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use super::plumbing::*;
use super::*;
use std::cell::Cell;
use std::iter::{self, Fuse};
/// `Intersperse` is an iterator that inserts a particular item between each
/// item of the adapted iterator. This struct is created by the
/// [`intersperse()`] method on [`ParallelIterator`]
///
/// [`intersperse()`]: trait.ParallelIterator.html#method.intersperse
/// [`ParallelIterator`]: trait.ParallelIterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct Intersperse<I>
where
I: ParallelIterator,
I::Item: Clone,
{
base: I,
item: I::Item,
}
impl<I> Intersperse<I>
where
I: ParallelIterator,
I::Item: Clone,
{
/// Creates a new `Intersperse` iterator
pub(super) fn new(base: I, item: I::Item) -> Self {
Intersperse { base, item }
}
}
impl<I> ParallelIterator for Intersperse<I>
where
I: ParallelIterator,
I::Item: Clone + Send,
{
type Item = I::Item;
fn drive_unindexed<C>(self, consumer: C) -> C::Result
where
C: UnindexedConsumer<I::Item>,
{
let consumer1 = IntersperseConsumer::new(consumer, self.item);
self.base.drive_unindexed(consumer1)
}
fn opt_len(&self) -> Option<usize> {
match self.base.opt_len()? {
0 => Some(0),
len => len.checked_add(len - 1),
}
}
}
impl<I> IndexedParallelIterator for Intersperse<I>
where
I: IndexedParallelIterator,
I::Item: Clone + Send,
{
fn drive<C>(self, consumer: C) -> C::Result
where
C: Consumer<Self::Item>,
{
let consumer1 = IntersperseConsumer::new(consumer, self.item);
self.base.drive(consumer1)
}
fn len(&self) -> usize {
let len = self.base.len();
if len > 0 {
len.checked_add(len - 1).expect("overflow")
} else {
0
}
}
fn with_producer<CB>(self, callback: CB) -> CB::Output
where
CB: ProducerCallback<Self::Item>,
{
let len = self.len();
return self.base.with_producer(Callback {
callback,
item: self.item,
len,
});
struct Callback<CB, T> {
callback: CB,
item: T,
len: usize,
}
impl<T, CB> ProducerCallback<T> for Callback<CB, T>
where
CB: ProducerCallback<T>,
T: Clone + Send,
{
type Output = CB::Output;
fn callback<P>(self, base: P) -> CB::Output
where
P: Producer<Item = T>,
{
let producer = IntersperseProducer::new(base, self.item, self.len);
self.callback.callback(producer)
}
}
}
}
struct IntersperseProducer<P>
where
P: Producer,
{
base: P,
item: P::Item,
len: usize,
clone_first: bool,
}
impl<P> IntersperseProducer<P>
where
P: Producer,
{
fn new(base: P, item: P::Item, len: usize) -> Self {
IntersperseProducer {
base,
item,
len,
clone_first: false,
}
}
}
impl<P> Producer for IntersperseProducer<P>
where
P: Producer,
P::Item: Clone + Send,
{
type Item = P::Item;
type IntoIter = IntersperseIter<P::IntoIter>;
fn into_iter(self) -> Self::IntoIter {
IntersperseIter {
base: self.base.into_iter().fuse(),
item: self.item,
clone_first: self.len > 0 && self.clone_first,
// If there's more than one item, then even lengths end the opposite
// of how they started with respect to interspersed clones.
clone_last: self.len > 1 && ((self.len & 1 == 0) ^ self.clone_first),
}
}
fn min_len(&self) -> usize {
self.base.min_len()
}
fn max_len(&self) -> usize {
self.base.max_len()
}
fn split_at(self, index: usize) -> (Self, Self) {
debug_assert!(index <= self.len);
// The left needs half of the items from the base producer, and the
// other half will be our interspersed item. If we're not leading with
// a cloned item, then we need to round up the base number of items,
// otherwise round down.
let base_index = (index + !self.clone_first as usize) / 2;
let (left_base, right_base) = self.base.split_at(base_index);
let left = IntersperseProducer {
base: left_base,
item: self.item.clone(),
len: index,
clone_first: self.clone_first,
};
let right = IntersperseProducer {
base: right_base,
item: self.item,
len: self.len - index,
// If the index is odd, the right side toggles `clone_first`.
clone_first: (index & 1 == 1) ^ self.clone_first,
};
(left, right)
}
fn fold_with<F>(self, folder: F) -> F
where
F: Folder<Self::Item>,
{
let folder1 = IntersperseFolder {
base: folder,
item: self.item,
clone_first: self.clone_first,
};
self.base.fold_with(folder1).base
}
}
struct IntersperseIter<I>
where
I: Iterator,
{
base: Fuse<I>,
item: I::Item,
clone_first: bool,
clone_last: bool,
}
impl<I> Iterator for IntersperseIter<I>
where
I: DoubleEndedIterator + ExactSizeIterator,
I::Item: Clone,
{
type Item = I::Item;
fn next(&mut self) -> Option<Self::Item> {
if self.clone_first {
self.clone_first = false;
Some(self.item.clone())
} else if let next @ Some(_) = self.base.next() {
// If there are any items left, we'll need another clone in front.
self.clone_first = self.base.len() != 0;
next
} else if self.clone_last {
self.clone_last = false;
Some(self.item.clone())
} else {
None
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let len = self.len();
(len, Some(len))
}
}
impl<I> DoubleEndedIterator for IntersperseIter<I>
where
I: DoubleEndedIterator + ExactSizeIterator,
I::Item: Clone,
{
fn next_back(&mut self) -> Option<Self::Item> {
if self.clone_last {
self.clone_last = false;
Some(self.item.clone())
} else if let next_back @ Some(_) = self.base.next_back() {
// If there are any items left, we'll need another clone in back.
self.clone_last = self.base.len() != 0;
next_back
} else if self.clone_first {
self.clone_first = false;
Some(self.item.clone())
} else {
None
}
}
}
impl<I> ExactSizeIterator for IntersperseIter<I>
where
I: DoubleEndedIterator + ExactSizeIterator,
I::Item: Clone,
{
fn len(&self) -> usize {
let len = self.base.len();
len + len.saturating_sub(1) + self.clone_first as usize + self.clone_last as usize
}
}
struct IntersperseConsumer<C, T> {
base: C,
item: T,
clone_first: Cell<bool>,
}
impl<C, T> IntersperseConsumer<C, T>
where
C: Consumer<T>,
{
fn new(base: C, item: T) -> Self {
IntersperseConsumer {
base,
item,
clone_first: false.into(),
}
}
}
impl<C, T> Consumer<T> for IntersperseConsumer<C, T>
where
C: Consumer<T>,
T: Clone + Send,
{
type Folder = IntersperseFolder<C::Folder, T>;
type Reducer = C::Reducer;
type Result = C::Result;
fn split_at(mut self, index: usize) -> (Self, Self, Self::Reducer) {
// We'll feed twice as many items to the base consumer, except if we're
// not currently leading with a cloned item, then it's one less.
let base_index = index + index.saturating_sub(!self.clone_first.get() as usize);
let (left, right, reducer) = self.base.split_at(base_index);
let right = IntersperseConsumer {
base: right,
item: self.item.clone(),
clone_first: true.into(),
};
self.base = left;
(self, right, reducer)
}
fn into_folder(self) -> Self::Folder {
IntersperseFolder {
base: self.base.into_folder(),
item: self.item,
clone_first: self.clone_first.get(),
}
}
fn full(&self) -> bool {
self.base.full()
}
}
impl<C, T> UnindexedConsumer<T> for IntersperseConsumer<C, T>
where
C: UnindexedConsumer<T>,
T: Clone + Send,
{
fn split_off_left(&self) -> Self {
let left = IntersperseConsumer {
base: self.base.split_off_left(),
item: self.item.clone(),
clone_first: self.clone_first.clone(),
};
self.clone_first.set(true);
left
}
fn to_reducer(&self) -> Self::Reducer {
self.base.to_reducer()
}
}
struct IntersperseFolder<C, T> {
base: C,
item: T,
clone_first: bool,
}
impl<C, T> Folder<T> for IntersperseFolder<C, T>
where
C: Folder<T>,
T: Clone,
{
type Result = C::Result;
fn consume(mut self, item: T) -> Self {
if self.clone_first {
self.base = self.base.consume(self.item.clone());
if self.base.full() {
return self;
}
} else {
self.clone_first = true;
}
self.base = self.base.consume(item);
self
}
fn consume_iter<I>(self, iter: I) -> Self
where
I: IntoIterator<Item = T>,
{
let mut clone_first = self.clone_first;
let between_item = self.item;
let base = self.base.consume_iter(iter.into_iter().flat_map(|item| {
let first = if clone_first {
Some(between_item.clone())
} else {
clone_first = true;
None
};
first.into_iter().chain(iter::once(item))
}));
IntersperseFolder {
base,
item: between_item,
clone_first,
}
}
fn complete(self) -> C::Result {
self.base.complete()
}
fn full(&self) -> bool {
self.base.full()
}
}