itertools/
lazy_buffer.rs

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}
itertools/lazy_buffer.rs

itertools/
lazy_buffer.rs
