Is there any way to avoid having to cast an enum every time you want to print it?

[persona94]

If I have an enum class

enum class values : int32_t
{
val1=0,
val2,
};

I still need to cast it to int32_t while passing as an argument

LOG_INFO(logger, "{value}", static_cast<int32_t>(values::val1));

Is there any way to pass the enum value to the logger directly?

[odygrd]

Hey, if you want to print the underlying value you have to cast it.

if you want to print it as string then you have to define a formatter. The underlying value is copied and the conversion will happen by the backend logging thread.

For example see this test demonstrating both cases

quill/test/integration_tests/EnumLoggingTest.cpp

Line 17 in 3df568b

enum TestEnum : int

[persona94]

Thanks! Writing a formatter for each enum was infeasible because we have hundreds of enums.

I ended up writing a few template helpers to accomplish this

namespace fmtquill
{

template <class E>
requires std::is_enum_v<E>
auto format_as(E e)
{
    return static_cast<std::underlying_type_t<E>>(e);
}

}
template <class E>
requires std::is_enum_v<E>
auto format_as(E e)
{
    return static_cast<std::underlying_type_t<E>>(e);
}

template <typename T>
using format_as_type = decltype(format_as(std::declval<T>()));

template <class T>
requires requires { typename format_as_type<T>; }
struct fmt::formatter<T> : formatter<format_as_type<T>>
{
    auto format(T e, auto& ctx) const
    {
        return formatter<format_as_type<T>>::format(fmtquill::format_as(e), ctx);
    }
};

I stuck this at the very top of my header that bridges Quill and our code. Now I can pass enums directly without casting

[odygrd]

Seems good. If you use a library like https://github.com/Neargye/magic_enum you can easily return the enum name as string instead of the underlying type, just be aware that it has some restrictions on enum values range