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-rw-r--r--library/core/src/slice/mod.rs132
1 files changed, 90 insertions, 42 deletions
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 6a7150d29..4f1bb1734 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -9,7 +9,7 @@
use crate::cmp::Ordering::{self, Greater, Less};
use crate::intrinsics::{assert_unsafe_precondition, exact_div};
use crate::marker::Copy;
-use crate::mem;
+use crate::mem::{self, SizedTypeProperties};
use crate::num::NonZeroUsize;
use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
use crate::option::Option;
@@ -123,18 +123,11 @@ impl<T> [T] {
#[lang = "slice_len_fn"]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
+ #[rustc_allow_const_fn_unstable(ptr_metadata)]
#[inline]
#[must_use]
- // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
pub const fn len(&self) -> usize {
- // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
- // As of this writing this causes a "Const-stable functions can only call other
- // const-stable functions" error.
-
- // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
- // and PtrComponents<T> have the same memory layouts. Only std can make this
- // guarantee.
- unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
+ ptr::metadata(self)
}
/// Returns `true` if the slice has a length of 0.
@@ -660,7 +653,10 @@ impl<T> [T] {
let ptr = this.as_mut_ptr();
// SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
unsafe {
- assert_unsafe_precondition!([T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len());
+ assert_unsafe_precondition!(
+ "slice::swap_unchecked requires that the indices are within the slice",
+ [T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len()
+ );
ptr::swap(ptr.add(a), ptr.add(b));
}
}
@@ -976,7 +972,10 @@ impl<T> [T] {
let this = self;
// SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
let new_len = unsafe {
- assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+ assert_unsafe_precondition!(
+ "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
+ [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
+ );
exact_div(self.len(), N)
};
// SAFETY: We cast a slice of `new_len * N` elements into
@@ -1116,7 +1115,10 @@ impl<T> [T] {
let this = &*self;
// SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
let new_len = unsafe {
- assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+ assert_unsafe_precondition!(
+ "slice::as_chunks_unchecked_mut requires `N != 0` and the slice to split exactly into `N`-element chunks",
+ [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
+ );
exact_div(this.len(), N)
};
// SAFETY: We cast a slice of `new_len * N` elements into
@@ -1580,7 +1582,8 @@ impl<T> [T] {
#[inline]
#[track_caller]
#[must_use]
- pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+ #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
+ pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
assert!(mid <= self.len());
// SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
// fulfills the requirements of `from_raw_parts_mut`.
@@ -1679,9 +1682,10 @@ impl<T> [T] {
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
+ #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
#[inline]
#[must_use]
- pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+ pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
let len = self.len();
let ptr = self.as_mut_ptr();
@@ -1690,7 +1694,10 @@ impl<T> [T] {
// `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
// is fine.
unsafe {
- assert_unsafe_precondition!((mid: usize, len: usize) => mid <= len);
+ assert_unsafe_precondition!(
+ "slice::split_at_mut_unchecked requires the index to be within the slice",
+ (mid: usize, len: usize) => mid <= len
+ );
(from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
}
}
@@ -2074,7 +2081,7 @@ impl<T> [T] {
SplitN::new(self.split(pred), n)
}
- /// Returns an iterator over subslices separated by elements that match
+ /// Returns an iterator over mutable subslices separated by elements that match
/// `pred`, limited to returning at most `n` items. The matched element is
/// not contained in the subslices.
///
@@ -2357,6 +2364,28 @@ impl<T> [T] {
/// assert!(match r { Ok(1..=4) => true, _ => false, });
/// ```
///
+ /// If you want to find that whole *range* of matching items, rather than
+ /// an arbitrary matching one, that can be done using [`partition_point`]:
+ /// ```
+ /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+ ///
+ /// let low = s.partition_point(|x| x < &1);
+ /// assert_eq!(low, 1);
+ /// let high = s.partition_point(|x| x <= &1);
+ /// assert_eq!(high, 5);
+ /// let r = s.binary_search(&1);
+ /// assert!((low..high).contains(&r.unwrap()));
+ ///
+ /// assert!(s[..low].iter().all(|&x| x < 1));
+ /// assert!(s[low..high].iter().all(|&x| x == 1));
+ /// assert!(s[high..].iter().all(|&x| x > 1));
+ ///
+ /// // For something not found, the "range" of equal items is empty
+ /// assert_eq!(s.partition_point(|x| x < &11), 9);
+ /// assert_eq!(s.partition_point(|x| x <= &11), 9);
+ /// assert_eq!(s.binary_search(&11), Err(9));
+ /// ```
+ ///
/// If you want to insert an item to a sorted vector, while maintaining
/// sort order, consider using [`partition_point`]:
///
@@ -2424,15 +2453,20 @@ impl<T> [T] {
where
F: FnMut(&'a T) -> Ordering,
{
+ // INVARIANTS:
+ // - 0 <= left <= left + size = right <= self.len()
+ // - f returns Less for everything in self[..left]
+ // - f returns Greater for everything in self[right..]
let mut size = self.len();
let mut left = 0;
let mut right = size;
while left < right {
let mid = left + size / 2;
- // SAFETY: the call is made safe by the following invariants:
- // - `mid >= 0`
- // - `mid < size`: `mid` is limited by `[left; right)` bound.
+ // SAFETY: the while condition means `size` is strictly positive, so
+ // `size/2 < size`. Thus `left + size/2 < left + size`, which
+ // coupled with the `left + size <= self.len()` invariant means
+ // we have `left + size/2 < self.len()`, and this is in-bounds.
let cmp = f(unsafe { self.get_unchecked(mid) });
// The reason why we use if/else control flow rather than match
@@ -2450,6 +2484,10 @@ impl<T> [T] {
size = right - left;
}
+
+ // SAFETY: directly true from the overall invariant.
+ // Note that this is `<=`, unlike the assume in the `Ok` path.
+ unsafe { crate::intrinsics::assume(left <= self.len()) };
Err(left)
}
@@ -2540,7 +2578,7 @@ impl<T> [T] {
where
T: Ord,
{
- sort::quicksort(self, |a, b| a.lt(b));
+ sort::quicksort(self, T::lt);
}
/// Sorts the slice with a comparator function, but might not preserve the order of equal
@@ -2643,9 +2681,10 @@ impl<T> [T] {
/// less than or equal to any value at a position `j > index`. Additionally, this reordering is
/// unstable (i.e. any number of equal elements may end up at position `index`), in-place
/// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
- /// element" in other libraries. It returns a triplet of the following values: all elements less
- /// than the one at the given index, the value at the given index, and all elements greater than
- /// the one at the given index.
+ /// element" in other libraries. It returns a triplet of the following from the reordered slice:
+ /// the subslice prior to `index`, the element at `index`, and the subslice after `index`;
+ /// accordingly, the values in those two subslices will respectively all be less-than-or-equal-to
+ /// and greater-than-or-equal-to the value of the element at `index`.
///
/// # Current implementation
///
@@ -2679,8 +2718,7 @@ impl<T> [T] {
where
T: Ord,
{
- let mut f = |a: &T, b: &T| a.lt(b);
- sort::partition_at_index(self, index, &mut f)
+ sort::partition_at_index(self, index, T::lt)
}
/// Reorder the slice with a comparator function such that the element at `index` is at its
@@ -2690,10 +2728,11 @@ impl<T> [T] {
/// less than or equal to any value at a position `j > index` using the comparator function.
/// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
/// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
- /// is also known as "kth element" in other libraries. It returns a triplet of the following
- /// values: all elements less than the one at the given index, the value at the given index,
- /// and all elements greater than the one at the given index, using the provided comparator
- /// function.
+ /// is also known as "kth element" in other libraries. It returns a triplet of the following from
+ /// the slice reordered according to the provided comparator function: the subslice prior to
+ /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
+ /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
+ /// the value of the element at `index`.
///
/// # Current implementation
///
@@ -2731,8 +2770,7 @@ impl<T> [T] {
where
F: FnMut(&T, &T) -> Ordering,
{
- let mut f = |a: &T, b: &T| compare(a, b) == Less;
- sort::partition_at_index(self, index, &mut f)
+ sort::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
}
/// Reorder the slice with a key extraction function such that the element at `index` is at its
@@ -2742,10 +2780,11 @@ impl<T> [T] {
/// less than or equal to any value at a position `j > index` using the key extraction function.
/// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
/// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
- /// is also known as "kth element" in other libraries. It returns a triplet of the following
- /// values: all elements less than the one at the given index, the value at the given index, and
- /// all elements greater than the one at the given index, using the provided key extraction
- /// function.
+ /// is also known as "kth element" in other libraries. It returns a triplet of the following from
+ /// the slice reordered according to the provided key extraction function: the subslice prior to
+ /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
+ /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
+ /// the value of the element at `index`.
///
/// # Current implementation
///
@@ -2784,8 +2823,7 @@ impl<T> [T] {
F: FnMut(&T) -> K,
K: Ord,
{
- let mut g = |a: &T, b: &T| f(a).lt(&f(b));
- sort::partition_at_index(self, index, &mut g)
+ sort::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
}
/// Moves all consecutive repeated elements to the end of the slice according to the
@@ -3459,7 +3497,7 @@ impl<T> [T] {
#[must_use]
pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
// Note that most of this function will be constant-evaluated,
- if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+ if U::IS_ZST || T::IS_ZST {
// handle ZSTs specially, which is – don't handle them at all.
return (self, &[], &[]);
}
@@ -3520,7 +3558,7 @@ impl<T> [T] {
#[must_use]
pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
// Note that most of this function will be constant-evaluated,
- if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+ if U::IS_ZST || T::IS_ZST {
// handle ZSTs specially, which is – don't handle them at all.
return (self, &mut [], &mut []);
}
@@ -3776,6 +3814,16 @@ impl<T> [T] {
/// assert!(v[i..].iter().all(|&x| !(x < 5)));
/// ```
///
+ /// If all elements of the slice match the predicate, including if the slice
+ /// is empty, then the length of the slice will be returned:
+ ///
+ /// ```
+ /// let a = [2, 4, 8];
+ /// assert_eq!(a.partition_point(|x| x < &100), a.len());
+ /// let a: [i32; 0] = [];
+ /// assert_eq!(a.partition_point(|x| x < &100), 0);
+ /// ```
+ ///
/// If you want to insert an item to a sorted vector, while maintaining
/// sort order:
///
@@ -4066,7 +4114,7 @@ impl<T, const N: usize> [[T; N]] {
/// ```
#[unstable(feature = "slice_flatten", issue = "95629")]
pub fn flatten(&self) -> &[T] {
- let len = if crate::mem::size_of::<T>() == 0 {
+ let len = if T::IS_ZST {
self.len().checked_mul(N).expect("slice len overflow")
} else {
// SAFETY: `self.len() * N` cannot overflow because `self` is
@@ -4104,7 +4152,7 @@ impl<T, const N: usize> [[T; N]] {
/// ```
#[unstable(feature = "slice_flatten", issue = "95629")]
pub fn flatten_mut(&mut self) -> &mut [T] {
- let len = if crate::mem::size_of::<T>() == 0 {
+ let len = if T::IS_ZST {
self.len().checked_mul(N).expect("slice len overflow")
} else {
// SAFETY: `self.len() * N` cannot overflow because `self` is
generated by cgit v1.2.3 (git 2.39.1) at 2024-07-10 19:58:05 +0000