Prefer `Option::map`/etc over `match` wherever it improves clarity
This isn't intended to change behavior anywhere. A lot of times statements like `match x { None => None, Some(y) => [...] }` can be rewritten using `Option::map` or `Option::and_then` in a way that preserves or improves clarity, so that's what I've done here.
I think it's particularly valuable to keep things in `libcore` and `libstd` pretty/idiomatic since it's not uncommon to follow the `[src]` links when browsing the rust-lang.org docs for std/core. If there's any concern about pushing style-based changes though, I'll happily back out the non-std/core commits here.
impl PartialEq+Eq for BuildHasherDefault
`BuildHasherDefault`is only one way of implementing `BuildHasher`. Clearly, every `BuildHasherDefault` for the same type `H` is identical, since it just uses `Default<H>` to construct `H`. In general, this is not true for every `BuildHasher`, so I think it is helpful to implement `PartialEq` and `Eq`.
Add unaligned volatile intrinsics
Surprisingly enough, it turns out that unaligned volatile loads are actually useful for certain (very niche) types of lock-free code. I included unaligned volatile stores for completeness, but I currently do not know of any use cases for them.
These are only exposed as intrinsics for now. If they turn out to be useful in practice, we can work towards stabilizing them.
r? @alexcrichton
Forget Waker when cloning LocalWaker
Since NonNull is Copy the inner field of the cloned Waker was copied for
use in the new LocalWaker, however this left Waker to be dropped. Which
means that when cloning LocalWaker would also erroneously call drop_raw.
This change forgets the Waker, rather then dropping it, leaving the
inner field to be used by the returned LocalWaker.
Closes#52629.
Implement rfc 1789: Conversions from `&mut T` to `&Cell<T>`
I'm surprised that RFC 1789 has not been implemented for several months. Tracking issue: https://github.com/rust-lang/rust/issues/43038
Please note: when I was writing tests for `&Cell<[i32]>`, I found it is not easy to get the length of the contained slice. So I designed a `get_with` method which might be useful for similar cases. This method is not designed in the RFC, and it certainly needs to be reviewed by core team. I think it has some connections with `Cell::update` https://github.com/rust-lang/rust/issues/50186 , which is also in design phase.
Since NonNull is Copy the inner field of the cloned Waker was copied for
use in the new LocalWaker, however this left Waker to be dropped. Which
means that when cloning LocalWaker would also erroneously call drop_raw.
This change forgets the Waker, rather then dropping it, leaving the
inner field to be used by the returned LocalWaker.
Closes#52629.
Document that Unique::empty() and NonNull::dangling() aren't sentinel values
The documentation of Unique::empty() and NonNull::dangling() could
potentially suggest that they work as sentinel values indicating a
not-yet-initialized pointer. However, they both declare a non-null
pointer equal to the alignment of the type, which could potentially
reference a valid value of that type (specifically, the first such valid
value in memory). Explicitly document that the return value of these
functions does not work as a sentinel value.
Deprecation of str::slice_unchecked(_mut)
Closes#51715
I am not sure if 1.28.0 or 1.29.0 should be used for deprecation version, for now it's 1.28.0.
Additionally I've replaced `slice_unchecked` uses with `get_unchecked`. The only places where this method is still used are `src/liballoc/tests/str.rs` and `src/liballoc/tests/str.rs`.
LLVM isn't able to remove the alloca for the unaligned block in the SIMD tail in some cases, so doing this helps SRoA work in cases where it currently doesn't. Found in the `replace_with` RFC discussion.
fix unsafety: don't call ptr_rotate for ZST
`rotate::ptr_rotate` has a comment saying
```
/// # Safety
///
/// The specified range must be valid for reading and writing.
/// The type `T` must have non-zero size.
```
So we better make sure we don't call it on ZST...
Cc @scottmcm (author of https://github.com/rust-lang/rust/pull/41670)
The documentation of Unique::empty() and NonNull::dangling() could
potentially suggest that they work as sentinel values indicating a
not-yet-initialized pointer. However, they both declare a non-null
pointer equal to the alignment of the type, which could potentially
reference a valid value of that type (specifically, the first such valid
value in memory). Explicitly document that the return value of these
functions does not work as a sentinel value.
Amend option.take examples
It wasn't abundantly clear to me what `.take` returned. Perhaps this is a slightly frivolous change, but I think it's an improvement. =)
Apologies if I'm not following proper procedures.
Handle array manually in str case conversion methods
Avoiding the overhead incurred from `String.extend(char.to_lowercase())` showed a notable performance improvement when I benchmarked it.
I tested on these strings:
```rust
ALL_LOWER: "loremipsumdolorsitametduosensibusmnesarchumabcdefgh"
ALL_UPPER: "LOREMIPSUMDOLORSITAMETDUOSENSIBUSMNESARCHUMABCDEFGH"
REALISTIC_UPPER: "LOREM IPSUM DOLOR SIT AMET, DUO SENSIBUS MNESARCHUM"
SIGMAS: "ΣΣΣΣΣ ΣΣΣΣΣ ΣΣΣΣΣ ΣΣΣ ΣΣΣΣ, ΣΣΣ ΣΣΣΣΣΣΣΣ ΣΣΣΣΣΣΣΣΣΣ"
WORD_UPPER: "Lorem Ipsum Dolor Sit Amet, Duo Sensibus Mnesarchum"
```
the performance improvements of `to_lowercase()` were
```
running 10 tests
test tests::all_lower ... bench: 1,752 ns/iter (+/- 49)
test tests::all_lower_new ... bench: 1,266 ns/iter (+/- 15) -28%
test tests::all_upper ... bench: 1,832 ns/iter (+/- 39)
test tests::all_upper_new ... bench: 1,337 ns/iter (+/- 18) -27%
test tests::realistic_upper ... bench: 1,993 ns/iter (+/- 14)
test tests::realistic_upper_new ... bench: 1,445 ns/iter (+/- 22) -27%
test tests::sigmas ... bench: 1,342 ns/iter (+/- 39)
test tests::sigmas_new ... bench: 1,226 ns/iter (+/- 16) -9%
test tests::word_upper ... bench: 1,899 ns/iter (+/- 12)
test tests::word_upper_new ... bench: 1,381 ns/iter (+/- 26) -27%
```
and of `to_uppercase()`
```
running 10 tests
test tests::all_lower ... bench: 1,813 ns/iter (+/- 20)
test tests::all_lower_new ... bench: 1,321 ns/iter (+/- 16) -27%
test tests::all_upper ... bench: 1,629 ns/iter (+/- 22)
test tests::all_upper_new ... bench: 1,241 ns/iter (+/- 9) -24%
test tests::realistic_upper ... bench: 1,670 ns/iter (+/- 24)
test tests::realistic_upper_new ... bench: 1,241 ns/iter (+/- 17) -26%
test tests::sigmas ... bench: 2,053 ns/iter (+/- 20)
test tests::sigmas_new ... bench: 1,753 ns/iter (+/- 23) -15%
test tests::word_upper ... bench: 1,873 ns/iter (+/- 30)
test tests::word_upper_new ... bench: 1,412 ns/iter (+/- 25) -25%
```
I gave up on the more advanced method from #52061 as it wasn't always a clear improvement and would help in even less cases if this PR was merged.
Now also the documentations of `subsec_millis`, `subsec_micros`, `as_millis` and `as_micros` make clear that the fractional nanosecond component is rounded down to whole units.
task: remove wrong comments about non-existent LocalWake trait
~~A `LocalWaker` is specifically `!Send `, and the unsafety comment around
`LocalWaker::new` only specifies that it be safe to call `wake_local`.
One could then accidentally promote a `LocalWaker` into a `Waker`, which
is universally `Send`, simply via `Waker::from(local_waker)`. A
`LocalWaker` the was built expecting to not be `Send`, such as using
`Rc`, could be sent to other threads safely.~~
~~Separately, though somewhat related, `Context` holds a `&LocalWaker`
internally, and exposes a `waker() -> &Waker` method. This simply
transmutes the `&LocalWaker` to `&Waker`, which would be unsound, except
that you can't "send" a `&Waker`, you'd need to clone it first. Since
`UnsafeWake::clone_raw` requires that it return a `Waker`, the transmute
is not unsound. The transmuted `LocalWaker` will be promoted to a
`Waker` correctly.~~
~~That would mean that if `UnsafeWake::clone_raw` were to be changed, such
as returning `Self` instead of `Waker`, this would no longer be sound.
Thus, this also adds a comment to `clone_raw` to remember this.~~
r? @cramertj
Change RangeInclusive to a three-field struct.
Fix#45222.
This PR also reverts #48012 (i.e. removed the `try_fold`/`try_rfold` specialization for `RangeInclusive`) because LLVM no longer has trouble recognizing a RangeInclusive loop.
Add ExactChunks::remainder and ExactChunks::into_remainder
These allow to get the leftover items of the slice that are not being
iterated as part of the iterator due to not filling a complete chunk.
The mutable version consumes the slice because otherwise we would either
a) have to borrow the iterator instead of taking the lifetime of
the underlying slice, which is not what *any* of the other iterator
functions is doing, or
b) would allow returning multiple mutable references to the same data
The current behaviour of consuming the iterator is consistent with
IterMut::into_slice for the normal iterator.
----
This is related to https://github.com/rust-lang/rust/issues/47115#issuecomment-392685177 and the following comments.
While there the discussion was first about a way to get the "tail" of the iterator (everything from the slice that is still not iterated yet), this gives kind of unintuitive behaviour and is inconsistent with how the other slice iterators work.
Unintuitive because the `next_back` would have no effect on the tail (or otherwise the tail could not include the remainder items), inconsistent because a) generally the idea of the slice iterators seems to be to only ever return items that were not iterated yet (and don't provide a way to access the same item twice) and b) we would return a "flat" `&[T]` slice but the iterator's shape is `&[[T]]` instead, c) the mutable variant would have to borrow from the iterator instead of the underlying slice (all other iterator functions borrow from the underlying slice!)
As such, I've only implemented functions to get the remainder. This also allows the implementation to be completely safe still (and around slices instead of raw pointers), while getting the tail would either be inefficient or would have to be implemented around raw pointers.
CC @kerollmops
