1use std::ops::Index;
2use alloc::vec::Vec;
3
4#[derive(Debug, Clone)]
5pub struct LazyBuffer<I: Iterator> {
6 pub it: I,
7 done: bool,
8 buffer: Vec<I::Item>,
9}
10
11impl<I> LazyBuffer<I>
12where
13 I: Iterator,
14{
15 pub fn new(it: I) -> LazyBuffer<I> {
16 LazyBuffer {
17 it,
18 done: false,
19 buffer: Vec::new(),
20 }
21 }
22
23 pub fn len(&self) -> usize {
24 self.buffer.len()
25 }
26
27 pub fn get_next(&mut self) -> bool {
28 if self.done {
29 return false;
30 }
31 if let Some(x) = self.it.next() {
32 self.buffer.push(x);
33 true
34 } else {
35 self.done = true;
36 false
37 }
38 }
39
40 pub fn prefill(&mut self, len: usize) {
41 let buffer_len = self.buffer.len();
42
43 if !self.done && len > buffer_len {
44 let delta = len - buffer_len;
45
46 self.buffer.extend(self.it.by_ref().take(delta));
47 self.done = self.buffer.len() < len;
48 }
49 }
50}
51
52impl<I, J> Index<J> for LazyBuffer<I>
53where
54 I: Iterator,
55 I::Item: Sized,
56 Vec<I::Item>: Index<J>
57{
58 type Output = <Vec<I::Item> as Index<J>>::Output;
59
60 fn index(&self, index: J) -> &Self::Output {
61 self.buffer.index(index)
62 }
63}
64