make use of template using compile time instead of runtime to call the funcs

Signed-off-by: Chen Lihui <[email protected]>

Author: Chen Lihui

rclcpp/include/rclcpp/typesupport_helpers.hpp

@@ -45,23 +45,52 @@ get_typesupport_library(const std::string & type, const std::string & typesuppor
 namespace internal
 {
 
-/// The type support of ros idl
-enum class TypeSupport
-{
-  UNKNOWN,
-  MESSAGE,
-  SERVICE,
-  ACTION
+struct typesupport_message_tag {};
+struct typesupport_service_tag {};
+struct typesupport_action_tag {};
+
+template <typename T>
+struct typesupport_traits {
+  typedef T type;
+};
+
+template <>
+struct typesupport_traits<rosidl_message_type_support_t> {
+  typedef typesupport_message_tag type_tag;
+};
+
+template <>
+struct typesupport_traits<rosidl_service_type_support_t> {
+  typedef typesupport_service_tag type_tag;
+};
+
+template <>
+struct typesupport_traits<rosidl_action_type_support_t> {
+  typedef typesupport_action_tag type_tag;
 };
 
 using SymbolNameErrorFuncPair = std::pair<std::string, std::function<std::string()>>;
 
-/// Get the symbol name.
+/// Get the symbol name with different typesupport tags.
+RCLCPP_PUBLIC
+SymbolNameErrorFuncPair _get_typesupport_symbol_name(
+  const std::string & type,
+  const std::string & typesupport_identifier,
+  typesupport_message_tag
+);
+
+RCLCPP_PUBLIC
+SymbolNameErrorFuncPair _get_typesupport_symbol_name(
+  const std::string & type,
+  const std::string & typesupport_identifier,
+  typesupport_service_tag
+);
+
 RCLCPP_PUBLIC
-SymbolNameErrorFuncPair get_typesupport_symbol_name(
+SymbolNameErrorFuncPair _get_typesupport_symbol_name(
   const std::string & type,
   const std::string & typesupport_identifier,
-  TypeSupport type_support
+  typesupport_action_tag
 );
 
 }  // namespace internal
@@ -82,16 +111,8 @@ get_typesupport_handle(
   const std::string & typesupport_identifier,
   rcpputils::SharedLibrary & library)
 {
-  internal::TypeSupport typesupport = internal::TypeSupport::UNKNOWN;
-  if constexpr (std::is_same_v<T, rosidl_message_type_support_t>) {
-    typesupport = internal::TypeSupport::MESSAGE;
-  } else if constexpr (std::is_same_v<T, rosidl_service_type_support_t>) {
-    typesupport = internal::TypeSupport::SERVICE;
-  } else if constexpr (std::is_same_v<T, rosidl_action_type_support_t>) {
-    typesupport = internal::TypeSupport::ACTION;
-  }
-
-  auto ret = internal::get_typesupport_symbol_name(type, typesupport_identifier, typesupport);
+  auto ret = internal::_get_typesupport_symbol_name(
+    type, typesupport_identifier, typename internal::typesupport_traits<T>::type_tag());
   try {
     const T * (* get_ts)() = nullptr;
     // This will throw runtime_error if the symbol was not found.

rclcpp/src/rclcpp/typesupport_helpers.cpp

@@ -96,44 +96,22 @@ extract_type_identifier(const std::string & full_type)
 namespace internal
 {
 
-SymbolNameErrorFuncPair get_typesupport_symbol_name(
+static SymbolNameErrorFuncPair _get_typesupport_symbol_name_impl(
   const std::string & type,
   const std::string & typesupport_identifier,
-  TypeSupport type_support)
+  const std::string & typesupport_name,
+  const std::string & symbol_part_name,
+  const std::string & middle_module_additional)
 {
   std::string package_name;
   std::string middle_module;
   std::string type_name;
   std::tie(package_name, middle_module, type_name) = extract_type_identifier(type);
 
-  std::string typesupport_name;
-  std::string symbol_part_name;
-  switch (type_support) {
-    case TypeSupport::MESSAGE:
-      typesupport_name = "message";
-      symbol_part_name = "__get_message_type_support_handle__";
-      if (middle_module.empty()) {
-        middle_module = "msg";
-      }
-      break;
-    case TypeSupport::SERVICE:
-      typesupport_name = "service";
-      symbol_part_name = "__get_service_type_support_handle__";
-      if (middle_module.empty()) {
-        middle_module = "srv";
-      }
-      break;
-    case TypeSupport::ACTION:
-      typesupport_name = "action";
-      symbol_part_name = "__get_action_type_support_handle__";
-      if (middle_module.empty()) {
-        middle_module = "action";
-      }
-      break;
-    default:
-      typesupport_name = "unknown";
-      break;
+  if (middle_module.empty()) {
+    middle_module = middle_module_additional;
   }
+
   auto mk_error = [&package_name, &type_name, &typesupport_name]() {
       std::stringstream rcutils_dynamic_loading_error;
       rcutils_dynamic_loading_error <<
@@ -149,6 +127,48 @@ SymbolNameErrorFuncPair get_typesupport_symbol_name(
   return {std::move(symbol_name), std::move(mk_error)};
 }
 
+SymbolNameErrorFuncPair _get_typesupport_symbol_name(
+  const std::string & type,
+  const std::string & typesupport_identifier,
+  typesupport_message_tag)
+{
+  std::string typesupport_name = "message";
+  std::string symbol_part_name = "__get_message_type_support_handle__";
+  std::string middle_module_additional = "msg";
+
+  return _get_typesupport_symbol_name_impl(
+    type, typesupport_identifier, typesupport_name, symbol_part_name, middle_module_additional
+  );
+}
+
+SymbolNameErrorFuncPair _get_typesupport_symbol_name(
+  const std::string & type,
+  const std::string & typesupport_identifier,
+  typesupport_service_tag)
+{
+  std::string typesupport_name = "service";
+  std::string symbol_part_name = "__get_service_type_support_handle__";
+  std::string middle_module_additional = "srv";
+
+  return _get_typesupport_symbol_name_impl(
+    type, typesupport_identifier, typesupport_name, symbol_part_name, middle_module_additional
+  );
+}
+
+SymbolNameErrorFuncPair _get_typesupport_symbol_name(
+  const std::string & type,
+  const std::string & typesupport_identifier,
+  typesupport_action_tag)
+{
+  std::string typesupport_name = "action";
+  std::string symbol_part_name = "__get_action_type_support_handle__";
+  std::string middle_module_additional = "action";
+
+  return _get_typesupport_symbol_name_impl(
+    type, typesupport_identifier, typesupport_name, symbol_part_name, middle_module_additional
+  );
+}
+
 }  // namespace internal
 
 std::shared_ptr<rcpputils::SharedLibrary>