Enable bi-directional iter on `UArray`

server/src/engine/mem/tests.rs

@@ -251,4 +251,24 @@ mod uarray {
         let b = a.clone();
         assert_eq!(a, b);
     }
+    #[test]
+    fn into_iter_rev() {
+        let a: UArray<CAP, String> = (0u8..8).into_iter().map(|v| v.to_string()).collect();
+        let r: Vec<String> = a.into_iter().rev().collect();
+        (0..8)
+            .rev()
+            .into_iter()
+            .zip(r.into_iter())
+            .for_each(|(x, y)| assert_eq!(x.to_string(), y));
+    }
+    #[test]
+    fn into_iter_rev_partial() {
+        let a: UArray<CAP, String> = (0u8..8).into_iter().map(|v| v.to_string()).collect();
+        let r: Vec<String> = a.into_iter().rev().take(4).collect();
+        (4..8)
+            .rev()
+            .into_iter()
+            .zip(r.into_iter())
+            .for_each(|(x, y)| assert_eq!(x.to_string(), y));
+    }
 }

server/src/engine/mem/uarray.rs

@@ -181,6 +181,7 @@ pub struct IntoIter<const N: usize, T> {
 }
 
 impl<const N: usize, T> IntoIter<N, T> {
+    #[inline(always)]
     fn _next(&mut self) -> Option<T> {
         if self.i == self.l {
             return None;
@@ -194,6 +195,17 @@ impl<const N: usize, T> IntoIter<N, T> {
             Some(ret)
         }
     }
+    #[inline(always)]
+    fn _next_back(&mut self) -> Option<T> {
+        if self.i == self.l {
+            return None;
+        }
+        unsafe {
+            self.l -= 1;
+            // UNSAFE(@ohsayan): we always ensure EOA condition
+            Some(ptr::read(self.d.a.as_ptr().add(self.l).cast()))
+        }
+    }
 }
 
 impl<const N: usize, T> Drop for IntoIter<N, T> {
@@ -218,6 +230,11 @@ impl<const N: usize, T> Iterator for IntoIter<N, T> {
 }
 impl<const N: usize, T> ExactSizeIterator for IntoIter<N, T> {}
 impl<const N: usize, T> FusedIterator for IntoIter<N, T> {}
+impl<const N: usize, T> DoubleEndedIterator for IntoIter<N, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self._next_back()
+    }
+}
 
 impl<const N: usize, T> IntoIterator for UArray<N, T> {
     type Item = T;