Forward Iterator::{count,last,nth} for IdxRange random access

lib/la-arena/src/lib.rs

@@ -184,6 +184,24 @@ impl<T> Iterator for IdxRange<T> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.range.size_hint()
     }
+
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.range.count()
+    }
+
+    fn last(self) -> Option<Self::Item>
+    where
+        Self: Sized,
+    {
+        self.range.last().map(|raw| Idx::from_raw(raw.into()))
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        self.range.nth(n).map(|raw| Idx::from_raw(raw.into()))
+    }
 }
 
 impl<T> DoubleEndedIterator for IdxRange<T> {