Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 1 | use std::ops::Index; |
Joel Galenson | 6f79871 | 2021-04-01 17:03:06 -0700 | [diff] [blame] | 2 | use alloc::vec::Vec; |
Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 3 | |
| 4 | #[derive(Debug, Clone)] |
| 5 | pub struct LazyBuffer<I: Iterator> { |
| 6 | pub it: I, |
| 7 | done: bool, |
| 8 | buffer: Vec<I::Item>, |
| 9 | } |
| 10 | |
| 11 | impl<I> LazyBuffer<I> |
| 12 | where |
| 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 | |
Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 27 | pub fn get_next(&mut self) -> bool { |
| 28 | if self.done { |
| 29 | return false; |
| 30 | } |
| 31 | let next_item = self.it.next(); |
| 32 | match next_item { |
| 33 | Some(x) => { |
| 34 | self.buffer.push(x); |
| 35 | true |
| 36 | } |
| 37 | None => { |
| 38 | self.done = true; |
| 39 | false |
| 40 | } |
| 41 | } |
| 42 | } |
Joel Galenson | 6f79871 | 2021-04-01 17:03:06 -0700 | [diff] [blame] | 43 | |
| 44 | pub fn prefill(&mut self, len: usize) { |
| 45 | let buffer_len = self.buffer.len(); |
| 46 | |
| 47 | if !self.done && len > buffer_len { |
| 48 | let delta = len - buffer_len; |
| 49 | |
| 50 | self.buffer.extend(self.it.by_ref().take(delta)); |
| 51 | self.done = self.buffer.len() < len; |
| 52 | } |
| 53 | } |
Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 54 | } |
| 55 | |
| 56 | impl<I, J> Index<J> for LazyBuffer<I> |
| 57 | where |
| 58 | I: Iterator, |
| 59 | I::Item: Sized, |
| 60 | Vec<I::Item>: Index<J> |
| 61 | { |
| 62 | type Output = <Vec<I::Item> as Index<J>>::Output; |
| 63 | |
| 64 | fn index(&self, _index: J) -> &Self::Output { |
| 65 | self.buffer.index(_index) |
| 66 | } |
| 67 | } |