Add a FusedIterator trait.

This trait can be used to avoid the overhead of a fuse wrapper when an iterator
is already well-behaved.

Conforming to: RFC 1581
Closes: #35602

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libcollections/enum_set.rs b/src/libcollections/enum_set.rs
index 0c66c0564c3..2456a04e40a 100644
--- a/src/libcollections/enum_set.rs
+++ b/src/libcollections/enum_set.rs
@@ -20,7 +20,7 @@
 
 use core::marker;
 use core::fmt;
-use core::iter::FromIterator;
+use core::iter::{FromIterator, FusedIterator};
 use core::ops::{Sub, BitOr, BitAnd, BitXor};
 
 // FIXME(contentions): implement union family of methods? (general design may be
@@ -266,6 +266,9 @@ impl<E: CLike> Iterator for Iter<E> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<E: CLike> FusedIterator for Iter<E> {}
+
 impl<E: CLike> FromIterator<E> for EnumSet<E> {
     fn from_iter<I: IntoIterator<Item = E>>(iter: I) -> EnumSet<E> {
         let mut ret = EnumSet::new();