Merge pull request #2973 from rstudio/feature/call-method-argument-count

automatically deduce number of arguments when registering methods
rstudio · Jun 11, 2018 · 770b2b5 · 770b2b5
2 parents a12c67c + 4f41823
commit 770b2b5
Showing 1 changed file with 23 additions and 8 deletions.
diff --git a/src/cpp/r/include/r/RRoutines.hpp b/src/cpp/r/include/r/RRoutines.hpp
@@ -24,18 +24,33 @@ namespace rstudio {
 namespace r {
 namespace routines {
 
+namespace internal {
+
+template <typename ReturnType, typename... ArgumentTypes>
+int n_arguments(ReturnType(ArgumentTypes...)) {
+    return sizeof...(ArgumentTypes);
+}
+
+} // end namespace internal
+
 void addCallMethod(const R_CallMethodDef method);
 void registerCallMethod(const char* name, DL_FUNC fun, int numArgs);
 void registerAll();
 
-#define RS_REGISTER_CALL_METHOD(__NAME__, __NUM_ARGS__)                        \
-   do                                                                          \
-   {                                                                           \
-      R_CallMethodDef callMethodDef;                                           \
-      callMethodDef.name = #__NAME__;                                          \
-      callMethodDef.fun = (DL_FUNC) __NAME__;                                  \
-      callMethodDef.numArgs = __NUM_ARGS__;                                    \
-      ::rstudio::r::routines::addCallMethod(callMethodDef);                    \
+// NOTE: This macro accepts multiple arguments but only uses the first one.
+// This is just for backwards compatibility, so that existing calls that
+// attempt to declare the number of arguments can continue to do so, while new
+// usages can omit it and still do the right thing. (This is done primarily to
+// avoid noisy diffs across the codebase where this macro is used)
+#define RS_REGISTER_CALL_METHOD(__NAME__, ...)                         \
+   do                                                                  \
+   {                                                                   \
+      int n = ::rstudio::r::routines::internal::n_arguments(__NAME__); \
+      R_CallMethodDef callMethodDef;                                   \
+      callMethodDef.name = #__NAME__;                                  \
+      callMethodDef.fun = (DL_FUNC) __NAME__;                          \
+      callMethodDef.numArgs = n;                                       \
+      ::rstudio::r::routines::addCallMethod(callMethodDef);            \
    } while (false)
 
 } // namespace routines