1 // SPDX-License-Identifier: Apache-2.0 OR MIT
2 
3 //! Utilities for the slice primitive type.
4 //!
5 //! *[See also the slice primitive type](slice).*
6 //!
7 //! Most of the structs in this module are iterator types which can only be created
8 //! using a certain function. For example, `slice.iter()` yields an [`Iter`].
9 //!
10 //! A few functions are provided to create a slice from a value reference
11 //! or from a raw pointer.
12 #![stable(feature = "rust1", since = "1.0.0")]
13 // Many of the usings in this module are only used in the test configuration.
14 // It's cleaner to just turn off the unused_imports warning than to fix them.
15 #![cfg_attr(test, allow(unused_imports, dead_code))]
16 
17 use core::borrow::{Borrow, BorrowMut};
18 #[cfg(not(no_global_oom_handling))]
19 use core::cmp::Ordering::{self, Less};
20 #[cfg(not(no_global_oom_handling))]
21 use core::mem::{self, SizedTypeProperties};
22 #[cfg(not(no_global_oom_handling))]
23 use core::ptr;
24 #[cfg(not(no_global_oom_handling))]
25 use core::slice::sort;
26 
27 use crate::alloc::Allocator;
28 #[cfg(not(no_global_oom_handling))]
29 use crate::alloc::{self, Global};
30 #[cfg(not(no_global_oom_handling))]
31 use crate::borrow::ToOwned;
32 use crate::boxed::Box;
33 use crate::vec::Vec;
34 
35 #[cfg(test)]
36 mod tests;
37 
38 #[unstable(feature = "slice_range", issue = "76393")]
39 pub use core::slice::range;
40 #[unstable(feature = "array_chunks", issue = "74985")]
41 pub use core::slice::ArrayChunks;
42 #[unstable(feature = "array_chunks", issue = "74985")]
43 pub use core::slice::ArrayChunksMut;
44 #[unstable(feature = "array_windows", issue = "75027")]
45 pub use core::slice::ArrayWindows;
46 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
47 pub use core::slice::EscapeAscii;
48 #[stable(feature = "slice_get_slice", since = "1.28.0")]
49 pub use core::slice::SliceIndex;
50 #[stable(feature = "from_ref", since = "1.28.0")]
51 pub use core::slice::{from_mut, from_ref};
52 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
53 pub use core::slice::{from_mut_ptr_range, from_ptr_range};
54 #[stable(feature = "rust1", since = "1.0.0")]
55 pub use core::slice::{from_raw_parts, from_raw_parts_mut};
56 #[stable(feature = "rust1", since = "1.0.0")]
57 pub use core::slice::{Chunks, Windows};
58 #[stable(feature = "chunks_exact", since = "1.31.0")]
59 pub use core::slice::{ChunksExact, ChunksExactMut};
60 #[stable(feature = "rust1", since = "1.0.0")]
61 pub use core::slice::{ChunksMut, Split, SplitMut};
62 #[unstable(feature = "slice_group_by", issue = "80552")]
63 pub use core::slice::{GroupBy, GroupByMut};
64 #[stable(feature = "rust1", since = "1.0.0")]
65 pub use core::slice::{Iter, IterMut};
66 #[stable(feature = "rchunks", since = "1.31.0")]
67 pub use core::slice::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
68 #[stable(feature = "slice_rsplit", since = "1.27.0")]
69 pub use core::slice::{RSplit, RSplitMut};
70 #[stable(feature = "rust1", since = "1.0.0")]
71 pub use core::slice::{RSplitN, RSplitNMut, SplitN, SplitNMut};
72 #[stable(feature = "split_inclusive", since = "1.51.0")]
73 pub use core::slice::{SplitInclusive, SplitInclusiveMut};
74 
75 ////////////////////////////////////////////////////////////////////////////////
76 // Basic slice extension methods
77 ////////////////////////////////////////////////////////////////////////////////
78 
79 // HACK(japaric) needed for the implementation of `vec!` macro during testing
80 // N.B., see the `hack` module in this file for more details.
81 #[cfg(test)]
82 pub use hack::into_vec;
83 
84 // HACK(japaric) needed for the implementation of `Vec::clone` during testing
85 // N.B., see the `hack` module in this file for more details.
86 #[cfg(test)]
87 pub use hack::to_vec;
88 
89 // HACK(japaric): With cfg(test) `impl [T]` is not available, these three
90 // functions are actually methods that are in `impl [T]` but not in
91 // `core::slice::SliceExt` - we need to supply these functions for the
92 // `test_permutations` test
93 pub(crate) mod hack {
94     use core::alloc::Allocator;
95 
96     use crate::boxed::Box;
97     use crate::vec::Vec;
98 
99     // We shouldn't add inline attribute to this since this is used in
100     // `vec!` macro mostly and causes perf regression. See #71204 for
101     // discussion and perf results.
into_vec<T, A: Allocator>(b: Box<[T], A>) -> Vec<T, A>102     pub fn into_vec<T, A: Allocator>(b: Box<[T], A>) -> Vec<T, A> {
103         unsafe {
104             let len = b.len();
105             let (b, alloc) = Box::into_raw_with_allocator(b);
106             Vec::from_raw_parts_in(b as *mut T, len, len, alloc)
107         }
108     }
109 
110     #[cfg(not(no_global_oom_handling))]
111     #[inline]
to_vec<T: ConvertVec, A: Allocator>(s: &[T], alloc: A) -> Vec<T, A>112     pub fn to_vec<T: ConvertVec, A: Allocator>(s: &[T], alloc: A) -> Vec<T, A> {
113         T::to_vec(s, alloc)
114     }
115 
116     #[cfg(not(no_global_oom_handling))]
117     pub trait ConvertVec {
to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> where Self: Sized118         fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A>
119         where
120             Self: Sized;
121     }
122 
123     #[cfg(not(no_global_oom_handling))]
124     impl<T: Clone> ConvertVec for T {
125         #[inline]
to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A>126         default fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> {
127             struct DropGuard<'a, T, A: Allocator> {
128                 vec: &'a mut Vec<T, A>,
129                 num_init: usize,
130             }
131             impl<'a, T, A: Allocator> Drop for DropGuard<'a, T, A> {
132                 #[inline]
133                 fn drop(&mut self) {
134                     // SAFETY:
135                     // items were marked initialized in the loop below
136                     unsafe {
137                         self.vec.set_len(self.num_init);
138                     }
139                 }
140             }
141             let mut vec = Vec::with_capacity_in(s.len(), alloc);
142             let mut guard = DropGuard { vec: &mut vec, num_init: 0 };
143             let slots = guard.vec.spare_capacity_mut();
144             // .take(slots.len()) is necessary for LLVM to remove bounds checks
145             // and has better codegen than zip.
146             for (i, b) in s.iter().enumerate().take(slots.len()) {
147                 guard.num_init = i;
148                 slots[i].write(b.clone());
149             }
150             core::mem::forget(guard);
151             // SAFETY:
152             // the vec was allocated and initialized above to at least this length.
153             unsafe {
154                 vec.set_len(s.len());
155             }
156             vec
157         }
158     }
159 
160     #[cfg(not(no_global_oom_handling))]
161     impl<T: Copy> ConvertVec for T {
162         #[inline]
to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A>163         fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> {
164             let mut v = Vec::with_capacity_in(s.len(), alloc);
165             // SAFETY:
166             // allocated above with the capacity of `s`, and initialize to `s.len()` in
167             // ptr::copy_to_non_overlapping below.
168             unsafe {
169                 s.as_ptr().copy_to_nonoverlapping(v.as_mut_ptr(), s.len());
170                 v.set_len(s.len());
171             }
172             v
173         }
174     }
175 }
176 
177 #[cfg(not(test))]
178 impl<T> [T] {
179     /// Sorts the slice.
180     ///
181     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case.
182     ///
183     /// When applicable, unstable sorting is preferred because it is generally faster than stable
184     /// sorting and it doesn't allocate auxiliary memory.
185     /// See [`sort_unstable`](slice::sort_unstable).
186     ///
187     /// # Current implementation
188     ///
189     /// The current algorithm is an adaptive, iterative merge sort inspired by
190     /// [timsort](https://en.wikipedia.org/wiki/Timsort).
191     /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
192     /// two or more sorted sequences concatenated one after another.
193     ///
194     /// Also, it allocates temporary storage half the size of `self`, but for short slices a
195     /// non-allocating insertion sort is used instead.
196     ///
197     /// # Examples
198     ///
199     /// ```
200     /// let mut v = [-5, 4, 1, -3, 2];
201     ///
202     /// v.sort();
203     /// assert!(v == [-5, -3, 1, 2, 4]);
204     /// ```
205     #[cfg(not(no_global_oom_handling))]
206     #[rustc_allow_incoherent_impl]
207     #[stable(feature = "rust1", since = "1.0.0")]
208     #[inline]
sort(&mut self) where T: Ord,209     pub fn sort(&mut self)
210     where
211         T: Ord,
212     {
213         stable_sort(self, T::lt);
214     }
215 
216     /// Sorts the slice with a comparator function.
217     ///
218     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case.
219     ///
220     /// The comparator function must define a total ordering for the elements in the slice. If
221     /// the ordering is not total, the order of the elements is unspecified. An order is a
222     /// total order if it is (for all `a`, `b` and `c`):
223     ///
224     /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
225     /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
226     ///
227     /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
228     /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
229     ///
230     /// ```
231     /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
232     /// floats.sort_by(|a, b| a.partial_cmp(b).unwrap());
233     /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
234     /// ```
235     ///
236     /// When applicable, unstable sorting is preferred because it is generally faster than stable
237     /// sorting and it doesn't allocate auxiliary memory.
238     /// See [`sort_unstable_by`](slice::sort_unstable_by).
239     ///
240     /// # Current implementation
241     ///
242     /// The current algorithm is an adaptive, iterative merge sort inspired by
243     /// [timsort](https://en.wikipedia.org/wiki/Timsort).
244     /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
245     /// two or more sorted sequences concatenated one after another.
246     ///
247     /// Also, it allocates temporary storage half the size of `self`, but for short slices a
248     /// non-allocating insertion sort is used instead.
249     ///
250     /// # Examples
251     ///
252     /// ```
253     /// let mut v = [5, 4, 1, 3, 2];
254     /// v.sort_by(|a, b| a.cmp(b));
255     /// assert!(v == [1, 2, 3, 4, 5]);
256     ///
257     /// // reverse sorting
258     /// v.sort_by(|a, b| b.cmp(a));
259     /// assert!(v == [5, 4, 3, 2, 1]);
260     /// ```
261     #[cfg(not(no_global_oom_handling))]
262     #[rustc_allow_incoherent_impl]
263     #[stable(feature = "rust1", since = "1.0.0")]
264     #[inline]
sort_by<F>(&mut self, mut compare: F) where F: FnMut(&T, &T) -> Ordering,265     pub fn sort_by<F>(&mut self, mut compare: F)
266     where
267         F: FnMut(&T, &T) -> Ordering,
268     {
269         stable_sort(self, |a, b| compare(a, b) == Less);
270     }
271 
272     /// Sorts the slice with a key extraction function.
273     ///
274     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* \* log(*n*))
275     /// worst-case, where the key function is *O*(*m*).
276     ///
277     /// For expensive key functions (e.g. functions that are not simple property accesses or
278     /// basic operations), [`sort_by_cached_key`](slice::sort_by_cached_key) is likely to be
279     /// significantly faster, as it does not recompute element keys.
280     ///
281     /// When applicable, unstable sorting is preferred because it is generally faster than stable
282     /// sorting and it doesn't allocate auxiliary memory.
283     /// See [`sort_unstable_by_key`](slice::sort_unstable_by_key).
284     ///
285     /// # Current implementation
286     ///
287     /// The current algorithm is an adaptive, iterative merge sort inspired by
288     /// [timsort](https://en.wikipedia.org/wiki/Timsort).
289     /// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
290     /// two or more sorted sequences concatenated one after another.
291     ///
292     /// Also, it allocates temporary storage half the size of `self`, but for short slices a
293     /// non-allocating insertion sort is used instead.
294     ///
295     /// # Examples
296     ///
297     /// ```
298     /// let mut v = [-5i32, 4, 1, -3, 2];
299     ///
300     /// v.sort_by_key(|k| k.abs());
301     /// assert!(v == [1, 2, -3, 4, -5]);
302     /// ```
303     #[cfg(not(no_global_oom_handling))]
304     #[rustc_allow_incoherent_impl]
305     #[stable(feature = "slice_sort_by_key", since = "1.7.0")]
306     #[inline]
sort_by_key<K, F>(&mut self, mut f: F) where F: FnMut(&T) -> K, K: Ord,307     pub fn sort_by_key<K, F>(&mut self, mut f: F)
308     where
309         F: FnMut(&T) -> K,
310         K: Ord,
311     {
312         stable_sort(self, |a, b| f(a).lt(&f(b)));
313     }
314 
315     /// Sorts the slice with a key extraction function.
316     ///
317     /// During sorting, the key function is called at most once per element, by using
318     /// temporary storage to remember the results of key evaluation.
319     /// The order of calls to the key function is unspecified and may change in future versions
320     /// of the standard library.
321     ///
322     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* + *n* \* log(*n*))
323     /// worst-case, where the key function is *O*(*m*).
324     ///
325     /// For simple key functions (e.g., functions that are property accesses or
326     /// basic operations), [`sort_by_key`](slice::sort_by_key) is likely to be
327     /// faster.
328     ///
329     /// # Current implementation
330     ///
331     /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
332     /// which combines the fast average case of randomized quicksort with the fast worst case of
333     /// heapsort, while achieving linear time on slices with certain patterns. It uses some
334     /// randomization to avoid degenerate cases, but with a fixed seed to always provide
335     /// deterministic behavior.
336     ///
337     /// In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the
338     /// length of the slice.
339     ///
340     /// # Examples
341     ///
342     /// ```
343     /// let mut v = [-5i32, 4, 32, -3, 2];
344     ///
345     /// v.sort_by_cached_key(|k| k.to_string());
346     /// assert!(v == [-3, -5, 2, 32, 4]);
347     /// ```
348     ///
349     /// [pdqsort]: https://github.com/orlp/pdqsort
350     #[cfg(not(no_global_oom_handling))]
351     #[rustc_allow_incoherent_impl]
352     #[stable(feature = "slice_sort_by_cached_key", since = "1.34.0")]
353     #[inline]
sort_by_cached_key<K, F>(&mut self, f: F) where F: FnMut(&T) -> K, K: Ord,354     pub fn sort_by_cached_key<K, F>(&mut self, f: F)
355     where
356         F: FnMut(&T) -> K,
357         K: Ord,
358     {
359         // Helper macro for indexing our vector by the smallest possible type, to reduce allocation.
360         macro_rules! sort_by_key {
361             ($t:ty, $slice:ident, $f:ident) => {{
362                 let mut indices: Vec<_> =
363                     $slice.iter().map($f).enumerate().map(|(i, k)| (k, i as $t)).collect();
364                 // The elements of `indices` are unique, as they are indexed, so any sort will be
365                 // stable with respect to the original slice. We use `sort_unstable` here because
366                 // it requires less memory allocation.
367                 indices.sort_unstable();
368                 for i in 0..$slice.len() {
369                     let mut index = indices[i].1;
370                     while (index as usize) < i {
371                         index = indices[index as usize].1;
372                     }
373                     indices[i].1 = index;
374                     $slice.swap(i, index as usize);
375                 }
376             }};
377         }
378 
379         let sz_u8 = mem::size_of::<(K, u8)>();
380         let sz_u16 = mem::size_of::<(K, u16)>();
381         let sz_u32 = mem::size_of::<(K, u32)>();
382         let sz_usize = mem::size_of::<(K, usize)>();
383 
384         let len = self.len();
385         if len < 2 {
386             return;
387         }
388         if sz_u8 < sz_u16 && len <= (u8::MAX as usize) {
389             return sort_by_key!(u8, self, f);
390         }
391         if sz_u16 < sz_u32 && len <= (u16::MAX as usize) {
392             return sort_by_key!(u16, self, f);
393         }
394         if sz_u32 < sz_usize && len <= (u32::MAX as usize) {
395             return sort_by_key!(u32, self, f);
396         }
397         sort_by_key!(usize, self, f)
398     }
399 
400     /// Copies `self` into a new `Vec`.
401     ///
402     /// # Examples
403     ///
404     /// ```
405     /// let s = [10, 40, 30];
406     /// let x = s.to_vec();
407     /// // Here, `s` and `x` can be modified independently.
408     /// ```
409     #[cfg(not(no_global_oom_handling))]
410     #[rustc_allow_incoherent_impl]
411     #[rustc_conversion_suggestion]
412     #[stable(feature = "rust1", since = "1.0.0")]
413     #[inline]
to_vec(&self) -> Vec<T> where T: Clone,414     pub fn to_vec(&self) -> Vec<T>
415     where
416         T: Clone,
417     {
418         self.to_vec_in(Global)
419     }
420 
421     /// Copies `self` into a new `Vec` with an allocator.
422     ///
423     /// # Examples
424     ///
425     /// ```
426     /// #![feature(allocator_api)]
427     ///
428     /// use std::alloc::System;
429     ///
430     /// let s = [10, 40, 30];
431     /// let x = s.to_vec_in(System);
432     /// // Here, `s` and `x` can be modified independently.
433     /// ```
434     #[cfg(not(no_global_oom_handling))]
435     #[rustc_allow_incoherent_impl]
436     #[inline]
437     #[unstable(feature = "allocator_api", issue = "32838")]
to_vec_in<A: Allocator>(&self, alloc: A) -> Vec<T, A> where T: Clone,438     pub fn to_vec_in<A: Allocator>(&self, alloc: A) -> Vec<T, A>
439     where
440         T: Clone,
441     {
442         // N.B., see the `hack` module in this file for more details.
443         hack::to_vec(self, alloc)
444     }
445 
446     /// Converts `self` into a vector without clones or allocation.
447     ///
448     /// The resulting vector can be converted back into a box via
449     /// `Vec<T>`'s `into_boxed_slice` method.
450     ///
451     /// # Examples
452     ///
453     /// ```
454     /// let s: Box<[i32]> = Box::new([10, 40, 30]);
455     /// let x = s.into_vec();
456     /// // `s` cannot be used anymore because it has been converted into `x`.
457     ///
458     /// assert_eq!(x, vec![10, 40, 30]);
459     /// ```
460     #[rustc_allow_incoherent_impl]
461     #[stable(feature = "rust1", since = "1.0.0")]
462     #[inline]
into_vec<A: Allocator>(self: Box<Self, A>) -> Vec<T, A>463     pub fn into_vec<A: Allocator>(self: Box<Self, A>) -> Vec<T, A> {
464         // N.B., see the `hack` module in this file for more details.
465         hack::into_vec(self)
466     }
467 
468     /// Creates a vector by copying a slice `n` times.
469     ///
470     /// # Panics
471     ///
472     /// This function will panic if the capacity would overflow.
473     ///
474     /// # Examples
475     ///
476     /// Basic usage:
477     ///
478     /// ```
479     /// assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]);
480     /// ```
481     ///
482     /// A panic upon overflow:
483     ///
484     /// ```should_panic
485     /// // this will panic at runtime
486     /// b"0123456789abcdef".repeat(usize::MAX);
487     /// ```
488     #[rustc_allow_incoherent_impl]
489     #[cfg(not(no_global_oom_handling))]
490     #[stable(feature = "repeat_generic_slice", since = "1.40.0")]
repeat(&self, n: usize) -> Vec<T> where T: Copy,491     pub fn repeat(&self, n: usize) -> Vec<T>
492     where
493         T: Copy,
494     {
495         if n == 0 {
496             return Vec::new();
497         }
498 
499         // If `n` is larger than zero, it can be split as
500         // `n = 2^expn + rem (2^expn > rem, expn >= 0, rem >= 0)`.
501         // `2^expn` is the number represented by the leftmost '1' bit of `n`,
502         // and `rem` is the remaining part of `n`.
503 
504         // Using `Vec` to access `set_len()`.
505         let capacity = self.len().checked_mul(n).expect("capacity overflow");
506         let mut buf = Vec::with_capacity(capacity);
507 
508         // `2^expn` repetition is done by doubling `buf` `expn`-times.
509         buf.extend(self);
510         {
511             let mut m = n >> 1;
512             // If `m > 0`, there are remaining bits up to the leftmost '1'.
513             while m > 0 {
514                 // `buf.extend(buf)`:
515                 unsafe {
516                     ptr::copy_nonoverlapping(
517                         buf.as_ptr(),
518                         (buf.as_mut_ptr() as *mut T).add(buf.len()),
519                         buf.len(),
520                     );
521                     // `buf` has capacity of `self.len() * n`.
522                     let buf_len = buf.len();
523                     buf.set_len(buf_len * 2);
524                 }
525 
526                 m >>= 1;
527             }
528         }
529 
530         // `rem` (`= n - 2^expn`) repetition is done by copying
531         // first `rem` repetitions from `buf` itself.
532         let rem_len = capacity - buf.len(); // `self.len() * rem`
533         if rem_len > 0 {
534             // `buf.extend(buf[0 .. rem_len])`:
535             unsafe {
536                 // This is non-overlapping since `2^expn > rem`.
537                 ptr::copy_nonoverlapping(
538                     buf.as_ptr(),
539                     (buf.as_mut_ptr() as *mut T).add(buf.len()),
540                     rem_len,
541                 );
542                 // `buf.len() + rem_len` equals to `buf.capacity()` (`= self.len() * n`).
543                 buf.set_len(capacity);
544             }
545         }
546         buf
547     }
548 
549     /// Flattens a slice of `T` into a single value `Self::Output`.
550     ///
551     /// # Examples
552     ///
553     /// ```
554     /// assert_eq!(["hello", "world"].concat(), "helloworld");
555     /// assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);
556     /// ```
557     #[rustc_allow_incoherent_impl]
558     #[stable(feature = "rust1", since = "1.0.0")]
concat<Item: ?Sized>(&self) -> <Self as Concat<Item>>::Output where Self: Concat<Item>,559     pub fn concat<Item: ?Sized>(&self) -> <Self as Concat<Item>>::Output
560     where
561         Self: Concat<Item>,
562     {
563         Concat::concat(self)
564     }
565 
566     /// Flattens a slice of `T` into a single value `Self::Output`, placing a
567     /// given separator between each.
568     ///
569     /// # Examples
570     ///
571     /// ```
572     /// assert_eq!(["hello", "world"].join(" "), "hello world");
573     /// assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
574     /// assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]);
575     /// ```
576     #[rustc_allow_incoherent_impl]
577     #[stable(feature = "rename_connect_to_join", since = "1.3.0")]
join<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output where Self: Join<Separator>,578     pub fn join<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output
579     where
580         Self: Join<Separator>,
581     {
582         Join::join(self, sep)
583     }
584 
585     /// Flattens a slice of `T` into a single value `Self::Output`, placing a
586     /// given separator between each.
587     ///
588     /// # Examples
589     ///
590     /// ```
591     /// # #![allow(deprecated)]
592     /// assert_eq!(["hello", "world"].connect(" "), "hello world");
593     /// assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]);
594     /// ```
595     #[rustc_allow_incoherent_impl]
596     #[stable(feature = "rust1", since = "1.0.0")]
597     #[deprecated(since = "1.3.0", note = "renamed to join")]
connect<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output where Self: Join<Separator>,598     pub fn connect<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output
599     where
600         Self: Join<Separator>,
601     {
602         Join::join(self, sep)
603     }
604 }
605 
606 #[cfg(not(test))]
607 impl [u8] {
608     /// Returns a vector containing a copy of this slice where each byte
609     /// is mapped to its ASCII upper case equivalent.
610     ///
611     /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
612     /// but non-ASCII letters are unchanged.
613     ///
614     /// To uppercase the value in-place, use [`make_ascii_uppercase`].
615     ///
616     /// [`make_ascii_uppercase`]: slice::make_ascii_uppercase
617     #[cfg(not(no_global_oom_handling))]
618     #[rustc_allow_incoherent_impl]
619     #[must_use = "this returns the uppercase bytes as a new Vec, \
620                   without modifying the original"]
621     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
622     #[inline]
to_ascii_uppercase(&self) -> Vec<u8>623     pub fn to_ascii_uppercase(&self) -> Vec<u8> {
624         let mut me = self.to_vec();
625         me.make_ascii_uppercase();
626         me
627     }
628 
629     /// Returns a vector containing a copy of this slice where each byte
630     /// is mapped to its ASCII lower case equivalent.
631     ///
632     /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
633     /// but non-ASCII letters are unchanged.
634     ///
635     /// To lowercase the value in-place, use [`make_ascii_lowercase`].
636     ///
637     /// [`make_ascii_lowercase`]: slice::make_ascii_lowercase
638     #[cfg(not(no_global_oom_handling))]
639     #[rustc_allow_incoherent_impl]
640     #[must_use = "this returns the lowercase bytes as a new Vec, \
641                   without modifying the original"]
642     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
643     #[inline]
to_ascii_lowercase(&self) -> Vec<u8>644     pub fn to_ascii_lowercase(&self) -> Vec<u8> {
645         let mut me = self.to_vec();
646         me.make_ascii_lowercase();
647         me
648     }
649 }
650 
651 ////////////////////////////////////////////////////////////////////////////////
652 // Extension traits for slices over specific kinds of data
653 ////////////////////////////////////////////////////////////////////////////////
654 
655 /// Helper trait for [`[T]::concat`](slice::concat).
656 ///
657 /// Note: the `Item` type parameter is not used in this trait,
658 /// but it allows impls to be more generic.
659 /// Without it, we get this error:
660 ///
661 /// ```error
662 /// error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predica
663 ///    --> library/alloc/src/slice.rs:608:6
664 ///     |
665 /// 608 | impl<T: Clone, V: Borrow<[T]>> Concat for [V] {
666 ///     |      ^ unconstrained type parameter
667 /// ```
668 ///
669 /// This is because there could exist `V` types with multiple `Borrow<[_]>` impls,
670 /// such that multiple `T` types would apply:
671 ///
672 /// ```
673 /// # #[allow(dead_code)]
674 /// pub struct Foo(Vec<u32>, Vec<String>);
675 ///
676 /// impl std::borrow::Borrow<[u32]> for Foo {
677 ///     fn borrow(&self) -> &[u32] { &self.0 }
678 /// }
679 ///
680 /// impl std::borrow::Borrow<[String]> for Foo {
681 ///     fn borrow(&self) -> &[String] { &self.1 }
682 /// }
683 /// ```
684 #[unstable(feature = "slice_concat_trait", issue = "27747")]
685 pub trait Concat<Item: ?Sized> {
686     #[unstable(feature = "slice_concat_trait", issue = "27747")]
687     /// The resulting type after concatenation
688     type Output;
689 
690     /// Implementation of [`[T]::concat`](slice::concat)
691     #[unstable(feature = "slice_concat_trait", issue = "27747")]
concat(slice: &Self) -> Self::Output692     fn concat(slice: &Self) -> Self::Output;
693 }
694 
695 /// Helper trait for [`[T]::join`](slice::join)
696 #[unstable(feature = "slice_concat_trait", issue = "27747")]
697 pub trait Join<Separator> {
698     #[unstable(feature = "slice_concat_trait", issue = "27747")]
699     /// The resulting type after concatenation
700     type Output;
701 
702     /// Implementation of [`[T]::join`](slice::join)
703     #[unstable(feature = "slice_concat_trait", issue = "27747")]
join(slice: &Self, sep: Separator) -> Self::Output704     fn join(slice: &Self, sep: Separator) -> Self::Output;
705 }
706 
707 #[cfg(not(no_global_oom_handling))]
708 #[unstable(feature = "slice_concat_ext", issue = "27747")]
709 impl<T: Clone, V: Borrow<[T]>> Concat<T> for [V] {
710     type Output = Vec<T>;
711 
concat(slice: &Self) -> Vec<T>712     fn concat(slice: &Self) -> Vec<T> {
713         let size = slice.iter().map(|slice| slice.borrow().len()).sum();
714         let mut result = Vec::with_capacity(size);
715         for v in slice {
716             result.extend_from_slice(v.borrow())
717         }
718         result
719     }
720 }
721 
722 #[cfg(not(no_global_oom_handling))]
723 #[unstable(feature = "slice_concat_ext", issue = "27747")]
724 impl<T: Clone, V: Borrow<[T]>> Join<&T> for [V] {
725     type Output = Vec<T>;
726 
join(slice: &Self, sep: &T) -> Vec<T>727     fn join(slice: &Self, sep: &T) -> Vec<T> {
728         let mut iter = slice.iter();
729         let first = match iter.next() {
730             Some(first) => first,
731             None => return vec![],
732         };
733         let size = slice.iter().map(|v| v.borrow().len()).sum::<usize>() + slice.len() - 1;
734         let mut result = Vec::with_capacity(size);
735         result.extend_from_slice(first.borrow());
736 
737         for v in iter {
738             result.push(sep.clone());
739             result.extend_from_slice(v.borrow())
740         }
741         result
742     }
743 }
744 
745 #[cfg(not(no_global_oom_handling))]
746 #[unstable(feature = "slice_concat_ext", issue = "27747")]
747 impl<T: Clone, V: Borrow<[T]>> Join<&[T]> for [V] {
748     type Output = Vec<T>;
749 
join(slice: &Self, sep: &[T]) -> Vec<T>750     fn join(slice: &Self, sep: &[T]) -> Vec<T> {
751         let mut iter = slice.iter();
752         let first = match iter.next() {
753             Some(first) => first,
754             None => return vec![],
755         };
756         let size =
757             slice.iter().map(|v| v.borrow().len()).sum::<usize>() + sep.len() * (slice.len() - 1);
758         let mut result = Vec::with_capacity(size);
759         result.extend_from_slice(first.borrow());
760 
761         for v in iter {
762             result.extend_from_slice(sep);
763             result.extend_from_slice(v.borrow())
764         }
765         result
766     }
767 }
768 
769 ////////////////////////////////////////////////////////////////////////////////
770 // Standard trait implementations for slices
771 ////////////////////////////////////////////////////////////////////////////////
772 
773 #[stable(feature = "rust1", since = "1.0.0")]
774 impl<T, A: Allocator> Borrow<[T]> for Vec<T, A> {
borrow(&self) -> &[T]775     fn borrow(&self) -> &[T] {
776         &self[..]
777     }
778 }
779 
780 #[stable(feature = "rust1", since = "1.0.0")]
781 impl<T, A: Allocator> BorrowMut<[T]> for Vec<T, A> {
borrow_mut(&mut self) -> &mut [T]782     fn borrow_mut(&mut self) -> &mut [T] {
783         &mut self[..]
784     }
785 }
786 
787 // Specializable trait for implementing ToOwned::clone_into. This is
788 // public in the crate and has the Allocator parameter so that
789 // vec::clone_from use it too.
790 #[cfg(not(no_global_oom_handling))]
791 pub(crate) trait SpecCloneIntoVec<T, A: Allocator> {
clone_into(&self, target: &mut Vec<T, A>)792     fn clone_into(&self, target: &mut Vec<T, A>);
793 }
794 
795 #[cfg(not(no_global_oom_handling))]
796 impl<T: Clone, A: Allocator> SpecCloneIntoVec<T, A> for [T] {
clone_into(&self, target: &mut Vec<T, A>)797     default fn clone_into(&self, target: &mut Vec<T, A>) {
798         // drop anything in target that will not be overwritten
799         target.truncate(self.len());
800 
801         // target.len <= self.len due to the truncate above, so the
802         // slices here are always in-bounds.
803         let (init, tail) = self.split_at(target.len());
804 
805         // reuse the contained values' allocations/resources.
806         target.clone_from_slice(init);
807         target.extend_from_slice(tail);
808     }
809 }
810 
811 #[cfg(not(no_global_oom_handling))]
812 impl<T: Copy, A: Allocator> SpecCloneIntoVec<T, A> for [T] {
clone_into(&self, target: &mut Vec<T, A>)813     fn clone_into(&self, target: &mut Vec<T, A>) {
814         target.clear();
815         target.extend_from_slice(self);
816     }
817 }
818 
819 #[cfg(not(no_global_oom_handling))]
820 #[stable(feature = "rust1", since = "1.0.0")]
821 impl<T: Clone> ToOwned for [T] {
822     type Owned = Vec<T>;
823     #[cfg(not(test))]
to_owned(&self) -> Vec<T>824     fn to_owned(&self) -> Vec<T> {
825         self.to_vec()
826     }
827 
828     #[cfg(test)]
to_owned(&self) -> Vec<T>829     fn to_owned(&self) -> Vec<T> {
830         hack::to_vec(self, Global)
831     }
832 
clone_into(&self, target: &mut Vec<T>)833     fn clone_into(&self, target: &mut Vec<T>) {
834         SpecCloneIntoVec::clone_into(self, target);
835     }
836 }
837 
838 ////////////////////////////////////////////////////////////////////////////////
839 // Sorting
840 ////////////////////////////////////////////////////////////////////////////////
841 
842 #[inline]
843 #[cfg(not(no_global_oom_handling))]
stable_sort<T, F>(v: &mut [T], mut is_less: F) where F: FnMut(&T, &T) -> bool,844 fn stable_sort<T, F>(v: &mut [T], mut is_less: F)
845 where
846     F: FnMut(&T, &T) -> bool,
847 {
848     if T::IS_ZST {
849         // Sorting has no meaningful behavior on zero-sized types. Do nothing.
850         return;
851     }
852 
853     let elem_alloc_fn = |len: usize| -> *mut T {
854         // SAFETY: Creating the layout is safe as long as merge_sort never calls this with len >
855         // v.len(). Alloc in general will only be used as 'shadow-region' to store temporary swap
856         // elements.
857         unsafe { alloc::alloc(alloc::Layout::array::<T>(len).unwrap_unchecked()) as *mut T }
858     };
859 
860     let elem_dealloc_fn = |buf_ptr: *mut T, len: usize| {
861         // SAFETY: Creating the layout is safe as long as merge_sort never calls this with len >
862         // v.len(). The caller must ensure that buf_ptr was created by elem_alloc_fn with the same
863         // len.
864         unsafe {
865             alloc::dealloc(buf_ptr as *mut u8, alloc::Layout::array::<T>(len).unwrap_unchecked());
866         }
867     };
868 
869     let run_alloc_fn = |len: usize| -> *mut sort::TimSortRun {
870         // SAFETY: Creating the layout is safe as long as merge_sort never calls this with an
871         // obscene length or 0.
872         unsafe {
873             alloc::alloc(alloc::Layout::array::<sort::TimSortRun>(len).unwrap_unchecked())
874                 as *mut sort::TimSortRun
875         }
876     };
877 
878     let run_dealloc_fn = |buf_ptr: *mut sort::TimSortRun, len: usize| {
879         // SAFETY: The caller must ensure that buf_ptr was created by elem_alloc_fn with the same
880         // len.
881         unsafe {
882             alloc::dealloc(
883                 buf_ptr as *mut u8,
884                 alloc::Layout::array::<sort::TimSortRun>(len).unwrap_unchecked(),
885             );
886         }
887     };
888 
889     sort::merge_sort(v, &mut is_less, elem_alloc_fn, elem_dealloc_fn, run_alloc_fn, run_dealloc_fn);
890 }
891