vendor/itertools/src/lazy_buffer.rs

   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 {
  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
  52 impl<I, J> Index<J> for LazyBuffer<I>
  53 where
  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 }