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Avoid MSVC 2015's C4800 for enums with underlying type bool

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MSVC 2015 warns about any conversion to bool (C4800), even with an
explicit cast, so the enum conversions from #5754 (#5671) failed the
AppVeyor build with /WX. Convert to bool by comparing with zero via the
new detail::bool_aware_static_cast, and keep doctest from printing the
enum in the test.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-10-05 13:29:32 +02:00
parent 413dd2d2c9
commit 556027f109
5 changed files with 38 additions and 6 deletions
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include/nlohmann/detail/conversions/from_json.hpp
+1 -1
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@@ -172,7 +172,7 @@ inline void from_json(const BasicJsonType& j, EnumType& e)
typename BasicJsonType::number_unsigned_t, underlying_type>::type;
value_type val;
get_arithmetic_value(j, val);
e = static_cast<EnumType>(static_cast<underlying_type>(val));
e = static_cast<EnumType>(bool_aware_static_cast<underlying_type>(val));
}
#endif // JSON_DISABLE_ENUM_SERIALIZATION
include/nlohmann/detail/conversions/to_json.hpp
+1 -1
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@@ -365,7 +365,7 @@ inline void to_json(BasicJsonType& j, EnumType e) noexcept
{
using underlying_type = typename std::underlying_type<EnumType>::type;
static constexpr value_t integral_value_t = std::is_unsigned<underlying_type>::value ? value_t::number_unsigned : value_t::number_integer;
external_constructor<integral_value_t>::construct(j, static_cast<underlying_type>(e));
external_constructor<integral_value_t>::construct(j, bool_aware_static_cast<underlying_type>(e));
}
#endif // JSON_DISABLE_ENUM_SERIALIZATION
include/nlohmann/detail/meta/type_traits.hpp
+15
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@@ -906,6 +906,21 @@ T conditional_static_cast(U value)
return value;
}
// like conditional_static_cast, but converts to bool by comparing with zero,
// because MSVC 2015 warns about any conversion to bool (C4800), even with an
// explicit cast; used for enums whose underlying type is bool
template < typename T, typename U, enable_if_t < !std::is_same<T, bool>::value, int > = 0 >
T bool_aware_static_cast(U value)
{
return conditional_static_cast<T>(value);
}
template<typename T, typename U, enable_if_t<std::is_same<T, bool>::value, int> = 0>
bool bool_aware_static_cast(U value)
{
return value != U();
}
template<typename... Types>
using all_integral = conjunction<std::is_integral<Types>...>;