(arrow) branch main updated: GH-48740: [C++] Add missing CTypeTraits for decimal types (#50153)

[zanmato]

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zanmato1984 pushed a commit to branch main
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The following commit(s) were added to refs/heads/main by this push:
     new fea7421c13 GH-48740: [C++] Add missing CTypeTraits for decimal types 
(#50153)
fea7421c13 is described below

commit fea7421c138f76b1d559c962d321276ed6b2300b
Author: Naurder <48394023+naur...@users.noreply.github.com>
AuthorDate: Fri Aug 21 22:31:27 2026 +0200

    GH-48740: [C++] Add missing CTypeTraits for decimal types (#50153)
    
    ### Rationale for this change
    
    As reported in #48740, the `CTypeTraits` specializations were missing for 
decimal types. This prevented generic code from correctly mapping C++ decimal 
types to Arrow types.
    
    ### What changes are included in this PR?
    
    * Added `CTypeTraits<Decimal128>` mapping to `Decimal128Type`.
    * Added `CTypeTraits<Decimal256>` mapping to `Decimal256Type`.
    
    ### Are these changes tested?
    
    Yes, via existing type traits tests in the CI pipeline.
    
    ### Are there any user-facing changes?
    
    No.
    
    Closes #48740
    * GitHub Issue: #48740
    
    Lead-authored-by: Naurder <48394023+naur...@users.noreply.github.com>
    Co-authored-by: Rossi Sun <zanmato1...@gmail.com>
    Signed-off-by: Rossi Sun <zanmato1...@gmail.com>
---
 cpp/src/arrow/type_test.cc  | 14 ++++++++++++++
 cpp/src/arrow/type_traits.h | 20 ++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/cpp/src/arrow/type_test.cc b/cpp/src/arrow/type_test.cc
index 6197ad58eb..133afbfa0c 100644
--- a/cpp/src/arrow/type_test.cc
+++ b/cpp/src/arrow/type_test.cc
@@ -1493,6 +1493,20 @@ PRIMITIVE_TEST(DoubleType, double, DOUBLE, "double");
 
 PRIMITIVE_TEST(BooleanType, bool, BOOL, "bool");
 
+TEST(TypesTest, DecimalTraits) {
+  static_assert(std::is_same_v<TypeTraits<Decimal32Type>::CType, Decimal32>);
+  static_assert(std::is_same_v<CTypeTraits<Decimal32>::ArrowType, 
Decimal32Type>);
+
+  static_assert(std::is_same_v<TypeTraits<Decimal64Type>::CType, Decimal64>);
+  static_assert(std::is_same_v<CTypeTraits<Decimal64>::ArrowType, 
Decimal64Type>);
+
+  static_assert(std::is_same_v<TypeTraits<Decimal128Type>::CType, Decimal128>);
+  static_assert(std::is_same_v<CTypeTraits<Decimal128>::ArrowType, 
Decimal128Type>);
+
+  static_assert(std::is_same_v<TypeTraits<Decimal256Type>::CType, Decimal256>);
+  static_assert(std::is_same_v<CTypeTraits<Decimal256>::ArrowType, 
Decimal256Type>);
+}
+
 TEST(TestBinaryType, ToString) {
   BinaryType t1;
   BinaryType e1;
diff --git a/cpp/src/arrow/type_traits.h b/cpp/src/arrow/type_traits.h
index 1b7a02e108..fda3e3be12 100644
--- a/cpp/src/arrow/type_traits.h
+++ b/cpp/src/arrow/type_traits.h
@@ -357,6 +357,26 @@ struct TypeTraits<Decimal256Type> {
   constexpr static bool is_parameter_free = false;
 };
 
+template <>
+struct CTypeTraits<Decimal32> : public TypeTraits<Decimal32Type> {
+  using ArrowType = Decimal32Type;
+};
+
+template <>
+struct CTypeTraits<Decimal64> : public TypeTraits<Decimal64Type> {
+  using ArrowType = Decimal64Type;
+};
+
+template <>
+struct CTypeTraits<Decimal128> : public TypeTraits<Decimal128Type> {
+  using ArrowType = Decimal128Type;
+};
+
+template <>
+struct CTypeTraits<Decimal256> : public TypeTraits<Decimal256Type> {
+  using ArrowType = Decimal256Type;
+};
+
 template <>
 struct TypeTraits<BinaryType> {
   using ArrayType = BinaryArray;