76 lines
1.5 KiB
Rust
76 lines
1.5 KiB
Rust
use alloc::vec::Vec;
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use std::iter::Fuse;
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use std::ops::Index;
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use crate::size_hint::{self, SizeHint};
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#[derive(Debug, Clone)]
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pub struct LazyBuffer<I: Iterator> {
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it: Fuse<I>,
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buffer: Vec<I::Item>,
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}
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impl<I> LazyBuffer<I>
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where
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I: Iterator,
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{
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pub fn new(it: I) -> Self {
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Self {
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it: it.fuse(),
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buffer: Vec::new(),
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}
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}
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pub fn len(&self) -> usize {
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self.buffer.len()
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}
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pub fn size_hint(&self) -> SizeHint {
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size_hint::add_scalar(self.it.size_hint(), self.len())
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}
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pub fn count(self) -> usize {
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self.len() + self.it.count()
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}
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pub fn get_next(&mut self) -> bool {
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if let Some(x) = self.it.next() {
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self.buffer.push(x);
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true
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} else {
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false
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}
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}
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pub fn prefill(&mut self, len: usize) {
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let buffer_len = self.buffer.len();
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if len > buffer_len {
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let delta = len - buffer_len;
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self.buffer.extend(self.it.by_ref().take(delta));
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}
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}
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}
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impl<I> LazyBuffer<I>
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where
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I: Iterator,
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I::Item: Clone,
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{
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pub fn get_at(&self, indices: &[usize]) -> Vec<I::Item> {
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indices.iter().map(|i| self.buffer[*i].clone()).collect()
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}
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}
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impl<I, J> Index<J> for LazyBuffer<I>
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where
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I: Iterator,
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I::Item: Sized,
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Vec<I::Item>: Index<J>,
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{
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type Output = <Vec<I::Item> as Index<J>>::Output;
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fn index(&self, index: J) -> &Self::Output {
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self.buffer.index(index)
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}
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}
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