parsing into private fields

Currently my biggest gripe with Spirit.X3 is that you can't parse into a class with private fields. This leaves you with two options:

1. use a proxy type, e.g.

```cpp

class Myclass_impl {
public:
char c;
};

class Myclass : private Myclass_impl {
public:
Myclass_impl &base() { return *this; }
};

bp::rule rule{"rule"};
const auto rule_def = bp::char_;
BOOST_PARSER_DEFINE_RULES(rule);

void func() {
std::string str{"c"};
Myclass result;

bp::parse(str, rule, result.base());
}

```

2. Just don't use private members, which means your parser is no longer a parser, just a validator.

`1.` makes public headers unreadable as users would have to look into implementation headers to see the actual class body, while
`2.` violates the [parse, don't validate](https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-validate/) principle and thus allows for invalidly constructed objects that would never be returned from a successful parse.

Are there any plans to remedy this, e.g. via a Boost.Parser helper class that the user class could befriend, or via a specialization that grants access to the private members (Boost.Describe comes to mind) ?

Or am I just missing a workaround that everyone has been using for the past decade