Jinchul81 commented on code in PR #335:
URL: https://github.com/apache/iceberg-cpp/pull/335#discussion_r2553970555


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src/iceberg/expression/aggregate.cc:
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@@ -0,0 +1,289 @@
+/*
+ * 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.
+ */
+
+#include "iceberg/expression/aggregate.h"
+
+#include <format>
+#include <optional>
+
+#include "iceberg/exception.h"
+#include "iceberg/expression/binder.h"
+#include "iceberg/expression/expression.h"
+#include "iceberg/row/struct_like.h"
+#include "iceberg/type.h"
+#include "iceberg/util/checked_cast.h"
+#include "iceberg/util/macros.h"
+
+namespace iceberg {
+
+namespace {
+
+std::string OperationToPrefix(Expression::Operation op) {
+  switch (op) {
+    case Expression::Operation::kMax:
+      return "max";
+    case Expression::Operation::kMin:
+      return "min";
+    case Expression::Operation::kCount:
+    case Expression::Operation::kCountStar:
+      return "count";
+    default:
+      break;
+  }
+  return "aggregate";
+}
+
+Result<std::shared_ptr<PrimitiveType>> GetPrimitiveType(const BoundTerm& term) 
{
+  auto primitive = std::dynamic_pointer_cast<PrimitiveType>(term.type());
+  if (primitive == nullptr) {
+    return InvalidExpression("Aggregate requires primitive type, got {}",
+                             term.type()->ToString());
+  }
+  return primitive;
+}
+
+}  // namespace
+
+CountAggregate::CountAggregate(Expression::Operation op, Mode mode,
+                               std::shared_ptr<UnboundTerm<BoundReference>> 
term,
+                               std::shared_ptr<NamedReference> reference)
+    : UnboundAggregate(op),
+      mode_(mode),
+      term_(std::move(term)),
+      reference_(std::move(reference)) {}
+
+Result<std::unique_ptr<CountAggregate>> CountAggregate::Count(
+    std::shared_ptr<UnboundTerm<BoundReference>> term) {
+  auto ref = term->reference();
+  return std::unique_ptr<CountAggregate>(new CountAggregate(
+      Expression::Operation::kCount, Mode::kNonNull, std::move(term), 
std::move(ref)));
+}
+
+Result<std::unique_ptr<CountAggregate>> CountAggregate::CountNull(
+    std::shared_ptr<UnboundTerm<BoundReference>> term) {
+  auto ref = term->reference();
+  return std::unique_ptr<CountAggregate>(new CountAggregate(
+      Expression::Operation::kCount, Mode::kNull, std::move(term), 
std::move(ref)));
+}
+
+std::unique_ptr<CountAggregate> CountAggregate::CountStar() {
+  return std::unique_ptr<CountAggregate>(new CountAggregate(
+      Expression::Operation::kCountStar, Mode::kStar, nullptr, nullptr));
+}
+
+std::string CountAggregate::ToString() const {
+  if (mode_ == Mode::kStar) {

Review Comment:
   I am still curious the special handling should be required in not only C++ 
but also Java. Can you please try to apply `kStar` in the generic manner? I 
don't accept we just follow the implementation of the Java version.



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