Custom conversion doesn't work

[htrefil]

I tried to define a custom specialization of toml::from for my type, but it ends up with a compile time error.

Here's the code:

#include "toml11/toml.hpp"

enum class animal {
	DOG,
	CAT,
};

namespace toml {

template<>
struct from<animal> {
	animal from_toml(const value& value) {
		return animal::DOG;
	}
};

}

int main(int argc, char** argv) {
	auto data = toml::parse(argv[1]);
	auto a = toml::find<animal>(data, "a");
}

Apart from a bunch of template substitution failure errors, I get

toml11/toml/get.hpp:415:3: note: template argument deduction/substitution failed:
toml11/toml/get.hpp:259:26: error: invalid application of ‘sizeof’ to incomplete type ‘toml::into’
std::size_t S = sizeof(::toml::into)>
^~~~~~~~~~~~~~~~~~~~~~~
toml11/toml/get.hpp:259:48: error: could not convert template argument ‘’ from ‘’ to ‘long unsigned int’
std::size_t S = sizeof(::toml::into)>

Compiled with g++ 8.3.0 with -std=c++17.
Using the latest toml11 cloned from GitHub.

Is this a bug or am I doing something wrong?

[jcmoyer]

I think the documentation is incorrect (from_toml should be static), see this test for correct usage: https://github.com/ToruNiina/toml11/blob/master/tests/test_extended_conversions.cpp#L38-L57

EDIT:
After a bit of testing, I've determined that there's another issue where you have to specialize both toml::into and toml::from for your type, even if you're only reading toml. I'm not sure if this is intended or a bug.

[ToruNiina]

Thank you @htrefil for the report!
And thank you @jcmoyer for the PR and finding out the problem!

This is a bug.
As you pointed out, there is a defect in the code and it requires conversion in both directions even if only one direction is needed. I've just fixed that and will push it soon.