Workaround for libc++ incompatibility with C++ standard

Signed-off-by: Vladislav Shchapov <[email protected]>
fmtlib · Aug 5, 2023 · c456d05 · c456d05
1 parent bdbbee2
commit c456d05
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diff --git a/include/fmt/std.h b/include/fmt/std.h
@@ -421,6 +421,22 @@ struct formatter<BitRef, Char,
   }
 };
 
+#ifdef _LIBCPP_VERSION
+
+// Workaround for libc++ incompatibility with C++ standard.
+// According to the Standard, `bitset::operator[] const` returns bool.
+FMT_EXPORT
+template <typename C, typename Char>
+struct formatter<std::__bit_const_reference<C>, Char> : formatter<bool, Char> {
+  template <typename FormatContext>
+  FMT_CONSTEXPR20 auto format(const std::__bit_const_reference<C>& v,
+                              FormatContext& ctx) const -> decltype(ctx.out()) {
+    return formatter<bool, Char>::format(static_cast<bool>(v), ctx);
+  }
+};
+
+#endif
+
 FMT_END_NAMESPACE
 
 #endif  // FMT_STD_H_
diff --git a/test/std-test.cc b/test/std-test.cc
@@ -229,3 +229,10 @@ TEST(std_test, format_bit_reference) {
   std::vector<bool> v = {true, false};
   EXPECT_EQ(fmt::format("{} {}", v[0], v[1]), "true false");
 }
+
+TEST(std_test, format_const_bit_reference) {
+  const std::bitset<2> bs(1);
+  EXPECT_EQ(fmt::format("{} {}", bs[0], bs[1]), "true false");
+  const std::vector<bool> v = {true, false};
+  EXPECT_EQ(fmt::format("{} {}", v[0], v[1]), "true false");
+}