From 17b0e310ccb1b48b49c026664a6f1f3a6e982df3 Mon Sep 17 00:00:00 2001
From: Dmitry Chigarev <dmitry.chigarev@intel.com>
Date: Mon, 12 Oct 2020 14:27:53 +0300
Subject: [PATCH] Get rid of code duplication at DecimalScalar

Signed-off-by: Dmitry Chigarev <dmitry.chigarev@intel.com>
---
 cpp/src/arrow/scalar.h | 25 ++++++++++++-------------
 cpp/src/arrow/type.cc  | 12 +++++-------
 2 files changed, 17 insertions(+), 20 deletions(-)

diff --git a/cpp/src/arrow/scalar.h b/cpp/src/arrow/scalar.h
index a6ec9d3afefde..bb6500d419ba3 100644
--- a/cpp/src/arrow/scalar.h
+++ b/cpp/src/arrow/scalar.h
@@ -36,6 +36,7 @@
 #include "arrow/type_traits.h"
 #include "arrow/util/compare.h"
 #include "arrow/util/decimal.h"
+#include "arrow/util/decimal_type_traits.h"
 #include "arrow/util/string_view.h"
 #include "arrow/util/visibility.h"
 
@@ -336,26 +337,24 @@ struct ARROW_EXPORT DurationScalar : public TemporalScalar<DurationType> {
   using TemporalScalar<DurationType>::TemporalScalar;
 };
 
-struct ARROW_EXPORT Decimal128Scalar : public Scalar {
+template<uint32_t width>
+struct BaseDecimalScalar : public Scalar {
   using Scalar::Scalar;
-  using TypeClass = Decimal128Type;
-  using ValueType = Decimal128;
+  using TypeClass = typename DecimalTypeTraits<width>::TypeClass;
+  using ValueType = typename DecimalTypeTraits<width>::ValueType;
 
-  Decimal128Scalar(Decimal128 value, std::shared_ptr<DataType> type)
+  BaseDecimalScalar(ValueType value, std::shared_ptr<DataType> type)
       : Scalar(std::move(type), true), value(value) {}
 
-  Decimal128 value;
+  ValueType value;
 };
 
-struct ARROW_EXPORT Decimal256Scalar : public Scalar {
-  using Scalar::Scalar;
-  using TypeClass = Decimal256Type;
-  using ValueType = Decimal256;
-
-  Decimal256Scalar(Decimal256 value, std::shared_ptr<DataType> type)
-      : Scalar(std::move(type), true), value(value) {}
+struct ARROW_EXPORT Decimal128Scalar : public BaseDecimalScalar<128> {
+  using BaseDecimalScalar<128>::BaseDecimalScalar;
+};
 
-  Decimal256 value;
+struct ARROW_EXPORT Decimal256Scalar : public BaseDecimalScalar<256> {
+  using BaseDecimalScalar<256>::BaseDecimalScalar;
 };
 
 struct ARROW_EXPORT BaseListScalar : public Scalar {
diff --git a/cpp/src/arrow/type.cc b/cpp/src/arrow/type.cc
index a64394aa93b30..0b092b43a569a 100644
--- a/cpp/src/arrow/type.cc
+++ b/cpp/src/arrow/type.cc
@@ -2149,15 +2149,13 @@ std::shared_ptr<DataType> decimal(int32_t precision, int32_t scale) {
                                                     : decimal256(precision, scale);
 }
 
-#define DECIMAL_BUILDER_DECL(width)                                          \
-std::shared_ptr<DataType> decimal##width(int32_t precision, int32_t scale) { \
-  return std::make_shared<Decimal##width##Type>(precision, scale);           \
+std::shared_ptr<DataType> decimal128(int32_t precision, int32_t scale) {
+  return std::make_shared<Decimal128Type>(precision, scale);
 }
 
-DECIMAL_BUILDER_DECL(128)
-DECIMAL_BUILDER_DECL(256)
-
-#undef DECIMAL_BUILDER_DECL
+std::shared_ptr<DataType> decimal256(int32_t precision, int32_t scale) {
+  return std::make_shared<Decimal256Type>(precision, scale);
+}
 
 template<uint32_t width>
 std::string BaseDecimalType<width>::ToString() const {