Fuse is an iterator that yields None forever after the underlying iterator yields None once. USage:
1
2
let values = [1,2,3,4];
let iter = values.iter().fuse();
Why is it useful? see example in this bite.
Sometimes an underlying iterator may or may yield Some(T) again after None was returned.
fuse ensures that after a None is returned for the first time, it always returns None.
Example from the rust documentation:
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
struct Alternate {
state: i32,
}
impl Iterator for Alternate {
type Item = i32;
fn next(&mut self) -> Option<i32> {
let val = self.state;
self.state = self.state + 1;
if val % 2 == 0 {
Some(val)
} else {
None
}
}
}
let mut iter = Alternate { state: 0 };
assert_eq!(iter.next(), Some(0));
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), Some(2));
assert_eq!(iter.next(), None);
let mut iter = iter.fuse();
assert_eq!(iter.next(), Some(4));
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);
assert_eq!(iter.next(), None);