From 0678222faa86111eb3cc2e2ada341bf390231982 Mon Sep 17 00:00:00 2001
From: Naurder <48394023+Naurder@users.noreply.github.com>
Date: Wed, 10 Jun 2026 22:41:58 +0200
Subject: [PATCH 1/2] GH-48740: [C++] Add missing CTypeTraits for decimal types

---
 cpp/src/arrow/type_traits.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/cpp/src/arrow/type_traits.h b/cpp/src/arrow/type_traits.h
index 1b7a02e1085a..78fb08cd3058 100644
--- a/cpp/src/arrow/type_traits.h
+++ b/cpp/src/arrow/type_traits.h
@@ -103,6 +103,16 @@ struct CTypeTraits {};
 
 /// \addtogroup type-traits
 /// @{
+template <>
+struct CTypeTraits<Decimal128> {
+  using ArrowType = Decimal128Type;
+};
+
+template <>
+struct CTypeTraits<Decimal256> {
+  using ArrowType = Decimal256Type;
+};
+
 template <>
 struct TypeTraits<NullType> {
   using ArrayType = NullArray;

From c1e09556ff41fe7c33ead3135a0a14076134582a Mon Sep 17 00:00:00 2001
From: Naurder <48394023+Naurder@users.noreply.github.com>
Date: Thu, 11 Jun 2026 19:15:50 +0200
Subject: [PATCH 2/2] apply reviewer suggestion: inherit from TypeTraits

---
 cpp/src/arrow/type_traits.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cpp/src/arrow/type_traits.h b/cpp/src/arrow/type_traits.h
index 78fb08cd3058..900c3e05a56b 100644
--- a/cpp/src/arrow/type_traits.h
+++ b/cpp/src/arrow/type_traits.h
@@ -104,12 +104,12 @@ struct CTypeTraits {};
 /// \addtogroup type-traits
 /// @{
 template <>
-struct CTypeTraits<Decimal128> {
+struct CTypeTraits<Decimal128> : TypeTraits<Decimal128Type> {
   using ArrowType = Decimal128Type;
 };
 
 template <>
-struct CTypeTraits<Decimal256> {
+struct CTypeTraits<Decimal256> : TypeTraits<Decimal256Type> {
   using ArrowType = Decimal256Type;
 };