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matthiaskrgrmatthiaskrgr
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Rollup merge of #88502 - ibraheemdev:slice-take, r=dtolnay
Add slice take methods Revival of #62282 This PR adds the following slice methods: - `take` - `take_mut` - `take_first` - `take_first_mut` - `take_last` - `take_last_mut` r? `@LukasKalbertodt`
2 parents f04a2f4 + 8db85a3 commit 9f1f428

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‎library/core/src/ops/mod.rs‎

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@@ -181,6 +181,9 @@ pub use self::range::{Range, RangeFrom, RangeFull, RangeTo};
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#[stable(feature = "inclusive_range", since = "1.26.0")]
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pub use self::range::{Bound, RangeBounds, RangeInclusive, RangeToInclusive};
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#[unstable(feature = "one_sided_range", issue = "69780")]
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pub use self::range::OneSidedRange;
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#[unstable(feature = "try_trait_v2", issue = "84277")]
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pub use self::try_trait::{FromResidual, Try};
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‎library/core/src/ops/range.rs‎

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@@ -971,3 +971,21 @@ impl<T> RangeBounds<T> for RangeToInclusive<&T> {
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Included(self.end)
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}
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}
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/// `OneSidedRange` is implemented for built-in range types that are unbounded
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/// on one side. For example, `a..`, `..b` and `..=c` implement `OneSidedRange`,
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/// but `..`, `d..e`, and `f..=g` do not.
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///
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/// Types that implement `OneSidedRange<T>` must return `Bound::Unbounded`
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/// from one of `RangeBounds::start_bound` or `RangeBounds::end_bound`.
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#[unstable(feature = "one_sided_range", issue = "69780")]
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pub trait OneSidedRange<T: ?Sized>: RangeBounds<T> {}
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#[unstable(feature = "one_sided_range", issue = "69780")]
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impl<T> OneSidedRange<T> for RangeTo<T> where Self: RangeBounds<T> {}
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#[unstable(feature = "one_sided_range", issue = "69780")]
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impl<T> OneSidedRange<T> for RangeFrom<T> where Self: RangeBounds<T> {}
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#[unstable(feature = "one_sided_range", issue = "69780")]
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impl<T> OneSidedRange<T> for RangeToInclusive<T> where Self: RangeBounds<T> {}

‎library/core/src/slice/mod.rs‎

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@@ -10,7 +10,7 @@ use crate::cmp::Ordering::{self, Greater, Less};
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use crate::marker::Copy;
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use crate::mem;
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use crate::num::NonZeroUsize;
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use crate::ops::{FnMut, Range, RangeBounds};
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use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
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use crate::option::Option;
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use crate::option::Option::{None, Some};
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use crate::ptr;
@@ -82,6 +82,29 @@ pub use index::range;
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#[unstable(feature = "inherent_ascii_escape", issue = "77174")]
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pub use ascii::EscapeAscii;
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/// Calculates the direction and split point of a one-sided range.
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///
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/// This is a helper function for `take` and `take_mut` that returns
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/// the direction of the split (front or back) as well as the index at
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/// which to split. Returns `None` if the split index would overflow.
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#[inline]
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fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
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use Bound::*;
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Some(match (range.start_bound(), range.end_bound()) {
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(Unbounded, Excluded(i)) => (Direction::Front, *i),
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(Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
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(Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
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(Included(i), Unbounded) => (Direction::Back, *i),
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_ => unreachable!(),
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})
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}
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enum Direction {
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Front,
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Back,
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}
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#[lang = "slice"]
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#[cfg(not(test))]
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impl<T> [T] {
@@ -3517,6 +3540,245 @@ impl<T> [T] {
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{
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self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
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}
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/// Removes the subslice corresponding to the given range
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/// and returns a reference to it.
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///
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/// Returns `None` and does not modify the slice if the given
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/// range is out of bounds.
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///
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/// Note that this method only accepts one-sided ranges such as
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/// `2..` or `..6`, but not `2..6`.
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///
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/// # Examples
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///
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/// Taking the first three elements of a slice:
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///
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/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
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/// let mut first_three = slice.take(..3).unwrap();
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///
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/// assert_eq!(slice, &['d']);
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/// assert_eq!(first_three, &['a', 'b', 'c']);
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/// ```
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///
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/// Taking the last two elements of a slice:
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///
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/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
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/// let mut tail = slice.take(2..).unwrap();
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///
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/// assert_eq!(slice, &['a', 'b']);
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/// assert_eq!(tail, &['c', 'd']);
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/// ```
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///
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/// Getting `None` when `range` is out of bounds:
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///
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/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
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///
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/// assert_eq!(None, slice.take(5..));
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/// assert_eq!(None, slice.take(..5));
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/// assert_eq!(None, slice.take(..=4));
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/// let expected: &[char] = &['a', 'b', 'c', 'd'];
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/// assert_eq!(Some(expected), slice.take(..4));
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/// ```
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#[inline]
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#[must_use = "method does not modify the slice if the range is out of bounds"]
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#[unstable(feature = "slice_take", issue = "62280")]
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pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
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let (direction, split_index) = split_point_of(range)?;
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if split_index > self.len() {
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return None;
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}
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let (front, back) = self.split_at(split_index);
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match direction {
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Direction::Front => {
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*self = back;
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Some(front)
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}
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Direction::Back => {
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*self = front;
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Some(back)
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}
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}
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}
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/// Removes the subslice corresponding to the given range
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/// and returns a mutable reference to it.
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///
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/// Returns `None` and does not modify the slice if the given
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/// range is out of bounds.
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///
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/// Note that this method only accepts one-sided ranges such as
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/// `2..` or `..6`, but not `2..6`.
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///
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/// # Examples
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///
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/// Taking the first three elements of a slice:
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///
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/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
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/// let mut first_three = slice.take_mut(..3).unwrap();
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///
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/// assert_eq!(slice, &mut ['d']);
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/// assert_eq!(first_three, &mut ['a', 'b', 'c']);
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/// ```
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///
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/// Taking the last two elements of a slice:
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///
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/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
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/// let mut tail = slice.take_mut(2..).unwrap();
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///
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/// assert_eq!(slice, &mut ['a', 'b']);
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/// assert_eq!(tail, &mut ['c', 'd']);
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/// ```
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///
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/// Getting `None` when `range` is out of bounds:
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///
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/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
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///
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/// assert_eq!(None, slice.take_mut(5..));
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/// assert_eq!(None, slice.take_mut(..5));
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/// assert_eq!(None, slice.take_mut(..=4));
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/// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
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/// assert_eq!(Some(expected), slice.take_mut(..4));
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/// ```
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#[inline]
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#[must_use = "method does not modify the slice if the range is out of bounds"]
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#[unstable(feature = "slice_take", issue = "62280")]
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pub fn take_mut<'a, R: OneSidedRange<usize>>(
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self: &mut &'a mut Self,
3666+
range: R,
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) -> Option<&'a mut Self> {
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let (direction, split_index) = split_point_of(range)?;
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if split_index > self.len() {
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return None;
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}
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let (front, back) = mem::take(self).split_at_mut(split_index);
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match direction {
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Direction::Front => {
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*self = back;
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Some(front)
3677+
}
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Direction::Back => {
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*self = front;
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Some(back)
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}
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}
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}
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/// Removes the first element of the slice and returns a reference
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/// to it.
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///
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/// Returns `None` if the slice is empty.
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///
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/// # Examples
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///
3692+
/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &[_] = &['a', 'b', 'c'];
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/// let first = slice.take_first().unwrap();
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///
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/// assert_eq!(slice, &['b', 'c']);
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/// assert_eq!(first, &'a');
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/// ```
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#[inline]
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#[unstable(feature = "slice_take", issue = "62280")]
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pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
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let (first, rem) = self.split_first()?;
3705+
*self = rem;
3706+
Some(first)
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}
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/// Removes the first element of the slice and returns a mutable
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/// reference to it.
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///
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/// Returns `None` if the slice is empty.
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///
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/// # Examples
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///
3716+
/// ```
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/// #![feature(slice_take)]
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///
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/// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
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/// let first = slice.take_first_mut().unwrap();
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/// *first = 'd';
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///
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/// assert_eq!(slice, &['b', 'c']);
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/// assert_eq!(first, &'d');
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/// ```
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#[inline]
3727+
#[unstable(feature = "slice_take", issue = "62280")]
3728+
pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3729+
let (first, rem) = mem::take(self).split_first_mut()?;
3730+
*self = rem;
3731+
Some(first)
3732+
}
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3734+
/// Removes the last element of the slice and returns a reference
3735+
/// to it.
3736+
///
3737+
/// Returns `None` if the slice is empty.
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///
3739+
/// # Examples
3740+
///
3741+
/// ```
3742+
/// #![feature(slice_take)]
3743+
///
3744+
/// let mut slice: &[_] = &['a', 'b', 'c'];
3745+
/// let last = slice.take_last().unwrap();
3746+
///
3747+
/// assert_eq!(slice, &['a', 'b']);
3748+
/// assert_eq!(last, &'c');
3749+
/// ```
3750+
#[inline]
3751+
#[unstable(feature = "slice_take", issue = "62280")]
3752+
pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
3753+
let (last, rem) = self.split_last()?;
3754+
*self = rem;
3755+
Some(last)
3756+
}
3757+
3758+
/// Removes the last element of the slice and returns a mutable
3759+
/// reference to it.
3760+
///
3761+
/// Returns `None` if the slice is empty.
3762+
///
3763+
/// # Examples
3764+
///
3765+
/// ```
3766+
/// #![feature(slice_take)]
3767+
///
3768+
/// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3769+
/// let last = slice.take_last_mut().unwrap();
3770+
/// *last = 'd';
3771+
///
3772+
/// assert_eq!(slice, &['a', 'b']);
3773+
/// assert_eq!(last, &'d');
3774+
/// ```
3775+
#[inline]
3776+
#[unstable(feature = "slice_take", issue = "62280")]
3777+
pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3778+
let (last, rem) = mem::take(self).split_last_mut()?;
3779+
*self = rem;
3780+
Some(last)
3781+
}
35203782
}
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35223784
trait CloneFromSpec<T> {

‎library/core/tests/lib.rs‎

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@@ -36,6 +36,7 @@
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#![feature(pattern)]
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#![feature(sort_internals)]
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#![feature(slice_partition_at_index)]
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#![feature(slice_take)]
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#![feature(maybe_uninit_uninit_array)]
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#![feature(maybe_uninit_array_assume_init)]
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#![feature(maybe_uninit_extra)]

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