[C++] Add support for nested class types in row encoder (apache#1173)

src/fury/encoder/row_encoder.h

@@ -23,6 +23,7 @@
 #include <string_view>
 #include <type_traits>
 #include <utility>
+#include <variant>
 
 namespace fury {
 
@@ -94,7 +95,8 @@ struct RowEncodeTrait<
   }
 
   static auto Write(const T &value, RowWriter &writer, int index) {
-    return writer.Write(index, value);
+    writer.Write(index, value);
+    return std::monostate{};
   }
 };
 
@@ -104,7 +106,8 @@ struct RowEncodeTrait<
   static auto Type() { return arrow::utf8(); }
 
   static auto Write(const T &value, RowWriter &writer, int index) {
-    return writer.WriteString(index, value);
+    writer.WriteString(index, value);
+    return std::monostate{};
   }
 };
 
@@ -123,10 +126,10 @@ struct RowEncodeTrait<
   template <typename FieldInfo, size_t... I>
   static auto WriteImpl(const T &value, RowWriter &writer,
                         std::index_sequence<I...>) {
-    (RowEncodeTrait<meta::RemoveMemberPointerCVRefT<decltype(std::get<I>(
-         FieldInfo::Ptrs))>>::Write(value.*std::get<I>(FieldInfo::Ptrs), writer,
-                                    I),
-     ...);
+    return std::tuple{
+        RowEncodeTrait<meta::RemoveMemberPointerCVRefT<decltype(std::get<I>(
+            FieldInfo::Ptrs))>>::Write(value.*std::get<I>(FieldInfo::Ptrs),
+                                       writer, I)...};
   }
 
 public:
@@ -147,6 +150,20 @@ struct RowEncodeTrait<
     return WriteImpl<FieldInfo>(value, writer,
                                 std::make_index_sequence<FieldInfo::Size>());
   }
+
+  static auto Write(const T &value, RowWriter &writer, int index) {
+    auto offset = writer.cursor();
+
+    auto inner_writer = std::make_shared<RowWriter>(
+        arrow::schema(writer.schema()->field(index)->type()->fields()),
+        &writer);
+
+    inner_writer->Reset();
+    RowEncodeTrait<std::remove_cv_t<T>>::Write(value, *inner_writer.get());
+
+    writer.SetOffsetAndSize(index, offset, writer.cursor() - offset);
+    return inner_writer;
+  }
 };
 
 } // namespace encoder

src/fury/encoder/row_encoder_test.cc

@@ -74,6 +74,8 @@ TEST(RowEncoder, String) {
   auto row = writer.ToRow();
   ASSERT_EQ(row->GetString(1), "hello");
   ASSERT_EQ(row->GetInt32(0), 233);
+
+  ASSERT_EQ(writer.schema()->field(1)->type()->name(), "utf8");
 }
 
 struct C {
@@ -97,6 +99,50 @@ TEST(RowEncoder, Const) {
   ASSERT_EQ(row->GetBoolean(2), true);
 }
 
+struct D {
+  int x;
+  A y;
+  B z;
+};
+
+FURY_FIELD_INFO(D, x, y, z);
+
+TEST(RowEncoder, NestedStruct) {
+  RowWriter writer(encoder::RowEncodeTrait<D>::Schema());
+  writer.Reset();
+
+  D d{233, {234, 3.14, true}, {235, "hi"}};
+  auto _ = encoder::RowEncodeTrait<D>::Write(d, writer);
+
+  auto row = writer.ToRow();
+  ASSERT_EQ(row->GetInt32(0), 233);
+
+  auto y_row = row->GetStruct(1);
+  ASSERT_EQ(y_row->GetInt32(0), 234);
+  ASSERT_FLOAT_EQ(y_row->GetFloat(1), 3.14);
+  ASSERT_EQ(y_row->GetBoolean(2), true);
+
+  auto z_row = row->GetStruct(2);
+  ASSERT_EQ(z_row->GetString(1), "hi");
+  ASSERT_EQ(z_row->GetInt32(0), 235);
+
+  ASSERT_EQ(writer.schema()->field(0)->type()->name(), "int32");
+  ASSERT_EQ(writer.schema()->field(1)->type()->name(), "struct");
+  ASSERT_EQ(writer.schema()->field(2)->type()->name(), "struct");
+
+  auto y_writer = dynamic_cast<RowWriter *>(writer.children()[0]);
+  ASSERT_TRUE(y_writer);
+
+  auto y_schema = y_writer->schema();
+  ASSERT_EQ(y_schema->field(0)->name(), "x");
+  ASSERT_EQ(y_schema->field(1)->name(), "y");
+  ASSERT_EQ(y_schema->field(2)->name(), "z");
+
+  ASSERT_EQ(y_schema->field(0)->type()->name(), "int32");
+  ASSERT_EQ(y_schema->field(1)->type()->name(), "float");
+  ASSERT_EQ(y_schema->field(2)->type()->name(), "bool");
+}
+
 } // namespace test
 
 } // namespace fury