1 use std::ops::Index; 2 use alloc::vec::Vec; 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 { new(it: I) -> LazyBuffer<I>15 pub fn new(it: I) -> LazyBuffer<I> { 16 LazyBuffer { 17 it, 18 done: false, 19 buffer: Vec::new(), 20 } 21 } 22 len(&self) -> usize23 pub fn len(&self) -> usize { 24 self.buffer.len() 25 } 26 get_next(&mut self) -> bool27 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 } 43 prefill(&mut self, len: usize)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 } 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 index(&self, _index: J) -> &Self::Output64 fn index(&self, _index: J) -> &Self::Output { 65 self.buffer.index(_index) 66 } 67 } 68