1use alloc::vec::Vec;
2use std::iter::Fuse;
3use std::ops::Index;
4
5use crate::size_hint::{self, SizeHint};
6
7#[derive(Debug, Clone)]
8pub struct LazyBuffer<I: Iterator> {
9 it: Fuse<I>,
10 buffer: Vec<I::Item>,
11}
12
13impl<I> LazyBuffer<I>
14where
15 I: Iterator,
16{
17 pub fn new(it: I) -> Self {
18 Self {
19 it: it.fuse(),
20 buffer: Vec::new(),
21 }
22 }
23
24 pub fn len(&self) -> usize {
25 self.buffer.len()
26 }
27
28 pub fn size_hint(&self) -> SizeHint {
29 size_hint::add_scalar(self.it.size_hint(), self.len())
30 }
31
32 pub fn count(self) -> usize {
33 self.len() + self.it.count()
34 }
35
36 pub fn get_next(&mut self) -> bool {
37 if let Some(x) = self.it.next() {
38 self.buffer.push(x);
39 true
40 } else {
41 false
42 }
43 }
44
45 pub fn prefill(&mut self, len: usize) {
46 let buffer_len = self.buffer.len();
47 if len > buffer_len {
48 let delta = len - buffer_len;
49 self.buffer.extend(self.it.by_ref().take(delta));
50 }
51 }
52}
53
54impl<I, J> Index<J> for LazyBuffer<I>
55where
56 I: Iterator,
57 I::Item: Sized,
58 Vec<I::Item>: Index<J>,
59{
60 type Output = <Vec<I::Item> as Index<J>>::Output;
61
62 fn index(&self, index: J) -> &Self::Output {
63 self.buffer.index(index)
64 }
65}
66