resiter/
map.rs

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
148
149
150
151
152
153
154
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
//

/// Extension trait for `Iterator<Item = Result<O, E>>` to selectively transform Oks and Errors.
pub trait Map<O, E>: Sized {
    /// Map all `Ok` items while leaving `Err` as is
    ///
    /// ```
    /// use resiter::map::Map;
    /// use std::str::FromStr;
    ///
    /// let mapped: Vec<_> = ["1", "2", "a", "4", "5"]
    ///     .iter()
    ///     .map(|txt| usize::from_str(txt))
    ///     .map_ok(|i| 2 * i)
    ///     .collect();
    ///
    /// assert_eq!(mapped[0], Ok(2));
    /// assert_eq!(mapped[1], Ok(4));
    /// assert!(mapped[2].is_err());
    /// assert_eq!(mapped[3], Ok(8));
    /// assert_eq!(mapped[4], Ok(10));
    /// ```
    fn map_ok<F, O2>(self, _: F) -> MapOk<Self, F>
    where
        F: FnMut(O) -> O2;

    /// Map all `Err` items while leaving `Ok` as is
    ///
    /// ```
    /// use resiter::map::Map;
    /// use std::str::FromStr;
    /// let mapped: Vec<_> = ["1", "2", "a", "4", "5"]
    ///     .iter()
    ///     .map(|txt| usize::from_str(txt))
    ///     .map_err(|e| format!("{:?}", e))
    ///     .collect();
    ///
    /// assert_eq!(
    ///     mapped,
    ///     vec![
    ///         Ok(1),
    ///         Ok(2),
    ///         Err("ParseIntError { kind: InvalidDigit }".to_string()),
    ///         Ok(4),
    ///         Ok(5),
    ///     ]
    /// );
    /// ```
    fn map_err<F, E2>(self, _: F) -> MapErr<Self, F>
    where
        F: FnMut(E) -> E2;
}

impl<I, O, E> Map<O, E> for I
where
    I: Iterator<Item = Result<O, E>> + Sized,
{
    #[inline]
    fn map_ok<F, O2>(self, f: F) -> MapOk<Self, F>
    where
        F: FnMut(O) -> O2,
    {
        MapOk { iter: self, f }
    }

    #[inline]
    fn map_err<F, E2>(self, f: F) -> MapErr<Self, F>
    where
        F: FnMut(E) -> E2,
    {
        MapErr { iter: self, f }
    }
}

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct MapOk<I, F> {
    iter: I,
    f: F,
}

impl<I, O, E, F, O2> Iterator for MapOk<I, F>
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(O) -> O2,
{
    type Item = Result<O2, E>;

    fn next(&mut self) -> Option<Self::Item> {
        self.iter.next().map(|r| r.map(&mut self.f))
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct MapErr<I, F> {
    iter: I,
    f: F,
}

impl<I, O, E, F, E2> Iterator for MapErr<I, F>
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(E) -> E2,
{
    type Item = Result<O, E2>;

    fn next(&mut self) -> Option<Self::Item> {
        self.iter.next().map(|r| r.map_err(&mut self.f))
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_map_ok_hint() {
        use std::str::FromStr;

        let hint = ["1", "2", "a", "4", "5"]
            .iter()
            .map(|txt| usize::from_str(txt))
            .map_ok(|i| 2 * i)
            .size_hint();

        assert_eq!(hint, (5, Some(5)));
    }

    #[test]
    fn test_map_err_hint() {
        use std::str::FromStr;

        let hint = ["1", "2", "a", "4", "5"]
            .iter()
            .map(|txt| usize::from_str(txt))
            .map_err(|e| format!("{:?}", e))
            .size_hint();

        assert_eq!(hint, (5, Some(5)));
    }
}