1 use super::plumbing::*;
2 use super::*;
3 
4 use 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)]
13 pub struct FlatMap<I: ParallelIterator, F> {
14     base: I,
15     map_op: F,
16 }
17 
18 impl<I: ParallelIterator + Debug, F> Debug for FlatMap<I, F> {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result19     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
20         f.debug_struct("FlatMap").field("base", &self.base).finish()
21     }
22 }
23 
24 impl<I: ParallelIterator, F> FlatMap<I, F> {
25     /// Creates a new `FlatMap` iterator.
new(base: I, map_op: F) -> Self26     pub(super) fn new(base: I, map_op: F) -> Self {
27         FlatMap { base, map_op }
28     }
29 }
30 
31 impl<I, F, PI> ParallelIterator for FlatMap<I, F>
32 where
33     I: ParallelIterator,
34     F: Fn(I::Item) -> PI + Sync + Send,
35     PI: IntoParallelIterator,
36 {
37     type Item = PI::Item;
38 
drive_unindexed<C>(self, consumer: C) -> C::Result where C: UnindexedConsumer<Self::Item>,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 
51 struct FlatMapConsumer<'f, C, F> {
52     base: C,
53     map_op: &'f F,
54 }
55 
56 impl<'f, C, F> FlatMapConsumer<'f, C, F> {
new(base: C, map_op: &'f F) -> Self57     fn new(base: C, map_op: &'f F) -> Self {
58         FlatMapConsumer { base, map_op }
59     }
60 }
61 
62 impl<'f, T, U, C, F> Consumer<T> for FlatMapConsumer<'f, C, F>
63 where
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 
split_at(self, index: usize) -> (Self, Self, C::Reducer)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 
into_folder(self) -> Self::Folder81     fn into_folder(self) -> Self::Folder {
82         FlatMapFolder {
83             base: self.base,
84             map_op: self.map_op,
85             previous: None,
86         }
87     }
88 
full(&self) -> bool89     fn full(&self) -> bool {
90         self.base.full()
91     }
92 }
93 
94 impl<'f, T, U, C, F> UnindexedConsumer<T> for FlatMapConsumer<'f, C, F>
95 where
96     C: UnindexedConsumer<U::Item>,
97     F: Fn(T) -> U + Sync,
98     U: IntoParallelIterator,
99 {
split_off_left(&self) -> Self100     fn split_off_left(&self) -> Self {
101         FlatMapConsumer::new(self.base.split_off_left(), self.map_op)
102     }
103 
to_reducer(&self) -> Self::Reducer104     fn to_reducer(&self) -> Self::Reducer {
105         self.base.to_reducer()
106     }
107 }
108 
109 struct FlatMapFolder<'f, C, F, R> {
110     base: C,
111     map_op: &'f F,
112     previous: Option<R>,
113 }
114 
115 impl<'f, T, U, C, F> Folder<T> for FlatMapFolder<'f, C, F, C::Result>
116 where
117     C: UnindexedConsumer<U::Item>,
118     F: Fn(T) -> U + Sync,
119     U: IntoParallelIterator,
120 {
121     type Result = C::Result;
122 
consume(self, item: T) -> Self123     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 
complete(self) -> Self::Result144     fn complete(self) -> Self::Result {
145         match self.previous {
146             Some(previous) => previous,
147             None => self.base.into_folder().complete(),
148         }
149     }
150 
full(&self) -> bool151     fn full(&self) -> bool {
152         self.base.full()
153     }
154 }
155