add bug example with g++ compilation error

test/CMakeLists.txt

@@ -12,7 +12,7 @@ FetchContent_MakeAvailable(Catch2)
 add_library( napp_test_lib1  lib1.cpp)
 target_link_libraries(napp_test_lib1 PRIVATE ${NAPP_TARGET_NAME} )
 
-file(GLOB files unit-*.cpp)
+file(GLOB files unit-*.cpp bug-ftbs-*.cpp)
 foreach(file ${files})
   get_filename_component(file_basename ${file} NAME_WE)
   #string(REGEX REPLACE "unit-([^$]+)" "test-\\1" testcase ${file_basename})

test/bug-ftbs-gcc.cpp

@@ -0,0 +1,27 @@
+#include <napp/na.hpp>
+
+using element1 = NA::named_argument_t<struct element1_tag>;
+constexpr auto& _element1 = NA::identifier<element1>;
+
+template <typename Ts>
+void func( Ts && v )
+{
+    // body
+}
+
+// NOTE: g++ compilation error only when use a template
+template <typename T>
+class Foo
+{
+public:
+    Foo(){
+        func( _element1=("toto") ); // error
+        func( _element1.operator=("toto") ); // OK
+    }
+};
+
+int main()
+{
+    Foo<int> a;
+    return 0;
+}