itertools/
lazy_buffer.rs

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> LazyBuffer<I>
55where
56    I: Iterator,
57    I::Item: Clone,
58{
59    pub fn get_at(&self, indices: &[usize]) -> Vec<I::Item> {
60        indices.iter().map(|i| self.buffer[*i].clone()).collect()
61    }
62
63    pub fn get_array<const K: usize>(&self, indices: [usize; K]) -> [I::Item; K] {
64        indices.map(|i| self.buffer[i].clone())
65    }
66}
67
68impl<I, J> Index<J> for LazyBuffer<I>
69where
70    I: Iterator,
71    I::Item: Sized,
72    Vec<I::Item>: Index<J>,
73{
74    type Output = <Vec<I::Item> as Index<J>>::Output;
75
76    fn index(&self, index: J) -> &Self::Output {
77        self.buffer.index(index)
78    }
79}
itertools/lazy_buffer.rs

itertools/
lazy_buffer.rs
