```  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
```
``````use crate::iter::{FusedIterator, TrustedLen};

/// Creates a new iterator that endlessly repeats a single element.
///
/// The `repeat()` function repeats a single value over and over again.
///
/// Infinite iterators like `repeat()` are often used with adapters like
/// [`Iterator::take()`], in order to make them finite.
///
/// If the element type of the iterator you need does not implement `Clone`,
/// or if you do not want to keep the repeated element in memory, you can
/// instead use the [`repeat_with()`] function.
///
/// [`repeat_with()`]: crate::iter::repeat_with
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // the number four 4ever:
/// let mut fours = iter::repeat(4);
///
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
///
/// // yup, still four
/// assert_eq!(Some(4), fours.next());
/// ```
///
/// Going finite with [`Iterator::take()`]:
///
/// ```
/// use std::iter;
///
/// // that last example was too many fours. Let's only have four fours.
/// let mut four_fours = iter::repeat(4).take(4);
///
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
///
/// // ... and now we're done
/// assert_eq!(None, four_fours.next());
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "iter_repeat")]
pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
Repeat { element: elt }
}

/// An iterator that repeats an element endlessly.
///
/// This `struct` is created by the [`repeat()`] function. See its documentation for more.
#[derive(Clone, Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Repeat<A> {
element: A,
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> Iterator for Repeat<A> {
type Item = A;

#[inline]
fn next(&mut self) -> Option<A> {
Some(self.element.clone())
}

#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
(usize::MAX, None)
}

#[inline]
fn advance_by(&mut self, n: usize) -> Result<(), usize> {
// Advancing an infinite iterator of a single element is a no-op.
let _ = n;
Ok(())
}

#[inline]
fn nth(&mut self, n: usize) -> Option<A> {
let _ = n;
Some(self.element.clone())
}

fn last(self) -> Option<A> {
loop {}
}

fn count(self) -> usize {
loop {}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> DoubleEndedIterator for Repeat<A> {
#[inline]
fn next_back(&mut self) -> Option<A> {
Some(self.element.clone())
}

#[inline]
fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
// Advancing an infinite iterator of a single element is a no-op.
let _ = n;
Ok(())
}

#[inline]
fn nth_back(&mut self, n: usize) -> Option<A> {
let _ = n;
Some(self.element.clone())
}
}

#[stable(feature = "fused", since = "1.26.0")]
impl<A: Clone> FusedIterator for Repeat<A> {}

#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A: Clone> TrustedLen for Repeat<A> {}
``````