feat: Add IndexByName and IndexById to Namemapping

crates/iceberg/src/expr/visitors/mod.rs

@@ -20,6 +20,7 @@ pub(crate) mod expression_evaluator;
 pub(crate) mod inclusive_metrics_evaluator;
 pub(crate) mod inclusive_projection;
 pub(crate) mod manifest_evaluator;
+pub(crate) mod name_mapping_visitor;
 pub(crate) mod page_index_evaluator;
 pub(crate) mod row_group_metrics_evaluator;
 pub(crate) mod strict_metrics_evaluator;

crates/iceberg/src/expr/visitors/name_mapping_visitor.rs

@@ -0,0 +1,35 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use crate::spec::MappedField;
+
+/// A trait for visiting and transforming a name mapping
+pub trait NameMappingVisitor {
+    /// Aggregated result of `MappedField`s
+    type S;
+    /// Result type for processing one `MappedField`
+    type T;
+
+    /// Handles entire `NameMapping` field
+    fn mapping(&self, field_result: Self::S) -> Self::S;
+
+    /// Takes all visited child maps and merges into one map
+    fn fields(&self, field_results: Vec<Self::T>) -> Self::S;
+
+    /// Handles a single `MappedField`
+    fn field(&self, field: &MappedField, field_result: Self::S) -> Self::T;
+}