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
use std::iter::Peekable;
pub struct MarkLast<I>
where
I: Iterator,
{
iter: Peekable<I>,
}
impl<I> MarkLast<I>
where
I: Iterator,
{
fn new(iter: I) -> MarkLast<I> {
MarkLast {
iter: iter.peekable(),
}
}
}
impl<I> Iterator for MarkLast<I>
where
I: Iterator,
{
type Item = (bool, I::Item);
fn next(&mut self) -> Option<(bool, I::Item)> {
let val = self.iter.next()?;
let last = self.iter.peek().is_none();
Some((last, val))
}
}
pub trait MarkLastIterator<I>
where
I: Iterator,
{
fn mark_last(self) -> MarkLast<I>;
}
impl<I> MarkLastIterator<I> for I
where
I: Iterator,
{
fn mark_last(self) -> MarkLast<Self>
where
Self: Sized,
{
MarkLast::new(self)
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn marks_last() {
let in_data = vec![1, 2, 3, 5, 99];
let out_data: Vec<_> = in_data.into_iter().mark_last().collect();
assert_eq!(
out_data,
vec![(false, 1), (false, 2), (false, 3), (false, 5), (true, 99)]
)
}
#[test]
fn marks_last_empty() {
let in_data: [i32; 0] = [];
let out_data: Vec<_> = in_data.iter().mark_last().collect();
assert_eq!(out_data, vec![])
}
#[test]
fn marks_last_length_one() {
let in_data = vec![3];
let out_data: Vec<_> = in_data.into_iter().mark_last().collect();
assert_eq!(out_data, vec![(true, 3)])
}
#[test]
fn marks_nothing_infinite() {
let in_data = 0..;
assert!(in_data.mark_last().take(1_000_000).all(|(last, _)| !last))
}
}