Added ExactSizeIterator support.

This allows people to just use `.len()` on the iterators.

Author: Binero

src/lib.rs

@@ -1197,6 +1197,12 @@ impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V> {
     }
 }
 
+impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
 pub struct Values<'a, K: 'a, V: 'a> {
     iter: SliceIter<'a, Bucket<K, V>>,
 }
@@ -1231,6 +1237,12 @@ impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V> {
     }
 }
 
+impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
 pub struct ValuesMut<'a, K: 'a, V: 'a> {
     iter: SliceIterMut<'a, Bucket<K, V>>,
 }
@@ -1265,6 +1277,12 @@ impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V> {
     }
 }
 
+impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
 pub struct Iter<'a, K: 'a, V: 'a> {
     iter: SliceIter<'a, Bucket<K, V>>,
 }
@@ -1299,6 +1317,12 @@ impl<'a, K, V> DoubleEndedIterator for Iter<'a, K, V> {
     }
 }
 
+impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
 pub struct IterMut<'a, K: 'a, V: 'a> {
     iter: SliceIterMut<'a, Bucket<K, V>>,
 }
@@ -1333,6 +1357,12 @@ impl<'a, K, V> DoubleEndedIterator for IterMut<'a, K, V> {
     }
 }
 
+impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
 pub struct IntoIter<K, V> {
     iter: VecIntoIter<Bucket<K, V>>,
 }
@@ -1367,6 +1397,13 @@ impl<'a, K, V> DoubleEndedIterator for IntoIter<K, V> {
     }
 }
 
+impl<K, V> ExactSizeIterator for IntoIter<K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+
 impl<'a, K, V, S> IntoIterator for &'a OrderMap<K, V, S>
     where K: Hash + Eq,
           S: BuildHasher,