104 lines
2.1 KiB
Rust
104 lines
2.1 KiB
Rust
use crate::iter::plumbing::*;
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use crate::iter::*;
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use std::fmt;
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use std::marker::PhantomData;
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/// Creates a parallel iterator that produces nothing.
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///
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/// This admits no parallelism on its own, but it could be used for code that
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/// deals with generic parallel iterators.
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///
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/// # Examples
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///
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/// ```
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/// use rayon::prelude::*;
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/// use rayon::iter::empty;
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///
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/// let pi = (0..1234).into_par_iter()
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/// .chain(empty())
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/// .chain(1234..10_000);
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///
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/// assert_eq!(pi.count(), 10_000);
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/// ```
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pub fn empty<T: Send>() -> Empty<T> {
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Empty {
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marker: PhantomData,
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}
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}
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/// Iterator adaptor for [the `empty()` function](fn.empty.html).
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pub struct Empty<T: Send> {
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marker: PhantomData<T>,
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}
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impl<T: Send> Clone for Empty<T> {
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fn clone(&self) -> Self {
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empty()
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}
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}
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impl<T: Send> fmt::Debug for Empty<T> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.pad("Empty")
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}
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}
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impl<T: Send> ParallelIterator for Empty<T> {
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type Item = T;
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fn drive_unindexed<C>(self, consumer: C) -> C::Result
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where
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C: UnindexedConsumer<Self::Item>,
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{
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self.drive(consumer)
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}
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fn opt_len(&self) -> Option<usize> {
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Some(0)
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}
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}
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impl<T: Send> IndexedParallelIterator for Empty<T> {
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fn drive<C>(self, consumer: C) -> C::Result
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where
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C: Consumer<Self::Item>,
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{
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consumer.into_folder().complete()
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}
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fn len(&self) -> usize {
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0
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}
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fn with_producer<CB>(self, callback: CB) -> CB::Output
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where
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CB: ProducerCallback<Self::Item>,
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{
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callback.callback(EmptyProducer(PhantomData))
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}
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}
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/// Private empty producer
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struct EmptyProducer<T: Send>(PhantomData<T>);
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impl<T: Send> Producer for EmptyProducer<T> {
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type Item = T;
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type IntoIter = std::iter::Empty<T>;
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fn into_iter(self) -> Self::IntoIter {
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std::iter::empty()
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}
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fn split_at(self, index: usize) -> (Self, Self) {
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debug_assert_eq!(index, 0);
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(self, EmptyProducer(PhantomData))
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}
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fn fold_with<F>(self, folder: F) -> F
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where
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F: Folder<Self::Item>,
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{
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folder
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}
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}
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