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use std::ops::Index;
use alloc::vec::Vec;
#[derive(Debug, Clone)]
pub struct LazyBuffer<I: Iterator> {
pub it: I,
done: bool,
buffer: Vec<I::Item>,
}
impl<I> LazyBuffer<I>
where
I: Iterator,
{
pub fn new(it: I) -> LazyBuffer<I> {
LazyBuffer {
it,
done: false,
buffer: Vec::new(),
}
}
pub fn len(&self) -> usize {
self.buffer.len()
}
pub fn get_next(&mut self) -> bool {
if self.done {
return false;
}
if let Some(x) = self.it.next() {
self.buffer.push(x);
true
} else {
self.done = true;
false
}
}
pub fn prefill(&mut self, len: usize) {
let buffer_len = self.buffer.len();
if !self.done && len > buffer_len {
let delta = len - buffer_len;
self.buffer.extend(self.it.by_ref().take(delta));
self.done = self.buffer.len() < len;
}
}
}
impl<I, J> Index<J> for LazyBuffer<I>
where
I: Iterator,
I::Item: Sized,
Vec<I::Item>: Index<J>
{
type Output = <Vec<I::Item> as Index<J>>::Output;
fn index(&self, index: J) -> &Self::Output {
self.buffer.index(index)
}
}