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)) => {
59                 Some(second)
60             }
61             None => {
62                 self.inner.next()
63             }
64         }
65     }
66 
size_hint(&self) -> (usize, Option<usize>)67     fn size_hint(&self) -> (usize, Option<usize>) {
68         size_hint::add_scalar(self.inner.size_hint(), self.additional_len())
69     }
70 }
71 
72 
73 impl<I> ExactSizeIterator for ExactlyOneError<I> where I: ExactSizeIterator {}
74 
75 impl<I> Display for ExactlyOneError<I>
76     where I: Iterator,
77 {
fmt(&self, f: &mut Formatter) -> FmtResult78     fn fmt(&self, f: &mut Formatter) -> FmtResult {
79         let additional = self.additional_len();
80         if additional > 0 {
81             write!(f, "got at least 2 elements when exactly one was expected")
82         } else {
83             write!(f, "got zero elements when exactly one was expected")
84         }
85     }
86 }
87 
88 impl<I> Debug for ExactlyOneError<I>
89     where I: Iterator + Debug,
90           I::Item: Debug,
91 {
fmt(&self, f: &mut Formatter) -> FmtResult92     fn fmt(&self, f: &mut Formatter) -> FmtResult {
93         match &self.first_two {
94             Some(Either::Left([first, second])) => {
95                 write!(f, "ExactlyOneError[First: {:?}, Second: {:?}, RemainingIter: {:?}]", first, second, self.inner)
96             },
97             Some(Either::Right(second)) => {
98                 write!(f, "ExactlyOneError[Second: {:?}, RemainingIter: {:?}]", second, self.inner)
99             }
100             None => {
101                 write!(f, "ExactlyOneError[RemainingIter: {:?}]", self.inner)
102             }
103         }
104     }
105 }
106 
107 #[cfg(feature = "use_std")]
108 impl<I> Error for ExactlyOneError<I>  where I: Iterator + Debug, I::Item: Debug, {}
109 
110 
111