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Map not int enum to correct underlying_type #1286

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Aug 31, 2019
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Map not int enum to correct underlying_type #1286

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471dfa4
Map not int enum to correct underlying_type
Aug 29, 2019
93d1d15
Use non-zero constant in TestFixedEnum
Aug 29, 2019
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4 changes: 2 additions & 2 deletions include/fmt/core.h
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Original file line number Diff line number Diff line change
Expand Up @@ -824,8 +824,8 @@ template <typename Context> struct arg_mapper {
FMT_ENABLE_IF(std::is_enum<T>::value &&
!has_formatter<T, Context>::value &&
!has_fallback_formatter<T, Context>::value)>
FMT_CONSTEXPR int map(const T& val) {
return static_cast<int>(val);
FMT_CONSTEXPR auto map(const T& val) -> decltype(map(static_cast<typename std::underlying_type<T>::type>(val))) {
return map(static_cast<typename std::underlying_type<T>::type>(val));
}
template <typename T,
FMT_ENABLE_IF(!is_string<T>::value && !is_char<T>::value &&
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4 changes: 2 additions & 2 deletions test/format-test.cc
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Expand Up @@ -1906,9 +1906,9 @@ TEST(FormatTest, FormatterNotSpecialized) {
}

#if FMT_HAS_FEATURE(cxx_strong_enums)
enum TestFixedEnum : short { B };
enum TestFixedEnum : short { B = 1 };
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Is it actually formatted differently if we don't map to underlying type?

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@agmt agmt Sep 4, 2019 •
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I don't understand the problem clearly but if map() returns short (which doesn't enumerated in enum type)

FMT_ENABLE_IF(std::is_enum<T>::value &&
                          !has_formatter<T, Context>::value &&
                          !has_fallback_formatter<T, Context>::value)>
  FMT_CONSTEXPR typename std::underlying_type<T>::type map(const T& val) {
    return static_cast<typename std::underlying_type<T>::type>(val);
  }

then after that will be called map(short) with correct argument and map(int) with garbage ( =0 almost always). It means that fmt::format(short_enum_value) will return "0" regardless of the argument.


TEST(FormatTest, FixedEnum) { EXPECT_EQ("0", fmt::format("{}", B)); }
TEST(FormatTest, FixedEnum) { EXPECT_EQ("1", fmt::format("{}", B)); }
#endif

using buffer_range = fmt::buffer_range<char>;
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