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Diffstat (limited to 'src/iter/chain.rs')
| -rw-r--r-- | src/iter/chain.rs | 268 |
1 files changed, 268 insertions, 0 deletions
diff --git a/src/iter/chain.rs b/src/iter/chain.rs new file mode 100644 index 0000000..48fce07 --- /dev/null +++ b/src/iter/chain.rs @@ -0,0 +1,268 @@ +use super::plumbing::*; +use super::*; +use rayon_core::join; +use std::cmp; +use std::iter; + +/// `Chain` is an iterator that joins `b` after `a` in one continuous iterator. +/// This struct is created by the [`chain()`] method on [`ParallelIterator`] +/// +/// [`chain()`]: trait.ParallelIterator.html#method.chain +/// [`ParallelIterator`]: trait.ParallelIterator.html +#[must_use = "iterator adaptors are lazy and do nothing unless consumed"] +#[derive(Debug, Clone)] +pub struct Chain<A, B> +where + A: ParallelIterator, + B: ParallelIterator<Item = A::Item>, +{ + a: A, + b: B, +} + +impl<A, B> Chain<A, B> +where + A: ParallelIterator, + B: ParallelIterator<Item = A::Item>, +{ + /// Creates a new `Chain` iterator. + pub(super) fn new(a: A, b: B) -> Self { + Chain { a, b } + } +} + +impl<A, B> ParallelIterator for Chain<A, B> +where + A: ParallelIterator, + B: ParallelIterator<Item = A::Item>, +{ + type Item = A::Item; + + fn drive_unindexed<C>(self, consumer: C) -> C::Result + where + C: UnindexedConsumer<Self::Item>, + { + let Chain { a, b } = self; + + // If we returned a value from our own `opt_len`, then the collect consumer in particular + // will balk at being treated like an actual `UnindexedConsumer`. But when we do know the + // length, we can use `Consumer::split_at` instead, and this is still harmless for other + // truly-unindexed consumers too. + let (left, right, reducer) = if let Some(len) = a.opt_len() { + consumer.split_at(len) + } else { + let reducer = consumer.to_reducer(); + (consumer.split_off_left(), consumer, reducer) + }; + + let (a, b) = join(|| a.drive_unindexed(left), || b.drive_unindexed(right)); + reducer.reduce(a, b) + } + + fn opt_len(&self) -> Option<usize> { + self.a.opt_len()?.checked_add(self.b.opt_len()?) + } +} + +impl<A, B> IndexedParallelIterator for Chain<A, B> +where + A: IndexedParallelIterator, + B: IndexedParallelIterator<Item = A::Item>, +{ + fn drive<C>(self, consumer: C) -> C::Result + where + C: Consumer<Self::Item>, + { + let Chain { a, b } = self; + let (left, right, reducer) = consumer.split_at(a.len()); + let (a, b) = join(|| a.drive(left), || b.drive(right)); + reducer.reduce(a, b) + } + + fn len(&self) -> usize { + self.a.len().checked_add(self.b.len()).expect("overflow") + } + + fn with_producer<CB>(self, callback: CB) -> CB::Output + where + CB: ProducerCallback<Self::Item>, + { + let a_len = self.a.len(); + return self.a.with_producer(CallbackA { + callback, + a_len, + b: self.b, + }); + + struct CallbackA<CB, B> { + callback: CB, + a_len: usize, + b: B, + } + + impl<CB, B> ProducerCallback<B::Item> for CallbackA<CB, B> + where + B: IndexedParallelIterator, + CB: ProducerCallback<B::Item>, + { + type Output = CB::Output; + + fn callback<A>(self, a_producer: A) -> Self::Output + where + A: Producer<Item = B::Item>, + { + self.b.with_producer(CallbackB { + callback: self.callback, + a_len: self.a_len, + a_producer, + }) + } + } + + struct CallbackB<CB, A> { + callback: CB, + a_len: usize, + a_producer: A, + } + + impl<CB, A> ProducerCallback<A::Item> for CallbackB<CB, A> + where + A: Producer, + CB: ProducerCallback<A::Item>, + { + type Output = CB::Output; + + fn callback<B>(self, b_producer: B) -> Self::Output + where + B: Producer<Item = A::Item>, + { + let producer = ChainProducer::new(self.a_len, self.a_producer, b_producer); + self.callback.callback(producer) + } + } + } +} + +/// //////////////////////////////////////////////////////////////////////// + +struct ChainProducer<A, B> +where + A: Producer, + B: Producer<Item = A::Item>, +{ + a_len: usize, + a: A, + b: B, +} + +impl<A, B> ChainProducer<A, B> +where + A: Producer, + B: Producer<Item = A::Item>, +{ + fn new(a_len: usize, a: A, b: B) -> Self { + ChainProducer { a_len, a, b } + } +} + +impl<A, B> Producer for ChainProducer<A, B> +where + A: Producer, + B: Producer<Item = A::Item>, +{ + type Item = A::Item; + type IntoIter = ChainSeq<A::IntoIter, B::IntoIter>; + + fn into_iter(self) -> Self::IntoIter { + ChainSeq::new(self.a.into_iter(), self.b.into_iter()) + } + + fn min_len(&self) -> usize { + cmp::max(self.a.min_len(), self.b.min_len()) + } + + fn max_len(&self) -> usize { + cmp::min(self.a.max_len(), self.b.max_len()) + } + + fn split_at(self, index: usize) -> (Self, Self) { + if index <= self.a_len { + let a_rem = self.a_len - index; + let (a_left, a_right) = self.a.split_at(index); + let (b_left, b_right) = self.b.split_at(0); + ( + ChainProducer::new(index, a_left, b_left), + ChainProducer::new(a_rem, a_right, b_right), + ) + } else { + let (a_left, a_right) = self.a.split_at(self.a_len); + let (b_left, b_right) = self.b.split_at(index - self.a_len); + ( + ChainProducer::new(self.a_len, a_left, b_left), + ChainProducer::new(0, a_right, b_right), + ) + } + } + + fn fold_with<F>(self, mut folder: F) -> F + where + F: Folder<A::Item>, + { + folder = self.a.fold_with(folder); + if folder.full() { + folder + } else { + self.b.fold_with(folder) + } + } +} + +/// //////////////////////////////////////////////////////////////////////// +/// Wrapper for Chain to implement ExactSizeIterator + +struct ChainSeq<A, B> { + chain: iter::Chain<A, B>, +} + +impl<A, B> ChainSeq<A, B> { + fn new(a: A, b: B) -> ChainSeq<A, B> + where + A: ExactSizeIterator, + B: ExactSizeIterator<Item = A::Item>, + { + ChainSeq { chain: a.chain(b) } + } +} + +impl<A, B> Iterator for ChainSeq<A, B> +where + A: Iterator, + B: Iterator<Item = A::Item>, +{ + type Item = A::Item; + + fn next(&mut self) -> Option<Self::Item> { + self.chain.next() + } + + fn size_hint(&self) -> (usize, Option<usize>) { + self.chain.size_hint() + } +} + +impl<A, B> ExactSizeIterator for ChainSeq<A, B> +where + A: ExactSizeIterator, + B: ExactSizeIterator<Item = A::Item>, +{ +} + +impl<A, B> DoubleEndedIterator for ChainSeq<A, B> +where + A: DoubleEndedIterator, + B: DoubleEndedIterator<Item = A::Item>, +{ + fn next_back(&mut self) -> Option<Self::Item> { + self.chain.next_back() + } +} |