FMT_VARIADIC_CONST - Support for const variadic methods (#591)

FMT_VARIADIC_CONST - Support for const variadic methods

fmt/format.h

@@ -3634,10 +3634,10 @@ void arg(WStringRef, const internal::NamedArg<Char>&) FMT_DELETED_OR_UNDEFINED;
 #define FMT_GET_ARG_NAME(type, index) arg##index
 
 #if FMT_USE_VARIADIC_TEMPLATES
-# define FMT_VARIADIC_(Char, ReturnType, func, call, ...) \
+# define FMT_VARIADIC_(Const, Char, ReturnType, func, call, ...) \
   template <typename... Args> \
   ReturnType func(FMT_FOR_EACH(FMT_ADD_ARG_NAME, __VA_ARGS__), \
-      const Args & ... args) { \
+      const Args & ... args) Const { \
     typedef fmt::internal::ArgArray<sizeof...(Args)> ArgArray; \
     typename ArgArray::Type array{ \
       ArgArray::template make<fmt::BasicFormatter<Char> >(args)...}; \
@@ -3647,35 +3647,35 @@ void arg(WStringRef, const internal::NamedArg<Char>&) FMT_DELETED_OR_UNDEFINED;
 #else
 // Defines a wrapper for a function taking __VA_ARGS__ arguments
 // and n additional arguments of arbitrary types.
-# define FMT_WRAP(Char, ReturnType, func, call, n, ...) \
+# define FMT_WRAP(Const, Char, ReturnType, func, call, n, ...) \
   template <FMT_GEN(n, FMT_MAKE_TEMPLATE_ARG)> \
   inline ReturnType func(FMT_FOR_EACH(FMT_ADD_ARG_NAME, __VA_ARGS__), \
-      FMT_GEN(n, FMT_MAKE_ARG)) { \
+      FMT_GEN(n, FMT_MAKE_ARG)) Const { \
     fmt::internal::ArgArray<n>::Type arr; \
     FMT_GEN(n, FMT_ASSIGN_##Char); \
     call(FMT_FOR_EACH(FMT_GET_ARG_NAME, __VA_ARGS__), fmt::ArgList( \
       fmt::internal::make_type(FMT_GEN(n, FMT_MAKE_REF2)), arr)); \
   }
 
-# define FMT_VARIADIC_(Char, ReturnType, func, call, ...) \
-  inline ReturnType func(FMT_FOR_EACH(FMT_ADD_ARG_NAME, __VA_ARGS__)) { \
+# define FMT_VARIADIC_(Const, Char, ReturnType, func, call, ...) \
+  inline ReturnType func(FMT_FOR_EACH(FMT_ADD_ARG_NAME, __VA_ARGS__)) Const { \
     call(FMT_FOR_EACH(FMT_GET_ARG_NAME, __VA_ARGS__), fmt::ArgList()); \
   } \
-  FMT_WRAP(Char, ReturnType, func, call, 1, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 2, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 3, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 4, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 5, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 6, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 7, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 8, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 9, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 10, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 11, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 12, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 13, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 14, __VA_ARGS__) \
-  FMT_WRAP(Char, ReturnType, func, call, 15, __VA_ARGS__)
+  FMT_WRAP(Const, Char, ReturnType, func, call, 1, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 2, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 3, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 4, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 5, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 6, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 7, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 8, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 9, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 10, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 11, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 12, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 13, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 14, __VA_ARGS__) \
+  FMT_WRAP(Const, Char, ReturnType, func, call, 15, __VA_ARGS__)
 #endif  // FMT_USE_VARIADIC_TEMPLATES
 
 /**
@@ -3706,10 +3706,16 @@ void arg(WStringRef, const internal::NamedArg<Char>&) FMT_DELETED_OR_UNDEFINED;
   \endrst
  */
 #define FMT_VARIADIC(ReturnType, func, ...) \
-  FMT_VARIADIC_(char, ReturnType, func, return func, __VA_ARGS__)
+  FMT_VARIADIC_(, char, ReturnType, func, return func, __VA_ARGS__)
+
+#define FMT_VARIADIC_CONST(ReturnType, func, ...) \
+  FMT_VARIADIC_(const, char, ReturnType, func, return func, __VA_ARGS__)
 
 #define FMT_VARIADIC_W(ReturnType, func, ...) \
-  FMT_VARIADIC_(wchar_t, ReturnType, func, return func, __VA_ARGS__)
+  FMT_VARIADIC_(, wchar_t, ReturnType, func, return func, __VA_ARGS__)
+
+#define FMT_VARIADIC_CONST_W(ReturnType, func, ...) \
+  FMT_VARIADIC_(const, wchar_t, ReturnType, func, return func, __VA_ARGS__)
 
 #define FMT_CAPTURE_ARG_(id, index) ::fmt::arg(#id, id)
 

test/format-test.cc

@@ -1630,6 +1630,24 @@ TEST(FormatTest, FormatMessageExample) {
       format_message(42, "{} happened", "something"));
 }
 
+class test_class
+{
+public:
+  std::string format_message(int id, const char *format,const fmt::ArgList &args) const {
+    MemoryWriter w;
+    w.write("[{}] ", id);
+    w.write(format, args);
+    return w.str();
+  }
+  FMT_VARIADIC_CONST(std::string, format_message, int, const char *)
+};
+
+TEST(FormatTest, ConstFormatMessage) {
+  test_class c;
+  EXPECT_EQ("[42] something happened",
+    c.format_message(42, "{} happened", "something"));
+}
+
 #if FMT_USE_VARIADIC_TEMPLATES
 template<typename... Args>
 void print_error(const char *file, int line, const char *format,