Add slice::ExactChunks and ::ExactChunksMut iterators
These guarantee that always the requested slice size will be returned
and any leftoever elements at the end will be ignored. It allows llvm to
get rid of bounds checks in the code using the iterator.
This is inspired by the same iterators provided by ndarray.
Fixes https://github.com/rust-lang/rust/issues/47115
I'll add unit tests for all this if the general idea and behaviour makes sense for everybody.
Also see https://github.com/rust-lang/rust/issues/47115#issuecomment-354715511 for an example what this improves.
These guarantee that always the requested slice size will be returned
and any leftoever elements at the end will be ignored. It allows llvm to
get rid of bounds checks in the code using the iterator.
This is inspired by the same iterators provided by ndarray.
See https://github.com/rust-lang/rust/issues/47115
type error method suggestions use whitelisted identity-like conversions
Previously, on a type mismatch (and if this wasn't preëmpted by a
higher-priority suggestion), we would look for argumentless methods
returning the expected type, and list them in a `help` note. This had two
major shortcomings: firstly, a lot of the suggestions didn't really make
sense (if you used a &str where a String was expected,
`.to_ascii_uppercase()` is probably not the solution you were hoping
for). Secondly, we weren't generating suggestions from the most useful
traits! We address the first problem with an internal
`#[rustc_conversion_suggestion]` attribute meant to mark methods that keep
the "same value" in the relevant sense, just converting the type. We
address the second problem by making `FnCtxt.probe_for_return_type` pass
the `ProbeScope::AllTraits` to `probe_op`: this would seem to be safe
because grep reveals no other callers of `probe_for_return_type`.
Also, structured suggestions are pretty and good for RLS and friends.
Unfortunately, the trait probing is still not all one would hope for: at a
minimum, we don't know how to rule out `into()` in cases where it wouldn't
actually work, and we don't know how to rule in `.to_owned()` where it
would. Issues #46459 and #46460 have been filed and are ref'd in a FIXME.
This is hoped to resolve#42929, #44672, and #45777.
Deprecate [T]::rotate in favor of [T]::rotate_{left,right}.
Background
==========
Slices currently have an **unstable** [`rotate`] method which rotates
elements in the slice to the _left_ N positions. [Here][tracking] is the
tracking issue for this unstable feature.
```rust
let mut a = ['a', 'b' ,'c', 'd', 'e', 'f'];
a.rotate(2);
assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
```
Proposal
========
Deprecate the [`rotate`] method and introduce `rotate_left` and
`rotate_right` methods.
```rust
let mut a = ['a', 'b' ,'c', 'd', 'e', 'f'];
a.rotate_left(2);
assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
```
```rust
let mut a = ['a', 'b' ,'c', 'd', 'e', 'f'];
a.rotate_right(2);
assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
```
Justification
=============
I used this method today for my first time and (probably because I’m a
naive westerner who reads LTR) was surprised when the docs mentioned that
elements get rotated in a left-ward direction. I was in a situation
where I needed to shift elements in a right-ward direction and had to
context switch from the main problem I was working on and think how much
to rotate left in order to accomplish the right-ward rotation I needed.
Ruby’s `Array.rotate` shifts left-ward, Python’s `deque.rotate` shifts
right-ward. Both of their implementations allow passing negative numbers
to shift in the opposite direction respectively. The current `rotate`
implementation takes an unsigned integer argument which doesn't allow
the negative number behavior.
Introducing `rotate_left` and `rotate_right` would:
- remove ambiguity about direction (alleviating need to read docs 😉)
- make it easier for people who need to rotate right
[`rotate`]: https://doc.rust-lang.org/std/primitive.slice.html#method.rotate
[tracking]: https://github.com/rust-lang/rust/issues/41891
Previously, on a type mismatch (and if this wasn't preëmpted by a
higher-priority suggestion), we would look for argumentless methods
returning the expected type, and list them in a `help` note.
This had two major shortcomings. Firstly, a lot of the suggestions didn't
really make sense (if you used a &str where a String was expected,
`.to_ascii_uppercase()` is probably not the solution you were hoping
for). Secondly, we weren't generating suggestions from the most useful
traits!
We address the first problem with an internal
`#[rustc_conversion_suggestion]` attribute meant to mark methods that keep
the "same value" in the relevant sense, just converting the type. We
address the second problem by making `FnCtxt.probe_for_return_type` pass
the `ProbeScope::AllTraits` to `probe_op`: this would seem to be safe
because grep reveals no other callers of `probe_for_return_type`.
Also, structured suggestions are preferred (because they're pretty, but
also for RLS and friends).
Also also, we make the E0055 autoderef recursion limit error use the
one-time-diagnostics set, because we can potentially hit the limit a lot
during probing. (Without this,
test/ui/did_you_mean/recursion_limit_deref.rs would report "aborting due to
51 errors").
Unfortunately, the trait probing is still not all one would hope for: at a
minimum, we don't know how to rule out `into()` in cases where it wouldn't
actually work, and we don't know how to rule in `.to_owned()` where it
would. Issues #46459 and #46460 have been filed and are ref'd in a FIXME.
This is hoped to resolve#42929, #44672, and #45777.
Mention SliceConcatExt's stability in its docs
Just saw someone in IRC mention there being no stable way to join string slices! It isn't entirely clear from the rust documentation that `SliceConcatExt` is usable. While this is mentioned in https://doc.rust-lang.org/std/prelude/, the trait has nothing to indicate that it's currently usable if found via a documentation search.
The wording on this could probably be improved, but I'm hoping its better than nothing.
SliceConcatExt's status as an unstable trait with stable methods is
documented in the compiler error for using it, and in
https://doc.rust-lang.org/std/prelude/, but it is not mentioned in the
trait itself.
Mentioning the methods can be used in stable rust today should help
users who are looking for a `join` method while working on stable rust.
Background
==========
Slices currently have an unstable [`rotate`] method which rotates
elements in the slice to the _left_ N positions. [Here][tracking] is the
tracking issue for this unstable feature.
```rust
let mut a = ['a', 'b' ,'c', 'd', 'e', 'f'];
a.rotate(2);
assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
```
Proposal
========
Deprecate the [`rotate`] method and introduce `rotate_left` and
`rotate_right` methods.
```rust
let mut a = ['a', 'b' ,'c', 'd', 'e', 'f'];
a.rotate_left(2);
assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
```
```rust
let mut a = ['a', 'b' ,'c', 'd', 'e', 'f'];
a.rotate_right(2);
assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
```
Justification
=============
I used this method today for my first time and (probably because I’m a
naive westerner who reads LTR) was surprised when the docs mentioned that
elements get rotated in a left-ward direction. I was in a situation
where I needed to shift elements in a right-ward direction and had to
context switch from the main problem I was working on and think how much
to rotate left in order to accomplish the right-ward rotation I needed.
Ruby’s `Array.rotate` shifts left-ward, Python’s `deque.rotate` shifts
right-ward. Both of their implementations allow passing negative numbers
to shift in the opposite direction respectively.
Introducing `rotate_left` and `rotate_right` would:
- remove ambiguity about direction (alleviating need to read docs 😉)
- make it easier for people who need to rotate right
[`rotate`]: https://doc.rust-lang.org/std/primitive.slice.html#method.rotate
[tracking]: https://github.com/rust-lang/rust/issues/41891
The ascii_methods_on_intrinsics feature stabilization
didn't land in time for 1.21.0. Update the annotation
so the documentation is correct about when these
methods became available.
Improve documentation for slice swap/copy/clone operations.
Fixes#45636.
- Demonstrate how to use these operations with slices of differing
lengths
- Demonstrate how to swap/copy/clone sub-slices of a slice using
`split_at_mut`
Stabilize some `ascii_ctype` methods
As discussed in #39658, this PR stabilizes those methods for `u8` and `char`. All inherent `ascii_ctype` for `[u8]` and `str` are removed as we prefer the more explicit version `s.chars().all(|c| c.is_ascii_())`.
This PR doesn't modify the `AsciiExt` trait. There, the `ascii_ctype` methods are still unstable. It is planned to remove those in the future (I think). I had to modify some code in `ascii.rs` to properly implement `AsciiExt` for all types.
Fixes#39658.
Fixes#45636.
- Demonstrate how to use these operations with slices of differing
lengths
- Demonstrate how to swap/copy/clone sub-slices of a slice using
`split_at_mut`
This has been discussed in #39658. It's a bit ambiguous how those
methods work for a sequence of ascii values. We prefer users writing
`s.iter().all(|b| b.is_ascii_...())` explicitly.
The AsciiExt methods still exist and are implemented for `str`
and `[u8]`. We will deprecated or remove those later.
We don't want to stabilize them now already. The goal of this set of
commits is just to add inherent methods to the four types. Stabilizing
all of those methods can be done later.
This is done in order to deprecate AsciiExt eventually. Note that
this commit contains a bunch of `cfg(stage0)` statements. This is
due to a new compiler feature this commit depends on: the
`slice_u8` lang item. Once this lang item is available in the
stage0 compiler, all those cfg flags (and more) can be removed.
This is done in order to deprecate AsciiExt eventually. Note that
this commit contains a bunch of `cfg(stage0)` statements. This is
due to a new compiler feature I am using: the `slice_u8` lang item.
Once this lang item is available in the stage0 compiler, all those
cfg flags (and more) can be removed.
These functions were deprecated and removed in 1.5, but such simple
functionality shouldn't require using unsafe code, and it isn't
cluttering libstd too much.
Fix inconsistent doc headings
This fixes headings reading "Unsafety" and "Example", they should be "Safety" and "Examples" according to RFC 1574.
r? @steveklabnik
