Re: [PFR][review] Andrzej's review

From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2020-10-07 15:20:12

śr., 7 paź 2020 o 17:11 Antony Polukhin <antoshkka_at_[hidden]> napisał(a):

> ср, 7 окт. 2020 г. в 15:48, Andrzej Krzemienski <akrzemi1_at_[hidden]>:
> > Interesting. I do not understand enough about the implementation to be
> making definite statements, but based on my superficial knowledge I expect
> that it should be possible to reimplement a "flat" reflection on top of
> "precise" one.
> > 1. First you call structure_to_tuple() and you get std::tuple<T1&, T2&,
> ..., Tn&>
> > 2. For every Tn that is an aggregate type you apply structure_to_tuple()
> recursively.
> > 3. Then you potentially get a tuple of nested tuples and you need to
> flatten it.
>
> Yes, that's doable. But is that really a popular feature?
>
> Flat representation was useful, because there was no precise
> representation in the early versions of the library. That was the only
> way to do things.
>
> Back to your example:
>
> struct Person {
>   std::string firstName;
>   std::string lastName;
>   int age;
> };
>
> struct Employee : Person {
>   double salary;
> };
>
> struct Prisoner : Person {
>   int cellNumber;
> };
>
> Probably composition would work better than inheritance for your needs?
>
> struct Person {
>   std::string firstName;
>   std::string lastName;
>   int age;
> };
>
> struct Employee {
>   Person person;
>   double salary;
> };
>
> struct Prisoner {
>   Person person;
>   int cellNumber;
> };
>
> With composition you get more flexibility:
>
> std::ostream& operator<<(std::ostream& os, const Person& p) {
>     os << "person: ";
>     pfr::write(os, p);
>     return os;
> }
>
>
> std::ostream& operator<<(std::ostream& os, const Prisoner& p) {
>     using pfr::ops;
>     return os << p;
> }
>
> // Outputs: {person: {"Harley ", "Quinn", 21}, 100500}
> std::cout << Prinsoner{{"Harley ", "Quinn", 21}, 100500};
>

I admit that the motivation for the flat reflection is much smaller than
for the precise one, so in the end it may not be worth the effort.

Regards,
&rzej;