break[array]: Remove unimplemented child() method from VTable implementations (#8870)

Remove unneeded methods `child` and `nchildren` from the vtable these
always have a default impl and so are uneeded.

# Break
While this is a VTable break it likely used outside of vortex.

---------

Signed-off-by: Claude <noreply@anthropic.com>
Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: joseph-isaacs

vortex-array/src/array/erased.rs

@@ -671,29 +671,46 @@ 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.
+    /// Returns the names of the children of the array: the slot names of the non-None slots
+    /// in order.
     pub fn children_names(&self) -> Vec<String> {
-        self.0.data.children_names(self)
+        self.0
+            .slots
+            .iter()
+            .enumerate()
+            .filter(|(_, s)| s.is_some())
+            .map(|(slot_idx, _)| self.slot_name(slot_idx))
+            .collect()
     }
 
     /// 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 +80,6 @@ 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>;
 
@@ -267,35 +250,6 @@ impl<V: VTable> DynArrayData for ArrayData<V> {
         Ok(())
     }
 
-    fn children(&self, this: &ArrayRef) -> Vec<ArrayRef> {
-        let view = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        (0..V::nchildren(view)).map(|i| V::child(view, i)).collect()
-    }
-
-    fn nchildren(&self, this: &ArrayRef) -> usize {
-        let view = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        V::nchildren(view)
-    }
-
-    fn nth_child(&self, this: &ArrayRef, idx: usize) -> Option<ArrayRef> {
-        let view = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        (idx < V::nchildren(view)).then(|| V::child(view, idx))
-    }
-
-    fn children_names(&self, this: &ArrayRef) -> Vec<String> {
-        let view = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        (0..V::nchildren(view))
-            .map(|i| V::child_name(view, i))
-            .collect()
-    }
-
-    fn named_children(&self, this: &ArrayRef) -> Vec<(String, ArrayRef)> {
-        let view = unsafe { ArrayView::new_unchecked(this, &self.data) };
-        (0..V::nchildren(view))
-            .map(|i| (V::child_name(view, i), V::child(view, i)))
-            .collect()
-    }
-
     fn buffers(&self, this: &ArrayRef) -> Vec<ByteBuffer> {
         let view = unsafe { ArrayView::new_unchecked(this, &self.data) };
         (0..V::nbuffers(view))

vortex-array/src/array/vtable/mod.rs

@@ -115,45 +115,6 @@ pub trait VTable: 'static + Clone + Sized + Send + Sync + Debug {
         buffers: &[BufferHandle],
     ) -> VortexResult<ArrayParts<Self>>;
 
-    /// Returns the number of children in the array.
-    ///
-    /// The default counts non-None slots.
-    fn nchildren(array: ArrayView<'_, Self>) -> usize {
-        array.slots().iter().filter(|s| s.is_some()).count()
-    }
-
-    /// Returns the child at the given index.
-    ///
-    /// The default returns the `idx`-th non-None slot.
-    ///
-    /// # Panics
-    /// Panics if `idx >= nchildren(array)`.
-    fn child(array: ArrayView<'_, Self>, idx: usize) -> ArrayRef {
-        array
-            .slots()
-            .iter()
-            .filter_map(|s| s.clone())
-            .nth(idx)
-            .vortex_expect("child index out of bounds")
-    }
-
-    /// Returns the name of the child at the given index.
-    ///
-    /// The default returns the slot name of the `idx`-th non-None slot.
-    ///
-    /// # Panics
-    /// Panics if `idx >= nchildren(array)`.
-    fn child_name(array: ArrayView<'_, Self>, idx: usize) -> String {
-        array
-            .slots()
-            .iter()
-            .enumerate()
-            .filter(|(_, s)| s.is_some())
-            .nth(idx)
-            .map(|(slot_idx, _)| Self::slot_name(array, slot_idx))
-            .vortex_expect("child_name index out of bounds")
-    }
-
     /// Serialize encoding metadata into a byte buffer for IPC or file storage.
     ///
     /// Return `None` if the array cannot be serialized by this encoding. Buffers and children are

vortex-array/src/arrays/patched/vtable/mod.rs

@@ -138,16 +138,6 @@ impl VTable for Patched {
         with_empty_buffers(self, array, buffers)
     }
 
-    fn child(array: ArrayView<'_, Self>, idx: usize) -> ArrayRef {
-        match idx {
-            PatchedSlots::INNER => array.inner().clone(),
-            PatchedSlots::LANE_OFFSETS => array.lane_offsets().clone(),
-            PatchedSlots::PATCH_INDICES => array.patch_indices().clone(),
-            PatchedSlots::PATCH_VALUES => array.patch_values().clone(),
-            _ => vortex_panic!("invalid child index for PatchedArray: {idx}"),
-        }
-    }
-
     fn serialize(
         array: ArrayView<'_, Self>,
         _session: &VortexSession,

vortex-python/src/arrays/py/vtable.rs

@@ -92,18 +92,6 @@ impl VTable for PythonVTable {
         with_empty_buffers(self, array, buffers)
     }
 
-    fn nchildren(_array: ArrayView<'_, Self>) -> usize {
-        0
-    }
-
-    fn child(_array: ArrayView<'_, Self>, idx: usize) -> ArrayRef {
-        vortex_panic!("PythonArray child index {idx} out of bounds")
-    }
-
-    fn child_name(_array: ArrayView<'_, Self>, idx: usize) -> String {
-        vortex_panic!("PythonArray child_name index {idx} out of bounds")
-    }
-
     fn serialize(
         _array: ArrayView<'_, Self>,
         _session: &VortexSession,