Forward declaration for fkyaml::node

[abcminiuser]

Hello - thanks for the library!

It would be great if the standard fkyaml::node could be forward declared in a separate header, so that translation units that don't directly use the library can be built without having to pay for the compile time cost of including the full library header. Ideally this means I could use the forward-declaration version in my file loader class header, and then only include the actual library code inside the one CPP file that needs to work with the nodes.

[fktn-k]

@abcminiuser
Thanks for sharing your idea!
I agree with this:

Ideally this means I could use the forward-declaration version in my file loader class header, and then only include the actual library code inside the one CPP file that needs to work with the nodes.

Regarding such a header file which contains forward declarations, I'm planning to add one which is similar to the ones in nlohmann json or in spdlog. They contains forward declarations of types which either implement library APIs or provide a customization point. Is that what you expect?

[abcminiuser]

Yes, the <nlohmann/json_fwd.hpp> is actually the header I was thinking of when I suggested this. Having an equivalent here would be great.

[fktn-k]

I got your point. Thanks!

[fktn-k]

@abcminiuser
The header file for forward declarations has been added in the PR #422.
You can use the file fkyaml_fwd.hpp from either the include or single_include directory for forward declarations.