I think that’s a source of bugs. If I understand correctly, that means users have to manually call the inner constructor from the outer constructor with positional arguments. If there are many structs with more than 5 fields (say) it would be terrifying to do any kind of refactoring touching the fields.
(OK. We need to do that already when calling new. But please don’t increase the burden.)
Obviously, it does not imply that @with_kw is a bad design since it also generates a keyword-only constructor as well.
If you let users to write a inner-constructor, it has to be usable by humans. Positional-only constructor is not for humans. Humans are good at referring to things by names, not positions. I think that’s the primary reason why we use structs instead of tuples.
Then what is required for packages like Reconstructables.jl and Setfield.jl are to generate constructor usable by programs. That means a keyword-only or positional-only constructor. They both have pros and cons.