core: Forward ExactSizeIterator methods for important iterator adaptors

src/libcore/iter/mod.rs

@@ -368,7 +368,16 @@ fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next() }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I> ExactSizeIterator for Rev<I>
-    where I: ExactSizeIterator + DoubleEndedIterator {}
+    where I: ExactSizeIterator + DoubleEndedIterator
+{
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
 
 #[unstable(feature = "fused", issue = "35602")]
 impl<I> FusedIterator for Rev<I>
@@ -425,7 +434,15 @@ fn next_back(&mut self) -> Option<T> {
 #[stable(feature = "iter_cloned", since = "1.1.0")]
 impl<'a, I, T: 'a> ExactSizeIterator for Cloned<I>
     where I: ExactSizeIterator<Item=&'a T>, T: Clone
-{}
+{
+    fn len(&self) -> usize {
+        self.it.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.it.is_empty()
+    }
+}
 
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, I, T: 'a> FusedIterator for Cloned<I>
@@ -1007,7 +1024,16 @@ fn next_back(&mut self) -> Option<B> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
-    where F: FnMut(I::Item) -> B {}
+    where F: FnMut(I::Item) -> B
+{
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
 
 #[unstable(feature = "fused", issue = "35602")]
 impl<B, I: FusedIterator, F> FusedIterator for Map<I, F>
@@ -1236,7 +1262,15 @@ fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<I> ExactSizeIterator for Enumerate<I> where I: ExactSizeIterator {}
+impl<I> ExactSizeIterator for Enumerate<I> where I: ExactSizeIterator {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
 
 #[doc(hidden)]
 unsafe impl<I> TrustedRandomAccess for Enumerate<I>
@@ -1927,7 +1961,15 @@ fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
 
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {}
+impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
 
 /// An iterator that calls a function with a reference to each element before
 /// yielding it.
@@ -1994,7 +2036,16 @@ fn next_back(&mut self) -> Option<I::Item> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
-    where F: FnMut(&I::Item) {}
+    where F: FnMut(&I::Item)
+{
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
 
 #[unstable(feature = "fused", issue = "35602")]
 impl<I: FusedIterator, F> FusedIterator for Inspect<I, F>