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use super::plumbing::*;
use super::*;
use std::fmt::{self, Debug};
/// `FlatMap` maps each element to a parallel iterator, then flattens these iterators together.
/// This struct is created by the [`flat_map()`] method on [`ParallelIterator`]
///
/// [`flat_map()`]: trait.ParallelIterator.html#method.flat_map
/// [`ParallelIterator`]: trait.ParallelIterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[derive(Clone)]
pub struct FlatMap<I: ParallelIterator, F> {
base: I,
map_op: F,
}
impl<I: ParallelIterator + Debug, F> Debug for FlatMap<I, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("FlatMap").field("base", &self.base).finish()
}
}
impl<I: ParallelIterator, F> FlatMap<I, F> {
/// Creates a new `FlatMap` iterator.
pub(super) fn new(base: I, map_op: F) -> Self {
FlatMap { base, map_op }
}
}
impl<I, F, PI> ParallelIterator for FlatMap<I, F>
where
I: ParallelIterator,
F: Fn(I::Item) -> PI + Sync + Send,
PI: IntoParallelIterator,
{
type Item = PI::Item;
fn drive_unindexed<C>(self, consumer: C) -> C::Result
where
C: UnindexedConsumer<Self::Item>,
{
let consumer = FlatMapConsumer::new(consumer, &self.map_op);
self.base.drive_unindexed(consumer)
}
}
/// ////////////////////////////////////////////////////////////////////////
/// Consumer implementation
struct FlatMapConsumer<'f, C, F> {
base: C,
map_op: &'f F,
}
impl<'f, C, F> FlatMapConsumer<'f, C, F> {
fn new(base: C, map_op: &'f F) -> Self {
FlatMapConsumer { base, map_op }
}
}
impl<'f, T, U, C, F> Consumer<T> for FlatMapConsumer<'f, C, F>
where
C: UnindexedConsumer<U::Item>,
F: Fn(T) -> U + Sync,
U: IntoParallelIterator,
{
type Folder = FlatMapFolder<'f, C, F, C::Result>;
type Reducer = C::Reducer;
type Result = C::Result;
fn split_at(self, index: usize) -> (Self, Self, C::Reducer) {
let (left, right, reducer) = self.base.split_at(index);
(
FlatMapConsumer::new(left, self.map_op),
FlatMapConsumer::new(right, self.map_op),
reducer,
)
}
fn into_folder(self) -> Self::Folder {
FlatMapFolder {
base: self.base,
map_op: self.map_op,
previous: None,
}
}
fn full(&self) -> bool {
self.base.full()
}
}
impl<'f, T, U, C, F> UnindexedConsumer<T> for FlatMapConsumer<'f, C, F>
where
C: UnindexedConsumer<U::Item>,
F: Fn(T) -> U + Sync,
U: IntoParallelIterator,
{
fn split_off_left(&self) -> Self {
FlatMapConsumer::new(self.base.split_off_left(), self.map_op)
}
fn to_reducer(&self) -> Self::Reducer {
self.base.to_reducer()
}
}
struct FlatMapFolder<'f, C, F, R> {
base: C,
map_op: &'f F,
previous: Option<R>,
}
impl<'f, T, U, C, F> Folder<T> for FlatMapFolder<'f, C, F, C::Result>
where
C: UnindexedConsumer<U::Item>,
F: Fn(T) -> U + Sync,
U: IntoParallelIterator,
{
type Result = C::Result;
fn consume(self, item: T) -> Self {
let map_op = self.map_op;
let par_iter = map_op(item).into_par_iter();
let consumer = self.base.split_off_left();
let result = par_iter.drive_unindexed(consumer);
let previous = match self.previous {
None => Some(result),
Some(previous) => {
let reducer = self.base.to_reducer();
Some(reducer.reduce(previous, result))
}
};
FlatMapFolder {
base: self.base,
map_op,
previous,
}
}
fn complete(self) -> Self::Result {
match self.previous {
Some(previous) => previous,
None => self.base.into_folder().complete(),
}
}
fn full(&self) -> bool {
self.base.full()
}
}