Feat: add user callback

README.md

@@ -422,6 +422,11 @@ if (param_listener->is_old(params_)) {
 }
 ```
 
+Alternatively, you can bind a callback function that triggers whenever a parameter is updated. When activated, the callback receives the updated parameters as an argument.
+```c++
+parameter_listener.setUserCallback([this](const auto& params) { reconfigure_callback(params); });
+```
+
 ### Parameter documentation
 
 In some cases, parameters might be unknown only at compile-time, and cannot be part of the generated C++ code. However, for documentation purpose of such parameters, the type `none` was introduced.

example/include/generate_parameter_library_example/minimal_publisher.hpp

@@ -41,6 +41,7 @@ class MinimalPublisher : public rclcpp::Node {
 
  private:
   void timer_callback();
+  void reconfigure_callback(const admittance_controller::Params& params);
 
   rclcpp::TimerBase::SharedPtr timer_;
   std::shared_ptr<admittance_controller::ParamListener> param_listener_;

example/src/minimal_publisher.cpp

@@ -42,6 +42,8 @@ MinimalPublisher::MinimalPublisher(const rclcpp::NodeOptions& options)
       500ms, std::bind(&MinimalPublisher::timer_callback, this));
   param_listener_ =
       std::make_shared<ParamListener>(get_node_parameters_interface());
+  param_listener_->setUserCallback(
+      [this](const auto& params) { reconfigure_callback(params); });
   params_ = param_listener_->get_params();
 
   [[maybe_unused]] StackParams s_params = param_listener_->get_stack_params();
@@ -71,4 +73,17 @@ void MinimalPublisher::timer_callback() {
   }
 }
 
+void MinimalPublisher::reconfigure_callback(
+    const admittance_controller::Params& params) {
+  RCLCPP_INFO(get_logger(), "Reconfigure callback fired!");
+  RCLCPP_INFO(get_logger(), "New control frame parameter is: '%s'",
+              params.control.frame.id.c_str());
+  RCLCPP_INFO(get_logger(), "fixed string is: '%s'",
+              std::string{params.fixed_string}.c_str());
+  const auto fixed_array = params.fixed_array;
+  for (auto d : fixed_array) {
+    RCLCPP_INFO(get_logger(), "value: '%s'", std::to_string(d).c_str());
+  }
+}
+
 }  // namespace admittance_controller

generate_parameter_library_py/generate_parameter_library_py/jinja_templates/cpp/parameter_library_header

@@ -182,6 +182,9 @@ struct StackParams {
 {%- endif %}
       updated_params.__stamp = clock_.now();
       update_internal_params(updated_params);
+      if (user_callback_) {
+         user_callback_(updated_params);
+      }
       return rsl::to_parameter_result_msg({});
     }
 
@@ -208,6 +211,15 @@ struct StackParams {
       update_internal_params(updated_params);
     }
 
+    using userParameterUpdateCB = std::function<void(const Params&)>;
+    void setUserCallback(const userParameterUpdateCB& callback){
+      user_callback_ = callback;
+    }
+
+    void clearUserCallback(){
+      user_callback_ = {};
+    }
+
     private:
       void update_internal_params(Params updated_params) {
         std::lock_guard<std::mutex> lock(mutex_);
@@ -219,6 +231,7 @@ struct StackParams {
       rclcpp::Clock clock_;
       std::shared_ptr<rclcpp::node_interfaces::OnSetParametersCallbackHandle> handle_;
       std::shared_ptr<rclcpp::node_interfaces::NodeParametersInterface> parameters_interface_;
+      userParameterUpdateCB user_callback_;
 
       // rclcpp::Logger cannot be default-constructed
       // so we must provide a initialization here even though