Define child traversal once on ArrayRef via children_iter

children/nchildren/nth_child/named_children no longer need the encoding
vtable: implement them directly on ArrayRef over a single children_iter
helper (the non-None slots in order) and drop them from DynArrayData.
Only children_names still dispatches, for VTable::child_name.

Signed-off-by: "Joe Isaacs" <joe.isaacs@live.co.uk>

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XbjnDVZQ9KqXgAAhxy9g7D

Author: claude

vortex-array/src/array/erased.rs

@@ -685,19 +685,26 @@ impl ArrayRef {
 
     // ArrayVisitor delegation methods
 
+    /// Returns an iterator over the children of the array: its non-None slots in order.
+    pub fn children_iter(&self) -> impl Iterator<Item = &ArrayRef> {
+        self.0.slots.iter().filter_map(|s| s.as_ref())
+    }
+
     /// Returns the children of the array.
     pub fn children(&self) -> Vec<ArrayRef> {
-        self.0.data.children(self)
+        self.children_iter().cloned().collect()
     }
 
     /// Returns the number of children of the array.
     pub fn nchildren(&self) -> usize {
-        self.0.data.nchildren(self)
+        self.children_iter().count()
     }
 
     /// Returns the nth child of the array without allocating a Vec.
+    ///
+    /// Returns `None` if the index is out of bounds.
     pub fn nth_child(&self, idx: usize) -> Option<ArrayRef> {
-        self.0.data.nth_child(self, idx)
+        self.children_iter().nth(idx).cloned()
     }
 
     /// Returns the names of the children of the array.
@@ -707,7 +714,10 @@ impl ArrayRef {
 
     /// Returns the array's children with their names.
     pub fn named_children(&self) -> Vec<(String, ArrayRef)> {
-        self.0.data.named_children(self)
+        self.children_names()
+            .into_iter()
+            .zip(self.children_iter().cloned())
+            .collect()
     }
 
     /// Returns the data buffers of the array.

vortex-array/src/array/mod.rs

@@ -80,23 +80,9 @@ pub(crate) trait DynArrayData: 'static + private::Sealed + Send + Sync + Debug {
 
     // --- Visitor methods (formerly in ArrayVisitor) ---
 
-    /// Returns the children of the array.
-    fn children(&self, this: &ArrayRef) -> Vec<ArrayRef>;
-
-    /// Returns the number of children of the array.
-    fn nchildren(&self, this: &ArrayRef) -> usize;
-
-    /// Returns the nth child of the array without allocating a Vec.
-    ///
-    /// Returns `None` if the index is out of bounds.
-    fn nth_child(&self, this: &ArrayRef, idx: usize) -> Option<ArrayRef>;
-
     /// Returns the names of the children of the array.
     fn children_names(&self, this: &ArrayRef) -> Vec<String>;
 
-    /// Returns the array's children with their names.
-    fn named_children(&self, this: &ArrayRef) -> Vec<(String, ArrayRef)>;
-
     /// Returns the buffers of the array.
     fn buffers(&self, this: &ArrayRef) -> Vec<ByteBuffer>;
 
@@ -267,42 +253,10 @@ impl<V: VTable> DynArrayData for ArrayData<V> {
         Ok(())
     }
 
-    fn children(&self, this: &ArrayRef) -> Vec<ArrayRef> {
-        let view: ArrayView<'_, V> = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        view.slots().iter().filter_map(|s| s.clone()).collect()
-    }
-
-    fn nchildren(&self, this: &ArrayRef) -> usize {
-        let view: ArrayView<'_, V> = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        view.slots().iter().filter(|s| s.is_some()).count()
-    }
-
-    fn nth_child(&self, this: &ArrayRef, idx: usize) -> Option<ArrayRef> {
-        let view: ArrayView<'_, V> = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        view.slots()
-            .iter()
-            .filter_map(|s| s.as_ref())
-            .nth(idx)
-            .cloned()
-    }
-
     fn children_names(&self, this: &ArrayRef) -> Vec<String> {
         let view: ArrayView<'_, V> = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        view.slots()
-            .iter()
-            .filter(|s| s.is_some())
-            .enumerate()
-            .map(|(i, _)| V::child_name(view, i))
-            .collect()
-    }
-
-    fn named_children(&self, this: &ArrayRef) -> Vec<(String, ArrayRef)> {
-        let view: ArrayView<'_, V> = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        view.slots()
-            .iter()
-            .filter_map(|s| s.as_ref())
-            .enumerate()
-            .map(|(i, child)| (V::child_name(view, i), child.clone()))
+        (0..this.nchildren())
+            .map(|i| V::child_name(view, i))
             .collect()
     }