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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<A, I> {
backlog: VecDeque<A>,
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()`](crate::Itertools::tee) for more information.
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[derive(Debug)]
pub struct Tee<I>
where I: Iterator
{
rcbuffer: Rc<RefCell<TeeBuffer<I::Item, I>>>,
id: bool,
}
pub fn new<I>(iter: I) -> (Tee<I>, Tee<I>)
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<I> Iterator for Tee<I>
where I: Iterator,
I::Item: Clone
{
type Item = I::Item;
fn next(&mut self) -> Option<Self::Item> {
// .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<usize>) {
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<I> ExactSizeIterator for Tee<I>
where I: ExactSizeIterator,
I::Item: Clone
{}