use super::size_hint; use std::cell::RefCell; use alloc::collections::VecDeque; use alloc::rc::Rc; /// Common buffer object for the two tee halves #[derive(Debug)] struct TeeBuffer { backlog: VecDeque, iter: I, /// The owner field indicates which id should read from the backlog owner: bool, } /// One half of an iterator pair where both return the same elements. /// /// See [`.tee()`](../trait.Itertools.html#method.tee) for more information. #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] #[derive(Debug)] pub struct Tee where I: Iterator { rcbuffer: Rc>>, id: bool, } pub fn new(iter: I) -> (Tee, Tee) where I: Iterator { let buffer = TeeBuffer{backlog: VecDeque::new(), iter, owner: false}; let t1 = Tee{rcbuffer: Rc::new(RefCell::new(buffer)), id: true}; let t2 = Tee{rcbuffer: t1.rcbuffer.clone(), id: false}; (t1, t2) } impl Iterator for Tee where I: Iterator, I::Item: Clone { type Item = I::Item; fn next(&mut self) -> Option { // .borrow_mut may fail here -- but only if the user has tied some kind of weird // knot where the iterator refers back to itself. let mut buffer = self.rcbuffer.borrow_mut(); if buffer.owner == self.id { match buffer.backlog.pop_front() { None => {} some_elt => return some_elt, } } match buffer.iter.next() { None => None, Some(elt) => { buffer.backlog.push_back(elt.clone()); buffer.owner = !self.id; Some(elt) } } } fn size_hint(&self) -> (usize, Option) { let buffer = self.rcbuffer.borrow(); let sh = buffer.iter.size_hint(); if buffer.owner == self.id { let log_len = buffer.backlog.len(); size_hint::add_scalar(sh, log_len) } else { sh } } } impl ExactSizeIterator for Tee where I: ExactSizeIterator, I::Item: Clone {}