* Necessarily evil preprocessor-related amenities.
*/
+// MSVC's preprocessor is a pain, so we have to
+// forcefully expand the VA args in some places.
+#define FB_VA_GLUE(a, b) a b
+
/**
* FB_ONE_OR_NONE(hello, world) expands to hello and
* FB_ONE_OR_NONE(hello) expands to nothing. This macro is used to
* insert or eliminate text based on the presence of another argument.
*/
-#ifdef _MSC_VER
-
-#define VA_NARGS_IMPL(_1, _2, _3, _4, _5, N, ...) N
-#define VA_NARGS(...) VA_NARGS_IMPL(X,##__VA_ARGS__, 4, 3, 2, 1, 0)
-#define VARARG_IMPL2(base, count, ...) base##count(__VA_ARGS__)
-#define VARARG_IMPL(base, count, ...) VARARG_IMPL2(base, count, __VA_ARGS__)
-#define VARARG(base, ...) VARARG_IMPL(base, VA_NARGS(__VA_ARGS__), __VA_ARGS__)
-
-#define FB_ONE_OR_NONE0() /* */
-#define FB_ONE_OR_NONE1(x) /* */
-#define FB_ONE_OR_NONE2(x, y) x
-#define FB_ONE_OR_NONE3(x, y, z) x
-#define FB_ONE_OR_NONE(...) VARARG(FB_ONE_OR_NONE, __VA_ARGS__)
-
-#else
-#define FB_ONE_OR_NONE(a, ...) FB_THIRD(a, ## __VA_ARGS__, a)
+#define FB_ONE_OR_NONE(a, ...) FB_VA_GLUE(FB_THIRD, (a, ## __VA_ARGS__, a))
#define FB_THIRD(a, b, ...) __VA_ARGS__
-#endif
/**
* Helper macro that extracts the first argument out of a list of any
* number of arguments. If only one argument is given, it returns
* that.
*/
+#ifdef _MSC_VER
+// GCC refuses to expand this correctly if this macro itself was
+// called with FB_VA_GLUE :(
+#define FB_ARG_2_OR_1(...) \
+ FB_VA_GLUE(FB_ARG_2_OR_1_IMPL, (__VA_ARGS__, __VA_ARGS__))
+#else
#define FB_ARG_2_OR_1(...) FB_ARG_2_OR_1_IMPL(__VA_ARGS__, __VA_ARGS__)
+#endif
// Support macro for the above
#define FB_ARG_2_OR_1_IMPL(a, b, ...) b
*/
#define FB_SINGLE_ARG(...) __VA_ARGS__
+/**
+ * Helper macro that just ignores its parameters.
+ */
+#define FOLLY_IGNORE(...)
+
+/**
+ * Helper macro that just ignores its parameters and inserts a semicolon.
+ */
+#define FOLLY_SEMICOLON(...) ;
+
/**
* FB_ANONYMOUS_VARIABLE(str) introduces an identifier starting with
* str and ending with a number that varies with the line.