Added example for using a struct instead of pod

	modified:   func_pattern.cxx

func_pattern.cxx

@@ -222,6 +222,16 @@ namespace func {
 
 } // namespace func
 
+
+struct XYZ_vec {
+  double x = 0.0;
+  double y = 0.0;
+  double z = 0.0;
+};
+
+template <typename Tag>
+using Vec_Var = NamedType<XYZ_vec, Tag>;
+
 int main() {
   using namespace func;
 
@@ -236,8 +246,13 @@ int main() {
   using E_coord = Var<struct E_coord_tag>;
   using F_coord = Var<struct F_coord_tag>;
 
+  using XYZ_coord = Vec_Var<struct test_vector_variable_tag>;
+
+  // X_coord and Y_coord are the independent variables that must be provided
+  // to compute all the subsquently defined variables.
   auto vars0 = make_independent_vars<X_coord, Y_coord>();
 
+  // Add Z_coord = x+y
   auto vars1 = vars0.add<Z_coord>([](const auto& v) constexpr  {
     const auto& x = std::get<X_coord>(v);
     const auto& y = std::get<Y_coord>(v);
@@ -264,20 +279,7 @@ int main() {
         return 1.0/(x * y * z);
       });
 
-  //auto values1 = vars1.ComputeValues(std::make_tuple(X_coord{2.0}, Y_coord{3.0}));
 
-  //std::cout << std::get<0>(values1) << "\n";
-  //std::cout << std::get<1>(values1) << "\n";
-  //std::cout << std::get<2>(values1) << "\n";
-
-  //auto values2 = vars2.ComputeValues(std::make_tuple(X_coord{2.0}, Y_coord{3.0}));
-
-  //std::cout << std::get<0>(values2) << "\n";
-  //std::cout << std::get<1>(values2) << "\n";
-  //std::cout << std::get<2>(values2) << "\n";
-  //std::cout <<  " A_coord  " << std::get<A_coord>(values2) << "\n";
-  //std::cout <<  " B_coord  " << std::get<B_coord>(values2) << "\n";
-  //std::cout <<  " C_coord  " << std::get<C_coord>(values2) << "\n";
 
   auto vars3 = vars2.add<D_coord, E_coord, F_coord>(
       [](const auto& v) constexpr {
@@ -308,6 +310,7 @@ int main() {
         return c/(x * y * z);
       });
 
+
   auto values3 = vars3.ComputeValues(std::make_tuple(X_coord{2.0}, Y_coord{77.0}));
 
   //std::cout << std::get<0>(values3) << "\n";
@@ -322,5 +325,19 @@ int main() {
   std::cout  << std::get<D_coord>(values3) << "\n";
   std::cout  << std::get<E_coord>(values3) << "\n";
   std::cout  << std::get<F_coord>(values3) << "\n";
+
+  auto vars4 = vars3.add<XYZ_coord>(
+      [](const auto& v) constexpr {
+        const auto&  x = std::get<X_coord>(v);
+        const auto&  y = std::get<Y_coord>(v);
+        const auto&  z = std::get<Z_coord>(v);
+        return XYZ_vec{x, y, z};
+      }); 
+
+  auto values4 = vars4.ComputeValues(std::make_tuple(X_coord{2.0}, Y_coord{77.0}));
+  std::cout  << std::get<XYZ_coord>(values4).get().x << "\n";
+  std::cout  << std::get<XYZ_coord>(values4).get().y << "\n";
+  std::cout  << std::get<XYZ_coord>(values4).get().z << "\n";
+
 }