itertools/
flatten_ok.rs

1use crate::size_hint;
2use std::{
3    fmt,
4    iter::{DoubleEndedIterator, FusedIterator},
5};
6
7pub fn flatten_ok<I, T, E>(iter: I) -> FlattenOk<I, T, E>
8where
9    I: Iterator<Item = Result<T, E>>,
10    T: IntoIterator,
11{
12    FlattenOk {
13        iter,
14        inner_front: None,
15        inner_back: None,
16    }
17}
18
19/// An iterator adaptor that flattens `Result::Ok` values and
20/// allows `Result::Err` values through unchanged.
21///
22/// See [`.flatten_ok()`](crate::Itertools::flatten_ok) for more information.
23#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
24pub struct FlattenOk<I, T, E>
25where
26    I: Iterator<Item = Result<T, E>>,
27    T: IntoIterator,
28{
29    iter: I,
30    inner_front: Option<T::IntoIter>,
31    inner_back: Option<T::IntoIter>,
32}
33
34impl<I, T, E> Iterator for FlattenOk<I, T, E>
35where
36    I: Iterator<Item = Result<T, E>>,
37    T: IntoIterator,
38{
39    type Item = Result<T::Item, E>;
40
41    fn next(&mut self) -> Option<Self::Item> {
42        loop {
43            // Handle the front inner iterator.
44            if let Some(inner) = &mut self.inner_front {
45                if let Some(item) = inner.next() {
46                    return Some(Ok(item));
47                }
48
49                // This is necessary for the iterator to implement `FusedIterator`
50                // with only the original iterator being fused.
51                self.inner_front = None;
52            }
53
54            match self.iter.next() {
55                Some(Ok(ok)) => self.inner_front = Some(ok.into_iter()),
56                Some(Err(e)) => return Some(Err(e)),
57                None => {
58                    // Handle the back inner iterator.
59                    if let Some(inner) = &mut self.inner_back {
60                        if let Some(item) = inner.next() {
61                            return Some(Ok(item));
62                        }
63
64                        // This is necessary for the iterator to implement `FusedIterator`
65                        // with only the original iterator being fused.
66                        self.inner_back = None;
67                    } else {
68                        return None;
69                    }
70                }
71            }
72        }
73    }
74
75    fn size_hint(&self) -> (usize, Option<usize>) {
76        let inner_hint = |inner: &Option<T::IntoIter>| {
77            inner
78                .as_ref()
79                .map(Iterator::size_hint)
80                .unwrap_or((0, Some(0)))
81        };
82        let inner_front = inner_hint(&self.inner_front);
83        let inner_back = inner_hint(&self.inner_back);
84        // The outer iterator `Ok` case could be (0, None) as we don't know its size_hint yet.
85        let outer = match self.iter.size_hint() {
86            (0, Some(0)) => (0, Some(0)),
87            _ => (0, None),
88        };
89
90        size_hint::add(size_hint::add(inner_front, inner_back), outer)
91    }
92}
93
94impl<I, T, E> DoubleEndedIterator for FlattenOk<I, T, E>
95where
96    I: DoubleEndedIterator<Item = Result<T, E>>,
97    T: IntoIterator,
98    T::IntoIter: DoubleEndedIterator,
99{
100    fn next_back(&mut self) -> Option<Self::Item> {
101        loop {
102            // Handle the back inner iterator.
103            if let Some(inner) = &mut self.inner_back {
104                if let Some(item) = inner.next_back() {
105                    return Some(Ok(item));
106                }
107
108                // This is necessary for the iterator to implement `FusedIterator`
109                // with only the original iterator being fused.
110                self.inner_back = None;
111            }
112
113            match self.iter.next_back() {
114                Some(Ok(ok)) => self.inner_back = Some(ok.into_iter()),
115                Some(Err(e)) => return Some(Err(e)),
116                None => {
117                    // Handle the front inner iterator.
118                    if let Some(inner) = &mut self.inner_front {
119                        if let Some(item) = inner.next_back() {
120                            return Some(Ok(item));
121                        }
122
123                        // This is necessary for the iterator to implement `FusedIterator`
124                        // with only the original iterator being fused.
125                        self.inner_front = None;
126                    } else {
127                        return None;
128                    }
129                }
130            }
131        }
132    }
133}
134
135impl<I, T, E> Clone for FlattenOk<I, T, E>
136where
137    I: Iterator<Item = Result<T, E>> + Clone,
138    T: IntoIterator,
139    T::IntoIter: Clone,
140{
141    clone_fields!(iter, inner_front, inner_back);
142}
143
144impl<I, T, E> fmt::Debug for FlattenOk<I, T, E>
145where
146    I: Iterator<Item = Result<T, E>> + fmt::Debug,
147    T: IntoIterator,
148    T::IntoIter: fmt::Debug,
149{
150    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
151        f.debug_struct("FlattenOk")
152            .field("iter", &self.iter)
153            .field("inner_front", &self.inner_front)
154            .field("inner_back", &self.inner_back)
155            .finish()
156    }
157}
158
159/// Only the iterator being flattened needs to implement [`FusedIterator`].
160impl<I, T, E> FusedIterator for FlattenOk<I, T, E>
161where
162    I: FusedIterator<Item = Result<T, E>>,
163    T: IntoIterator,
164{
165}
itertools/flatten_ok.rs

itertools/
flatten_ok.rs
