bug not depend of napp

test/bug-ftbs-gcc.cpp

@@ -1,22 +1,39 @@
-#include <napp/na.hpp>
+//!
 
-using element1 = NA::named_argument_t<struct element1_tag>;
-constexpr auto& _element1 = NA::identifier<element1>;
+struct A {};
+
+struct B
+{
+    constexpr B() = default;
+    B(const B&) = delete;
+    B& operator=(const B&) = delete;
+
+    template <typename V>
+    constexpr A operator=(V && v) const { return A{}; }
+};
 
 template <typename Ts>
 void func( Ts && v )
 {
     // body
 }
 
+template <typename Ts>
+void func2( Ts const& v )
+{
+
+}
+
 // 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
+        B b;
+        func( b=3 ); // error
+        func( b.operator=(3) ); // OK
+        func2( b=3 ); // OK
     }
 };