rfl::toml::read() doesn't compile (cannot convert from 'toml::v3::noex::parse_result *' to 'rfl::toml::InputVarType')

[Please-just-dont]

So I see that reflect-cpp switched back to toml++ back from toml11. So I downloaded the latest version of reflect-cpp and the latest version of toml++ and there is a compile error in Reader.hpp.

struct MyStruct { int a; }

std::string str;

rfl::toml::read<MyStruct>(str); // DOESN'T COMPILE 

Error:

Reason: cannot convert from 'toml::v3::noex::parse_result *' to 'const std::string'

And:

'initializing': cannot convert from 'toml::v3::noex::parse_result *' to 'rfl::toml::InputVarType'

Which is the same issue I was having months back when I raised this point, see:

#383

[Please-just-dont]

What's going on? rfl::toml::read<>() doesn't work at all, not even with a string view. It stopped working for me and I don't know what the problem is, as I downloaded the latest reflect-cpp and latest toml++ but I don't know if it's a change in toml++ or reflect-cpp changing from toml11 to toml++.

[liuzicheng1987]

@Please-just-dont , yes, we switched back to toml++.

The reason for the back-and-forth is that the vcpkg toml++ recipe did not expose a cmake.config, which made it impossible to support it as a feature. So we switched to toml11. Shortly after that, they actually added a cmake.config, so we switched back, because toml++ is actually faster. Sorry for the confusion this created.

Why it isn't working on your machine, I don't know. But we have automated tests for this on Linux, macOS and Windows using a wide variety of compilers and I can guarantee that it does work. So my guess is that you are maybe somehow still using reflect-cpp 0.17.0 instead of 0.18.0. Maybe you are somehow linking to the wrong version?

The latest version of toml++ is 3.4.0, which is the one we are using as well, so it can't be that?

[Please-just-dont]

@liuzicheng1987 Hi, I thought I already posted this but I don't see it so I'll post again. The problem is I defined TOML_EXCEPTION 0. None of the functions to parse toml work if exceptions are disabled.

At the top of toml++/impl/parse_result.hpp there is the note:

\availability <strong>This type only exists when exceptions are disabled.</strong>
   /// 		 Otherwise parse_result is just an alias for toml::table: \cpp
   /// #if TOML_EXCEPTIONS
   ///		using parse_result = table;

So that's the problem I'm having. I mentioned this issue at the Github repository for TOML++ here and the response I got was that this could be resolved with something like this:

std::optional<toml::table> parse_toml_file(std::string_view file_path)
	{
#if TOML_EXCEPTIONS
		try
		{
			return toml::parse_file(file_path);
		}
		catch (const toml::parse_error& err)
		{
			std::cerr << err << "\n";
			return std::nullopt;
		}
#else
		const auto result = toml::parse_file(file_path);
		if (!result)
		{
			std::cerr << result.error() << "\n";
			return std::nullopt;
		}
		return std::optional{ std::move(result).table() };
#endif
	}

[liuzicheng1987]

All right, this is something we should fix. If you want to open a PR, feel free, otherwise I will fix it some time soon.

[liuzicheng1987]

@Please-just-dont , this PR (#447) should resolve the issue.