Cannot deserialize types using std::ratio

[GabrielDav]

Given
void from_json(const json& j, std::ratio<60>& r) { // parsing }
I expect to get parsed value back when used like this:
auto data = j.at("Data").get<std::ratio<60>>()
However, instead I'm getting a compilation error:

could not find from_json() method in T's namespace

This problem impacts usage of std::chrono::duration and std::crhono::time_point

This is really weird, because I copied implementation of std::ratio and renamed struct to rat

template<intmax_t _Nx,
		intmax_t _Dx = 1>
		struct rat
	{	// holds the ratio of _Nx to _Dx
		static_assert(_Dx != 0,
			"zero denominator");
		static_assert(-INTMAX_MAX <= _Nx,
			"numerator too negative");
		static_assert(-INTMAX_MAX <= _Dx,
			"denominator too negative");

		static constexpr intmax_t num = _Sign_of<_Nx>::value
			* _Sign_of<_Dx>::value * _Abs<_Nx>::value / _Gcd<_Nx, _Dx>::value;

		static constexpr intmax_t den = _Abs<_Dx>::value / _Gcd<_Nx, _Dx>::value;

		typedef rat<num, den> type;
	};

void from_json(const json& j, rat<60>& r)
	{
            // parsing
	}

auto data = j.at("Data").get<rat<60>>();

Surprisingly this works as expected.
I'm using Visual Studio 2017 msvc compiler. Project uses std::chrono across solution without any issues.

[nlohmann]

I think the reason for this is that the from_json function must be defined in the same namespace as the respective type. That's why it does not work for std::ratio, but for rat. Please have a look at https://github.com/nlohmann/json#arbitrary-types-conversions - there is an example how to deal with these situations by specializing adl_serializer.

[GabrielDav]

Works like charm. I can't believe I tried to solve 'the issue' and even opened new issue without reading documentation carefully. Sorry about that and thank you for pointing me to the right direction

[nlohmann]

No worries!