ZENOTME commented on code in PR #731:
URL: https://github.com/apache/iceberg-rust/pull/731#discussion_r1899341695
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crates/iceberg/src/spec/schema.rs:
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@@ -1132,6 +1132,213 @@ impl ReassignFieldIds {
}
}
+/// A post order schema visitor with partner.
+///
+/// For order of methods called, please refer to [`visit_schema_with_partner`].
+pub trait SchemaWithPartnerVisitor<P> {
+ /// Return type of this visitor.
+ type T;
+
+ /// Called before struct field.
+ fn before_struct_field(&mut self, _field: &NestedFieldRef, _partner: &P)
-> Result<()> {
+ Ok(())
+ }
+ /// Called after struct field.
+ fn after_struct_field(&mut self, _field: &NestedFieldRef, _partner: &P) ->
Result<()> {
+ Ok(())
+ }
+ /// Called before list field.
+ fn before_list_element(&mut self, _field: &NestedFieldRef, _partner: &P)
-> Result<()> {
+ Ok(())
+ }
+ /// Called after list field.
+ fn after_list_element(&mut self, _field: &NestedFieldRef, _partner: &P) ->
Result<()> {
+ Ok(())
+ }
+ /// Called before map key field.
+ fn before_map_key(&mut self, _field: &NestedFieldRef, _partner: &P) ->
Result<()> {
+ Ok(())
+ }
+ /// Called after map key field.
+ fn after_map_key(&mut self, _field: &NestedFieldRef, _partner: &P) ->
Result<()> {
+ Ok(())
+ }
+ /// Called before map value field.
+ fn before_map_value(&mut self, _field: &NestedFieldRef, _partner: &P) ->
Result<()> {
+ Ok(())
+ }
+ /// Called after map value field.
+ fn after_map_value(&mut self, _field: &NestedFieldRef, _partner: &P) ->
Result<()> {
+ Ok(())
+ }
+
+ /// Called before every type, if this function return `Some`, the
following visiting will be skipped.
+ /// This function used to implement early return.
+ fn visit_type_before(&mut self, _ty: &Type, _partner: &P) ->
Result<Option<Self::T>> {
Review Comment:
> why we don't prune unnecessary fields before visiting?
I think this prune will also incur visits recursively. Let me explain why we
need this prune. In arrow, the struct array maybe represent as a nullarray
which means that all child field are null. So in this case, we need to
recognize this and stop to visit child column. But in our visitor pattern, we
can't control this, the control path is in the visit_function rather than
vistor. So we need to use this function to notify the visit function that stop
visit child column if this function return Some.
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