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Auto merge of #75207 - dylni:add-slice-check-range, r=KodrAus

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Add `slice::check_range`

This method is useful for [`RangeBounds`] parameters. It's even been [rewritten](22ee68dc58/src/librustc_data_structures/sorted_map.rs (L214)) [many](22ee68dc58/library/alloc/src/vec.rs (L1299)) [times](22ee68dc58/library/core/src/slice/mod.rs (L2441)) in the standard library, sometimes assuming that the bounds won't be [`usize::MAX`].

For example, [`Vec::drain`] creates an empty iterator when [`usize::MAX`] is used as an inclusive end bound:

```rust
assert!(vec![1].drain(..=usize::max_value()).eq(iter::empty()));
```

If this PR is merged, I'll create another to use it for those methods.

[`RangeBounds`]: https://doc.rust-lang.org/std/ops/trait.RangeBounds.html
[`usize::MAX`]: https://doc.rust-lang.org/std/primitive.usize.html#associatedconstant.MAX
[`Vec::drain`]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.drain
This commit is contained in:
bors 2020-09-04 12:21:43 +00:00
commit ef55a0a92f
7 changed files with 111 additions and 94 deletions
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33
library/alloc/src/vec.rs
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@ -63,8 +63,7 @@ use core::iter::{
};
use core::marker::PhantomData;
use core::mem::{self, ManuallyDrop, MaybeUninit};
use core::ops::Bound::{Excluded, Included, Unbounded};
use core::ops::{self, Index, IndexMut, RangeBounds};
use core::ops::{self, Index, IndexMut, Range, RangeBounds};
use core::ptr::{self, NonNull};
use core::slice::{self, SliceIndex};
@ -1306,35 +1305,7 @@ impl<T> Vec<T> {
// the hole, and the vector length is restored to the new length.
//
let len = self.len();
let start = match range.start_bound() {
Included(&n) => n,
Excluded(&n) => n + 1,
Unbounded => 0,
};
let end = match range.end_bound() {
Included(&n) => n + 1,
Excluded(&n) => n,
Unbounded => len,
};
#[cold]
#[inline(never)]
fn start_assert_failed(start: usize, end: usize) -> ! {
panic!("start drain index (is {}) should be <= end drain index (is {})", start, end);
}
#[cold]
#[inline(never)]
fn end_assert_failed(end: usize, len: usize) -> ! {
panic!("end drain index (is {}) should be <= len (is {})", end, len);
}
if start > end {
start_assert_failed(start, end);
}
if end > len {
end_assert_failed(end, len);
}
let Range { start, end } = self.check_range(range);
unsafe {
// set self.vec length's to start, to be safe in case Drain is leaked