async-itertools 0.0.0-a.4

`itertools` for `Stream`s
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147

use core::{
    pin::Pin,
    task::{Context, Poll, ready},
};

use futures_lite::Stream;
use option_entry::OptionEntry;
use pin_project_lite::pin_project;

use crate::internal::check::assert_stream;

pin_project! {
    #[project = Proj]
    pub struct CoalesceBy<S: Stream, F, C: CountItem<S::Item>> {
        #[pin]
        stream: S,
        last: Option<Option<C::CItem>>,
        f: F,
    }
}

pub trait CoalescePredicate<Item, T> {
    fn coalesce_pair(&mut self, t: T, item: Item) -> Result<T, (T, T)>;
}

impl<S: Stream, F: CoalescePredicate<S::Item, C::CItem>, C: CountItem<S::Item>> Stream
    for CoalesceBy<S, F, C>
{
    type Item = C::CItem;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let Proj {
            mut stream,
            last,
            f,
        } = self.project();
        let current = match last {
            Some(elt) => elt,
            None => last.insert(ready!(stream.as_mut().poll_next(cx)).map(C::new)),
        };
        let option_entry::Entry::Occupied(mut entry) = current.entry() else {
            return Poll::Ready(None);
        };
        while let Some(next) = ready!(stream.as_mut().poll_next(cx)) {
            match f.coalesce_pair(entry.remove(), next) {
                Ok(item) => entry = current.entry().insert_entry(item),
                Err((last, next)) => {
                    *current = Some(next);
                    return Poll::Ready(Some(last));
                }
            }
        }
        Poll::Ready(Some(entry.remove()))
    }
}

pub struct NoCount;

pub trait CountItem<T> {
    type CItem;
    fn new(t: T) -> Self::CItem;
}

impl<T> CountItem<T> for NoCount {
    type CItem = T;
    fn new(t: T) -> Self::CItem {
        t
    }
}

pub type Coalesce<S, F> = CoalesceBy<S, F, NoCount>;

impl<F, Item, T> CoalescePredicate<Item, T> for F
where
    F: FnMut(T, Item) -> Result<T, (T, T)>,
{
    fn coalesce_pair(&mut self, t: T, item: Item) -> Result<T, (T, T)> {
        self(t, item)
    }
}

pub fn coalesce<S: Stream, F>(stream: S, f: F) -> Coalesce<S, F>
where
    F: FnMut(S::Item, S::Item) -> Result<S::Item, (S::Item, S::Item)>,
{
    assert_stream(CoalesceBy {
        stream,
        last: None,
        f,
    })
}

pub type DedupBy<S, Pred> = CoalesceBy<S, DedupPred2CoalescePred<Pred>, NoCount>;

pub struct DedupPred2CoalescePred<DP>(DP);

pub trait DedupPredicate<T> {
    fn dedup_pair(&mut self, a: &T, b: &T) -> bool;
}

impl<DP, T> CoalescePredicate<T, T> for DedupPred2CoalescePred<DP>
where
    DP: DedupPredicate<T>,
{
    fn coalesce_pair(&mut self, t: T, item: T) -> Result<T, (T, T)> {
        if self.0.dedup_pair(&t, &item) {
            Ok(t)
        } else {
            Err((t, item))
        }
    }
}

pub struct DedupEq;

impl<T: PartialEq> DedupPredicate<T> for DedupEq {
    fn dedup_pair(&mut self, a: &T, b: &T) -> bool {
        a == b
    }
}

impl<T, F: FnMut(&T, &T) -> bool> DedupPredicate<T> for F {
    fn dedup_pair(&mut self, a: &T, b: &T) -> bool {
        self(a, b)
    }
}

pub fn dedup_by<S: Stream, Pred>(stream: S, dedup_pred: Pred) -> DedupBy<S, Pred>
where
    Pred: FnMut(&S::Item, &S::Item) -> bool,
{
    assert_stream(CoalesceBy {
        stream,
        last: None,
        f: DedupPred2CoalescePred(dedup_pred),
    })
}

pub type Dedup<S> = DedupBy<S, DedupEq>;

pub fn dedup<S: Stream<Item: PartialEq>>(stream: S) -> Dedup<S> {
    assert_stream(CoalesceBy {
        stream,
        last: None,
        f: DedupPred2CoalescePred(DedupEq),
    })
}