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1// SPDX-License-Identifier: Apache-2.0 OR MIT
2
3//! A dynamically-sized view into a contiguous sequence, `[T]`.
4//!
5//! *[See also the slice primitive type](slice).*
6//!
7//! Slices are a view into a block of memory represented as a pointer and a
8//! length.
9//!
10//! ```
11//! // slicing a Vec
12//! let vec = vec![1, 2, 3];
13//! let int_slice = &vec[..];
14//! // coercing an array to a slice
15//! let str_slice: &[&str] = &["one", "two", "three"];
16//! ```
17//!
18//! Slices are either mutable or shared. The shared slice type is `&[T]`,
19//! while the mutable slice type is `&mut [T]`, where `T` represents the element
20//! type. For example, you can mutate the block of memory that a mutable slice
21//! points to:
22//!
23//! ```
24//! let x = &mut [1, 2, 3];
25//! x[1] = 7;
26//! assert_eq!(x, &[1, 7, 3]);
27//! ```
28//!
29//! Here are some of the things this module contains:
30//!
31//! ## Structs
32//!
33//! There are several structs that are useful for slices, such as [`Iter`], which
34//! represents iteration over a slice.
35//!
36//! ## Trait Implementations
37//!
38//! There are several implementations of common traits for slices. Some examples
39//! include:
40//!
41//! * [`Clone`]
42//! * [`Eq`], [`Ord`] - for slices whose element type are [`Eq`] or [`Ord`].
43//! * [`Hash`] - for slices whose element type is [`Hash`].
44//!
45//! ## Iteration
46//!
47//! The slices implement `IntoIterator`. The iterator yields references to the
48//! slice elements.
49//!
50//! ```
51//! let numbers = &[0, 1, 2];
52//! for n in numbers {
53//! println!("{n} is a number!");
54//! }
55//! ```
56//!
57//! The mutable slice yields mutable references to the elements:
58//!
59//! ```
60//! let mut scores = [7, 8, 9];
61//! for score in &mut scores[..] {
62//! *score += 1;
63//! }
64//! ```
65//!
66//! This iterator yields mutable references to the slice's elements, so while
67//! the element type of the slice is `i32`, the element type of the iterator is
68//! `&mut i32`.
69//!
70//! * [`.iter`] and [`.iter_mut`] are the explicit methods to return the default
71//! iterators.
72//! * Further methods that return iterators are [`.split`], [`.splitn`],
73//! [`.chunks`], [`.windows`] and more.
74//!
75//! [`Hash`]: core::hash::Hash
76//! [`.iter`]: slice::iter
77//! [`.iter_mut`]: slice::iter_mut
78//! [`.split`]: slice::split
79//! [`.splitn`]: slice::splitn
80//! [`.chunks`]: slice::chunks
81//! [`.windows`]: slice::windows
82#![stable(feature = "rust1", since = "1.0.0")]
83// Many of the usings in this module are only used in the test configuration.
84// It's cleaner to just turn off the unused_imports warning than to fix them.
85#![cfg_attr(test, allow(unused_imports, dead_code))]
86
87use core::borrow::{Borrow, BorrowMut};
88#[cfg(not(no_global_oom_handling))]
89use core::cmp::Ordering::{self, Less};
90#[cfg(not(no_global_oom_handling))]
91use core::mem;
92#[cfg(not(no_global_oom_handling))]
93use core::mem::size_of;
94#[cfg(not(no_global_oom_handling))]
95use core::ptr;
96
97use crate::alloc::Allocator;
98#[cfg(not(no_global_oom_handling))]
99use crate::alloc::Global;
100#[cfg(not(no_global_oom_handling))]
101use crate::borrow::ToOwned;
102use crate::boxed::Box;
103use crate::vec::Vec;
104
105#[unstable(feature = "slice_range", issue = "76393")]
106pub use core::slice::range;
107#[unstable(feature = "array_chunks", issue = "74985")]
108pub use core::slice::ArrayChunks;
109#[unstable(feature = "array_chunks", issue = "74985")]
110pub use core::slice::ArrayChunksMut;
111#[unstable(feature = "array_windows", issue = "75027")]
112pub use core::slice::ArrayWindows;
113#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
114pub use core::slice::EscapeAscii;
115#[stable(feature = "slice_get_slice", since = "1.28.0")]
116pub use core::slice::SliceIndex;
117#[stable(feature = "from_ref", since = "1.28.0")]
118pub use core::slice::{from_mut, from_ref};
119#[stable(feature = "rust1", since = "1.0.0")]
120pub use core::slice::{from_raw_parts, from_raw_parts_mut};
121#[stable(feature = "rust1", since = "1.0.0")]
122pub use core::slice::{Chunks, Windows};
123#[stable(feature = "chunks_exact", since = "1.31.0")]
124pub use core::slice::{ChunksExact, ChunksExactMut};
125#[stable(feature = "rust1", since = "1.0.0")]
126pub use core::slice::{ChunksMut, Split, SplitMut};
127#[unstable(feature = "slice_group_by", issue = "80552")]
128pub use core::slice::{GroupBy, GroupByMut};
129#[stable(feature = "rust1", since = "1.0.0")]
130pub use core::slice::{Iter, IterMut};
131#[stable(feature = "rchunks", since = "1.31.0")]
132pub use core::slice::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
133#[stable(feature = "slice_rsplit", since = "1.27.0")]
134pub use core::slice::{RSplit, RSplitMut};
135#[stable(feature = "rust1", since = "1.0.0")]
136pub use core::slice::{RSplitN, RSplitNMut, SplitN, SplitNMut};
137#[stable(feature = "split_inclusive", since = "1.51.0")]
138pub use core::slice::{SplitInclusive, SplitInclusiveMut};
139
140////////////////////////////////////////////////////////////////////////////////
141// Basic slice extension methods
142////////////////////////////////////////////////////////////////////////////////
143
144// HACK(japaric) needed for the implementation of `vec!` macro during testing
145// N.B., see the `hack` module in this file for more details.
146#[cfg(test)]
147pub use hack::into_vec;
148
149// HACK(japaric) needed for the implementation of `Vec::clone` during testing
150// N.B., see the `hack` module in this file for more details.
151#[cfg(test)]
152pub use hack::to_vec;
153
154// HACK(japaric): With cfg(test) `impl [T]` is not available, these three
155// functions are actually methods that are in `impl [T]` but not in
156// `core::slice::SliceExt` - we need to supply these functions for the
157// `test_permutations` test
158pub(crate) mod hack {
159 use core::alloc::Allocator;
160
161 use crate::boxed::Box;
162 use crate::vec::Vec;
163
164 // We shouldn't add inline attribute to this since this is used in
165 // `vec!` macro mostly and causes perf regression. See #71204 for
166 // discussion and perf results.
167 pub fn into_vec<T, A: Allocator>(b: Box<[T], A>) -> Vec<T, A> {
168 unsafe {
169 let len = b.len();
170 let (b, alloc) = Box::into_raw_with_allocator(b);
171 Vec::from_raw_parts_in(b as *mut T, len, len, alloc)
172 }
173 }
174
175 #[cfg(not(no_global_oom_handling))]
176 #[inline]
177 pub fn to_vec<T: ConvertVec, A: Allocator>(s: &[T], alloc: A) -> Vec<T, A> {
178 T::to_vec(s, alloc)
179 }
180
181 #[cfg(not(no_global_oom_handling))]
182 pub trait ConvertVec {
183 fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A>
184 where
185 Self: Sized;
186 }
187
188 #[cfg(not(no_global_oom_handling))]
189 impl<T: Clone> ConvertVec for T {
190 #[inline]
191 default fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> {
192 struct DropGuard<'a, T, A: Allocator> {
193 vec: &'a mut Vec<T, A>,
194 num_init: usize,
195 }
196 impl<'a, T, A: Allocator> Drop for DropGuard<'a, T, A> {
197 #[inline]
198 fn drop(&mut self) {
199 // SAFETY:
200 // items were marked initialized in the loop below
201 unsafe {
202 self.vec.set_len(self.num_init);
203 }
204 }
205 }
206 let mut vec = Vec::with_capacity_in(s.len(), alloc);
207 let mut guard = DropGuard { vec: &mut vec, num_init: 0 };
208 let slots = guard.vec.spare_capacity_mut();
209 // .take(slots.len()) is necessary for LLVM to remove bounds checks
210 // and has better codegen than zip.
211 for (i, b) in s.iter().enumerate().take(slots.len()) {
212 guard.num_init = i;
213 slots[i].write(b.clone());
214 }
215 core::mem::forget(guard);
216 // SAFETY:
217 // the vec was allocated and initialized above to at least this length.
218 unsafe {
219 vec.set_len(s.len());
220 }
221 vec
222 }
223 }
224
225 #[cfg(not(no_global_oom_handling))]
226 impl<T: Copy> ConvertVec for T {
227 #[inline]
228 fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> {
229 let mut v = Vec::with_capacity_in(s.len(), alloc);
230 // SAFETY:
231 // allocated above with the capacity of `s`, and initialize to `s.len()` in
232 // ptr::copy_to_non_overlapping below.
233 unsafe {
234 s.as_ptr().copy_to_nonoverlapping(v.as_mut_ptr(), s.len());
235 v.set_len(s.len());
236 }
237 v
238 }
239 }
240}
241
242#[cfg(not(test))]
243impl<T> [T] {
244 /// Sorts the slice.
245 ///
246 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case.
247 ///
248 /// When applicable, unstable sorting is preferred because it is generally faster than stable
249 /// sorting and it doesn't allocate auxiliary memory.
250 /// See [`sort_unstable`](slice::sort_unstable).
251 ///
252 /// # Current implementation
253 ///
254 /// The current algorithm is an adaptive, iterative merge sort inspired by
255 /// [timsort](https://en.wikipedia.org/wiki/Timsort).
256 /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
257 /// two or more sorted sequences concatenated one after another.
258 ///
259 /// Also, it allocates temporary storage half the size of `self`, but for short slices a
260 /// non-allocating insertion sort is used instead.
261 ///
262 /// # Examples
263 ///
264 /// ```
265 /// let mut v = [-5, 4, 1, -3, 2];
266 ///
267 /// v.sort();
268 /// assert!(v == [-5, -3, 1, 2, 4]);
269 /// ```
270 #[cfg(not(no_global_oom_handling))]
271 #[rustc_allow_incoherent_impl]
272 #[stable(feature = "rust1", since = "1.0.0")]
273 #[inline]
274 pub fn sort(&mut self)
275 where
276 T: Ord,
277 {
278 merge_sort(self, |a, b| a.lt(b));
279 }
280
281 /// Sorts the slice with a comparator function.
282 ///
283 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case.
284 ///
285 /// The comparator function must define a total ordering for the elements in the slice. If
286 /// the ordering is not total, the order of the elements is unspecified. An order is a
287 /// total order if it is (for all `a`, `b` and `c`):
288 ///
289 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
290 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
291 ///
292 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
293 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
294 ///
295 /// ```
296 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
297 /// floats.sort_by(|a, b| a.partial_cmp(b).unwrap());
298 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
299 /// ```
300 ///
301 /// When applicable, unstable sorting is preferred because it is generally faster than stable
302 /// sorting and it doesn't allocate auxiliary memory.
303 /// See [`sort_unstable_by`](slice::sort_unstable_by).
304 ///
305 /// # Current implementation
306 ///
307 /// The current algorithm is an adaptive, iterative merge sort inspired by
308 /// [timsort](https://en.wikipedia.org/wiki/Timsort).
309 /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
310 /// two or more sorted sequences concatenated one after another.
311 ///
312 /// Also, it allocates temporary storage half the size of `self`, but for short slices a
313 /// non-allocating insertion sort is used instead.
314 ///
315 /// # Examples
316 ///
317 /// ```
318 /// let mut v = [5, 4, 1, 3, 2];
319 /// v.sort_by(|a, b| a.cmp(b));
320 /// assert!(v == [1, 2, 3, 4, 5]);
321 ///
322 /// // reverse sorting
323 /// v.sort_by(|a, b| b.cmp(a));
324 /// assert!(v == [5, 4, 3, 2, 1]);
325 /// ```
326 #[cfg(not(no_global_oom_handling))]
327 #[rustc_allow_incoherent_impl]
328 #[stable(feature = "rust1", since = "1.0.0")]
329 #[inline]
330 pub fn sort_by<F>(&mut self, mut compare: F)
331 where
332 F: FnMut(&T, &T) -> Ordering,
333 {
334 merge_sort(self, |a, b| compare(a, b) == Less);
335 }
336
337 /// Sorts the slice with a key extraction function.
338 ///
339 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* \* log(*n*))
340 /// worst-case, where the key function is *O*(*m*).
341 ///
342 /// For expensive key functions (e.g. functions that are not simple property accesses or
343 /// basic operations), [`sort_by_cached_key`](slice::sort_by_cached_key) is likely to be
344 /// significantly faster, as it does not recompute element keys.
345 ///
346 /// When applicable, unstable sorting is preferred because it is generally faster than stable
347 /// sorting and it doesn't allocate auxiliary memory.
348 /// See [`sort_unstable_by_key`](slice::sort_unstable_by_key).
349 ///
350 /// # Current implementation
351 ///
352 /// The current algorithm is an adaptive, iterative merge sort inspired by
353 /// [timsort](https://en.wikipedia.org/wiki/Timsort).
354 /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
355 /// two or more sorted sequences concatenated one after another.
356 ///
357 /// Also, it allocates temporary storage half the size of `self`, but for short slices a
358 /// non-allocating insertion sort is used instead.
359 ///
360 /// # Examples
361 ///
362 /// ```
363 /// let mut v = [-5i32, 4, 1, -3, 2];
364 ///
365 /// v.sort_by_key(|k| k.abs());
366 /// assert!(v == [1, 2, -3, 4, -5]);
367 /// ```
368 #[cfg(not(no_global_oom_handling))]
369 #[rustc_allow_incoherent_impl]
370 #[stable(feature = "slice_sort_by_key", since = "1.7.0")]
371 #[inline]
372 pub fn sort_by_key<K, F>(&mut self, mut f: F)
373 where
374 F: FnMut(&T) -> K,
375 K: Ord,
376 {
377 merge_sort(self, |a, b| f(a).lt(&f(b)));
378 }
379
380 /// Sorts the slice with a key extraction function.
381 ///
382 /// During sorting, the key function is called at most once per element, by using
383 /// temporary storage to remember the results of key evaluation.
384 /// The order of calls to the key function is unspecified and may change in future versions
385 /// of the standard library.
386 ///
387 /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* + *n* \* log(*n*))
388 /// worst-case, where the key function is *O*(*m*).
389 ///
390 /// For simple key functions (e.g., functions that are property accesses or
391 /// basic operations), [`sort_by_key`](slice::sort_by_key) is likely to be
392 /// faster.
393 ///
394 /// # Current implementation
395 ///
396 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
397 /// which combines the fast average case of randomized quicksort with the fast worst case of
398 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
399 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
400 /// deterministic behavior.
401 ///
402 /// In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the
403 /// length of the slice.
404 ///
405 /// # Examples
406 ///
407 /// ```
408 /// let mut v = [-5i32, 4, 32, -3, 2];
409 ///
410 /// v.sort_by_cached_key(|k| k.to_string());
411 /// assert!(v == [-3, -5, 2, 32, 4]);
412 /// ```
413 ///
414 /// [pdqsort]: https://github.com/orlp/pdqsort
415 #[cfg(not(no_global_oom_handling))]
416 #[rustc_allow_incoherent_impl]
417 #[stable(feature = "slice_sort_by_cached_key", since = "1.34.0")]
418 #[inline]
419 pub fn sort_by_cached_key<K, F>(&mut self, f: F)
420 where
421 F: FnMut(&T) -> K,
422 K: Ord,
423 {
424 // Helper macro for indexing our vector by the smallest possible type, to reduce allocation.
425 macro_rules! sort_by_key {
426 ($t:ty, $slice:ident, $f:ident) => {{
427 let mut indices: Vec<_> =
428 $slice.iter().map($f).enumerate().map(|(i, k)| (k, i as $t)).collect();
429 // The elements of `indices` are unique, as they are indexed, so any sort will be
430 // stable with respect to the original slice. We use `sort_unstable` here because
431 // it requires less memory allocation.
432 indices.sort_unstable();
433 for i in 0..$slice.len() {
434 let mut index = indices[i].1;
435 while (index as usize) < i {
436 index = indices[index as usize].1;
437 }
438 indices[i].1 = index;
439 $slice.swap(i, index as usize);
440 }
441 }};
442 }
443
444 let sz_u8 = mem::size_of::<(K, u8)>();
445 let sz_u16 = mem::size_of::<(K, u16)>();
446 let sz_u32 = mem::size_of::<(K, u32)>();
447 let sz_usize = mem::size_of::<(K, usize)>();
448
449 let len = self.len();
450 if len < 2 {
451 return;
452 }
453 if sz_u8 < sz_u16 && len <= (u8::MAX as usize) {
454 return sort_by_key!(u8, self, f);
455 }
456 if sz_u16 < sz_u32 && len <= (u16::MAX as usize) {
457 return sort_by_key!(u16, self, f);
458 }
459 if sz_u32 < sz_usize && len <= (u32::MAX as usize) {
460 return sort_by_key!(u32, self, f);
461 }
462 sort_by_key!(usize, self, f)
463 }
464
465 /// Copies `self` into a new `Vec`.
466 ///
467 /// # Examples
468 ///
469 /// ```
470 /// let s = [10, 40, 30];
471 /// let x = s.to_vec();
472 /// // Here, `s` and `x` can be modified independently.
473 /// ```
474 #[cfg(not(no_global_oom_handling))]
475 #[rustc_allow_incoherent_impl]
476 #[rustc_conversion_suggestion]
477 #[stable(feature = "rust1", since = "1.0.0")]
478 #[inline]
479 pub fn to_vec(&self) -> Vec<T>
480 where
481 T: Clone,
482 {
483 self.to_vec_in(Global)
484 }
485
486 /// Copies `self` into a new `Vec` with an allocator.
487 ///
488 /// # Examples
489 ///
490 /// ```
491 /// #![feature(allocator_api)]
492 ///
493 /// use std::alloc::System;
494 ///
495 /// let s = [10, 40, 30];
496 /// let x = s.to_vec_in(System);
497 /// // Here, `s` and `x` can be modified independently.
498 /// ```
499 #[cfg(not(no_global_oom_handling))]
500 #[rustc_allow_incoherent_impl]
501 #[inline]
502 #[unstable(feature = "allocator_api", issue = "32838")]
503 pub fn to_vec_in<A: Allocator>(&self, alloc: A) -> Vec<T, A>
504 where
505 T: Clone,
506 {
507 // N.B., see the `hack` module in this file for more details.
508 hack::to_vec(self, alloc)
509 }
510
511 /// Converts `self` into a vector without clones or allocation.
512 ///
513 /// The resulting vector can be converted back into a box via
514 /// `Vec<T>`'s `into_boxed_slice` method.
515 ///
516 /// # Examples
517 ///
518 /// ```
519 /// let s: Box<[i32]> = Box::new([10, 40, 30]);
520 /// let x = s.into_vec();
521 /// // `s` cannot be used anymore because it has been converted into `x`.
522 ///
523 /// assert_eq!(x, vec![10, 40, 30]);
524 /// ```
525 #[rustc_allow_incoherent_impl]
526 #[stable(feature = "rust1", since = "1.0.0")]
527 #[inline]
528 pub fn into_vec<A: Allocator>(self: Box<Self, A>) -> Vec<T, A> {
529 // N.B., see the `hack` module in this file for more details.
530 hack::into_vec(self)
531 }
532
533 /// Creates a vector by repeating a slice `n` times.
534 ///
535 /// # Panics
536 ///
537 /// This function will panic if the capacity would overflow.
538 ///
539 /// # Examples
540 ///
541 /// Basic usage:
542 ///
543 /// ```
544 /// assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]);
545 /// ```
546 ///
547 /// A panic upon overflow:
548 ///
549 /// ```should_panic
550 /// // this will panic at runtime
551 /// b"0123456789abcdef".repeat(usize::MAX);
552 /// ```
553 #[rustc_allow_incoherent_impl]
554 #[cfg(not(no_global_oom_handling))]
555 #[stable(feature = "repeat_generic_slice", since = "1.40.0")]
556 pub fn repeat(&self, n: usize) -> Vec<T>
557 where
558 T: Copy,
559 {
560 if n == 0 {
561 return Vec::new();
562 }
563
564 // If `n` is larger than zero, it can be split as
565 // `n = 2^expn + rem (2^expn > rem, expn >= 0, rem >= 0)`.
566 // `2^expn` is the number represented by the leftmost '1' bit of `n`,
567 // and `rem` is the remaining part of `n`.
568
569 // Using `Vec` to access `set_len()`.
570 let capacity = self.len().checked_mul(n).expect("capacity overflow");
571 let mut buf = Vec::with_capacity(capacity);
572
573 // `2^expn` repetition is done by doubling `buf` `expn`-times.
574 buf.extend(self);
575 {
576 let mut m = n >> 1;
577 // If `m > 0`, there are remaining bits up to the leftmost '1'.
578 while m > 0 {
579 // `buf.extend(buf)`:
580 unsafe {
581 ptr::copy_nonoverlapping(
582 buf.as_ptr(),
583 (buf.as_mut_ptr() as *mut T).add(buf.len()),
584 buf.len(),
585 );
586 // `buf` has capacity of `self.len() * n`.
587 let buf_len = buf.len();
588 buf.set_len(buf_len * 2);
589 }
590
591 m >>= 1;
592 }
593 }
594
595 // `rem` (`= n - 2^expn`) repetition is done by copying
596 // first `rem` repetitions from `buf` itself.
597 let rem_len = capacity - buf.len(); // `self.len() * rem`
598 if rem_len > 0 {
599 // `buf.extend(buf[0 .. rem_len])`:
600 unsafe {
601 // This is non-overlapping since `2^expn > rem`.
602 ptr::copy_nonoverlapping(
603 buf.as_ptr(),
604 (buf.as_mut_ptr() as *mut T).add(buf.len()),
605 rem_len,
606 );
607 // `buf.len() + rem_len` equals to `buf.capacity()` (`= self.len() * n`).
608 buf.set_len(capacity);
609 }
610 }
611 buf
612 }
613
614 /// Flattens a slice of `T` into a single value `Self::Output`.
615 ///
616 /// # Examples
617 ///
618 /// ```
619 /// assert_eq!(["hello", "world"].concat(), "helloworld");
620 /// assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);
621 /// ```
622 #[rustc_allow_incoherent_impl]
623 #[stable(feature = "rust1", since = "1.0.0")]
624 pub fn concat<Item: ?Sized>(&self) -> <Self as Concat<Item>>::Output
625 where
626 Self: Concat<Item>,
627 {
628 Concat::concat(self)
629 }
630
631 /// Flattens a slice of `T` into a single value `Self::Output`, placing a
632 /// given separator between each.
633 ///
634 /// # Examples
635 ///
636 /// ```
637 /// assert_eq!(["hello", "world"].join(" "), "hello world");
638 /// assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
639 /// assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]);
640 /// ```
641 #[rustc_allow_incoherent_impl]
642 #[stable(feature = "rename_connect_to_join", since = "1.3.0")]
643 pub fn join<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output
644 where
645 Self: Join<Separator>,
646 {
647 Join::join(self, sep)
648 }
649
650 /// Flattens a slice of `T` into a single value `Self::Output`, placing a
651 /// given separator between each.
652 ///
653 /// # Examples
654 ///
655 /// ```
656 /// # #![allow(deprecated)]
657 /// assert_eq!(["hello", "world"].connect(" "), "hello world");
658 /// assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]);
659 /// ```
660 #[rustc_allow_incoherent_impl]
661 #[stable(feature = "rust1", since = "1.0.0")]
662 #[deprecated(since = "1.3.0", note = "renamed to join")]
663 pub fn connect<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output
664 where
665 Self: Join<Separator>,
666 {
667 Join::join(self, sep)
668 }
669}
670
671#[cfg(not(test))]
672impl [u8] {
673 /// Returns a vector containing a copy of this slice where each byte
674 /// is mapped to its ASCII upper case equivalent.
675 ///
676 /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
677 /// but non-ASCII letters are unchanged.
678 ///
679 /// To uppercase the value in-place, use [`make_ascii_uppercase`].
680 ///
681 /// [`make_ascii_uppercase`]: slice::make_ascii_uppercase
682 #[cfg(not(no_global_oom_handling))]
683 #[rustc_allow_incoherent_impl]
684 #[must_use = "this returns the uppercase bytes as a new Vec, \
685 without modifying the original"]
686 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
687 #[inline]
688 pub fn to_ascii_uppercase(&self) -> Vec<u8> {
689 let mut me = self.to_vec();
690 me.make_ascii_uppercase();
691 me
692 }
693
694 /// Returns a vector containing a copy of this slice where each byte
695 /// is mapped to its ASCII lower case equivalent.
696 ///
697 /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
698 /// but non-ASCII letters are unchanged.
699 ///
700 /// To lowercase the value in-place, use [`make_ascii_lowercase`].
701 ///
702 /// [`make_ascii_lowercase`]: slice::make_ascii_lowercase
703 #[cfg(not(no_global_oom_handling))]
704 #[rustc_allow_incoherent_impl]
705 #[must_use = "this returns the lowercase bytes as a new Vec, \
706 without modifying the original"]
707 #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
708 #[inline]
709 pub fn to_ascii_lowercase(&self) -> Vec<u8> {
710 let mut me = self.to_vec();
711 me.make_ascii_lowercase();
712 me
713 }
714}
715
716////////////////////////////////////////////////////////////////////////////////
717// Extension traits for slices over specific kinds of data
718////////////////////////////////////////////////////////////////////////////////
719
720/// Helper trait for [`[T]::concat`](slice::concat).
721///
722/// Note: the `Item` type parameter is not used in this trait,
723/// but it allows impls to be more generic.
724/// Without it, we get this error:
725///
726/// ```error
727/// error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predica
728/// --> src/liballoc/slice.rs:608:6
729/// |
730/// 608 | impl<T: Clone, V: Borrow<[T]>> Concat for [V] {
731/// | ^ unconstrained type parameter
732/// ```
733///
734/// This is because there could exist `V` types with multiple `Borrow<[_]>` impls,
735/// such that multiple `T` types would apply:
736///
737/// ```
738/// # #[allow(dead_code)]
739/// pub struct Foo(Vec<u32>, Vec<String>);
740///
741/// impl std::borrow::Borrow<[u32]> for Foo {
742/// fn borrow(&self) -> &[u32] { &self.0 }
743/// }
744///
745/// impl std::borrow::Borrow<[String]> for Foo {
746/// fn borrow(&self) -> &[String] { &self.1 }
747/// }
748/// ```
749#[unstable(feature = "slice_concat_trait", issue = "27747")]
750pub trait Concat<Item: ?Sized> {
751 #[unstable(feature = "slice_concat_trait", issue = "27747")]
752 /// The resulting type after concatenation
753 type Output;
754
755 /// Implementation of [`[T]::concat`](slice::concat)
756 #[unstable(feature = "slice_concat_trait", issue = "27747")]
757 fn concat(slice: &Self) -> Self::Output;
758}
759
760/// Helper trait for [`[T]::join`](slice::join)
761#[unstable(feature = "slice_concat_trait", issue = "27747")]
762pub trait Join<Separator> {
763 #[unstable(feature = "slice_concat_trait", issue = "27747")]
764 /// The resulting type after concatenation
765 type Output;
766
767 /// Implementation of [`[T]::join`](slice::join)
768 #[unstable(feature = "slice_concat_trait", issue = "27747")]
769 fn join(slice: &Self, sep: Separator) -> Self::Output;
770}
771
772#[cfg(not(no_global_oom_handling))]
773#[unstable(feature = "slice_concat_ext", issue = "27747")]
774impl<T: Clone, V: Borrow<[T]>> Concat<T> for [V] {
775 type Output = Vec<T>;
776
777 fn concat(slice: &Self) -> Vec<T> {
778 let size = slice.iter().map(|slice| slice.borrow().len()).sum();
779 let mut result = Vec::with_capacity(size);
780 for v in slice {
781 result.extend_from_slice(v.borrow())
782 }
783 result
784 }
785}
786
787#[cfg(not(no_global_oom_handling))]
788#[unstable(feature = "slice_concat_ext", issue = "27747")]
789impl<T: Clone, V: Borrow<[T]>> Join<&T> for [V] {
790 type Output = Vec<T>;
791
792 fn join(slice: &Self, sep: &T) -> Vec<T> {
793 let mut iter = slice.iter();
794 let first = match iter.next() {
795 Some(first) => first,
796 None => return vec![],
797 };
798 let size = slice.iter().map(|v| v.borrow().len()).sum::<usize>() + slice.len() - 1;
799 let mut result = Vec::with_capacity(size);
800 result.extend_from_slice(first.borrow());
801
802 for v in iter {
803 result.push(sep.clone());
804 result.extend_from_slice(v.borrow())
805 }
806 result
807 }
808}
809
810#[cfg(not(no_global_oom_handling))]
811#[unstable(feature = "slice_concat_ext", issue = "27747")]
812impl<T: Clone, V: Borrow<[T]>> Join<&[T]> for [V] {
813 type Output = Vec<T>;
814
815 fn join(slice: &Self, sep: &[T]) -> Vec<T> {
816 let mut iter = slice.iter();
817 let first = match iter.next() {
818 Some(first) => first,
819 None => return vec![],
820 };
821 let size =
822 slice.iter().map(|v| v.borrow().len()).sum::<usize>() + sep.len() * (slice.len() - 1);
823 let mut result = Vec::with_capacity(size);
824 result.extend_from_slice(first.borrow());
825
826 for v in iter {
827 result.extend_from_slice(sep);
828 result.extend_from_slice(v.borrow())
829 }
830 result
831 }
832}
833
834////////////////////////////////////////////////////////////////////////////////
835// Standard trait implementations for slices
836////////////////////////////////////////////////////////////////////////////////
837
838#[stable(feature = "rust1", since = "1.0.0")]
839impl<T> Borrow<[T]> for Vec<T> {
840 fn borrow(&self) -> &[T] {
841 &self[..]
842 }
843}
844
845#[stable(feature = "rust1", since = "1.0.0")]
846impl<T> BorrowMut<[T]> for Vec<T> {
847 fn borrow_mut(&mut self) -> &mut [T] {
848 &mut self[..]
849 }
850}
851
852#[cfg(not(no_global_oom_handling))]
853#[stable(feature = "rust1", since = "1.0.0")]
854impl<T: Clone> ToOwned for [T] {
855 type Owned = Vec<T>;
856 #[cfg(not(test))]
857 fn to_owned(&self) -> Vec<T> {
858 self.to_vec()
859 }
860
861 #[cfg(test)]
862 fn to_owned(&self) -> Vec<T> {
863 hack::to_vec(self, Global)
864 }
865
866 fn clone_into(&self, target: &mut Vec<T>) {
867 // drop anything in target that will not be overwritten
868 target.truncate(self.len());
869
870 // target.len <= self.len due to the truncate above, so the
871 // slices here are always in-bounds.
872 let (init, tail) = self.split_at(target.len());
873
874 // reuse the contained values' allocations/resources.
875 target.clone_from_slice(init);
876 target.extend_from_slice(tail);
877 }
878}
879
880////////////////////////////////////////////////////////////////////////////////
881// Sorting
882////////////////////////////////////////////////////////////////////////////////
883
884/// Inserts `v[0]` into pre-sorted sequence `v[1..]` so that whole `v[..]` becomes sorted.
885///
886/// This is the integral subroutine of insertion sort.
887#[cfg(not(no_global_oom_handling))]
888fn insert_head<T, F>(v: &mut [T], is_less: &mut F)
889where
890 F: FnMut(&T, &T) -> bool,
891{
892 if v.len() >= 2 && is_less(&v[1], &v[0]) {
893 unsafe {
894 // There are three ways to implement insertion here:
895 //
896 // 1. Swap adjacent elements until the first one gets to its final destination.
897 // However, this way we copy data around more than is necessary. If elements are big
898 // structures (costly to copy), this method will be slow.
899 //
900 // 2. Iterate until the right place for the first element is found. Then shift the
901 // elements succeeding it to make room for it and finally place it into the
902 // remaining hole. This is a good method.
903 //
904 // 3. Copy the first element into a temporary variable. Iterate until the right place
905 // for it is found. As we go along, copy every traversed element into the slot
906 // preceding it. Finally, copy data from the temporary variable into the remaining
907 // hole. This method is very good. Benchmarks demonstrated slightly better
908 // performance than with the 2nd method.
909 //
910 // All methods were benchmarked, and the 3rd showed best results. So we chose that one.
911 let tmp = mem::ManuallyDrop::new(ptr::read(&v[0]));
912
913 // Intermediate state of the insertion process is always tracked by `hole`, which
914 // serves two purposes:
915 // 1. Protects integrity of `v` from panics in `is_less`.
916 // 2. Fills the remaining hole in `v` in the end.
917 //
918 // Panic safety:
919 //
920 // If `is_less` panics at any point during the process, `hole` will get dropped and
921 // fill the hole in `v` with `tmp`, thus ensuring that `v` still holds every object it
922 // initially held exactly once.
923 let mut hole = InsertionHole { src: &*tmp, dest: &mut v[1] };
924 ptr::copy_nonoverlapping(&v[1], &mut v[0], 1);
925
926 for i in 2..v.len() {
927 if !is_less(&v[i], &*tmp) {
928 break;
929 }
930 ptr::copy_nonoverlapping(&v[i], &mut v[i - 1], 1);
931 hole.dest = &mut v[i];
932 }
933 // `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
934 }
935 }
936
937 // When dropped, copies from `src` into `dest`.
938 struct InsertionHole<T> {
939 src: *const T,
940 dest: *mut T,
941 }
942
943 impl<T> Drop for InsertionHole<T> {
944 fn drop(&mut self) {
945 unsafe {
946 ptr::copy_nonoverlapping(self.src, self.dest, 1);
947 }
948 }
949 }
950}
951
952/// Merges non-decreasing runs `v[..mid]` and `v[mid..]` using `buf` as temporary storage, and
953/// stores the result into `v[..]`.
954///
955/// # Safety
956///
957/// The two slices must be non-empty and `mid` must be in bounds. Buffer `buf` must be long enough
958/// to hold a copy of the shorter slice. Also, `T` must not be a zero-sized type.
959#[cfg(not(no_global_oom_handling))]
960unsafe fn merge<T, F>(v: &mut [T], mid: usize, buf: *mut T, is_less: &mut F)
961where
962 F: FnMut(&T, &T) -> bool,
963{
964 let len = v.len();
965 let v = v.as_mut_ptr();
966 let (v_mid, v_end) = unsafe { (v.add(mid), v.add(len)) };
967
968 // The merge process first copies the shorter run into `buf`. Then it traces the newly copied
969 // run and the longer run forwards (or backwards), comparing their next unconsumed elements and
970 // copying the lesser (or greater) one into `v`.
971 //
972 // As soon as the shorter run is fully consumed, the process is done. If the longer run gets
973 // consumed first, then we must copy whatever is left of the shorter run into the remaining
974 // hole in `v`.
975 //
976 // Intermediate state of the process is always tracked by `hole`, which serves two purposes:
977 // 1. Protects integrity of `v` from panics in `is_less`.
978 // 2. Fills the remaining hole in `v` if the longer run gets consumed first.
979 //
980 // Panic safety:
981 //
982 // If `is_less` panics at any point during the process, `hole` will get dropped and fill the
983 // hole in `v` with the unconsumed range in `buf`, thus ensuring that `v` still holds every
984 // object it initially held exactly once.
985 let mut hole;
986
987 if mid <= len - mid {
988 // The left run is shorter.
989 unsafe {
990 ptr::copy_nonoverlapping(v, buf, mid);
991 hole = MergeHole { start: buf, end: buf.add(mid), dest: v };
992 }
993
994 // Initially, these pointers point to the beginnings of their arrays.
995 let left = &mut hole.start;
996 let mut right = v_mid;
997 let out = &mut hole.dest;
998
999 while *left < hole.end && right < v_end {
1000 // Consume the lesser side.
1001 // If equal, prefer the left run to maintain stability.
1002 unsafe {
1003 let to_copy = if is_less(&*right, &**left) {
1004 get_and_increment(&mut right)
1005 } else {
1006 get_and_increment(left)
1007 };
1008 ptr::copy_nonoverlapping(to_copy, get_and_increment(out), 1);
1009 }
1010 }
1011 } else {
1012 // The right run is shorter.
1013 unsafe {
1014 ptr::copy_nonoverlapping(v_mid, buf, len - mid);
1015 hole = MergeHole { start: buf, end: buf.add(len - mid), dest: v_mid };
1016 }
1017
1018 // Initially, these pointers point past the ends of their arrays.
1019 let left = &mut hole.dest;
1020 let right = &mut hole.end;
1021 let mut out = v_end;
1022
1023 while v < *left && buf < *right {
1024 // Consume the greater side.
1025 // If equal, prefer the right run to maintain stability.
1026 unsafe {
1027 let to_copy = if is_less(&*right.offset(-1), &*left.offset(-1)) {
1028 decrement_and_get(left)
1029 } else {
1030 decrement_and_get(right)
1031 };
1032 ptr::copy_nonoverlapping(to_copy, decrement_and_get(&mut out), 1);
1033 }
1034 }
1035 }
1036 // Finally, `hole` gets dropped. If the shorter run was not fully consumed, whatever remains of
1037 // it will now be copied into the hole in `v`.
1038
1039 unsafe fn get_and_increment<T>(ptr: &mut *mut T) -> *mut T {
1040 let old = *ptr;
1041 *ptr = unsafe { ptr.offset(1) };
1042 old
1043 }
1044
1045 unsafe fn decrement_and_get<T>(ptr: &mut *mut T) -> *mut T {
1046 *ptr = unsafe { ptr.offset(-1) };
1047 *ptr
1048 }
1049
1050 // When dropped, copies the range `start..end` into `dest..`.
1051 struct MergeHole<T> {
1052 start: *mut T,
1053 end: *mut T,
1054 dest: *mut T,
1055 }
1056
1057 impl<T> Drop for MergeHole<T> {
1058 fn drop(&mut self) {
1059 // `T` is not a zero-sized type, and these are pointers into a slice's elements.
1060 unsafe {
1061 let len = self.end.sub_ptr(self.start);
1062 ptr::copy_nonoverlapping(self.start, self.dest, len);
1063 }
1064 }
1065 }
1066}
1067
1068/// This merge sort borrows some (but not all) ideas from TimSort, which is described in detail
1069/// [here](https://github.com/python/cpython/blob/main/Objects/listsort.txt).
1070///
1071/// The algorithm identifies strictly descending and non-descending subsequences, which are called
1072/// natural runs. There is a stack of pending runs yet to be merged. Each newly found run is pushed
1073/// onto the stack, and then some pairs of adjacent runs are merged until these two invariants are
1074/// satisfied:
1075///
1076/// 1. for every `i` in `1..runs.len()`: `runs[i - 1].len > runs[i].len`
1077/// 2. for every `i` in `2..runs.len()`: `runs[i - 2].len > runs[i - 1].len + runs[i].len`
1078///
1079/// The invariants ensure that the total running time is *O*(*n* \* log(*n*)) worst-case.
1080#[cfg(not(no_global_oom_handling))]
1081fn merge_sort<T, F>(v: &mut [T], mut is_less: F)
1082where
1083 F: FnMut(&T, &T) -> bool,
1084{
1085 // Slices of up to this length get sorted using insertion sort.
1086 const MAX_INSERTION: usize = 20;
1087 // Very short runs are extended using insertion sort to span at least this many elements.
1088 const MIN_RUN: usize = 10;
1089
1090 // Sorting has no meaningful behavior on zero-sized types.
1091 if size_of::<T>() == 0 {
1092 return;
1093 }
1094
1095 let len = v.len();
1096
1097 // Short arrays get sorted in-place via insertion sort to avoid allocations.
1098 if len <= MAX_INSERTION {
1099 if len >= 2 {
1100 for i in (0..len - 1).rev() {
1101 insert_head(&mut v[i..], &mut is_less);
1102 }
1103 }
1104 return;
1105 }
1106
1107 // Allocate a buffer to use as scratch memory. We keep the length 0 so we can keep in it
1108 // shallow copies of the contents of `v` without risking the dtors running on copies if
1109 // `is_less` panics. When merging two sorted runs, this buffer holds a copy of the shorter run,
1110 // which will always have length at most `len / 2`.
1111 let mut buf = Vec::with_capacity(len / 2);
1112
1113 // In order to identify natural runs in `v`, we traverse it backwards. That might seem like a
1114 // strange decision, but consider the fact that merges more often go in the opposite direction
1115 // (forwards). According to benchmarks, merging forwards is slightly faster than merging
1116 // backwards. To conclude, identifying runs by traversing backwards improves performance.
1117 let mut runs = vec![];
1118 let mut end = len;
1119 while end > 0 {
1120 // Find the next natural run, and reverse it if it's strictly descending.
1121 let mut start = end - 1;
1122 if start > 0 {
1123 start -= 1;
1124 unsafe {
1125 if is_less(v.get_unchecked(start + 1), v.get_unchecked(start)) {
1126 while start > 0 && is_less(v.get_unchecked(start), v.get_unchecked(start - 1)) {
1127 start -= 1;
1128 }
1129 v[start..end].reverse();
1130 } else {
1131 while start > 0 && !is_less(v.get_unchecked(start), v.get_unchecked(start - 1))
1132 {
1133 start -= 1;
1134 }
1135 }
1136 }
1137 }
1138
1139 // Insert some more elements into the run if it's too short. Insertion sort is faster than
1140 // merge sort on short sequences, so this significantly improves performance.
1141 while start > 0 && end - start < MIN_RUN {
1142 start -= 1;
1143 insert_head(&mut v[start..end], &mut is_less);
1144 }
1145
1146 // Push this run onto the stack.
1147 runs.push(Run { start, len: end - start });
1148 end = start;
1149
1150 // Merge some pairs of adjacent runs to satisfy the invariants.
1151 while let Some(r) = collapse(&runs) {
1152 let left = runs[r + 1];
1153 let right = runs[r];
1154 unsafe {
1155 merge(
1156 &mut v[left.start..right.start + right.len],
1157 left.len,
1158 buf.as_mut_ptr(),
1159 &mut is_less,
1160 );
1161 }
1162 runs[r] = Run { start: left.start, len: left.len + right.len };
1163 runs.remove(r + 1);
1164 }
1165 }
1166
1167 // Finally, exactly one run must remain in the stack.
1168 debug_assert!(runs.len() == 1 && runs[0].start == 0 && runs[0].len == len);
1169
1170 // Examines the stack of runs and identifies the next pair of runs to merge. More specifically,
1171 // if `Some(r)` is returned, that means `runs[r]` and `runs[r + 1]` must be merged next. If the
1172 // algorithm should continue building a new run instead, `None` is returned.
1173 //
1174 // TimSort is infamous for its buggy implementations, as described here:
1175 // http://envisage-project.eu/timsort-specification-and-verification/
1176 //
1177 // The gist of the story is: we must enforce the invariants on the top four runs on the stack.
1178 // Enforcing them on just top three is not sufficient to ensure that the invariants will still
1179 // hold for *all* runs in the stack.
1180 //
1181 // This function correctly checks invariants for the top four runs. Additionally, if the top
1182 // run starts at index 0, it will always demand a merge operation until the stack is fully
1183 // collapsed, in order to complete the sort.
1184 #[inline]
1185 fn collapse(runs: &[Run]) -> Option<usize> {
1186 let n = runs.len();
1187 if n >= 2
1188 && (runs[n - 1].start == 0
1189 || runs[n - 2].len <= runs[n - 1].len
1190 || (n >= 3 && runs[n - 3].len <= runs[n - 2].len + runs[n - 1].len)
1191 || (n >= 4 && runs[n - 4].len <= runs[n - 3].len + runs[n - 2].len))
1192 {
1193 if n >= 3 && runs[n - 3].len < runs[n - 1].len { Some(n - 3) } else { Some(n - 2) }
1194 } else {
1195 None
1196 }
1197 }
1198
1199 #[derive(Clone, Copy)]
1200 struct Run {
1201 start: usize,
1202 len: usize,
1203 }
1204}