What if this library was built around std::variant?

[Ericson2314]

I get that major rewrites could well just be out of the question, but this nags at me from time to time so I figured I'd at least write it down?

What if this library was built around std::variant. Perhaps this would be even std::variant<nullptr_t, someNumberType, std::string, std::vector<json>, std::map<std::string, json>>, or perhaps it would be something with more json-specific variant types.

The big advantage would be that we would be able to leverage std::variant downcasting/visiting, to elide redundant checks and make sure all the cases are handled.

Most recently I thought of this when reviewing NixOS/nix#8760 (in a project that uses this library). Note how the new methods added for nice error do not have informative return types that indicate what is checked. That is an example of something we could do better on with std::variant without extra copying.

[nlohmann]

We target C++11.

[Ericson2314]

OK, fair enough. And no sign of that changing anytime soon?

[nlohmann]

Exactly