| use std::iter::Fuse; |
| use alloc::collections::VecDeque; |
| use crate::size_hint; |
| use crate::PeekingNext; |
| |
| /// See [`multipeek()`] for more information. |
| #[derive(Clone, Debug)] |
| pub struct MultiPeek<I> |
| where I: Iterator |
| { |
| iter: Fuse<I>, |
| buf: VecDeque<I::Item>, |
| index: usize, |
| } |
| |
| /// An iterator adaptor that allows the user to peek at multiple `.next()` |
| /// values without advancing the base iterator. |
| pub fn multipeek<I>(iterable: I) -> MultiPeek<I::IntoIter> |
| where I: IntoIterator |
| { |
| MultiPeek { |
| iter: iterable.into_iter().fuse(), |
| buf: VecDeque::new(), |
| index: 0, |
| } |
| } |
| |
| impl<I> MultiPeek<I> |
| where I: Iterator |
| { |
| /// Reset the peeking “cursor” |
| pub fn reset_peek(&mut self) { |
| self.index = 0; |
| } |
| } |
| |
| impl<I: Iterator> MultiPeek<I> { |
| /// Works exactly like `.next()` with the only difference that it doesn't |
| /// advance itself. `.peek()` can be called multiple times, to peek |
| /// further ahead. |
| pub fn peek(&mut self) -> Option<&I::Item> { |
| let ret = if self.index < self.buf.len() { |
| Some(&self.buf[self.index]) |
| } else { |
| match self.iter.next() { |
| Some(x) => { |
| self.buf.push_back(x); |
| Some(&self.buf[self.index]) |
| } |
| None => return None, |
| } |
| }; |
| |
| self.index += 1; |
| ret |
| } |
| } |
| |
| impl<I> PeekingNext for MultiPeek<I> |
| where I: Iterator, |
| { |
| fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item> |
| where F: FnOnce(&Self::Item) -> bool |
| { |
| if self.buf.is_empty() { |
| if let Some(r) = self.peek() { |
| if !accept(r) { return None } |
| } |
| } else { |
| if let Some(r) = self.buf.get(0) { |
| if !accept(r) { return None } |
| } |
| } |
| self.next() |
| } |
| } |
| |
| impl<I> Iterator for MultiPeek<I> |
| where I: Iterator |
| { |
| type Item = I::Item; |
| |
| fn next(&mut self) -> Option<Self::Item> { |
| self.index = 0; |
| self.buf.pop_front().or_else(|| self.iter.next()) |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| size_hint::add_scalar(self.iter.size_hint(), self.buf.len()) |
| } |
| } |
| |
| // Same size |
| impl<I> ExactSizeIterator for MultiPeek<I> |
| where I: ExactSizeIterator |
| {} |
| |
| |