Automatic serialization functions from pfr library

[adriensalon]

What do you all think about using pfr reflection library for having serialization functions be created from static reflection?
github.com/apolukhin/pfr

We could have :

• automatic serialization function from reflection for all aggregate types
• user can still declare specific serialization functions that will be picked up first
• with C++>=20 we even have automatic field names for those aggregate types

Motivating exemple :

struct Bar {
    std::string s1;
    std::string s2;
};

struct Foo {
    int int1;
    int int2;
    Bar bar1;
    float float1;
};

int main()
{
    Foo f { 42, 45, { "Hello", "World" }, 3.14f };
    std::stringstream ss;
    {
        cereal::JSONOutputArchive oar(ss);
        oar(f); // No manual serialize function needed
    }
    std::cout << ss.str() << "\n";
}

output :

{
    "value0": {
        "int1": 42,
        "int2": 45,
        "bar1": {
            "s1": "Hello",
            "s2": "World"
        },
        "float1": 3.140000104904175
    }
}

Example extension implementation :

#include <pfr.hpp>

namespace cereal {

#if PFR_CORE_NAME_ENABLED

template <typename Archive, typename T>
std::enable_if_t<std::is_aggregate_v<T>>
serialize(Archive& archive, T& object)
{
    pfr::for_each_field_with_name(object, [&](std::string_view name, auto& field) {
        archive(cereal::make_nvp(std::string(name).c_str(), field));
    });
}

#else

template <typename Archive, typename T>
std::enable_if_t<std::is_aggregate_v<T>>
serialize(Archive& archive, T& object)
{
    pfr::for_each_field(object, [&](auto& field) {
        archive(field);
    });
}

#endif

}