Allow Set() methods to handle reference types

Change-Id: I487ded77d28490189dd5d38236cb04bffaf5f11a

samples/monster_generated.h

@@ -119,12 +119,12 @@ struct EquipmentUnion {
   void Reset();
 
 #ifndef FLATBUFFERS_CPP98_STL
-  template <typename T>
+  template <typename T, typename RT = typename std::remove_reference<T>::type>
   void Set(T&& val) {
     Reset();
-    type = EquipmentTraits<typename T::TableType>::enum_value;
+    type = EquipmentTraits<typename RT::TableType>::enum_value;
     if (type != Equipment_NONE) {
-      value = new T(std::forward<T>(val));
+      value = new RT(std::forward<T>(val));
     }
   }
 #endif  // FLATBUFFERS_CPP98_STL

src/idl_gen_cpp.cpp

@@ -1096,13 +1096,12 @@ class CppGenerator : public BaseGenerator {
       code_ += "";
       if (!enum_def.uses_multiple_type_instances) {
         code_ += "#ifndef FLATBUFFERS_CPP98_STL";
-        code_ += "  template <typename T>";
+        code_ += "  template <typename T, typename RT = typename std::remove_reference<T>::type>";
         code_ += "  void Set(T&& val) {";
         code_ += "    Reset();";
-        code_ +=
-            "    type = {{NAME}}Traits<typename T::TableType>::enum_value;";
+        code_ += "    type = {{NAME}}Traits<typename RT::TableType>::enum_value;";
         code_ += "    if (type != {{NONE}}) {";
-        code_ += "      value = new T(std::forward<T>(val));";
+        code_ += "      value = new RT(std::forward<T>(val));";
         code_ += "    }";
         code_ += "  }";
         code_ += "#endif  // FLATBUFFERS_CPP98_STL";

tests/monster_test_generated.h

@@ -207,12 +207,12 @@ struct AnyUnion {
   void Reset();
 
 #ifndef FLATBUFFERS_CPP98_STL
-  template <typename T>
+  template <typename T, typename RT = typename std::remove_reference<T>::type>
   void Set(T&& val) {
     Reset();
-    type = AnyTraits<typename T::TableType>::enum_value;
+    type = AnyTraits<typename RT::TableType>::enum_value;
     if (type != Any_NONE) {
-      value = new T(std::forward<T>(val));
+      value = new RT(std::forward<T>(val));
     }
   }
 #endif  // FLATBUFFERS_CPP98_STL
@@ -348,12 +348,12 @@ struct AnyUniqueAliasesUnion {
   void Reset();
 
 #ifndef FLATBUFFERS_CPP98_STL
-  template <typename T>
+  template <typename T, typename RT = typename std::remove_reference<T>::type>
   void Set(T&& val) {
     Reset();
-    type = AnyUniqueAliasesTraits<typename T::TableType>::enum_value;
+    type = AnyUniqueAliasesTraits<typename RT::TableType>::enum_value;
     if (type != AnyUniqueAliases_NONE) {
-      value = new T(std::forward<T>(val));
+      value = new RT(std::forward<T>(val));
     }
   }
 #endif  // FLATBUFFERS_CPP98_STL