c++ warning unused parameter ‘j’ for empty object

[elionne]

I have this minimal json schema:

{
  "type": "object",
  "additionalProperties": false
}

which render as following code:

// ...
    struct Nop {};

    inline void from_json(const json & j, Nop& x) {}

    inline void to_json(json & j, const Nop & x) {
        j = json::object();
    }

The compiler raise warning about j or x are not used. And since I use the -Werror option, it turns into an error.

I can use #pragma GCC diagnostic … to change compiler warning behavior, but it is not satisfying and not portable. It will be better if the generated code does not create any warning.