diff --git a/CMakeLists.txt b/CMakeLists.txt
index 588bb58..cc6b8cc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -35,6 +35,8 @@ target_include_directories(
         "$<INSTALL_INTERFACE:include/${PROJECT_NAME}>"
 )
 
+target_link_libraries(${PROJECT_NAME} INTERFACE snipplib)
+
 if(BUILD_EXAM)
     add_executable(device_exam examples/device_exam.cpp)
     target_link_libraries(device_exam PRIVATE ${PROJECT_NAME})
diff --git a/examples/device_exam.cpp b/examples/device_exam.cpp
index 06acbce..5e46edd 100644
--- a/examples/device_exam.cpp
+++ b/examples/device_exam.cpp
@@ -13,15 +13,30 @@ int main()
     AdcGenericDevice<> dev;
 
     dev.addAttr(
-        "1", [&i]() { return adc_result_t<int>{i}; },
+        "1", [&i]() -> adc_result_t<int> { return i; },
         [&i](int ii) -> adc_error_t {
             i = ii;
             return AdcDeviceErrorCode::ERROR_OK;
-        });
+        },
+        std::tuple<double, long>{});
 
     adc_result_t<int> ri = dev["1"];
     if (ri) {
         std::println("dev[1] = {}", ri.value());
+    } else {
+        std::println("cannot get dev[1] as int: {}", ri.error().message());
+    }
+
+    auto err = dev["1"] = 77;
+    if (err) {
+        std::println("cannot set dev[1] as int: {}", err.message());
+    }
+
+    adc_result_t<double> rd = dev["1"];
+    if (rd) {
+        std::println("dev[1] = {}", rd.value());
+    } else {
+        std::println("cannot get dev[1] as double: {}", rd.error().message());
     }
 
     return 0;
diff --git a/include/adclib/adclib_device.h b/include/adclib/adclib_device.h
index 83bdaa6..e07f45e 100644
--- a/include/adclib/adclib_device.h
+++ b/include/adclib/adclib_device.h
@@ -5,6 +5,8 @@
  ****************************************************************************************/
 
 #include <concepts>
+#include <format>
+#include <functional>
 #include <string>
 #include <system_error>
 #include <type_traits>
@@ -69,9 +71,9 @@ struct AdcDeviceErrorCategory : std::error_category {
             case AdcDeviceErrorCode::ERROR_OK:
                 return "OK";
             case AdcDeviceErrorCode::ERROR_NO_CMD_ID:
-                return "invalud command ID";
+                return "invalid command ID";
             case AdcDeviceErrorCode::ERROR_NO_ATTR_ID:
-                return "invalud attribute ID";
+                return "invalid attribute ID";
             case AdcDeviceErrorCode::ERROR_RO_ATTR:
                 return "read-only attribute";
             case AdcDeviceErrorCode::ERROR_WO_ATTR:
@@ -94,6 +96,11 @@ struct AdcDeviceErrorCategory : std::error_category {
     }
 };
 
+inline std::error_code make_error_code(AdcDeviceErrorCode ec)
+{
+    return std::error_code(static_cast<int>(ec), AdcDeviceErrorCategory::get());
+}
+
 
 template <std::formattable<char> ATTR_ID_T = std::string_view, std::formattable<char> CMD_ID_T = std::string_view>
 class AdcGenericDevice
@@ -150,13 +157,13 @@ protected:
         template <typename VT>
         operator adc_result_t<VT>()
         {
-            auto v = _dev._attrs.template get<VT>(_id);
-            if (v) {
-                return v.value();
+            auto const& attr = _dev._attrs.template get<attr_t<VT>>(_id);
+            if (attr) {
+                return attr.value().getter();
             }
 
             // error
-            if (v.error() == snplib::HeterogenMap<ATTR_ID_T>::ERROR_NO_ELEM) {
+            if (attr.error() == snplib::HeterogenMap<ATTR_ID_T>::ERROR_NO_ELEM) {
                 return std::unexpected(AdcDeviceErrorCode::ERROR_NO_ATTR_ID);
             }
 
@@ -166,10 +173,12 @@ protected:
         template <typename VT>
         adc_error_t operator=(VT&& val)
         {
-            auto err = _dev._attrs.set(_id, std::forward<VT>(val));
-            if (err == snplib::HeterogenMap<ATTR_ID_T>::ERROR_OK) {
-                return AdcDeviceErrorCode::ERROR_OK;
-            } else if (err == snplib::HeterogenMap<ATTR_ID_T>::ERROR_NO_ELEM) {
+            auto const& attr = _dev._attrs.template get<attr_t<VT>>(_id);
+            if (attr) {
+                return attr.value().setter(std::forward<VT>(val));
+            }
+
+            if (attr.error() == snplib::HeterogenMap<ATTR_ID_T>::ERROR_NO_ELEM) {
                 return AdcDeviceErrorCode::ERROR_NO_ATTR_ID;
             } else {
                 return AdcDeviceErrorCode::ERROR_UNKNOWN;
@@ -196,8 +205,8 @@ public:
         _commands.emplace(std::move(id), std::forward<ET>(exec_func));
     }
 
-    template <typename GT, typename ST>
-    void addAttr(ATTR_ID_T id, GT&& getter, ST&& setter)
+    template <typename GT, typename ST, typename... VTs>
+    void addAttr(ATTR_ID_T id, GT&& getter, ST&& setter, std::tuple<VTs...> = std::tuple())
     {
         // deduce attribute value type
         using ret_t = std::invoke_result_t<GT>;
@@ -210,6 +219,19 @@ public:
                       "Invalid return type of the setter!");
 
         _attrs.push(std::move(id), attr_t<v_t>{.getter = std::forward<GT>(getter), .setter = std::forward<ST>(setter)});
+
+        // if constexpr (sizeof...(VTs)) {
+        //     auto func = [id, this]<size_t I>() {
+        //         using u_t = std::tuple_element_t<I, std::tuple<VTs...>>;
+        //         if constexpr (!requires(u_t u, v_t v) {
+        //                           u = v;
+        //                           v = u;
+        //                       }) {
+        //             static_assert(false, "Invalid user type!");
+        //         }
+        //         _attrs.push(std::move(id), attr_t<u_t>{.getter = []() {}, .setter = []() {}});
+        //     };
+        // }
     }
 
     adc_error_t operator()(CMD_ID_T id)