try to fix / work around msvc PP issue

See also swansontec/map-macro issue: swansontec/map-macro#4
cbeck88 · Aug 29, 2016 · a1b4bb9 · a1b4bb9
1 parent cb39d83
commit a1b4bb9
Showing 1 changed file with 29 additions and 3 deletions.
diff --git a/include/visit_struct/visit_struct.hpp b/include/visit_struct/visit_struct.hpp
@@ -63,15 +63,33 @@ VISIT_STRUCT_CONSTEXPR auto apply_visitor(V && v, S && s) ->
  * Takes the name of a macro as first parameter, and then at most 365 additional arguments.
  * Evaluates to produce an invocation of the given macro on each of the arguments.
  * The arguments must be simple identifiers, they cannot contain commas or parentheses.
+ *
+ * Note: We also incorporate an MSVC workaround described here:
+ * http://stackoverflow.com/questions/21869917/visual-studio-va-args-issue
  */
 
+#define VISIT_STRUCT_INDIRECT_EXPAND(m, args) m args
+
+#ifdef _MSC_VER
+
+#define VISIT_STRUCT_PP_MAP_EVAL0(...) __VA_ARGS__
+#define VISIT_STRUCT_PP_MAP_EVAL1(...) VISIT_STRUCT_PP_MAP_EVAL0(VISIT_STRUCT_PP_MAP_EVAL0(VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP_EVAL0, (__VA_ARGS__))))
+#define VISIT_STRUCT_PP_MAP_EVAL2(...) VISIT_STRUCT_PP_MAP_EVAL1(VISIT_STRUCT_PP_MAP_EVAL1(VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP_EVAL1, (__VA_ARGS__))))
+#define VISIT_STRUCT_PP_MAP_EVAL3(...) VISIT_STRUCT_PP_MAP_EVAL2(VISIT_STRUCT_PP_MAP_EVAL2(VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP_EVAL2, (__VA_ARGS__))))
+#define VISIT_STRUCT_PP_MAP_EVAL4(...) VISIT_STRUCT_PP_MAP_EVAL3(VISIT_STRUCT_PP_MAP_EVAL3(VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP_EVAL3, (__VA_ARGS__))))
+#define VISIT_STRUCT_PP_MAP_EVAL(...) VISIT_STRUCT_PP_MAP_EVAL4(VISIT_STRUCT_PP_MAP_EVAL4(VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP_EVAL4, (__VA_ARGS__))))
+
+#else
+
 #define VISIT_STRUCT_PP_MAP_EVAL0(...) __VA_ARGS__
 #define VISIT_STRUCT_PP_MAP_EVAL1(...) VISIT_STRUCT_PP_MAP_EVAL0(VISIT_STRUCT_PP_MAP_EVAL0(VISIT_STRUCT_PP_MAP_EVAL0(__VA_ARGS__)))
 #define VISIT_STRUCT_PP_MAP_EVAL2(...) VISIT_STRUCT_PP_MAP_EVAL1(VISIT_STRUCT_PP_MAP_EVAL1(VISIT_STRUCT_PP_MAP_EVAL1(__VA_ARGS__)))
 #define VISIT_STRUCT_PP_MAP_EVAL3(...) VISIT_STRUCT_PP_MAP_EVAL2(VISIT_STRUCT_PP_MAP_EVAL2(VISIT_STRUCT_PP_MAP_EVAL2(__VA_ARGS__)))
 #define VISIT_STRUCT_PP_MAP_EVAL4(...) VISIT_STRUCT_PP_MAP_EVAL3(VISIT_STRUCT_PP_MAP_EVAL3(VISIT_STRUCT_PP_MAP_EVAL3(__VA_ARGS__)))
 #define VISIT_STRUCT_PP_MAP_EVAL(...) VISIT_STRUCT_PP_MAP_EVAL4(VISIT_STRUCT_PP_MAP_EVAL4(VISIT_STRUCT_PP_MAP_EVAL4(__VA_ARGS__)))
 
+#endif
+
 #define VISIT_STRUCT_PP_MAP_END(...)
 #define VISIT_STRUCT_PP_MAP_OUT
 
@@ -84,6 +102,14 @@ VISIT_STRUCT_CONSTEXPR auto apply_visitor(V && v, S && s) ->
 #define VISIT_STRUCT_PP_MAP1(f, x, peek, ...) f(x) VISIT_STRUCT_PP_MAP_NEXT(peek, VISIT_STRUCT_PP_MAP0)(f, peek, __VA_ARGS__)
 #define VISIT_STRUCT_PP_MAP(f, ...) VISIT_STRUCT_PP_MAP_EVAL(VISIT_STRUCT_PP_MAP1(f, __VA_ARGS__, (), 0))
 
+/***
+ * Test of pp mechanism
+ */
+
+#define VISIT_STRUCT_TEST_PLUS(X) +X
+
+static_assert(6 == VISIT_STRUCT_PP_MAP(VISIT_STRUCT_TEST_PLUS, 1, 2, 3), "Failed a unit test");
+
 /***
  * VISIT_STRUCT implementation details: 
  */
@@ -106,19 +132,19 @@ struct visitable<STRUCT_NAME, void> {
   template <typename V>                                                                            \
   VISIT_STRUCT_CONSTEXPR static void apply(V && visitor, STRUCT_NAME & struct_instance)            \
   {                                                                                                \
-    VISIT_STRUCT_PP_MAP(VISIT_STRUCT_MEMBER_HELPER, __VA_ARGS__)                                   \
+    VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP, (VISIT_STRUCT_MEMBER_HELPER, __VA_ARGS__))   \
   }                                                                                                \
                                                                                                    \
   template <typename V>                                                                            \
   VISIT_STRUCT_CONSTEXPR static void apply(V && visitor, const STRUCT_NAME & struct_instance)      \
   {                                                                                                \
-    VISIT_STRUCT_PP_MAP(VISIT_STRUCT_MEMBER_HELPER, __VA_ARGS__)                                   \
+    VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP, (VISIT_STRUCT_MEMBER_HELPER, __VA_ARGS__))   \
   }                                                                                                \
                                                                                                    \
   template <typename V>                                                                            \
   VISIT_STRUCT_CONSTEXPR static void apply(V && visitor, STRUCT_NAME && struct_instance)           \
   {                                                                                                \
-    VISIT_STRUCT_PP_MAP(VISIT_STRUCT_MEMBER_HELPER_MOVE, __VA_ARGS__)                              \
+    VISIT_STRUCT_INDIRECT_EXPAND(VISIT_STRUCT_PP_MAP, (VISIT_STRUCT_MEMBER_HELPER_MOVE, __VA_ARGS__)) \
   }                                                                                                \
                                                                                                    \
   static constexpr bool value = true;                                                              \