rayon/iter/
flat_map.rs

1use super::plumbing::*;
2use super::*;
3
4use std::fmt::{self, Debug};
5
6/// `FlatMap` maps each element to a parallel iterator, then flattens these iterators together.
7/// This struct is created by the [`flat_map()`] method on [`ParallelIterator`]
8///
9/// [`flat_map()`]: trait.ParallelIterator.html#method.flat_map
10/// [`ParallelIterator`]: trait.ParallelIterator.html
11#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
12#[derive(Clone)]
13pub struct FlatMap<I: ParallelIterator, F> {
14    base: I,
15    map_op: F,
16}
17
18impl<I: ParallelIterator + Debug, F> Debug for FlatMap<I, F> {
19    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
20        f.debug_struct("FlatMap").field("base", &self.base).finish()
21    }
22}
23
24impl<I: ParallelIterator, F> FlatMap<I, F> {
25    /// Creates a new `FlatMap` iterator.
26    pub(super) fn new(base: I, map_op: F) -> Self {
27        FlatMap { base, map_op }
28    }
29}
30
31impl<I, F, PI> ParallelIterator for FlatMap<I, F>
32where
33    I: ParallelIterator,
34    F: Fn(I::Item) -> PI + Sync + Send,
35    PI: IntoParallelIterator,
36{
37    type Item = PI::Item;
38
39    fn drive_unindexed<C>(self, consumer: C) -> C::Result
40    where
41        C: UnindexedConsumer<Self::Item>,
42    {
43        let consumer = FlatMapConsumer::new(consumer, &self.map_op);
44        self.base.drive_unindexed(consumer)
45    }
46}
47
48/// ////////////////////////////////////////////////////////////////////////
49/// Consumer implementation
50
51struct FlatMapConsumer<'f, C, F> {
52    base: C,
53    map_op: &'f F,
54}
55
56impl<'f, C, F> FlatMapConsumer<'f, C, F> {
57    fn new(base: C, map_op: &'f F) -> Self {
58        FlatMapConsumer { base, map_op }
59    }
60}
61
62impl<'f, T, U, C, F> Consumer<T> for FlatMapConsumer<'f, C, F>
63where
64    C: UnindexedConsumer<U::Item>,
65    F: Fn(T) -> U + Sync,
66    U: IntoParallelIterator,
67{
68    type Folder = FlatMapFolder<'f, C, F, C::Result>;
69    type Reducer = C::Reducer;
70    type Result = C::Result;
71
72    fn split_at(self, index: usize) -> (Self, Self, C::Reducer) {
73        let (left, right, reducer) = self.base.split_at(index);
74        (
75            FlatMapConsumer::new(left, self.map_op),
76            FlatMapConsumer::new(right, self.map_op),
77            reducer,
78        )
79    }
80
81    fn into_folder(self) -> Self::Folder {
82        FlatMapFolder {
83            base: self.base,
84            map_op: self.map_op,
85            previous: None,
86        }
87    }
88
89    fn full(&self) -> bool {
90        self.base.full()
91    }
92}
93
94impl<'f, T, U, C, F> UnindexedConsumer<T> for FlatMapConsumer<'f, C, F>
95where
96    C: UnindexedConsumer<U::Item>,
97    F: Fn(T) -> U + Sync,
98    U: IntoParallelIterator,
99{
100    fn split_off_left(&self) -> Self {
101        FlatMapConsumer::new(self.base.split_off_left(), self.map_op)
102    }
103
104    fn to_reducer(&self) -> Self::Reducer {
105        self.base.to_reducer()
106    }
107}
108
109struct FlatMapFolder<'f, C, F, R> {
110    base: C,
111    map_op: &'f F,
112    previous: Option<R>,
113}
114
115impl<'f, T, U, C, F> Folder<T> for FlatMapFolder<'f, C, F, C::Result>
116where
117    C: UnindexedConsumer<U::Item>,
118    F: Fn(T) -> U + Sync,
119    U: IntoParallelIterator,
120{
121    type Result = C::Result;
122
123    fn consume(self, item: T) -> Self {
124        let map_op = self.map_op;
125        let par_iter = map_op(item).into_par_iter();
126        let consumer = self.base.split_off_left();
127        let result = par_iter.drive_unindexed(consumer);
128
129        let previous = match self.previous {
130            None => Some(result),
131            Some(previous) => {
132                let reducer = self.base.to_reducer();
133                Some(reducer.reduce(previous, result))
134            }
135        };
136
137        FlatMapFolder {
138            base: self.base,
139            map_op,
140            previous,
141        }
142    }
143
144    fn complete(self) -> Self::Result {
145        match self.previous {
146            Some(previous) => previous,
147            None => self.base.into_folder().complete(),
148        }
149    }
150
151    fn full(&self) -> bool {
152        self.base.full()
153    }
154}
rayon/iter/flat_map.rs

rayon/iter/
flat_map.rs
