Demacrify

include/fmt/core.h

@@ -187,25 +187,34 @@
 #  define FMT_ASSERT(condition, message) assert((condition) && message)
 #endif
 
+// An enable_if helper to be used in template parameters. enable_if in template
+// parameters results in much shorter symbols: https://godbolt.org/z/sWw4vP.
+#define FMT_ENABLE_IF_T(...) typename std::enable_if<(__VA_ARGS__), int>::type
+#define FMT_ENABLE_IF(...) FMT_ENABLE_IF_T(__VA_ARGS__) = 0
+
 // libc++ supports string_view in pre-c++17.
 #if (FMT_HAS_INCLUDE(<string_view>) &&                       \
      (__cplusplus > 201402L || defined(_LIBCPP_VERSION))) || \
     (defined(_MSVC_LANG) && _MSVC_LANG > 201402L && _MSC_VER >= 1910)
 #  include <string_view>
-#  define FMT_STRING_VIEW std::basic_string_view
+#  define FMT_USE_STRING_VIEW
 #elif FMT_HAS_INCLUDE("experimental/string_view") && __cplusplus >= 201402L
 #  include <experimental/string_view>
-#  define FMT_STRING_VIEW std::experimental::basic_string_view
+#  define FMT_USE_EXPERIMENTAL_STRING_VIEW
 #endif
 
-// An enable_if helper to be used in template parameters. enable_if in template
-// parameters results in much shorter symbols: https://godbolt.org/z/sWw4vP.
-#define FMT_ENABLE_IF_T(...) typename std::enable_if<(__VA_ARGS__), int>::type
-#define FMT_ENABLE_IF(...) FMT_ENABLE_IF_T(__VA_ARGS__) = 0
-
 FMT_BEGIN_NAMESPACE
 namespace internal {
 
+#if defined(FMT_USE_STRING_VIEW)
+template <typename Char> using std_string_view = std::basic_string_view<Char>;
+#elif defined(FMT_USE_EXPERIMENTAL_STRING_VIEW)
+template <typename Char>
+using std_string_view = std::experimental::basic_string_view<Char>;
+#else
+template <typename T> struct std_string_view {};
+#endif
+
 template <typename> struct result_of;
 
 #if (__cplusplus >= 201703L ||                          \
@@ -396,11 +405,11 @@ template <typename Char> class basic_string_view {
       FMT_NOEXCEPT : data_(s.data()),
                      size_(s.size()) {}
 
-#ifdef FMT_STRING_VIEW
-  FMT_CONSTEXPR basic_string_view(FMT_STRING_VIEW<Char> s) FMT_NOEXCEPT
-      : data_(s.data()),
-        size_(s.size()) {}
-#endif
+  template <
+      typename S,
+      FMT_ENABLE_IF(std::is_same<S, internal::std_string_view<Char>>::value)>
+  FMT_CONSTEXPR basic_string_view(S s) FMT_NOEXCEPT : data_(s.data()),
+                                                      size_(s.size()) {}
 
   /** Returns a pointer to the string data. */
   FMT_CONSTEXPR const Char* data() const { return data_; }
@@ -486,12 +495,12 @@ inline basic_string_view<Char> to_string_view(const Char* s) {
   return s;
 }
 
-#ifdef FMT_STRING_VIEW
-template <typename Char>
-inline basic_string_view<Char> to_string_view(FMT_STRING_VIEW<Char> s) {
+template <typename Char,
+          FMT_ENABLE_IF(!std::is_empty<internal::std_string_view<Char>>::value)>
+inline basic_string_view<Char> to_string_view(
+    internal::std_string_view<Char> s) {
   return s;
 }
-#endif
 
 // A base class for compile-time strings. It is defined in the fmt namespace to
 // make formatting functions visible via ADL, e.g. format(fmt("{}"), 42).

test/core-test.cc

@@ -475,9 +475,7 @@ class QString {
   QString(const wchar_t* s) : s_(std::make_shared<std::wstring>(s)) {}
   const wchar_t* utf16() const FMT_NOEXCEPT { return s_->data(); }
   int size() const FMT_NOEXCEPT { return static_cast<int>(s_->size()); }
-#ifdef FMT_STRING_VIEW
-  operator FMT_STRING_VIEW<wchar_t>() const FMT_NOEXCEPT { return *s_; }
-#endif
+
  private:
   std::shared_ptr<std::wstring> s_;
 };
@@ -499,21 +497,21 @@ struct derived_from_string_view : fmt::basic_string_view<Char> {};
 }  // namespace
 
 TYPED_TEST(IsStringTest, IsString) {
-  EXPECT_TRUE((fmt::internal::is_string<TypeParam*>::value));
-  EXPECT_TRUE((fmt::internal::is_string<const TypeParam*>::value));
-  EXPECT_TRUE((fmt::internal::is_string<TypeParam[2]>::value));
-  EXPECT_TRUE((fmt::internal::is_string<const TypeParam[2]>::value));
-  EXPECT_TRUE((fmt::internal::is_string<std::basic_string<TypeParam>>::value));
+  EXPECT_TRUE(fmt::internal::is_string<TypeParam*>::value);
+  EXPECT_TRUE(fmt::internal::is_string<const TypeParam*>::value);
+  EXPECT_TRUE(fmt::internal::is_string<TypeParam[2]>::value);
+  EXPECT_TRUE(fmt::internal::is_string<const TypeParam[2]>::value);
+  EXPECT_TRUE(fmt::internal::is_string<std::basic_string<TypeParam>>::value);
   EXPECT_TRUE(
-      (fmt::internal::is_string<fmt::basic_string_view<TypeParam>>::value));
+      fmt::internal::is_string<fmt::basic_string_view<TypeParam>>::value);
   EXPECT_TRUE(
-      (fmt::internal::is_string<derived_from_string_view<TypeParam>>::value));
-#ifdef FMT_STRING_VIEW
-  EXPECT_TRUE((fmt::internal::is_string<FMT_STRING_VIEW<TypeParam>>::value));
-#endif
-  EXPECT_TRUE((fmt::internal::is_string<my_ns::my_string<TypeParam>>::value));
-  EXPECT_FALSE((fmt::internal::is_string<my_ns::non_string>::value));
-  EXPECT_TRUE((fmt::internal::is_string<FakeQt::QString>::value));
+      fmt::internal::is_string<derived_from_string_view<TypeParam>>::value);
+  using string_view = fmt::internal::std_string_view<TypeParam>;
+  EXPECT_TRUE(std::is_empty<string_view>::value !=
+              fmt::internal::is_string<string_view>::value);
+  EXPECT_TRUE(fmt::internal::is_string<my_ns::my_string<TypeParam>>::value);
+  EXPECT_FALSE(fmt::internal::is_string<my_ns::non_string>::value);
+  EXPECT_TRUE(fmt::internal::is_string<FakeQt::QString>::value);
 }
 
 TEST(CoreTest, Format) {