Initial import of itertools-0.9.0.
Bug: 155309706
Change-Id: Id790c146e836f0eadfb0d8a103cbe2d226a598c3
diff --git a/src/tee.rs b/src/tee.rs
new file mode 100644
index 0000000..aa4be41
--- /dev/null
+++ b/src/tee.rs
@@ -0,0 +1,78 @@
+use super::size_hint;
+
+use std::cell::RefCell;
+use std::collections::VecDeque;
+use std::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()`](../trait.Itertools.html#method.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<I::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
+{}
