2041 #[inline(always)]
2042 pub fn is_empty(&self) -> bool {
2043 self.len() == 0
2044 }
2045
2046 /// Splits the collection into two at the given index.
2047 ///
2048 /// Returns a newly allocated vector containing the elements in the range
2049 /// `[at, len)`. After the call, the original vector will be left containing
2050 /// the elements `[0, at)` with its previous capacity unchanged.
2051 ///
2052 /// # Panics
2053 ///
2054 /// Panics if `at > len`.
2055 ///
2056 /// # Examples
2057 ///
2058 /// ```
2059 /// let mut vec = vec![1, 2, 3];
2060 /// let vec2 = vec.split_off(1);
2061 /// assert_eq!(vec, [1]);
2062 /// assert_eq!(vec2, [2, 3]);
2063 /// ```
2064 #[cfg(not(no_global_oom_handling))]
2065 #[inline(always)]
2066 #[must_use = "use `.truncate()` if you don't need the other half"]
2067 pub fn split_off(&mut self, at: usize) -> Self
2068 where
2069 A: Clone,
2070 {
2071 #[cold]
2072 #[inline(never)]
2073 fn assert_failed(at: usize, len: usize) -> ! {
2074 panic!("`at` split index (is {}) should be <= len (is {})", at, len);
2075 }
2076
2077 if at > self.len() {
2078 assert_failed(at, self.len());
2079 }
2080
2081 if at == 0 {
2082 // the new vector can take over the original buffer and avoid the copy
2083 return mem::replace(
2084 self,
2085 Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
2086 );
2087 }
2088
2089 let other_len = self.len - at;
2090 let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
2091
2092 // Unsafely `set_len` and copy items to `other`.
2093 unsafe {
2094 self.set_len(at);
2095 other.set_len(other_len);
2096
2097 ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
2098 }
2099 other
2100 }
2101
2102 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2103 ///
2104 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2105 /// difference, with each additional slot filled with the result of
2106 /// calling the closure `f`. The return values from `f` will end up
2107 /// in the `Vec` in the order they have been generated.
2108 ///
2109 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2110 ///
2111 /// This method uses a closure to create new values on every push. If
2112 /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
2113 /// want to use the [`Default`] trait to generate values, you can
2114 /// pass [`Default::default`] as the second argument.
2115 ///
2116 /// # Examples
2117 ///
2118 /// ```
2119 /// let mut vec = vec![1, 2, 3];
2120 /// vec.resize_with(5, Default::default);
2121 /// assert_eq!(vec, [1, 2, 3, 0, 0]);
2122 ///
2123 /// let mut vec = vec![];
2124 /// let mut p = 1;
2125 /// vec.resize_with(4, || { p *= 2; p });
2126 /// assert_eq!(vec, [2, 4, 8, 16]);
2127 /// ```
2128 #[cfg(not(no_global_oom_handling))]
2129 #[inline(always)]
2130 pub fn resize_with<F>(&mut self, new_len: usize, f: F)
2131 where
2132 F: FnMut() -> T,
2133 {
2134 let len = self.len();
2135 if new_len > len {
2136 self.extend(iter::repeat_with(f).take(new_len - len));
2137 } else {
2138 self.truncate(new_len);
2139 }
2140 }
2141
2142 /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
2143 /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
2144 /// `'a`. If the type has only static references, or none at all, then this
2145 /// may be chosen to be `'static`.
2146 ///
2147 /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
2148 /// so the leaked allocation may include unused capacity that is not part
2149 /// of the returned slice.
2150 ///
2151 /// This function is mainly useful for data that lives for the remainder of
2152 /// the program's life. Dropping the returned reference will cause a memory
2153 /// leak.
2154 ///
2155 /// # Examples
2156 ///
2157 /// Simple usage:
2158 ///
2159 /// ```
2160 /// let x = vec![1, 2, 3];
2161 /// let static_ref: &'static mut [usize] = x.leak();
2162 /// static_ref[0] += 1;
2163 /// assert_eq!(static_ref, &[2, 2, 3]);
2164 /// ```
2165 #[inline(always)]
2166 pub fn leak<'a>(self) -> &'a mut [T]
2167 where
2168 A: 'a,
2169 {
2170 let mut me = ManuallyDrop::new(self);
2171 unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
2172 }
2173
2174 /// Returns the remaining spare capacity of the vector as a slice of
2175 /// `MaybeUninit<T>`.
2176 ///
2177 /// The returned slice can be used to fill the vector with data (e.g. by
2178 /// reading from a file) before marking the data as initialized using the
2179 /// [`set_len`] method.
2180 ///
2181 /// [`set_len`]: Vec::set_len
2182 ///
2183 /// # Examples
2184 ///
2185 /// ```
2186 /// // Allocate vector big enough for 10 elements.
2187 /// let mut v = Vec::with_capacity(10);
2188 ///
2189 /// // Fill in the first 3 elements.
2190 /// let uninit = v.spare_capacity_mut();
2191 /// uninit[0].write(0);
2192 /// uninit[1].write(1);
2193 /// uninit[2].write(2);
2194 ///
2195 /// // Mark the first 3 elements of the vector as being initialized.
2196 /// unsafe {
2197 /// v.set_len(3);
2198 /// }
2199 ///
2200 /// assert_eq!(&v, &[0, 1, 2]);
2201 /// ```
2202 #[inline(always)]
2203 pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
2204 // Note:
2205 // This method is not implemented in terms of `split_at_spare_mut`,
2206 // to prevent invalidation of pointers to the buffer.
2207 unsafe {
2208 slice::from_raw_parts_mut(
2209 self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
2210 self.buf.capacity() - self.len,
2211 )
2212 }
2213 }
2214
2215 /// Returns vector content as a slice of `T`, along with the remaining spare
2216 /// capacity of the vector as a slice of `MaybeUninit<T>`.
2217 ///
2218 /// The returned spare capacity slice can be used to fill the vector with data
2219 /// (e.g. by reading from a file) before marking the data as initialized using
2220 /// the [`set_len`] method.
2221 ///
2222 /// [`set_len`]: Vec::set_len
2223 ///
2224 /// Note that this is a low-level API, which should be used with care for
2225 /// optimization purposes. If you need to append data to a `Vec`
2226 /// you can use [`push`], [`extend`], [`extend_from_slice`],
2227 /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
2228 /// [`resize_with`], depending on your exact needs.
2229 ///
2230 /// [`push`]: Vec::push
2231 /// [`extend`]: Vec::extend
2232 /// [`extend_from_slice`]: Vec::extend_from_slice
2233 /// [`extend_from_within`]: Vec::extend_from_within
2234 /// [`insert`]: Vec::insert
2235 /// [`append`]: Vec::append
2236 /// [`resize`]: Vec::resize
2237 /// [`resize_with`]: Vec::resize_with
2238 ///
2239 /// # Examples
2240 ///
2241 /// ```
2242 /// #![feature(vec_split_at_spare)]
2243 ///
2244 /// let mut v = vec![1, 1, 2];
2245 ///
2246 /// // Reserve additional space big enough for 10 elements.
2247 /// v.reserve(10);
2248 ///
2249 /// let (init, uninit) = v.split_at_spare_mut();
2250 /// let sum = init.iter().copied().sum::<u32>();
2251 ///
2252 /// // Fill in the next 4 elements.
2253 /// uninit[0].write(sum);
2254 /// uninit[1].write(sum * 2);
2255 /// uninit[2].write(sum * 3);
2256 /// uninit[3].write(sum * 4);
2257 ///
2258 /// // Mark the 4 elements of the vector as being initialized.
2259 /// unsafe {
2260 /// let len = v.len();
2261 /// v.set_len(len + 4);
2262 /// }
2263 ///
2264 /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
2265 /// ```
2266 #[inline(always)]
2267 pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
2268 // SAFETY:
2269 // - len is ignored and so never changed
2270 let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
2271 (init, spare)
2272 }
2273
2274 /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
2275 ///
2276 /// This method provides unique access to all vec parts at once in `extend_from_within`.
2277 unsafe fn split_at_spare_mut_with_len(
2278 &mut self,
2279 ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
2280 let ptr = self.as_mut_ptr();
2281 // SAFETY:
2282 // - `ptr` is guaranteed to be valid for `self.len` elements
2283 // - but the allocation extends out to `self.buf.capacity()` elements, possibly
2284 // uninitialized
2285 let spare_ptr = unsafe { ptr.add(self.len) };
2286 let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
2287 let spare_len = self.buf.capacity() - self.len;
2288
2289 // SAFETY:
2290 // - `ptr` is guaranteed to be valid for `self.len` elements
2291 // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
2292 unsafe {
2293 let initialized = slice::from_raw_parts_mut(ptr, self.len);
2294 let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
2295
2296 (initialized, spare, &mut self.len)
2297 }
2298 }
2299}
2300
2301impl<T: Clone, A: Allocator> Vec<T, A> {
2302 /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
2303 ///
2304 /// If `new_len` is greater than `len`, the `Vec` is extended by the
2305 /// difference, with each additional slot filled with `value`.
2306 /// If `new_len` is less than `len`, the `Vec` is simply truncated.
2307 ///
2308 /// This method requires `T` to implement [`Clone`],
2309 /// in order to be able to clone the passed value.
2310 /// If you need more flexibility (or want to rely on [`Default`] instead of
2311 /// [`Clone`]), use [`Vec::resize_with`].
2312 /// If you only need to resize to a smaller size, use [`Vec::truncate`].
2313 ///
2314 /// # Examples
2315 ///
2316 /// ```
2317 /// let mut vec = vec!["hello"];
2318 /// vec.resize(3, "world");
2319 /// assert_eq!(vec, ["hello", "world", "world"]);
2320 ///
2321 /// let mut vec = vec![1, 2, 3, 4];
2322 /// vec.resize(2, 0);
2323 /// assert_eq!(vec, [1, 2]);
2324 /// ```
2325 #[cfg(not(no_global_oom_handling))]
2326 #[inline(always)]
2327 pub fn resize(&mut self, new_len: usize, value: T) {
2328 let len = self.len();
2329
2330 if new_len > len {
2331 self.extend_with(new_len - len, ExtendElement(value))
2332 } else {
2333 self.truncate(new_len);
2334 }
2335 }
2336
2337 /// Clones and appends all elements in a slice to the `Vec`.
2338 ///
2339 /// Iterates over the slice `other`, clones each element, and then appends
2340 /// it to this `Vec`. The `other` slice is traversed in-order.
2341 ///
2342 /// Note that this function is same as [`extend`] except that it is
2343 /// specialized to work with slices instead. If and when Rust gets
2344 /// specialization this function will likely be deprecated (but still
2345 /// available).
2346 ///
2347 /// # Examples
2348 ///
2349 /// ```
2350 /// let mut vec = vec![1];
2351 /// vec.extend_from_slice(&[2, 3, 4]);
2352 /// assert_eq!(vec, [1, 2, 3, 4]);
2353 /// ```
2354 ///
2355 /// [`extend`]: Vec::extend
2356 #[cfg(not(no_global_oom_handling))]
2357 #[inline(always)]
2358 pub fn extend_from_slice(&mut self, other: &[T]) {
2359 self.extend(other.iter().cloned())
2360 }
2361
2362 /// Copies elements from `src` range to the end of the vector.
2363 ///
2364 /// # Panics
2365 ///
2366 /// Panics if the starting point is greater than the end point or if
2367 /// the end point is greater than the length of the vector.
2368 ///
2369 /// # Examples
2370 ///
2371 /// ```
2372 /// let mut vec = vec![0, 1, 2, 3, 4];
2373 ///
2374 /// vec.extend_from_within(2..);
2375 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
2376 ///
2377 /// vec.extend_from_within(..2);
2378 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
2379 ///
2380 /// vec.extend_from_within(4..8);
2381 /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
2382 /// ```
2383 #[cfg(not(no_global_oom_handling))]
2384 #[inline(always)]
2385 pub fn extend_from_within<R>(&mut self, src: R)
2386 where
2387 R: RangeBounds<usize>,
2388 {
2389 // let range = slice::range(src, ..self.len());
2390
2391 let _ = &self.as_slice()[(src.start_bound().cloned(), src.end_bound().cloned())];
2392
2393 let len = self.len();
2394
2395 let start: ops::Bound<&usize> = src.start_bound();
2396 let start = match start {
2397 ops::Bound::Included(&start) => start,
2398 ops::Bound::Excluded(start) => start + 1,
2399 ops::Bound::Unbounded => 0,
2400 };
2401
2402 let end: ops::Bound<&usize> = src.end_bound();
2403 let end = match end {
2404 ops::Bound::Included(end) => end + 1,
2405 ops::Bound::Excluded(&end) => end,
2406 ops::Bound::Unbounded => len,
2407 };
2408
2409 let range = start..end;
2410
2411 self.reserve(range.len());
2412
2413 // SAFETY:
2414 // - len is increased only after initializing elements
2415 let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
2416
2417 // SAFETY:
2418 // - caller guarantees that src is a valid index
2419 let to_clone = unsafe { this.get_unchecked(range) };
2420
2421 iter::zip(to_clone, spare)
2422 .map(|(src, dst)| dst.write(src.clone()))
2423 // Note:
2424 // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
2425 // - len is increased after each element to prevent leaks (see issue #82533)
2426 .for_each(|_| *len += 1);
2427 }
2428}
2429
2430impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
2431 /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
2432 ///
2433 /// # Panics
2434 ///
2435 /// Panics if the length of the resulting vector would overflow a `usize`.
2436 ///
2437 /// This is only possible when flattening a vector of arrays of zero-sized
2438 /// types, and thus tends to be irrelevant in practice. If
2439 /// `size_of::<T>() > 0`, this will never panic.
2440 ///
2441 /// # Examples
2442 ///
2443 /// ```
2444 /// #![feature(slice_flatten)]
2445 ///
2446 /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
2447 /// assert_eq!(vec.pop(), Some([7, 8, 9]));
2448 ///
2449 /// let mut flattened = vec.into_flattened();
2450 /// assert_eq!(flattened.pop(), Some(6));
2451 /// ```
2452 #[inline(always)]
2453 pub fn into_flattened(self) -> Vec<T, A> {
2454 let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
2455 let (new_len, new_cap) = if size_of::<T>() == 0 {
2456 (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
2457 } else {
2458 // SAFETY:
2459 // - `cap * N` cannot overflow because the allocation is already in
2460 // the address space.
2461 // - Each `[T; N]` has `N` valid elements, so there are `len * N`
2462 // valid elements in the allocation.
2463 (len * N, cap * N)
2464 };
2465 // SAFETY:
2466 // - `ptr` was allocated by `self`
2467 // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
2468 // - `new_cap` refers to the same sized allocation as `cap` because
2469 // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
2470 // - `len` <= `cap`, so `len * N` <= `cap * N`.
2471 unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
2472 }
2473}
2474
2475// This code generalizes `extend_with_{element,default}`.
2476trait ExtendWith<T> {
2477 fn next(&mut self) -> T;
2478 fn last(self) -> T;
2479}
2480
2481struct ExtendElement<T>(T);
2482impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
2483 #[inline(always)]
2484 fn next(&mut self) -> T {
2485 self.0.clone()
2486 }
2487
2488 #[inline(always)]
2489 fn last(self) -> T {
2490 self.0
2491 }
2492}
2493
2494impl<T, A: Allocator> Vec<T, A> {
2495 #[cfg(not(no_global_oom_handling))]
2496 #[inline(always)]
2497 /// Extend the vector by `n` values, using the given generator.
2498 fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
2499 self.reserve(n);
2500
2501 unsafe {
2502 let mut ptr = self.as_mut_ptr().add(self.len());
2503 // Use SetLenOnDrop to work around bug where compiler
2504 // might not realize the store through `ptr` through self.set_len()
2505 // don't alias.
2506 let mut local_len = SetLenOnDrop::new(&mut self.len);
2507
2508 // Write all elements except the last one
2509 for _ in 1..n {
2510 ptr::write(ptr, value.next());
2511 ptr = ptr.add(1);
2512 // Increment the length in every step in case next() panics
2513 local_len.increment_len(1);
2514 }
2515
2516 if n > 0 {
2517 // We can write the last element directly without cloning needlessly
2518 ptr::write(ptr, value.last());
2519 local_len.increment_len(1);
2520 }
2521
2522 // len set by scope guard
2523 }
2524 }
2525}
2526
2527impl<T: PartialEq, A: Allocator> Vec<T, A> {
2528 /// Removes consecutive repeated elements in the vector according to the
2529 /// [`PartialEq`] trait implementation.
2530 ///
2531 /// If the vector is sorted, this removes all duplicates.
2532 ///
2533 /// # Examples
2534 ///
2535 /// ```
2536 /// let mut vec = vec![1, 2, 2, 3, 2];
2537 ///
2538 /// vec.dedup();
2539 ///
2540 /// assert_eq!(vec, [1, 2, 3, 2]);
2541 /// ```
2542 #[inline(always)]
2543 pub fn dedup(&mut self) {
2544 self.dedup_by(|a: &mut T, b: &mut T| a == b)
2545 }
2546}
2547
2548////////////////////////////////////////////////////////////////////////////////
2549// Common trait implementations for Vec
2550////////////////////////////////////////////////////////////////////////////////
2551
2552impl<T, A: Allocator> ops::Deref for Vec<T, A> {
2553 type Target = [T];
2554
2555 #[inline(always)]
2556 fn deref(&self) -> &[T] {
2557 unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
2558 }
2559}
2560
2561impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
2562 #[inline(always)]
2563 fn deref_mut(&mut self) -> &mut [T] {
2564 unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
2565 }
2566}
2567
2568#[cfg(not(no_global_oom_handling))]
2569impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
2570 #[inline(always)]
2571 fn clone(&self) -> Self {
2572 let alloc: A = self.allocator().clone();
2573 let mut vec: Vec = Vec::with_capacity_in(self.len(), alloc);
2574 vec.extend_from_slice(self);
2575 vec
2576 }
2577
2578 #[inline(always)]
2579 fn clone_from(&mut self, other: &Self) {
2580 // drop anything that will not be overwritten
2581 self.truncate(other.len());
2582
2583 // self.len <= other.len due to the truncate above, so the
2584 // slices here are always in-bounds.
2585 let (init: &[T], tail: &[T]) = other.split_at(self.len());
2586
2587 // reuse the contained values' allocations/resources.
2588 self.clone_from_slice(src:init);
2589 self.extend_from_slice(tail);
2590 }
2591}
2592
2593/// The hash of a vector is the same as that of the corresponding slice,
2594/// as required by the `core::borrow::Borrow` implementation.
2595///
2596/// ```
2597/// #![feature(build_hasher_simple_hash_one)]
2598/// use std::hash::BuildHasher;
2599///
2600/// let b = std::collections::hash_map::RandomState::new();
2601/// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
2602/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
2603/// assert_eq!(b.hash_one(v), b.hash_one(s));
2604/// ```
2605impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
2606 #[inline(always)]
2607 fn hash<H: Hasher>(&self, state: &mut H) {
2608 Hash::hash(&**self, state)
2609 }
2610}
2611
2612impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
2613 type Output = I::Output;
2614
2615 #[inline(always)]
2616 fn index(&self, index: I) -> &Self::Output {
2617 Index::index(&**self, index)
2618 }
2619}
2620
2621impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
2622 #[inline(always)]
2623 fn index_mut(&mut self, index: I) -> &mut Self::Output {
2624 IndexMut::index_mut(&mut **self, index)
2625 }
2626}
2627
2628#[cfg(not(no_global_oom_handling))]
2629impl<T> FromIterator<T> for Vec<T> {
2630 #[inline(always)]
2631 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
2632 let mut vec: Vec = Vec::new();
2633 vec.extend(iter);
2634 vec
2635 }
2636}
2637
2638impl<T, A: Allocator> IntoIterator for Vec<T, A> {
2639 type Item = T;
2640 type IntoIter = IntoIter<T, A>;
2641
2642 /// Creates a consuming iterator, that is, one that moves each value out of
2643 /// the vector (from start to end). The vector cannot be used after calling
2644 /// this.
2645 ///
2646 /// # Examples
2647 ///
2648 /// ```
2649 /// let v = vec!["a".to_string(), "b".to_string()];
2650 /// let mut v_iter = v.into_iter();
2651 ///
2652 /// let first_element: Option<String> = v_iter.next();
2653 ///
2654 /// assert_eq!(first_element, Some("a".to_string()));
2655 /// assert_eq!(v_iter.next(), Some("b".to_string()));
2656 /// assert_eq!(v_iter.next(), None);
2657 /// ```
2658 #[inline(always)]
2659 fn into_iter(self) -> Self::IntoIter {
2660 unsafe {
2661 let mut me = ManuallyDrop::new(self);
2662 let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
2663 let begin = me.as_mut_ptr();
2664 let end = if size_of::<T>() == 0 {
2665 begin.cast::<u8>().wrapping_add(me.len()).cast()
2666 } else {
2667 begin.add(me.len()) as *const T
2668 };
2669 let cap = me.buf.capacity();
2670 IntoIter {
2671 buf: NonNull::new_unchecked(begin),
2672 phantom: PhantomData,
2673 cap,
2674 alloc,
2675 ptr: begin,
2676 end,
2677 }
2678 }
2679 }
2680}
2681
2682impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
2683 type Item = &'a T;
2684 type IntoIter = slice::Iter<'a, T>;
2685
2686 #[inline(always)]
2687 fn into_iter(self) -> Self::IntoIter {
2688 self.iter()
2689 }
2690}
2691
2692impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
2693 type Item = &'a mut T;
2694 type IntoIter = slice::IterMut<'a, T>;
2695
2696 fn into_iter(self) -> Self::IntoIter {
2697 self.iter_mut()
2698 }
2699}
2700
2701#[cfg(not(no_global_oom_handling))]
2702impl<T, A: Allocator> Extend<T> for Vec<T, A> {
2703 #[inline(always)]
2704 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2705 // This is the case for a general iter.
2706 //
2707 // This function should be the moral equivalent of:
2708 //
2709 // for item in iter {
2710 // self.push(item);
2711 // }
2712
2713 let mut iter = iter.into_iter();
2714 while let Some(element) = iter.next() {
2715 let len = self.len();
2716 if len == self.capacity() {
2717 let (lower, _) = iter.size_hint();
2718 self.reserve(lower.saturating_add(1));
2719 }
2720 unsafe {
2721 ptr::write(self.as_mut_ptr().add(len), element);
2722 // Since next() executes user code which can panic we have to bump the length
2723 // after each step.
2724 // NB can't overflow since we would have had to alloc the address space
2725 self.set_len(len + 1);
2726 }
2727 }
2728 }
2729}
2730
2731impl<T, A: Allocator> Vec<T, A> {
2732 /// Creates a splicing iterator that replaces the specified range in the vector
2733 /// with the given `replace_with` iterator and yields the removed items.
2734 /// `replace_with` does not need to be the same length as `range`.
2735 ///
2736 /// `range` is removed even if the iterator is not consumed until the end.
2737 ///
2738 /// It is unspecified how many elements are removed from the vector
2739 /// if the `Splice` value is leaked.
2740 ///
2741 /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
2742 ///
2743 /// This is optimal if:
2744 ///
2745 /// * The tail (elements in the vector after `range`) is empty,
2746 /// * or `replace_with` yields fewer or equal elements than `range`’s length
2747 /// * or the lower bound of its `size_hint()` is exact.
2748 ///
2749 /// Otherwise, a temporary vector is allocated and the tail is moved twice.
2750 ///
2751 /// # Panics
2752 ///
2753 /// Panics if the starting point is greater than the end point or if
2754 /// the end point is greater than the length of the vector.
2755 ///
2756 /// # Examples
2757 ///
2758 /// ```
2759 /// let mut v = vec![1, 2, 3, 4];
2760 /// let new = [7, 8, 9];
2761 /// let u: Vec<_> = v.splice(1..3, new).collect();
2762 /// assert_eq!(v, &[1, 7, 8, 9, 4]);
2763 /// assert_eq!(u, &[2, 3]);
2764 /// ```
2765 #[cfg(not(no_global_oom_handling))]
2766 #[inline(always)]
2767 pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
2768 where
2769 R: RangeBounds<usize>,
2770 I: IntoIterator<Item = T>,
2771 {
2772 Splice {
2773 drain: self.drain(range),
2774 replace_with: replace_with.into_iter(),
2775 }
2776 }
2777}
2778
2779/// Extend implementation that copies elements out of references before pushing them onto the Vec.
2780///
2781/// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
2782/// append the entire slice at once.
2783///
2784/// [`copy_from_slice`]: slice::copy_from_slice
2785#[cfg(not(no_global_oom_handling))]
2786impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
2787 #[inline(always)]
2788 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2789 let mut iter: ::IntoIter = iter.into_iter();
2790 while let Some(element: &'a T) = iter.next() {
2791 let len: usize = self.len();
2792 if len == self.capacity() {
2793 let (lower: usize, _) = iter.size_hint();
2794 self.reserve(additional:lower.saturating_add(1));
2795 }
2796 unsafe {
2797 ptr::write(self.as_mut_ptr().add(len), *element);
2798 // Since next() executes user code which can panic we have to bump the length
2799 // after each step.
2800 // NB can't overflow since we would have had to alloc the address space
2801 self.set_len(new_len:len + 1);
2802 }
2803 }
2804 }
2805}
2806
2807/// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2808impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
2809 #[inline(always)]
2810 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2811 PartialOrd::partial_cmp(&**self, &**other)
2812 }
2813}
2814
2815impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
2816
2817/// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
2818impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
2819 #[inline(always)]
2820 fn cmp(&self, other: &Self) -> Ordering {
2821 Ord::cmp(&**self, &**other)
2822 }
2823}
2824
2825impl<T, A: Allocator> Drop for Vec<T, A> {
2826 #[inline(always)]
2827 fn drop(&mut self) {
2828 unsafe {
2829 // use drop for [T]
2830 // use a raw slice to refer to the elements of the vector as weakest necessary type;
2831 // could avoid questions of validity in certain cases
2832 ptr::drop_in_place(to_drop:ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
2833 }
2834 // RawVec handles deallocation
2835 }
2836}
2837
2838impl<T> Default for Vec<T> {
2839 /// Creates an empty `Vec<T>`.
2840 ///
2841 /// The vector will not allocate until elements are pushed onto it.
2842 #[inline(always)]
2843 fn default() -> Vec<T> {
2844 Vec::new()
2845 }
2846}
2847
2848impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
2849 #[inline(always)]
2850 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2851 fmt::Debug::fmt(&**self, f)
2852 }
2853}
2854
2855impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
2856 #[inline(always)]
2857 fn as_ref(&self) -> &Vec<T, A> {
2858 self
2859 }
2860}
2861
2862impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
2863 #[inline(always)]
2864 fn as_mut(&mut self) -> &mut Vec<T, A> {
2865 self
2866 }
2867}
2868
2869impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
2870 #[inline(always)]
2871 fn as_ref(&self) -> &[T] {
2872 self
2873 }
2874}
2875
2876impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
2877 #[inline(always)]
2878 fn as_mut(&mut self) -> &mut [T] {
2879 self
2880 }
2881}
2882
2883#[cfg(not(no_global_oom_handling))]
2884impl<T: Clone> From<&[T]> for Vec<T> {
2885 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2886 ///
2887 /// # Examples
2888 ///
2889 /// ```
2890 /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
2891 /// ```
2892 #[inline(always)]
2893 fn from(s: &[T]) -> Vec<T> {
2894 let mut vec: Vec = Vec::with_capacity(s.len());
2895 vec.extend_from_slice(s);
2896 vec
2897 }
2898}
2899
2900#[cfg(not(no_global_oom_handling))]
2901impl<T: Clone> From<&mut [T]> for Vec<T> {
2902 /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
2903 ///
2904 /// # Examples
2905 ///
2906 /// ```
2907 /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
2908 /// ```
2909 #[inline(always)]
2910 fn from(s: &mut [T]) -> Vec<T> {
2911 let mut vec: Vec = Vec::with_capacity(s.len());
2912 vec.extend_from_slice(s);
2913 vec
2914 }
2915}
2916
2917#[cfg(not(no_global_oom_handling))]
2918impl<T, const N: usize> From<[T; N]> for Vec<T> {
2919 #[inline(always)]
2920 fn from(s: [T; N]) -> Vec<T> {
2921 Box::slice(Box::new(s)).into_vec()
2922 }
2923}
2924
2925impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
2926 /// Convert a boxed slice into a vector by transferring ownership of
2927 /// the existing heap allocation.
2928 ///
2929 /// # Examples
2930 ///
2931 /// ```
2932 /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
2933 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
2934 /// ```
2935 #[inline(always)]
2936 fn from(s: Box<[T], A>) -> Self {
2937 s.into_vec()
2938 }
2939}
2940
2941impl<T, A: Allocator, const N: usize> From<Box<[T; N], A>> for Vec<T, A> {
2942 /// Convert a boxed array into a vector by transferring ownership of
2943 /// the existing heap allocation.
2944 ///
2945 /// # Examples
2946 ///
2947 /// ```
2948 /// let b: Box<[i32; 3]> = Box::new([1, 2, 3]);
2949 /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
2950 /// ```
2951 #[inline(always)]
2952 fn from(s: Box<[T; N], A>) -> Self {
2953 s.into_vec()
2954 }
2955}
2956
2957// note: test pulls in libstd, which causes errors here
2958#[cfg(not(no_global_oom_handling))]
2959impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
2960 /// Convert a vector into a boxed slice.
2961 ///
2962 /// If `v` has excess capacity, its items will be moved into a
2963 /// newly-allocated buffer with exactly the right capacity.
2964 ///
2965 /// # Examples
2966 ///
2967 /// ```
2968 /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
2969 /// ```
2970 ///
2971 /// Any excess capacity is removed:
2972 /// ```
2973 /// let mut vec = Vec::with_capacity(10);
2974 /// vec.extend([1, 2, 3]);
2975 ///
2976 /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
2977 /// ```
2978 #[inline(always)]
2979 fn from(v: Vec<T, A>) -> Self {
2980 v.into_boxed_slice()
2981 }
2982}
2983
2984#[cfg(not(no_global_oom_handling))]
2985impl From<&str> for Vec<u8> {
2986 /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
2987 ///
2988 /// # Examples
2989 ///
2990 /// ```
2991 /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
2992 /// ```
2993 #[inline(always)]
2994 fn from(s: &str) -> Vec<u8> {
2995 From::from(s.as_bytes())
2996 }
2997}
2998
2999impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
3000 type Error = Vec<T, A>;
3001
3002 /// Gets the entire contents of the `Vec<T>` as an array,
3003 /// if its size exactly matches that of the requested array.
3004 ///
3005 /// # Examples
3006 ///
3007 /// ```
3008 /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
3009 /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
3010 /// ```
3011 ///
3012 /// If the length doesn't match, the input comes back in `Err`:
3013 /// ```
3014 /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
3015 /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
3016 /// ```
3017 ///
3018 /// If you're fine with just getting a prefix of the `Vec<T>`,
3019 /// you can call [`.truncate(N)`](Vec::truncate) first.
3020 /// ```
3021 /// let mut v = String::from("hello world").into_bytes();
3022 /// v.sort();
3023 /// v.truncate(2);
3024 /// let [a, b]: [_; 2] = v.try_into().unwrap();
3025 /// assert_eq!(a, b' ');
3026 /// assert_eq!(b, b'd');
3027 /// ```
3028 #[inline(always)]
3029 fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
3030 if vec.len() != N {
3031 return Err(vec);
3032 }
3033
3034 // SAFETY: `.set_len(0)` is always sound.
3035 unsafe { vec.set_len(0) };
3036
3037 // SAFETY: A `Vec`'s pointer is always aligned properly, and
3038 // the alignment the array needs is the same as the items.
3039 // We checked earlier that we have sufficient items.
3040 // The items will not double-drop as the `set_len`
3041 // tells the `Vec` not to also drop them.
3042 let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };
3043 Ok(array)
3044 }
3045}
3046
3047#[inline(always)]
3048#[cfg(not(no_global_oom_handling))]
3049#[doc(hidden)]
3050pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
3051 let mut v: Vec = Vec::with_capacity_in(capacity:n, alloc);
3052 v.extend_with(n, value:ExtendElement(elem));
3053 v
3054}
3055
3056#[inline(always)]
3057#[cfg(not(no_global_oom_handling))]
3058#[doc(hidden)]
3059pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
3060 let mut v: Vec = Vec::with_capacity(n);
3061 v.extend_with(n, value:ExtendElement(elem));
3062 v
3063}
3064
3065/// Write is implemented for `Vec<u8>` by appending to the vector.
3066/// The vector will grow as needed.
3067#[cfg(feature = "std")]
3068impl<A: Allocator> io::Write for Vec<u8, A> {
3069 #[inline]
3070 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
3071 self.extend_from_slice(buf);
3072 Ok(buf.len())
3073 }
3074
3075 #[inline]
3076 fn write_vectored(&mut self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
3077 let len = bufs.iter().map(|b| b.len()).sum();
3078 self.reserve(len);
3079 for buf in bufs {
3080 self.extend_from_slice(buf);
3081 }
3082 Ok(len)
3083 }
3084
3085 #[inline]
3086 fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
3087 self.extend_from_slice(buf);
3088 Ok(())
3089 }
3090
3091 #[inline]
3092 fn flush(&mut self) -> io::Result<()> {
3093 Ok(())
3094 }
3095}
3096
3097#[cfg(feature = "serde")]
3098impl<T, A> serde::Serialize for Vec<T, A>
3099where
3100 T: serde::Serialize,
3101 A: Allocator,
3102{
3103 #[inline(always)]
3104 fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
3105 where
3106 S: serde::ser::Serializer,
3107 {
3108 serializer.collect_seq(self)
3109 }
3110}
3111
3112#[cfg(feature = "serde")]
3113impl<'de, T, A> serde::de::Deserialize<'de> for Vec<T, A>
3114where
3115 T: serde::de::Deserialize<'de>,
3116 A: Allocator + Default,
3117{
3118 #[inline(always)]
3119 fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
3120 where
3121 D: serde::de::Deserializer<'de>,
3122 {
3123 struct VecVisitor<T, A> {
3124 marker: PhantomData<(T, A)>,
3125 }
3126
3127 impl<'de, T, A> serde::de::Visitor<'de> for VecVisitor<T, A>
3128 where
3129 T: serde::de::Deserialize<'de>,
3130 A: Allocator + Default,
3131 {
3132 type Value = Vec<T, A>;
3133
3134 fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
3135 formatter.write_str("a sequence")
3136 }
3137
3138 fn visit_seq<S>(self, mut seq: S) -> Result<Self::Value, S::Error>
3139 where
3140 S: serde::de::SeqAccess<'de>,
3141 {
3142 let mut values = Vec::with_capacity_in(cautious(seq.size_hint()), A::default());
3143
3144 while let Some(value) = seq.next_element()? {
3145 values.push(value);
3146 }
3147
3148 Ok(values)
3149 }
3150 }
3151
3152 let visitor = VecVisitor {
3153 marker: PhantomData,
3154 };
3155 deserializer.deserialize_seq(visitor)
3156 }
3157
3158 #[inline(always)]
3159 fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
3160 where
3161 D: serde::de::Deserializer<'de>,
3162 {
3163 struct VecInPlaceVisitor<'a, T: 'a, A: Allocator + 'a>(&'a mut Vec<T, A>);
3164
3165 impl<'a, 'de, T, A> serde::de::Visitor<'de> for VecInPlaceVisitor<'a, T, A>
3166 where
3167 T: serde::de::Deserialize<'de>,
3168 A: Allocator + Default,
3169 {
3170 type Value = ();
3171
3172 fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
3173 formatter.write_str("a sequence")
3174 }
3175
3176 fn visit_seq<S>(self, mut seq: S) -> Result<Self::Value, S::Error>
3177 where
3178 S: serde::de::SeqAccess<'de>,
3179 {
3180 let hint = cautious(seq.size_hint());
3181 if let Some(additional) = hint.checked_sub(self.0.len()) {
3182 self.0.reserve(additional);
3183 }
3184
3185 for i in 0..self.0.len() {
3186 let next = {
3187 let next_place = InPlaceSeed(&mut self.0[i]);
3188 seq.next_element_seed(next_place)?
3189 };
3190 if next.is_none() {
3191 self.0.truncate(i);
3192 return Ok(());
3193 }
3194 }
3195
3196 while let Some(value) = seq.next_element()? {
3197 self.0.push(value);
3198 }
3199
3200 Ok(())
3201 }
3202 }
3203
3204 deserializer.deserialize_seq(VecInPlaceVisitor(place))
3205 }
3206}
3207
3208#[cfg(feature = "serde")]
3209pub fn cautious(hint: Option<usize>) -> usize {
3210 cmp::min(hint.unwrap_or(0), 4096)
3211}
3212
3213/// A DeserializeSeed helper for implementing deserialize_in_place Visitors.
3214///
3215/// Wraps a mutable reference and calls deserialize_in_place on it.
3216
3217#[cfg(feature = "serde")]
3218pub struct InPlaceSeed<'a, T: 'a>(pub &'a mut T);
3219
3220#[cfg(feature = "serde")]
3221impl<'a, 'de, T> serde::de::DeserializeSeed<'de> for InPlaceSeed<'a, T>
3222where
3223 T: serde::de::Deserialize<'de>,
3224{
3225 type Value = ();
3226 fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
3227 where
3228 D: serde::de::Deserializer<'de>,
3229 {
3230 T::deserialize_in_place(deserializer, self.0)
3231 }
3232}
3233