You do have to tag struct fields with a macro, but you can attach contexpr-visitable attributes. There's also a static limit to how many reflectable fields you can have, all reflectable fields need to be at the front of the struct, and the struct needs to be an aggregate.
that forEachProp function... it brings back nightmares of when, before variadics, we used to macro generate up-to N-arity functions (with all the const/non-const permutations(.
Now I use the same trick in our code base to generically hash aggregates, but I limit it to 4 fields for sanity.
You do have to tag struct fields with a macro, but you can attach contexpr-visitable attributes. There's also a static limit to how many reflectable fields you can have, all reflectable fields need to be at the front of the struct, and the struct needs to be an aggregate.