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, 0 deletions

diff --git a/src/libcollections/str.rs b/src/libcollections/str.rs
index 4c64019de09..999c84ba705 100644
--- a/src/libcollections/str.rs
+++ b/src/libcollections/str.rs
@@ -23,6 +23,7 @@ use core::str as core_str;
 use core::str::pattern::Pattern;
 use core::str::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};
 use core::mem;
+use core::iter::FusedIterator;
 use rustc_unicode::str::{UnicodeStr, Utf16Encoder};
 
 use vec_deque::VecDeque;
@@ -136,6 +137,9 @@ impl<'a> Iterator for EncodeUtf16<'a> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a> FusedIterator for EncodeUtf16<'a> {}
+
 // Return the initial codepoint accumulator for the first byte.
 // The first byte is special, only want bottom 5 bits for width 2, 4 bits
 // for width 3, and 3 bits for width 4