Merge pull request #122 from ros2/expression-sfinae-windows

Work around VS2015's broken support for expression SFINAE

rclcpp/CMakeLists.txt

@@ -22,6 +22,7 @@ if(AMENT_ENABLE_TESTING)
 
   include_directories(include)
 
+  ament_add_gtest(test_function_traits test/test_function_traits.cpp)
   ament_add_gtest(test_mapped_ring_buffer test/test_mapped_ring_buffer.cpp)
   ament_add_gtest(test_intra_process_manager test/test_intra_process_manager.cpp)
   if(TARGET test_intra_process_manager)

rclcpp/include/rclcpp/any_subscription_callback.hpp

@@ -57,75 +57,83 @@ struct AnySubscriptionCallback
 
   AnySubscriptionCallback(const AnySubscriptionCallback &) = default;
 
-  template<typename CallbackT,
-  typename std::enable_if<
-    function_traits<CallbackT>::arity == 1
-  >::type * = nullptr,
-  typename std::enable_if<
-    std::is_same<
-      typename function_traits<CallbackT>::template argument_type<0>,
-      typename std::shared_ptr<MessageT>
-    >::value
-  >::type * = nullptr
+  template<
+    typename CallbackT,
+    std::size_t Arity = 1
   >
-  void set(CallbackT callback)
+  typename std::enable_if<rclcpp::arity_comparator<Arity, CallbackT>::value, void>::type
+  set(
+    CallbackT callback,
+    typename std::enable_if<
+      std::is_same<
+        typename function_traits<CallbackT>::template argument_type<0>,
+        typename std::shared_ptr<MessageT>
+      >::value
+    >::type * = nullptr)
   {
     shared_ptr_callback = callback;
   }
 
-  template<typename CallbackT,
-  typename std::enable_if<
-    function_traits<CallbackT>::arity == 2
-  >::type * = nullptr,
-  typename std::enable_if<
-    std::is_same<
-      typename function_traits<CallbackT>::template argument_type<0>,
-      typename std::shared_ptr<MessageT>
-    >::value
-  >::type * = nullptr
+  template<
+    typename CallbackT,
+    std::size_t Arity = 2
   >
-  void set(CallbackT callback)
-  {
-    static_assert(std::is_same<
+  typename std::enable_if<rclcpp::arity_comparator<Arity, CallbackT>::value, void>::type
+  set(
+    CallbackT callback,
+    typename std::enable_if<
+      std::is_same<
+        typename function_traits<CallbackT>::template argument_type<0>,
+        typename std::shared_ptr<MessageT>
+      >::value
+    >::type * = nullptr,
+    typename std::enable_if<
+      std::is_same<
         typename function_traits<CallbackT>::template argument_type<1>,
-        const rmw_message_info_t &>::value,
-      "Passed incorrect argument type to callback, should be rmw_message_info_t");
+        const rmw_message_info_t &
+      >::value
+    >::type * = nullptr)
+  {
     shared_ptr_with_info_callback = callback;
   }
 
-  template<typename CallbackT,
-  typename std::enable_if<
-    function_traits<CallbackT>::arity == 1
-  >::type * = nullptr,
-  typename std::enable_if<
-    std::is_same<
-      typename function_traits<CallbackT>::template argument_type<0>,
-      typename std::shared_ptr<const MessageT>
-    >::value
-  >::type * = nullptr
+  template<
+    typename CallbackT,
+    std::size_t Arity = 1
   >
-  void set(CallbackT callback)
+  typename std::enable_if<rclcpp::arity_comparator<Arity, CallbackT>::value, void>::type
+  set(
+    CallbackT callback,
+    typename std::enable_if<
+      std::is_same<
+        typename function_traits<CallbackT>::template argument_type<0>,
+        typename std::shared_ptr<const MessageT>
+      >::value
+    >::type * = nullptr)
   {
     const_shared_ptr_callback = callback;
   }
 
-  template<typename CallbackT,
-  typename std::enable_if<
-    function_traits<CallbackT>::arity == 2
-  >::type * = nullptr,
-  typename std::enable_if<
-    std::is_same<
-      typename function_traits<CallbackT>::template argument_type<0>,
-      typename std::shared_ptr<const MessageT>
-    >::value
-  >::type * = nullptr
+  template<
+    typename CallbackT,
+    std::size_t Arity = 2
   >
-  void set(CallbackT callback)
-  {
-    static_assert(std::is_same<
+  typename std::enable_if<rclcpp::arity_comparator<Arity, CallbackT>::value, void>::type
+  set(
+    CallbackT callback,
+    typename std::enable_if<
+      std::is_same<
+        typename function_traits<CallbackT>::template argument_type<0>,
+        typename std::shared_ptr<const MessageT>
+      >::value
+    >::type * = nullptr,
+    typename std::enable_if<
+      std::is_same<
         typename function_traits<CallbackT>::template argument_type<1>,
-        const rmw_message_info_t &>::value,
-      "Passed incorrect argument type to callback, should be rmw_message_info_t");
+        const rmw_message_info_t &
+      >::value
+    >::type * = nullptr)
+  {
     const_shared_ptr_with_info_callback = callback;
   }
 /*

rclcpp/include/rclcpp/function_traits.hpp

@@ -25,6 +25,7 @@ namespace rclcpp
  * but unfortunately std::function's constructor on VS2015 is too greedy,
  * so we need a mechanism for checking the arity and the type of each argument
  * in a callback function.
+ * See http://blogs.msdn.com/b/vcblog/archive/2015/06/19/c-11-14-17-features-in-vs-2015-rtm.aspx
  */
 
 
@@ -58,6 +59,16 @@ struct function_traits<ReturnTypeT (ClassT::*)(Args ...) const>
   : public function_traits<ReturnTypeT(ClassT &, Args ...)>
 {};
 
+/* NOTE(esteve):
+ * VS2015 does not support expression SFINAE, so we're using this template to evaluate
+ * the arity of a function.
+ */
+template<std::size_t Arity, typename FunctorT>
+struct arity_comparator
+{
+  static constexpr bool value = (Arity == function_traits<FunctorT>::arity);
+};
+
 } /* namespace rclcpp */
 
 #endif /* RCLCPP_RCLCPP_FUNCTION_TRAITS_HPP_ */

rclcpp/include/rclcpp/node.hpp

@@ -247,12 +247,30 @@ class Node
     bool ignore_local_publications,
     typename message_memory_strategy::MessageMemoryStrategy<MessageT>::SharedPtr msg_mem_strat);
 
+/* NOTE(esteve):
+ * The following template machinery works around VS2015's lack of support for expression SFINAE:
+ * - We first declare the arity we want to match, i.e. 2 or 3.
+ * - Then we use the arity_comparator template to SFINAE on the arity of the passed functor.
+ * - Lastly, we SFINAE on the types of the arguments of the functor.
+ * These steps happen in different parts of the function signature because we want to stagger
+ * instantation of the templates because VS2015 can't conditionally enable templates that depend
+ * on another template.
+ * See test_function_traits.cpp for streamlined examples of how to use this pattern.
+ */
   template<
     typename ServiceT,
     typename FunctorT,
-    typename std::enable_if<
-      function_traits<FunctorT>::arity == 2
-    >::type * = nullptr,
+    std::size_t Arity = 2
+  >
+  typename std::enable_if<
+    rclcpp::arity_comparator<Arity, FunctorT>::value,
+    typename rclcpp::service::Service<ServiceT>::SharedPtr
+  >::type
+  create_service_internal(
+    std::shared_ptr<rmw_node_t> node_handle,
+    rmw_service_t * service_handle,
+    const std::string & service_name,
+    FunctorT callback,
     typename std::enable_if<
       std::is_same<
         typename function_traits<FunctorT>::template argument_type<0>,
@@ -264,14 +282,7 @@ class Node
         typename function_traits<FunctorT>::template argument_type<1>,
         typename std::shared_ptr<typename ServiceT::Response>
       >::value
-    >::type * = nullptr
-  >
-  typename rclcpp::service::Service<ServiceT>::SharedPtr
-  create_service_internal(
-    std::shared_ptr<rmw_node_t> node_handle,
-    rmw_service_t * service_handle,
-    const std::string & service_name,
-    FunctorT callback)
+    >::type * = nullptr)
   {
     typename rclcpp::service::Service<ServiceT>::CallbackType callback_without_header =
       callback;
@@ -282,9 +293,17 @@ class Node
   template<
     typename ServiceT,
     typename FunctorT,
-    typename std::enable_if<
-      function_traits<FunctorT>::arity == 3
-    >::type * = nullptr,
+    std::size_t Arity = 3
+  >
+  typename std::enable_if<
+    arity_comparator<Arity, FunctorT>::value,
+    typename rclcpp::service::Service<ServiceT>::SharedPtr
+  >::type
+  create_service_internal(
+    std::shared_ptr<rmw_node_t> node_handle,
+    rmw_service_t * service_handle,
+    const std::string & service_name,
+    FunctorT callback,
     typename std::enable_if<
       std::is_same<
         typename function_traits<FunctorT>::template argument_type<0>,
@@ -296,35 +315,14 @@ class Node
         typename function_traits<FunctorT>::template argument_type<1>,
         typename std::shared_ptr<typename ServiceT::Request>
       >::value
-    >::type * = nullptr
-/*
-   TODO(esteve): reenable this block of code when VS2015 gets better support
-   for SFINAE and remove the static_assert from the body of this method. For
-   more info about the current support for SFINAE in VS2015 RC:
-
-   http://blogs.msdn.com/b/vcblog/archive/2015/04/29/c-11-14-17-features-in-vs-2015-rc.aspx
-   ,
+    >::type * = nullptr,
     typename std::enable_if<
       std::is_same<
         typename function_traits<FunctorT>::template argument_type<2>,
         typename std::shared_ptr<typename ServiceT::Response>
       >::value
-    >::type * = nullptr
- */
-  >
-  typename rclcpp::service::Service<ServiceT>::SharedPtr
-  create_service_internal(
-    std::shared_ptr<rmw_node_t> node_handle,
-    rmw_service_t * service_handle,
-    const std::string & service_name,
-    FunctorT callback)
+    >::type * = nullptr)
   {
-    static_assert(
-      std::is_same<
-        typename function_traits<FunctorT>::template argument_type<2>,
-        typename std::shared_ptr<typename ServiceT::Response>
-      >::value, "Third argument must be of type std::shared_ptr<ServiceT::Response>");
-
     typename rclcpp::service::Service<ServiceT>::CallbackWithHeaderType callback_with_header =
       callback;
     return service::Service<ServiceT>::make_shared(