1 //! A dynamically-sized view into a contiguous sequence, `[T]`.
3 //! *[See also the slice primitive type](slice).*
5 //! Slices are a view into a block of memory represented as a pointer and a
10 //! let vec = vec![1, 2, 3];
11 //! let int_slice = &vec[..];
12 //! // coercing an array to a slice
13 //! let str_slice: &[&str] = &["one", "two", "three"];
16 //! Slices are either mutable or shared. The shared slice type is `&[T]`,
17 //! while the mutable slice type is `&mut [T]`, where `T` represents the element
18 //! type. For example, you can mutate the block of memory that a mutable slice
22 //! let x = &mut [1, 2, 3];
24 //! assert_eq!(x, &[1, 7, 3]);
27 //! Here are some of the things this module contains:
31 //! There are several structs that are useful for slices, such as [`Iter`], which
32 //! represents iteration over a slice.
34 //! ## Trait Implementations
36 //! There are several implementations of common traits for slices. Some examples
40 //! * [`Eq`], [`Ord`] - for slices whose element type are [`Eq`] or [`Ord`].
41 //! * [`Hash`] - for slices whose element type is [`Hash`].
45 //! The slices implement `IntoIterator`. The iterator yields references to the
49 //! let numbers = &[0, 1, 2];
50 //! for n in numbers {
51 //! println!("{} is a number!", n);
55 //! The mutable slice yields mutable references to the elements:
58 //! let mut scores = [7, 8, 9];
59 //! for score in &mut scores[..] {
64 //! This iterator yields mutable references to the slice's elements, so while
65 //! the element type of the slice is `i32`, the element type of the iterator is
68 //! * [`.iter`] and [`.iter_mut`] are the explicit methods to return the default
70 //! * Further methods that return iterators are [`.split`], [`.splitn`],
71 //! [`.chunks`], [`.windows`] and more.
73 //! [`Hash`]: core::hash::Hash
74 //! [`.iter`]: slice::iter
75 //! [`.iter_mut`]: slice::iter_mut
76 //! [`.split`]: slice::split
77 //! [`.splitn`]: slice::splitn
78 //! [`.chunks`]: slice::chunks
79 //! [`.windows`]: slice::windows
80 #![stable(feature = "rust1", since = "1.0.0")]
81 // Many of the usings in this module are only used in the test configuration.
82 // It's cleaner to just turn off the unused_imports warning than to fix them.
83 #![cfg_attr(test, allow(unused_imports, dead_code))]
85 use core
::borrow
::{Borrow, BorrowMut}
;
86 use core
::cmp
::Ordering
::{self, Less}
;
87 use core
::mem
::{self, size_of}
;
90 use crate::alloc
::{Allocator, Global}
;
91 use crate::borrow
::ToOwned
;
92 use crate::boxed
::Box
;
95 #[unstable(feature = "slice_range", issue = "76393")]
96 pub use core
::slice
::range
;
97 #[unstable(feature = "array_chunks", issue = "74985")]
98 pub use core
::slice
::ArrayChunks
;
99 #[unstable(feature = "array_chunks", issue = "74985")]
100 pub use core
::slice
::ArrayChunksMut
;
101 #[unstable(feature = "array_windows", issue = "75027")]
102 pub use core
::slice
::ArrayWindows
;
103 #[stable(feature = "slice_get_slice", since = "1.28.0")]
104 pub use core
::slice
::SliceIndex
;
105 #[stable(feature = "from_ref", since = "1.28.0")]
106 pub use core
::slice
::{from_mut, from_ref}
;
107 #[stable(feature = "rust1", since = "1.0.0")]
108 pub use core
::slice
::{from_raw_parts, from_raw_parts_mut}
;
109 #[stable(feature = "rust1", since = "1.0.0")]
110 pub use core
::slice
::{Chunks, Windows}
;
111 #[stable(feature = "chunks_exact", since = "1.31.0")]
112 pub use core
::slice
::{ChunksExact, ChunksExactMut}
;
113 #[stable(feature = "rust1", since = "1.0.0")]
114 pub use core
::slice
::{ChunksMut, Split, SplitMut}
;
115 #[unstable(feature = "slice_group_by", issue = "80552")]
116 pub use core
::slice
::{GroupBy, GroupByMut}
;
117 #[stable(feature = "rust1", since = "1.0.0")]
118 pub use core
::slice
::{Iter, IterMut}
;
119 #[stable(feature = "rchunks", since = "1.31.0")]
120 pub use core
::slice
::{RChunks, RChunksExact, RChunksExactMut, RChunksMut}
;
121 #[stable(feature = "slice_rsplit", since = "1.27.0")]
122 pub use core
::slice
::{RSplit, RSplitMut}
;
123 #[stable(feature = "rust1", since = "1.0.0")]
124 pub use core
::slice
::{RSplitN, RSplitNMut, SplitN, SplitNMut}
;
126 ////////////////////////////////////////////////////////////////////////////////
127 // Basic slice extension methods
128 ////////////////////////////////////////////////////////////////////////////////
130 // HACK(japaric) needed for the implementation of `vec!` macro during testing
131 // N.B., see the `hack` module in this file for more details.
133 pub use hack
::into_vec
;
135 // HACK(japaric) needed for the implementation of `Vec::clone` during testing
136 // N.B., see the `hack` module in this file for more details.
138 pub use hack
::to_vec
;
140 // HACK(japaric): With cfg(test) `impl [T]` is not available, these three
141 // functions are actually methods that are in `impl [T]` but not in
142 // `core::slice::SliceExt` - we need to supply these functions for the
143 // `test_permutations` test
145 use core
::alloc
::Allocator
;
147 use crate::boxed
::Box
;
150 // We shouldn't add inline attribute to this since this is used in
151 // `vec!` macro mostly and causes perf regression. See #71204 for
152 // discussion and perf results.
153 pub fn into_vec
<T
, A
: Allocator
>(b
: Box
<[T
], A
>) -> Vec
<T
, A
> {
156 let (b
, alloc
) = Box
::into_raw_with_allocator(b
);
157 Vec
::from_raw_parts_in(b
as *mut T
, len
, len
, alloc
)
162 pub fn to_vec
<T
: ConvertVec
, A
: Allocator
>(s
: &[T
], alloc
: A
) -> Vec
<T
, A
> {
166 pub trait ConvertVec
{
167 fn to_vec
<A
: Allocator
>(s
: &[Self], alloc
: A
) -> Vec
<Self, A
>
172 impl<T
: Clone
> ConvertVec
for T
{
174 default fn to_vec
<A
: Allocator
>(s
: &[Self], alloc
: A
) -> Vec
<Self, A
> {
175 struct DropGuard
<'a
, T
, A
: Allocator
> {
176 vec
: &'a
mut Vec
<T
, A
>,
179 impl<'a
, T
, A
: Allocator
> Drop
for DropGuard
<'a
, T
, A
> {
183 // items were marked initialized in the loop below
185 self.vec
.set_len(self.num_init
);
189 let mut vec
= Vec
::with_capacity_in(s
.len(), alloc
);
190 let mut guard
= DropGuard { vec: &mut vec, num_init: 0 }
;
191 let slots
= guard
.vec
.spare_capacity_mut();
192 // .take(slots.len()) is necessary for LLVM to remove bounds checks
193 // and has better codegen than zip.
194 for (i
, b
) in s
.iter().enumerate().take(slots
.len()) {
196 slots
[i
].write(b
.clone());
198 core
::mem
::forget(guard
);
200 // the vec was allocated and initialized above to at least this length.
202 vec
.set_len(s
.len());
208 impl<T
: Copy
> ConvertVec
for T
{
210 fn to_vec
<A
: Allocator
>(s
: &[Self], alloc
: A
) -> Vec
<Self, A
> {
211 let mut v
= Vec
::with_capacity_in(s
.len(), alloc
);
213 // allocated above with the capacity of `s`, and initialize to `s.len()` in
214 // ptr::copy_to_non_overlapping below.
216 s
.as_ptr().copy_to_nonoverlapping(v
.as_mut_ptr(), s
.len());
224 #[lang = "slice_alloc"]
225 #[cfg_attr(not(test), rustc_diagnostic_item = "slice")]
230 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case.
232 /// When applicable, unstable sorting is preferred because it is generally faster than stable
233 /// sorting and it doesn't allocate auxiliary memory.
234 /// See [`sort_unstable`](slice::sort_unstable).
236 /// # Current implementation
238 /// The current algorithm is an adaptive, iterative merge sort inspired by
239 /// [timsort](https://en.wikipedia.org/wiki/Timsort).
240 /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
241 /// two or more sorted sequences concatenated one after another.
243 /// Also, it allocates temporary storage half the size of `self`, but for short slices a
244 /// non-allocating insertion sort is used instead.
249 /// let mut v = [-5, 4, 1, -3, 2];
252 /// assert!(v == [-5, -3, 1, 2, 4]);
254 #[stable(feature = "rust1", since = "1.0.0")]
256 pub fn sort(&mut self)
260 merge_sort(self, |a
, b
| a
.lt(b
));
263 /// Sorts the slice with a comparator function.
265 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case.
267 /// The comparator function must define a total ordering for the elements in the slice. If
268 /// the ordering is not total, the order of the elements is unspecified. An order is a
269 /// total order if it is (for all `a`, `b` and `c`):
271 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
272 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
274 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
275 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
278 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
279 /// floats.sort_by(|a, b| a.partial_cmp(b).unwrap());
280 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
283 /// When applicable, unstable sorting is preferred because it is generally faster than stable
284 /// sorting and it doesn't allocate auxiliary memory.
285 /// See [`sort_unstable_by`](slice::sort_unstable_by).
287 /// # Current implementation
289 /// The current algorithm is an adaptive, iterative merge sort inspired by
290 /// [timsort](https://en.wikipedia.org/wiki/Timsort).
291 /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
292 /// two or more sorted sequences concatenated one after another.
294 /// Also, it allocates temporary storage half the size of `self`, but for short slices a
295 /// non-allocating insertion sort is used instead.
300 /// let mut v = [5, 4, 1, 3, 2];
301 /// v.sort_by(|a, b| a.cmp(b));
302 /// assert!(v == [1, 2, 3, 4, 5]);
304 /// // reverse sorting
305 /// v.sort_by(|a, b| b.cmp(a));
306 /// assert!(v == [5, 4, 3, 2, 1]);
308 #[stable(feature = "rust1", since = "1.0.0")]
310 pub fn sort_by
<F
>(&mut self, mut compare
: F
)
312 F
: FnMut(&T
, &T
) -> Ordering
,
314 merge_sort(self, |a
, b
| compare(a
, b
) == Less
);
317 /// Sorts the slice with a key extraction function.
319 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* \* log(*n*))
320 /// worst-case, where the key function is *O*(*m*).
322 /// For expensive key functions (e.g. functions that are not simple property accesses or
323 /// basic operations), [`sort_by_cached_key`](slice::sort_by_cached_key) is likely to be
324 /// significantly faster, as it does not recompute element keys.
326 /// When applicable, unstable sorting is preferred because it is generally faster than stable
327 /// sorting and it doesn't allocate auxiliary memory.
328 /// See [`sort_unstable_by_key`](slice::sort_unstable_by_key).
330 /// # Current implementation
332 /// The current algorithm is an adaptive, iterative merge sort inspired by
333 /// [timsort](https://en.wikipedia.org/wiki/Timsort).
334 /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
335 /// two or more sorted sequences concatenated one after another.
337 /// Also, it allocates temporary storage half the size of `self`, but for short slices a
338 /// non-allocating insertion sort is used instead.
343 /// let mut v = [-5i32, 4, 1, -3, 2];
345 /// v.sort_by_key(|k| k.abs());
346 /// assert!(v == [1, 2, -3, 4, -5]);
348 #[stable(feature = "slice_sort_by_key", since = "1.7.0")]
350 pub fn sort_by_key
<K
, F
>(&mut self, mut f
: F
)
355 merge_sort(self, |a
, b
| f(a
).lt(&f(b
)));
358 /// Sorts the slice with a key extraction function.
360 /// During sorting, the key function is called only once per element.
362 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* + *n* \* log(*n*))
363 /// worst-case, where the key function is *O*(*m*).
365 /// For simple key functions (e.g., functions that are property accesses or
366 /// basic operations), [`sort_by_key`](slice::sort_by_key) is likely to be
369 /// # Current implementation
371 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
372 /// which combines the fast average case of randomized quicksort with the fast worst case of
373 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
374 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
375 /// deterministic behavior.
377 /// In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the
378 /// length of the slice.
383 /// let mut v = [-5i32, 4, 32, -3, 2];
385 /// v.sort_by_cached_key(|k| k.to_string());
386 /// assert!(v == [-3, -5, 2, 32, 4]);
389 /// [pdqsort]: https://github.com/orlp/pdqsort
390 #[stable(feature = "slice_sort_by_cached_key", since = "1.34.0")]
392 pub fn sort_by_cached_key
<K
, F
>(&mut self, f
: F
)
397 // Helper macro for indexing our vector by the smallest possible type, to reduce allocation.
398 macro_rules
! sort_by_key
{
399 ($t
:ty
, $slice
:ident
, $f
:ident
) => {{
400 let mut indices
: Vec
<_
> =
401 $slice
.iter().map($f
).enumerate().map(|(i
, k
)| (k
, i
as $t
)).collect();
402 // The elements of `indices` are unique, as they are indexed, so any sort will be
403 // stable with respect to the original slice. We use `sort_unstable` here because
404 // it requires less memory allocation.
405 indices
.sort_unstable();
406 for i
in 0..$slice
.len() {
407 let mut index
= indices
[i
].1;
408 while (index
as usize) < i
{
409 index
= indices
[index
as usize].1;
411 indices
[i
].1 = index
;
412 $slice
.swap(i
, index
as usize);
417 let sz_u8
= mem
::size_of
::<(K
, u8)>();
418 let sz_u16
= mem
::size_of
::<(K
, u16)>();
419 let sz_u32
= mem
::size_of
::<(K
, u32)>();
420 let sz_usize
= mem
::size_of
::<(K
, usize)>();
422 let len
= self.len();
426 if sz_u8
< sz_u16
&& len
<= (u8::MAX
as usize) {
427 return sort_by_key
!(u8, self, f
);
429 if sz_u16
< sz_u32
&& len
<= (u16::MAX
as usize) {
430 return sort_by_key
!(u16, self, f
);
432 if sz_u32
< sz_usize
&& len
<= (u32::MAX
as usize) {
433 return sort_by_key
!(u32, self, f
);
435 sort_by_key
!(usize, self, f
)
438 /// Copies `self` into a new `Vec`.
443 /// let s = [10, 40, 30];
444 /// let x = s.to_vec();
445 /// // Here, `s` and `x` can be modified independently.
447 #[rustc_conversion_suggestion]
448 #[stable(feature = "rust1", since = "1.0.0")]
450 pub fn to_vec(&self) -> Vec
<T
>
454 self.to_vec_in(Global
)
457 /// Copies `self` into a new `Vec` with an allocator.
462 /// #![feature(allocator_api)]
464 /// use std::alloc::System;
466 /// let s = [10, 40, 30];
467 /// let x = s.to_vec_in(System);
468 /// // Here, `s` and `x` can be modified independently.
471 #[unstable(feature = "allocator_api", issue = "32838")]
472 pub fn to_vec_in
<A
: Allocator
>(&self, alloc
: A
) -> Vec
<T
, A
>
476 // N.B., see the `hack` module in this file for more details.
477 hack
::to_vec(self, alloc
)
480 /// Converts `self` into a vector without clones or allocation.
482 /// The resulting vector can be converted back into a box via
483 /// `Vec<T>`'s `into_boxed_slice` method.
488 /// let s: Box<[i32]> = Box::new([10, 40, 30]);
489 /// let x = s.into_vec();
490 /// // `s` cannot be used anymore because it has been converted into `x`.
492 /// assert_eq!(x, vec![10, 40, 30]);
494 #[stable(feature = "rust1", since = "1.0.0")]
496 pub fn into_vec
<A
: Allocator
>(self: Box
<Self, A
>) -> Vec
<T
, A
> {
497 // N.B., see the `hack` module in this file for more details.
501 /// Creates a vector by repeating a slice `n` times.
505 /// This function will panic if the capacity would overflow.
512 /// assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]);
515 /// A panic upon overflow:
518 /// // this will panic at runtime
519 /// b"0123456789abcdef".repeat(usize::MAX);
521 #[stable(feature = "repeat_generic_slice", since = "1.40.0")]
522 pub fn repeat(&self, n
: usize) -> Vec
<T
>
530 // If `n` is larger than zero, it can be split as
531 // `n = 2^expn + rem (2^expn > rem, expn >= 0, rem >= 0)`.
532 // `2^expn` is the number represented by the leftmost '1' bit of `n`,
533 // and `rem` is the remaining part of `n`.
535 // Using `Vec` to access `set_len()`.
536 let capacity
= self.len().checked_mul(n
).expect("capacity overflow");
537 let mut buf
= Vec
::with_capacity(capacity
);
539 // `2^expn` repetition is done by doubling `buf` `expn`-times.
543 // If `m > 0`, there are remaining bits up to the leftmost '1'.
545 // `buf.extend(buf)`:
547 ptr
::copy_nonoverlapping(
549 (buf
.as_mut_ptr() as *mut T
).add(buf
.len()),
552 // `buf` has capacity of `self.len() * n`.
553 let buf_len
= buf
.len();
554 buf
.set_len(buf_len
* 2);
561 // `rem` (`= n - 2^expn`) repetition is done by copying
562 // first `rem` repetitions from `buf` itself.
563 let rem_len
= capacity
- buf
.len(); // `self.len() * rem`
565 // `buf.extend(buf[0 .. rem_len])`:
567 // This is non-overlapping since `2^expn > rem`.
568 ptr
::copy_nonoverlapping(
570 (buf
.as_mut_ptr() as *mut T
).add(buf
.len()),
573 // `buf.len() + rem_len` equals to `buf.capacity()` (`= self.len() * n`).
574 buf
.set_len(capacity
);
580 /// Flattens a slice of `T` into a single value `Self::Output`.
585 /// assert_eq!(["hello", "world"].concat(), "helloworld");
586 /// assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);
588 #[stable(feature = "rust1", since = "1.0.0")]
589 pub fn concat
<Item
: ?Sized
>(&self) -> <Self as Concat
<Item
>>::Output
596 /// Flattens a slice of `T` into a single value `Self::Output`, placing a
597 /// given separator between each.
602 /// assert_eq!(["hello", "world"].join(" "), "hello world");
603 /// assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
604 /// assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]);
606 #[stable(feature = "rename_connect_to_join", since = "1.3.0")]
607 pub fn join
<Separator
>(&self, sep
: Separator
) -> <Self as Join
<Separator
>>::Output
609 Self: Join
<Separator
>,
611 Join
::join(self, sep
)
614 /// Flattens a slice of `T` into a single value `Self::Output`, placing a
615 /// given separator between each.
620 /// # #![allow(deprecated)]
621 /// assert_eq!(["hello", "world"].connect(" "), "hello world");
622 /// assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]);
624 #[stable(feature = "rust1", since = "1.0.0")]
625 #[rustc_deprecated(since = "1.3.0", reason = "renamed to join")]
626 pub fn connect
<Separator
>(&self, sep
: Separator
) -> <Self as Join
<Separator
>>::Output
628 Self: Join
<Separator
>,
630 Join
::join(self, sep
)
634 #[lang = "slice_u8_alloc"]
637 /// Returns a vector containing a copy of this slice where each byte
638 /// is mapped to its ASCII upper case equivalent.
640 /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
641 /// but non-ASCII letters are unchanged.
643 /// To uppercase the value in-place, use [`make_ascii_uppercase`].
645 /// [`make_ascii_uppercase`]: u8::make_ascii_uppercase
646 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
648 pub fn to_ascii_uppercase(&self) -> Vec
<u8> {
649 let mut me
= self.to_vec();
650 me
.make_ascii_uppercase();
654 /// Returns a vector containing a copy of this slice where each byte
655 /// is mapped to its ASCII lower case equivalent.
657 /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
658 /// but non-ASCII letters are unchanged.
660 /// To lowercase the value in-place, use [`make_ascii_lowercase`].
662 /// [`make_ascii_lowercase`]: u8::make_ascii_lowercase
663 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
665 pub fn to_ascii_lowercase(&self) -> Vec
<u8> {
666 let mut me
= self.to_vec();
667 me
.make_ascii_lowercase();
672 ////////////////////////////////////////////////////////////////////////////////
673 // Extension traits for slices over specific kinds of data
674 ////////////////////////////////////////////////////////////////////////////////
676 /// Helper trait for [`[T]::concat`](slice::concat).
678 /// Note: the `Item` type parameter is not used in this trait,
679 /// but it allows impls to be more generic.
680 /// Without it, we get this error:
683 /// error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predica
684 /// --> src/liballoc/slice.rs:608:6
686 /// 608 | impl<T: Clone, V: Borrow<[T]>> Concat for [V] {
687 /// | ^ unconstrained type parameter
690 /// This is because there could exist `V` types with multiple `Borrow<[_]>` impls,
691 /// such that multiple `T` types would apply:
694 /// # #[allow(dead_code)]
695 /// pub struct Foo(Vec<u32>, Vec<String>);
697 /// impl std::borrow::Borrow<[u32]> for Foo {
698 /// fn borrow(&self) -> &[u32] { &self.0 }
701 /// impl std::borrow::Borrow<[String]> for Foo {
702 /// fn borrow(&self) -> &[String] { &self.1 }
705 #[unstable(feature = "slice_concat_trait", issue = "27747")]
706 pub trait Concat
<Item
: ?Sized
> {
707 #[unstable(feature = "slice_concat_trait", issue = "27747")]
708 /// The resulting type after concatenation
711 /// Implementation of [`[T]::concat`](slice::concat)
712 #[unstable(feature = "slice_concat_trait", issue = "27747")]
713 fn concat(slice
: &Self) -> Self::Output
;
716 /// Helper trait for [`[T]::join`](slice::join)
717 #[unstable(feature = "slice_concat_trait", issue = "27747")]
718 pub trait Join
<Separator
> {
719 #[unstable(feature = "slice_concat_trait", issue = "27747")]
720 /// The resulting type after concatenation
723 /// Implementation of [`[T]::join`](slice::join)
724 #[unstable(feature = "slice_concat_trait", issue = "27747")]
725 fn join(slice
: &Self, sep
: Separator
) -> Self::Output
;
728 #[unstable(feature = "slice_concat_ext", issue = "27747")]
729 impl<T
: Clone
, V
: Borrow
<[T
]>> Concat
<T
> for [V
] {
730 type Output
= Vec
<T
>;
732 fn concat(slice
: &Self) -> Vec
<T
> {
733 let size
= slice
.iter().map(|slice
| slice
.borrow().len()).sum();
734 let mut result
= Vec
::with_capacity(size
);
736 result
.extend_from_slice(v
.borrow())
742 #[unstable(feature = "slice_concat_ext", issue = "27747")]
743 impl<T
: Clone
, V
: Borrow
<[T
]>> Join
<&T
> for [V
] {
744 type Output
= Vec
<T
>;
746 fn join(slice
: &Self, sep
: &T
) -> Vec
<T
> {
747 let mut iter
= slice
.iter();
748 let first
= match iter
.next() {
749 Some(first
) => first
,
750 None
=> return vec
![],
752 let size
= slice
.iter().map(|v
| v
.borrow().len()).sum
::<usize>() + slice
.len() - 1;
753 let mut result
= Vec
::with_capacity(size
);
754 result
.extend_from_slice(first
.borrow());
757 result
.push(sep
.clone());
758 result
.extend_from_slice(v
.borrow())
764 #[unstable(feature = "slice_concat_ext", issue = "27747")]
765 impl<T
: Clone
, V
: Borrow
<[T
]>> Join
<&[T
]> for [V
] {
766 type Output
= Vec
<T
>;
768 fn join(slice
: &Self, sep
: &[T
]) -> Vec
<T
> {
769 let mut iter
= slice
.iter();
770 let first
= match iter
.next() {
771 Some(first
) => first
,
772 None
=> return vec
![],
775 slice
.iter().map(|v
| v
.borrow().len()).sum
::<usize>() + sep
.len() * (slice
.len() - 1);
776 let mut result
= Vec
::with_capacity(size
);
777 result
.extend_from_slice(first
.borrow());
780 result
.extend_from_slice(sep
);
781 result
.extend_from_slice(v
.borrow())
787 ////////////////////////////////////////////////////////////////////////////////
788 // Standard trait implementations for slices
789 ////////////////////////////////////////////////////////////////////////////////
791 #[stable(feature = "rust1", since = "1.0.0")]
792 impl<T
> Borrow
<[T
]> for Vec
<T
> {
793 fn borrow(&self) -> &[T
] {
798 #[stable(feature = "rust1", since = "1.0.0")]
799 impl<T
> BorrowMut
<[T
]> for Vec
<T
> {
800 fn borrow_mut(&mut self) -> &mut [T
] {
805 #[stable(feature = "rust1", since = "1.0.0")]
806 impl<T
: Clone
> ToOwned
for [T
] {
809 fn to_owned(&self) -> Vec
<T
> {
814 fn to_owned(&self) -> Vec
<T
> {
815 hack
::to_vec(self, Global
)
818 fn clone_into(&self, target
: &mut Vec
<T
>) {
819 // drop anything in target that will not be overwritten
820 target
.truncate(self.len());
822 // target.len <= self.len due to the truncate above, so the
823 // slices here are always in-bounds.
824 let (init
, tail
) = self.split_at(target
.len());
826 // reuse the contained values' allocations/resources.
827 target
.clone_from_slice(init
);
828 target
.extend_from_slice(tail
);
832 ////////////////////////////////////////////////////////////////////////////////
834 ////////////////////////////////////////////////////////////////////////////////
836 /// Inserts `v[0]` into pre-sorted sequence `v[1..]` so that whole `v[..]` becomes sorted.
838 /// This is the integral subroutine of insertion sort.
839 fn insert_head
<T
, F
>(v
: &mut [T
], is_less
: &mut F
)
841 F
: FnMut(&T
, &T
) -> bool
,
843 if v
.len() >= 2 && is_less(&v
[1], &v
[0]) {
845 // There are three ways to implement insertion here:
847 // 1. Swap adjacent elements until the first one gets to its final destination.
848 // However, this way we copy data around more than is necessary. If elements are big
849 // structures (costly to copy), this method will be slow.
851 // 2. Iterate until the right place for the first element is found. Then shift the
852 // elements succeeding it to make room for it and finally place it into the
853 // remaining hole. This is a good method.
855 // 3. Copy the first element into a temporary variable. Iterate until the right place
856 // for it is found. As we go along, copy every traversed element into the slot
857 // preceding it. Finally, copy data from the temporary variable into the remaining
858 // hole. This method is very good. Benchmarks demonstrated slightly better
859 // performance than with the 2nd method.
861 // All methods were benchmarked, and the 3rd showed best results. So we chose that one.
862 let mut tmp
= mem
::ManuallyDrop
::new(ptr
::read(&v
[0]));
864 // Intermediate state of the insertion process is always tracked by `hole`, which
865 // serves two purposes:
866 // 1. Protects integrity of `v` from panics in `is_less`.
867 // 2. Fills the remaining hole in `v` in the end.
871 // If `is_less` panics at any point during the process, `hole` will get dropped and
872 // fill the hole in `v` with `tmp`, thus ensuring that `v` still holds every object it
873 // initially held exactly once.
874 let mut hole
= InsertionHole { src: &mut *tmp, dest: &mut v[1] }
;
875 ptr
::copy_nonoverlapping(&v
[1], &mut v
[0], 1);
877 for i
in 2..v
.len() {
878 if !is_less(&v
[i
], &*tmp
) {
881 ptr
::copy_nonoverlapping(&v
[i
], &mut v
[i
- 1], 1);
882 hole
.dest
= &mut v
[i
];
884 // `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
888 // When dropped, copies from `src` into `dest`.
889 struct InsertionHole
<T
> {
894 impl<T
> Drop
for InsertionHole
<T
> {
897 ptr
::copy_nonoverlapping(self.src
, self.dest
, 1);
903 /// Merges non-decreasing runs `v[..mid]` and `v[mid..]` using `buf` as temporary storage, and
904 /// stores the result into `v[..]`.
908 /// The two slices must be non-empty and `mid` must be in bounds. Buffer `buf` must be long enough
909 /// to hold a copy of the shorter slice. Also, `T` must not be a zero-sized type.
910 unsafe fn merge
<T
, F
>(v
: &mut [T
], mid
: usize, buf
: *mut T
, is_less
: &mut F
)
912 F
: FnMut(&T
, &T
) -> bool
,
915 let v
= v
.as_mut_ptr();
916 let (v_mid
, v_end
) = unsafe { (v.add(mid), v.add(len)) }
;
918 // The merge process first copies the shorter run into `buf`. Then it traces the newly copied
919 // run and the longer run forwards (or backwards), comparing their next unconsumed elements and
920 // copying the lesser (or greater) one into `v`.
922 // As soon as the shorter run is fully consumed, the process is done. If the longer run gets
923 // consumed first, then we must copy whatever is left of the shorter run into the remaining
926 // Intermediate state of the process is always tracked by `hole`, which serves two purposes:
927 // 1. Protects integrity of `v` from panics in `is_less`.
928 // 2. Fills the remaining hole in `v` if the longer run gets consumed first.
932 // If `is_less` panics at any point during the process, `hole` will get dropped and fill the
933 // hole in `v` with the unconsumed range in `buf`, thus ensuring that `v` still holds every
934 // object it initially held exactly once.
937 if mid
<= len
- mid
{
938 // The left run is shorter.
940 ptr
::copy_nonoverlapping(v
, buf
, mid
);
941 hole
= MergeHole { start: buf, end: buf.add(mid), dest: v }
;
944 // Initially, these pointers point to the beginnings of their arrays.
945 let left
= &mut hole
.start
;
946 let mut right
= v_mid
;
947 let out
= &mut hole
.dest
;
949 while *left
< hole
.end
&& right
< v_end
{
950 // Consume the lesser side.
951 // If equal, prefer the left run to maintain stability.
953 let to_copy
= if is_less(&*right
, &**left
) {
954 get_and_increment(&mut right
)
956 get_and_increment(left
)
958 ptr
::copy_nonoverlapping(to_copy
, get_and_increment(out
), 1);
962 // The right run is shorter.
964 ptr
::copy_nonoverlapping(v_mid
, buf
, len
- mid
);
965 hole
= MergeHole { start: buf, end: buf.add(len - mid), dest: v_mid }
;
968 // Initially, these pointers point past the ends of their arrays.
969 let left
= &mut hole
.dest
;
970 let right
= &mut hole
.end
;
973 while v
< *left
&& buf
< *right
{
974 // Consume the greater side.
975 // If equal, prefer the right run to maintain stability.
977 let to_copy
= if is_less(&*right
.offset(-1), &*left
.offset(-1)) {
978 decrement_and_get(left
)
980 decrement_and_get(right
)
982 ptr
::copy_nonoverlapping(to_copy
, decrement_and_get(&mut out
), 1);
986 // Finally, `hole` gets dropped. If the shorter run was not fully consumed, whatever remains of
987 // it will now be copied into the hole in `v`.
989 unsafe fn get_and_increment
<T
>(ptr
: &mut *mut T
) -> *mut T
{
991 *ptr
= unsafe { ptr.offset(1) }
;
995 unsafe fn decrement_and_get
<T
>(ptr
: &mut *mut T
) -> *mut T
{
996 *ptr
= unsafe { ptr.offset(-1) }
;
1000 // When dropped, copies the range `start..end` into `dest..`.
1001 struct MergeHole
<T
> {
1007 impl<T
> Drop
for MergeHole
<T
> {
1008 fn drop(&mut self) {
1009 // `T` is not a zero-sized type, so it's okay to divide by its size.
1010 let len
= (self.end
as usize - self.start
as usize) / mem
::size_of
::<T
>();
1012 ptr
::copy_nonoverlapping(self.start
, self.dest
, len
);
1018 /// This merge sort borrows some (but not all) ideas from TimSort, which is described in detail
1019 /// [here](http://svn.python.org/projects/python/trunk/Objects/listsort.txt).
1021 /// The algorithm identifies strictly descending and non-descending subsequences, which are called
1022 /// natural runs. There is a stack of pending runs yet to be merged. Each newly found run is pushed
1023 /// onto the stack, and then some pairs of adjacent runs are merged until these two invariants are
1026 /// 1. for every `i` in `1..runs.len()`: `runs[i - 1].len > runs[i].len`
1027 /// 2. for every `i` in `2..runs.len()`: `runs[i - 2].len > runs[i - 1].len + runs[i].len`
1029 /// The invariants ensure that the total running time is *O*(*n* \* log(*n*)) worst-case.
1030 fn merge_sort
<T
, F
>(v
: &mut [T
], mut is_less
: F
)
1032 F
: FnMut(&T
, &T
) -> bool
,
1034 // Slices of up to this length get sorted using insertion sort.
1035 const MAX_INSERTION
: usize = 20;
1036 // Very short runs are extended using insertion sort to span at least this many elements.
1037 const MIN_RUN
: usize = 10;
1039 // Sorting has no meaningful behavior on zero-sized types.
1040 if size_of
::<T
>() == 0 {
1046 // Short arrays get sorted in-place via insertion sort to avoid allocations.
1047 if len
<= MAX_INSERTION
{
1049 for i
in (0..len
- 1).rev() {
1050 insert_head(&mut v
[i
..], &mut is_less
);
1056 // Allocate a buffer to use as scratch memory. We keep the length 0 so we can keep in it
1057 // shallow copies of the contents of `v` without risking the dtors running on copies if
1058 // `is_less` panics. When merging two sorted runs, this buffer holds a copy of the shorter run,
1059 // which will always have length at most `len / 2`.
1060 let mut buf
= Vec
::with_capacity(len
/ 2);
1062 // In order to identify natural runs in `v`, we traverse it backwards. That might seem like a
1063 // strange decision, but consider the fact that merges more often go in the opposite direction
1064 // (forwards). According to benchmarks, merging forwards is slightly faster than merging
1065 // backwards. To conclude, identifying runs by traversing backwards improves performance.
1066 let mut runs
= vec
![];
1069 // Find the next natural run, and reverse it if it's strictly descending.
1070 let mut start
= end
- 1;
1074 if is_less(v
.get_unchecked(start
+ 1), v
.get_unchecked(start
)) {
1075 while start
> 0 && is_less(v
.get_unchecked(start
), v
.get_unchecked(start
- 1)) {
1078 v
[start
..end
].reverse();
1080 while start
> 0 && !is_less(v
.get_unchecked(start
), v
.get_unchecked(start
- 1))
1088 // Insert some more elements into the run if it's too short. Insertion sort is faster than
1089 // merge sort on short sequences, so this significantly improves performance.
1090 while start
> 0 && end
- start
< MIN_RUN
{
1092 insert_head(&mut v
[start
..end
], &mut is_less
);
1095 // Push this run onto the stack.
1096 runs
.push(Run { start, len: end - start }
);
1099 // Merge some pairs of adjacent runs to satisfy the invariants.
1100 while let Some(r
) = collapse(&runs
) {
1101 let left
= runs
[r
+ 1];
1102 let right
= runs
[r
];
1105 &mut v
[left
.start
..right
.start
+ right
.len
],
1111 runs
[r
] = Run { start: left.start, len: left.len + right.len }
;
1116 // Finally, exactly one run must remain in the stack.
1117 debug_assert
!(runs
.len() == 1 && runs
[0].start
== 0 && runs
[0].len
== len
);
1119 // Examines the stack of runs and identifies the next pair of runs to merge. More specifically,
1120 // if `Some(r)` is returned, that means `runs[r]` and `runs[r + 1]` must be merged next. If the
1121 // algorithm should continue building a new run instead, `None` is returned.
1123 // TimSort is infamous for its buggy implementations, as described here:
1124 // http://envisage-project.eu/timsort-specification-and-verification/
1126 // The gist of the story is: we must enforce the invariants on the top four runs on the stack.
1127 // Enforcing them on just top three is not sufficient to ensure that the invariants will still
1128 // hold for *all* runs in the stack.
1130 // This function correctly checks invariants for the top four runs. Additionally, if the top
1131 // run starts at index 0, it will always demand a merge operation until the stack is fully
1132 // collapsed, in order to complete the sort.
1134 fn collapse(runs
: &[Run
]) -> Option
<usize> {
1137 && (runs
[n
- 1].start
== 0
1138 || runs
[n
- 2].len
<= runs
[n
- 1].len
1139 || (n
>= 3 && runs
[n
- 3].len
<= runs
[n
- 2].len
+ runs
[n
- 1].len
)
1140 || (n
>= 4 && runs
[n
- 4].len
<= runs
[n
- 3].len
+ runs
[n
- 2].len
))
1142 if n
>= 3 && runs
[n
- 3].len
< runs
[n
- 1].len { Some(n - 3) }
else { Some(n - 2) }
1148 #[derive(Clone, Copy)]