1 use super::plumbing::*;
2 use super::*;
3 use std::cmp::min;
4 
5 /// `Take` is an iterator that iterates over the first `n` elements.
6 /// This struct is created by the [`take()`] method on [`IndexedParallelIterator`]
7 ///
8 /// [`take()`]: trait.IndexedParallelIterator.html#method.take
9 /// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
10 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
11 #[derive(Debug, Clone)]
12 pub struct Take<I> {
13     base: I,
14     n: usize,
15 }
16 
17 impl<I> Take<I>
18 where
19     I: IndexedParallelIterator,
20 {
21     /// Creates a new `Take` iterator.
new(base: I, n: usize) -> Self22     pub(super) fn new(base: I, n: usize) -> Self {
23         let n = min(base.len(), n);
24         Take { base, n }
25     }
26 }
27 
28 impl<I> ParallelIterator for Take<I>
29 where
30     I: IndexedParallelIterator,
31 {
32     type Item = I::Item;
33 
drive_unindexed<C>(self, consumer: C) -> C::Result where C: UnindexedConsumer<Self::Item>,34     fn drive_unindexed<C>(self, consumer: C) -> C::Result
35     where
36         C: UnindexedConsumer<Self::Item>,
37     {
38         bridge(self, consumer)
39     }
40 
opt_len(&self) -> Option<usize>41     fn opt_len(&self) -> Option<usize> {
42         Some(self.len())
43     }
44 }
45 
46 impl<I> IndexedParallelIterator for Take<I>
47 where
48     I: IndexedParallelIterator,
49 {
len(&self) -> usize50     fn len(&self) -> usize {
51         self.n
52     }
53 
drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result54     fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result {
55         bridge(self, consumer)
56     }
57 
with_producer<CB>(self, callback: CB) -> CB::Output where CB: ProducerCallback<Self::Item>,58     fn with_producer<CB>(self, callback: CB) -> CB::Output
59     where
60         CB: ProducerCallback<Self::Item>,
61     {
62         return self.base.with_producer(Callback {
63             callback,
64             n: self.n,
65         });
66 
67         struct Callback<CB> {
68             callback: CB,
69             n: usize,
70         }
71 
72         impl<T, CB> ProducerCallback<T> for Callback<CB>
73         where
74             CB: ProducerCallback<T>,
75         {
76             type Output = CB::Output;
77             fn callback<P>(self, base: P) -> CB::Output
78             where
79                 P: Producer<Item = T>,
80             {
81                 let (producer, _) = base.split_at(self.n);
82                 self.callback.callback(producer)
83             }
84         }
85     }
86 }
87