commit ae3086eac4c4e2b5420847db7d7130677546ffe3
author Ben Wagner <bungeman@google.com> Tue Dec 04 13:05:20 2018 -0500
committer Ben Wagner <bungeman@google.com> Tue Dec 04 19:38:18 2018 +0000
tree 3c214bd5585a9de698aafa0e65fe18ae0f07df68
parent 7103cca7e2bc6de0fbd765d633436cf66b316ee9

Make callable traits work with msvc.

The msvc preprocessor interprets empty parentheses as zero parameters
instead of as a single empty parameter. Work around this by making all
marcos which may take a single empty parameter also take a second
ignored parameter.

Change-Id: Iea8bd386b7ffe3c14eb048d81e18c42c8d2894d9
Reviewed-on: https://skia-review.googlesource.com/c/174306
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>

src/utils/SkCallableTraits.h

diff --git a/src/utils/SkCallableTraits.h b/src/utils/SkCallableTraits.h
index 9103bf2..7df0124 100644
--- a/src/utils/SkCallableTraits.h
+++ b/src/utils/SkCallableTraits.h
@@ -19,32 +19,31 @@
     };
 };
 
-#define SK_CALLABLE_TRAITS__EMPTY
 #define SK_CALLABLE_TRAITS__COMMA ,
 
-#define SK_CALLABLE_TRAITS__VARARGS(quals) \
-SK_CALLABLE_TRAITS__INSTANCE(quals, SK_CALLABLE_TRAITS__EMPTY) \
+#define SK_CALLABLE_TRAITS__VARARGS(quals, _) \
+SK_CALLABLE_TRAITS__INSTANCE(quals,) \
 SK_CALLABLE_TRAITS__INSTANCE(quals, SK_CALLABLE_TRAITS__COMMA ...)
 
 #ifdef __cpp_noexcept_function_type
-#define SK_CALLABLE_TRAITS__NE_VARARGS(quals) \
-SK_CALLABLE_TRAITS__VARARGS(quals) \
-SK_CALLABLE_TRAITS__VARARGS(quals noexcept)
+#define SK_CALLABLE_TRAITS__NE_VARARGS(quals, _) \
+SK_CALLABLE_TRAITS__VARARGS(quals,) \
+SK_CALLABLE_TRAITS__VARARGS(quals noexcept,)
 #else
-#define SK_CALLABLE_TRAITS__NE_VARARGS(quals) \
-SK_CALLABLE_TRAITS__VARARGS(quals)
+#define SK_CALLABLE_TRAITS__NE_VARARGS(quals, _) \
+SK_CALLABLE_TRAITS__VARARGS(quals,)
 #endif
 
-#define SK_CALLABLE_TRAITS__REF_NE_VARARGS(quals) \
-SK_CALLABLE_TRAITS__NE_VARARGS(quals) \
-SK_CALLABLE_TRAITS__NE_VARARGS(quals &) \
-SK_CALLABLE_TRAITS__NE_VARARGS(quals &&)
+#define SK_CALLABLE_TRAITS__REF_NE_VARARGS(quals, _) \
+SK_CALLABLE_TRAITS__NE_VARARGS(quals,) \
+SK_CALLABLE_TRAITS__NE_VARARGS(quals &,) \
+SK_CALLABLE_TRAITS__NE_VARARGS(quals &&,)
 
 #define SK_CALLABLE_TRAITS__CV_REF_NE_VARARGS() \
-SK_CALLABLE_TRAITS__REF_NE_VARARGS(SK_CALLABLE_TRAITS__EMPTY) \
-SK_CALLABLE_TRAITS__REF_NE_VARARGS(const) \
-SK_CALLABLE_TRAITS__REF_NE_VARARGS(volatile) \
-SK_CALLABLE_TRAITS__REF_NE_VARARGS(const volatile)
+SK_CALLABLE_TRAITS__REF_NE_VARARGS(,) \
+SK_CALLABLE_TRAITS__REF_NE_VARARGS(const,) \
+SK_CALLABLE_TRAITS__REF_NE_VARARGS(volatile,) \
+SK_CALLABLE_TRAITS__REF_NE_VARARGS(const volatile,)
 
 /** Infer the return_type and argument<N> of a callable type T. */
 template <typename T> struct SkCallableTraits : SkCallableTraits<decltype(&T::operator())> {};
@@ -62,7 +61,7 @@
 template <typename R, typename... Args> \
 struct SkCallableTraits<R(*)(Args... varargs) quals> : sk_base_callable_traits<R, Args...> {};
 
-SK_CALLABLE_TRAITS__NE_VARARGS()
+SK_CALLABLE_TRAITS__NE_VARARGS(,)
 #undef SK_CALLABLE_TRAITS__INSTANCE
 
 // pointer to method (..., (const, volatile), (&, &&), noexcept)
@@ -82,6 +81,5 @@
 #undef SK_CALLABLE_TRAITS__NE_VARARGS
 #undef SK_CALLABLE_TRAITS__VARARGS
 #undef SK_CALLABLE_TRAITS__COMMA
-#undef SK_CALLABLE_TRAITS__EMPTY
 
 #endif