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gen_range(a, b) -> gen_range(a..b) and gen_range(a..=b) #1003

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merged 2 commits into from
Aug 1, 2020

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vks
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@vks vks commented Jul 27, 2020

Replaces and closes #821.

@vks vks changed the title Implement Distribution for Range gen_range(a, b) -> gen_range(a..b) and gen_range(a..=b) Jul 30, 2020
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vks commented Jul 30, 2020

The only failure is a spurious network error.

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Aha, shouldn't have tried reviewing this commit-by-commit!

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src/rng.rs Outdated
Comment on lines 124 to 165
fn gen_range<T: SampleUniform, B1, B2>(&mut self, low: B1, high: B2) -> T
fn gen_range<T, R>(&mut self, range: R) -> T
where
B1: SampleBorrow<T> + Sized,
B2: SampleBorrow<T> + Sized,
T: SampleUniform,
R: RangeBounds<T>
{
T::Sampler::sample_single(low, high, self)
use core::ops::Bound;
if let Bound::Included(low) = range.start_bound() {
match range.end_bound() {
Bound::Excluded(high) => T::Sampler::sample_single(low, high, self),
Bound::Included(high) => T::Sampler::sample_single_inclusive(low, high, self),
Bound::Unbounded => panic!("invalid upper bound"),
}
} else {
panic!("invalid lower bound");
}
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We shouldn't have to use run-time look-ups and panics. Can we do something like: where R: Into<Uniform<T>>?

No, really we need a specific trait for "sample single":

trait SampleSingle<X> {
    fn sample_single(self) -> X;
}
impl<X: SampleUniform> SampleSingle<X> for Range<X> { .. }
impl<X: SampleUniform> SampleSingle<X> for RangeInclusive<X> { .. }

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Yes, we would have to define such a trait if we want to avoid the lookup. Alternatively, we could inline gen_range and hope the lookup gets optimized away. What do you prefer?

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I added an implementation using static dispatch in the last commit. It required a new public trait that we may want to hide with #[doc(hidden)] to avoid users implementing it to add support for other range types.

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What do you think @newpavlov? Overall it seems more useful to expose the trait (sometimes users do want to extend generic APIs).

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vks commented Jul 31, 2020

Aha, shouldn't have tried reviewing this commit-by-commit!

Sorry, this should probably be rebased and squashed.

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@vks vks mentioned this pull request Jul 31, 2020
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vks commented Jul 31, 2020

I'm not sure how to work around packed_simd not implementing PartialOrd. Is it ok to break gen_range's support for SIMD?

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I think that's probably fine. Anyone who knows of the packed_simd support probably knows the API well enough to know about Uniform::sample_single

Ralith and others added 2 commits August 1, 2020 15:39
This includes a specialized implementation for integers.
This adds support for `Rng::range(a..b)` and `Rng::range(a..=b)`,
replacing `Rng::range(a, b)`. `a` and `b` must now implement
`PartialEq`.

This is a breaking change. In most cases, replacing
`Rng::gen_range(a, b)` with `Rng::gen_range(a..b)` should be enough,
however type annotations may be necessary, and `a` and `b` can no longer
be references or SIMD types.

SIMD types are still supported by `UniformSampler::sample_single`.

Some clippy warnings were fixed as well.
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4 participants