[Need Advice] How to Handle Many Private Variables and Dynamic Matrices?

[WanZhiQiu-ac]

Suppose there's a class that needs to be serialized to JSON:

class Example {
   int a, b, c, d, e, f; // ... and many many more
   Eigen::MatrixXd mat;
   Eigen::VectorXd vec;
};

The class contains many private variables and does not have getters or setters (so the class_with_const_mem_func example in json_test.cpp is not quite applicable). What is a recommended approach to handle this? Would using friend functions be a viable solution? Additionally, how should dynamic Eigen matrices within a struct or class be "properly" serialized?

[stephenberry]

Adding friend struct glz::meta<Example>; will allow you to serialize/deserialize without needing to write a bunch of getter/setters.
Here is an example in compiler explorer: https://godbolt.org/z/95eYE474a

The example uses fixed matrices, which Glaze has built in support for by including #include "glaze/ext/eigen.hpp". However, Glaze currently only reads/writes fixed size Eigen matrices/vectors. If you look at the code in "glaze/ext/eigen.hpp" you should get some ideas of how you can specialize the to/from functions in glz::detail and support these dynamically sized Eigen types. If you do get it to work, pasting the code here or opening a pull request would be great, so that Glaze could support dynamic matrices out of the box.

[WanZhiQiu-ac]

Thank you for your quick reply! I am working on issues related to dynamically sized Eigen types. Additionally, I would like to confirm if we cannot omit struct glz::meta<Example> because there is currently no way to automatically access information about private members?

[WanZhiQiu-ac]

PR here: #1541

[stephenberry]

Thanks for the PR!
There are hacks to access private members through member object pointers and additional indirection, I'll have to do some searching and experimenting. It might be possible to create a sort of wrapper in Glaze that exposes private members.

[WanZhiQiu-ac]

Yes, maybe some evil but handy things like this and that? It will be a wonderful feature, really looking forward to it!

[WanZhiQiu-ac]

@stephenberry BTW I did some research during the weekend but nothing worked out :( This capability would significantly enhance the library's flexibility and ease of use. I understand that it might involve some experimentation and careful handling, but I’m really looking forward to seeing what’s possible. Please let me know if there’s anything I can do to assist or contribute further to this feature.