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

use crate::iter::{FusedIterator, TrustedLen};
use crate::num::NonZeroUsize;
use crate::ops::Try;

/// A double-ended iterator with the direction inverted.
///
/// This `struct` is created by the [`rev`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`rev`]: Iterator::rev
/// [`Iterator`]: trait.Iterator.html
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Rev<T> {
    iter: T,
}

impl<T> Rev<T> {
    pub(in crate::iter) fn new(iter: T) -> Rev<T> {
        Rev { iter }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Rev<I>
where
    I: DoubleEndedIterator,
{
    type Item = <I as Iterator>::Item;

    #[inline]
    fn next(&mut self) -> Option<<I as Iterator>::Item> {
        self.iter.next_back()
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }

    #[inline]
    fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
        self.iter.advance_back_by(n)
    }

    #[inline]
    fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
        self.iter.nth_back(n)
    }

    fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
    where
        Self: Sized,
        F: FnMut(B, Self::Item) -> R,
        R: Try<Output = B>,
    {
        self.iter.try_rfold(init, f)
    }

    fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
    where
        F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.iter.rfold(init, f)
    }

    #[inline]
    fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
    where
        P: FnMut(&Self::Item) -> bool,
    {
        self.iter.rfind(predicate)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Rev<I>
where
    I: DoubleEndedIterator,
{
    #[inline]
    fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
        self.iter.next()
    }

    #[inline]
    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
        self.iter.advance_by(n)
    }

    #[inline]
    fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
        self.iter.nth(n)
    }

    fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
    where
        Self: Sized,
        F: FnMut(B, Self::Item) -> R,
        R: Try<Output = B>,
    {
        self.iter.try_fold(init, f)
    }

    fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
    where
        F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.iter.fold(init, f)
    }

    fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
    where
        P: FnMut(&Self::Item) -> bool,
    {
        self.iter.find(predicate)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Rev<I>
where
    I: ExactSizeIterator + DoubleEndedIterator,
{
    fn len(&self) -> usize {
        self.iter.len()
    }

    fn is_empty(&self) -> bool {
        self.iter.is_empty()
    }
}

#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Rev<I> where I: FusedIterator + DoubleEndedIterator {}

#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I> TrustedLen for Rev<I> where I: TrustedLen + DoubleEndedIterator {}

#[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
impl<I: Default> Default for Rev<I> {
    /// Creates a `Rev` iterator from the default value of `I`
    /// ```
    /// # use core::slice;
    /// # use core::iter::Rev;
    /// let iter: Rev<slice::Iter<'_, u8>> = Default::default();
    /// assert_eq!(iter.len(), 0);
    /// ```
    fn default() -> Self {
        Rev::new(Default::default())
    }
}