implement specialized nth_back() for Bytes, Fuse and Enumerate
Hi,
After my first PR has been successfully merged, here is my second pull request :-)
Also this PR contains some specializations for the problem discussed in #54054.
This commit changes the behavior of Formatter::debug_struct,
debug_tuple, debug_list, debug_set, and debug_map to render trailing
commas in {:#?} mode, which is the dominant style in modern Rust code.
Before:
Language {
name: "Rust",
trailing_commas: false
}
After:
Language {
name: "Rust",
trailing_commas: true,
}
Implement useful steps_between for all integers
We can use `usize::try_from` to convert steps from any size of integer.
This enables a meaningful `size_hint()` for larger ranges, rather than
always just `(0, None)`. Now they return the true `(len, Some(len))`
when it fits, otherwise `(usize::MAX, None)` for overflow.
Add FromStr impl for NonZero types
This is a WIP implementation because I do have some questions regarding the solution.
Somebody should ping the lang team on this I guess.
Please see the annotations on the code for more details.
Closes#58604
We can use `usize::try_from` to convert steps from any size of integer.
This enables a meaningful `size_hint()` for larger ranges, rather than
always just `(0, None)`. Now they return the true `(len, Some(len))`
when it fits, otherwise `(usize::MAX, None)` for overflow.
Implement specialized nth_back() for Box and Windows.
Hi there, this is my first pull request to rust :-)
I started implementing some specializations for DoubleEndedIterator::nth_back() and these are the first two. The problem has been discussed in #54054 and nth_back() is tracked in #56995.
I'm stuck with the next implementation so I though I do a PR for the ones I'm confident with to get some feedback.
Simplify Iterator::{min, max}
This PR simplifies the `select_fold1` helper method used to implmement `Iterator::{min, min_by, min_by_key, max, max_by, max_by_key}` by removing the projection argument, which was only used by the implementations of `min_by_key` and `max_by_key`.
I also added tests to ensure that the stability as mentioned in the comments of `min` and `max` is preserved, and fixed the `iter::{bench_max, bench_max_by_key}` benchmarks which the compiler presumably was able to collapse into closed-form expressions. None of the benchmark results were impacted, I suspect their generated assembly didn't change.
Add some more notes to the documentation:
- Mention that the median can be found if we used `len() / 2`.
- Mention that this function is usually called "kth element" in other libraries.
Address some comments in PR:
- Change wording on some of the documentation
- Change recursive function into a loop
Update name to `partition_at_index` and add convenience return values.
Address reviewer comments:
- Don't swap on each iteration when searching for min/max element.
- Add some docs about when we panic.
- Test that the sum of the lengths of the output matches the length of the input.
- Style fix for for-loop.
Address more reviewer comments
Fix Rng stuff for test
Fix doc test build
Don't run the partition_at_index test on wasm targets
Miri does not support entropy for test partition_at_index
RangeInclusive internal iteration performance improvement.
Specialize `Iterator::try_fold` and `DoubleEndedIterator::try_rfold` to improve code generation in all internal iteration scenarios.
This changes brings the performance of internal iteration with `RangeInclusive` on par with the performance of iteration with `Range`:
- Single conditional jump in hot loop,
- Unrolling and vectorization,
- And even Closed Form substitution.
Unfortunately, it only applies to internal iteration. Despite various attempts at stream-lining the implementation of `next` and `next_back`, LLVM has stubbornly refused to optimize external iteration appropriately, leaving me with a choice between:
- The current implementation, for which Closed Form substitution is performed, but which uses 2 conditional jumps in the hot loop when optimization fail.
- An implementation using a `is_done` boolean, which uses 1 conditional jump in the hot loop when optimization fail, allowing unrolling and vectorization, but for which Closed Form substitution fails.
In the absence of any conclusive evidence as to which usecase matters most, and with no assurance that the lack of Closed Form substitution is not indicative of other optimizations being foiled, there is no way
to pick one implementation over the other, and thus I defer to the statu quo as far as `next` and `next_back` are concerned.
