Make data_type and name traits constexpr (#929)

* make constexpr

Signed-off-by: Michael Carlstrom <rmc@carlstrom.com>

* lint

Signed-off-by: Michael Carlstrom <rmc@carlstrom.com>

---------

Signed-off-by: Michael Carlstrom <rmc@carlstrom.com>

Author: InvincibleRMC

rosidl_generator_cpp/resource/action__traits.hpp.em

@@ -59,13 +59,13 @@ namespace rosidl_generator_traits
 {
 
 template<>
-inline const char * data_type<@(action_typename)>()
+constexpr const char * data_type<@(action_typename)>()
 {
   return "@(action_typename)";
 }
 
 template<>
-inline const char * name<@(action_typename)>()
+constexpr const char * name<@(action_typename)>()
 {
   return "@(action_fully_qualified_name)";
 }

rosidl_generator_cpp/resource/msg__traits.hpp.em

@@ -223,13 +223,13 @@ namespace rosidl_generator_traits
 {
 
 template<>
-inline const char * data_type<@(message_typename)>()
+constexpr const char * data_type<@(message_typename)>()
 {
   return "@(message_typename)";
 }
 
 template<>
-inline const char * name<@(message_typename)>()
+constexpr const char * name<@(message_typename)>()
 {
   return "@(message_fully_qualified_name)";
 }

rosidl_generator_cpp/resource/srv__traits.hpp.em

@@ -29,13 +29,13 @@ namespace rosidl_generator_traits
 {
 
 template<>
-inline const char * data_type<@(service_typename)>()
+constexpr const char * data_type<@(service_typename)>()
 {
   return "@(service_typename)";
 }
 
 template<>
-inline const char * name<@(service_typename)>()
+constexpr const char * name<@(service_typename)>()
 {
   return "@(service_fully_qualified_name)";
 }

rosidl_generator_tests/test/rosidl_generator_cpp/test_traits.cpp

@@ -26,6 +26,8 @@
 #include "rosidl_generator_tests/msg/w_strings.hpp"
 #include "rosidl_generator_tests/srv/empty.hpp"
 
+using rosidl_generator_traits::name;
+using rosidl_generator_traits::data_type;
 using rosidl_generator_traits::is_message;
 using rosidl_generator_traits::is_service;
 using rosidl_generator_traits::is_service_request;
@@ -431,3 +433,17 @@ TEST(Test_rosidl_generator_traits, is_service) {
   EXPECT_FALSE(is_service_request<ServiceEvent>());
   EXPECT_FALSE(is_service_response<ServiceEvent>());
 }
+
+constexpr bool streq(const char * a, const char * b)
+{
+  while (*a && (*a == *b)) {
+    ++a;
+    ++b;
+  }
+  return *a == *b;
+}
+
+static_assert(streq(name<rosidl_generator_tests::srv::Empty>(),
+"rosidl_generator_tests/srv/Empty"));
+static_assert(streq(data_type<rosidl_generator_tests::srv::Empty>(),
+"rosidl_generator_tests::srv::Empty"));

rosidl_runtime_cpp/include/rosidl_runtime_cpp/traits.hpp

@@ -151,10 +151,10 @@ inline void value_to_yaml(const std::u16string & value, std::ostream & out)
 }
 
 template<typename T>
-inline const char * data_type();
+constexpr const char * data_type();
 
 template<typename T>
-inline const char * name();
+constexpr const char * name();
 
 template<typename T>
 struct has_fixed_size : std::false_type {};