1 #[cfg(feature = "use_std")]
2 use std::error::Error;
3 use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
4 
5 use std::iter::ExactSizeIterator;
6 
7 use either::Either;
8 
9 use crate::size_hint;
10 
11 /// Iterator returned for the error case of `Itertools::exactly_one()`
12 /// This iterator yields exactly the same elements as the input iterator.
13 ///
14 /// During the execution of `exactly_one` the iterator must be mutated.  This wrapper
15 /// effectively "restores" the state of the input iterator when it's handed back.
16 ///
17 /// This is very similar to `PutBackN` except this iterator only supports 0-2 elements and does not
18 /// use a `Vec`.
19 #[derive(Clone)]
20 pub struct ExactlyOneError<I>
21 where
22     I: Iterator,
23 {
24     first_two: Option<Either<[I::Item; 2], I::Item>>,
25     inner: I,
26 }
27 
28 impl<I> ExactlyOneError<I>
29 where
30     I: Iterator,
31 {
32     /// Creates a new `ExactlyOneErr` iterator.
new(first_two: Option<Either<[I::Item; 2], I::Item>>, inner: I) -> Self33     pub(crate) fn new(first_two: Option<Either<[I::Item; 2], I::Item>>, inner: I) -> Self {
34         Self { first_two, inner }
35     }
36 
additional_len(&self) -> usize37     fn additional_len(&self) -> usize {
38         match self.first_two {
39             Some(Either::Left(_)) => 2,
40             Some(Either::Right(_)) => 1,
41             None => 0,
42         }
43     }
44 }
45 
46 impl<I> Iterator for ExactlyOneError<I>
47 where
48     I: Iterator,
49 {
50     type Item = I::Item;
51 
next(&mut self) -> Option<Self::Item>52     fn next(&mut self) -> Option<Self::Item> {
53         match self.first_two.take() {
54             Some(Either::Left([first, second])) => {
55                 self.first_two = Some(Either::Right(second));
56                 Some(first)
57             }
58             Some(Either::Right(second)) => Some(second),
59             None => self.inner.next(),
60         }
61     }
62 
size_hint(&self) -> (usize, Option<usize>)63     fn size_hint(&self) -> (usize, Option<usize>) {
64         size_hint::add_scalar(self.inner.size_hint(), self.additional_len())
65     }
66 
fold<B, F>(self, mut init: B, mut f: F) -> B where F: FnMut(B, Self::Item) -> B,67     fn fold<B, F>(self, mut init: B, mut f: F) -> B
68     where
69         F: FnMut(B, Self::Item) -> B,
70     {
71         match self.first_two {
72             Some(Either::Left([first, second])) => {
73                 init = f(init, first);
74                 init = f(init, second);
75             }
76             Some(Either::Right(second)) => init = f(init, second),
77             None => {}
78         }
79         self.inner.fold(init, f)
80     }
81 }
82 
83 impl<I> ExactSizeIterator for ExactlyOneError<I> where I: ExactSizeIterator {}
84 
85 impl<I> Display for ExactlyOneError<I>
86 where
87     I: Iterator,
88 {
fmt(&self, f: &mut Formatter) -> FmtResult89     fn fmt(&self, f: &mut Formatter) -> FmtResult {
90         let additional = self.additional_len();
91         if additional > 0 {
92             write!(f, "got at least 2 elements when exactly one was expected")
93         } else {
94             write!(f, "got zero elements when exactly one was expected")
95         }
96     }
97 }
98 
99 impl<I> Debug for ExactlyOneError<I>
100 where
101     I: Iterator + Debug,
102     I::Item: Debug,
103 {
fmt(&self, f: &mut Formatter) -> FmtResult104     fn fmt(&self, f: &mut Formatter) -> FmtResult {
105         let mut dbg = f.debug_struct("ExactlyOneError");
106         match &self.first_two {
107             Some(Either::Left([first, second])) => {
108                 dbg.field("first", first).field("second", second);
109             }
110             Some(Either::Right(second)) => {
111                 dbg.field("second", second);
112             }
113             None => {}
114         }
115         dbg.field("inner", &self.inner).finish()
116     }
117 }
118 
119 #[cfg(feature = "use_std")]
120 impl<I> Error for ExactlyOneError<I>
121 where
122     I: Iterator + Debug,
123     I::Item: Debug,
124 {
125 }
126