From ece9eabf65a214e5c05b0831c5d7842addbc73e0 Mon Sep 17 00:00:00 2001
From: tzik <mail@tzik.jp>
Date: Fri, 17 Jan 2025 22:12:18 +0900
Subject: [PATCH] [C++] Use C++17 inline variables for enum_value

---
 src/idl_gen_cpp.cpp                           | 14 ++++++--
 .../generated_cpp17/monster_test_generated.h  | 32 +++++++++----------
 .../generated_cpp17/union_vector_generated.h  | 12 +++----
 3 files changed, 34 insertions(+), 24 deletions(-)

diff --git a/src/idl_gen_cpp.cpp b/src/idl_gen_cpp.cpp
index ba158ecb593..f9f7f74747b 100644
--- a/src/idl_gen_cpp.cpp
+++ b/src/idl_gen_cpp.cpp
@@ -1355,7 +1355,12 @@ class CppGenerator : public BaseGenerator {
         }
 
         auto value = GetEnumValUse(enum_def, ev);
-        code_ += "  static const {{ENUM_NAME}} enum_value = " + value + ";";
+        if (opts_.g_cpp_std >= cpp::CPP_STD_17) {
+          code_ +=
+              "  static inline const {{ENUM_NAME}} enum_value = " + value + ";";
+        } else {
+          code_ += "  static const {{ENUM_NAME}} enum_value = " + value + ";";
+        }
         code_ += "};";
         code_ += "";
       }
@@ -1390,7 +1395,12 @@ class CppGenerator : public BaseGenerator {
         }
 
         auto value = GetEnumValUse(enum_def, ev);
-        code_ += "  static const {{ENUM_NAME}} enum_value = " + value + ";";
+        if (opts_.g_cpp_std >= cpp::CPP_STD_17) {
+          code_ +=
+              "  static inline const {{ENUM_NAME}} enum_value = " + value + ";";
+        } else {
+          code_ += "  static const {{ENUM_NAME}} enum_value = " + value + ";";
+        }
         code_ += "};";
         code_ += "";
       }
diff --git a/tests/cpp17/generated_cpp17/monster_test_generated.h b/tests/cpp17/generated_cpp17/monster_test_generated.h
index 68c49af6716..103684f4882 100644
--- a/tests/cpp17/generated_cpp17/monster_test_generated.h
+++ b/tests/cpp17/generated_cpp17/monster_test_generated.h
@@ -236,35 +236,35 @@ inline const char *EnumNameAny(Any e) {
 }
 
 template<typename T> struct AnyTraits {
-  static const Any enum_value = Any::NONE;
+  static inline const Any enum_value = Any::NONE;
 };
 
 template<> struct AnyTraits<MyGame::Example::Monster> {
-  static const Any enum_value = Any::Monster;
+  static inline const Any enum_value = Any::Monster;
 };
 
 template<> struct AnyTraits<MyGame::Example::TestSimpleTableWithEnum> {
-  static const Any enum_value = Any::TestSimpleTableWithEnum;
+  static inline const Any enum_value = Any::TestSimpleTableWithEnum;
 };
 
 template<> struct AnyTraits<MyGame::Example2::Monster> {
-  static const Any enum_value = Any::MyGame_Example2_Monster;
+  static inline const Any enum_value = Any::MyGame_Example2_Monster;
 };
 
 template<typename T> struct AnyUnionTraits {
-  static const Any enum_value = Any::NONE;
+  static inline const Any enum_value = Any::NONE;
 };
 
 template<> struct AnyUnionTraits<MyGame::Example::MonsterT> {
-  static const Any enum_value = Any::Monster;
+  static inline const Any enum_value = Any::Monster;
 };
 
 template<> struct AnyUnionTraits<MyGame::Example::TestSimpleTableWithEnumT> {
-  static const Any enum_value = Any::TestSimpleTableWithEnum;
+  static inline const Any enum_value = Any::TestSimpleTableWithEnum;
 };
 
 template<> struct AnyUnionTraits<MyGame::Example2::MonsterT> {
-  static const Any enum_value = Any::MyGame_Example2_Monster;
+  static inline const Any enum_value = Any::MyGame_Example2_Monster;
 };
 
 struct AnyUnion {
@@ -363,35 +363,35 @@ inline const char *EnumNameAnyUniqueAliases(AnyUniqueAliases e) {
 }
 
 template<typename T> struct AnyUniqueAliasesTraits {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::NONE;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::NONE;
 };
 
 template<> struct AnyUniqueAliasesTraits<MyGame::Example::Monster> {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::M;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::M;
 };
 
 template<> struct AnyUniqueAliasesTraits<MyGame::Example::TestSimpleTableWithEnum> {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::TS;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::TS;
 };
 
 template<> struct AnyUniqueAliasesTraits<MyGame::Example2::Monster> {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::M2;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::M2;
 };
 
 template<typename T> struct AnyUniqueAliasesUnionTraits {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::NONE;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::NONE;
 };
 
 template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example::MonsterT> {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::M;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::M;
 };
 
 template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example::TestSimpleTableWithEnumT> {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::TS;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::TS;
 };
 
 template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example2::MonsterT> {
-  static const AnyUniqueAliases enum_value = AnyUniqueAliases::M2;
+  static inline const AnyUniqueAliases enum_value = AnyUniqueAliases::M2;
 };
 
 struct AnyUniqueAliasesUnion {
diff --git a/tests/cpp17/generated_cpp17/union_vector_generated.h b/tests/cpp17/generated_cpp17/union_vector_generated.h
index 0ef405c0b63..0a22f80b49d 100644
--- a/tests/cpp17/generated_cpp17/union_vector_generated.h
+++ b/tests/cpp17/generated_cpp17/union_vector_generated.h
@@ -195,27 +195,27 @@ inline const char *EnumNameGadget(Gadget e) {
 }
 
 template<typename T> struct GadgetTraits {
-  static const Gadget enum_value = Gadget::NONE;
+  static inline const Gadget enum_value = Gadget::NONE;
 };
 
 template<> struct GadgetTraits<FallingTub> {
-  static const Gadget enum_value = Gadget::FallingTub;
+  static inline const Gadget enum_value = Gadget::FallingTub;
 };
 
 template<> struct GadgetTraits<HandFan> {
-  static const Gadget enum_value = Gadget::HandFan;
+  static inline const Gadget enum_value = Gadget::HandFan;
 };
 
 template<typename T> struct GadgetUnionTraits {
-  static const Gadget enum_value = Gadget::NONE;
+  static inline const Gadget enum_value = Gadget::NONE;
 };
 
 template<> struct GadgetUnionTraits<FallingTub> {
-  static const Gadget enum_value = Gadget::FallingTub;
+  static inline const Gadget enum_value = Gadget::FallingTub;
 };
 
 template<> struct GadgetUnionTraits<HandFanT> {
-  static const Gadget enum_value = Gadget::HandFan;
+  static inline const Gadget enum_value = Gadget::HandFan;
 };
 
 struct GadgetUnion {