extending Iguana to support user defined types

[matth1j]

Hi - I'm not an expert C++ coder so apologies if I'm missing something obvious.

I have a class which wraps std::array to give it more std::vector-like functionality, and I want to serialize/deserialize it to/from json files. Please can someone help me get started - what do I need to add, and where?

Cheers
John

[qicosmos]

look at this example:
https://github.com/qicosmos/iguana/blob/master/test/test_some.cpp#L66
https://github.com/qicosmos/iguana/blob/master/test/test_some.cpp#L491

[matth1j]

Thanks, but I don't think this is what I'm looking for. I want Iguana to 'know' about my array wrapper class in the same way it 'knows' about std::array and std::vector. I didn't describe problem very well; I'll try adding some code.

Say my vector-like array wrapper class is this (simplified):

// Vector-like container with fixed maximum size and no dynamic memory allocation.
template<typename T, size_t N>
struct VecArray {
  std::array<T, N> els_;
  size_t size_ = 0;
  T& operator[](int index) { return els_[index]; }
  size_t size() const { return size_; }
  size_t capacity() const { return N; }
  void push_back(const T& el) { els_[size_++] = std::move(el); }
};

This structure isn't reflected, because I want Iguana to 'know' about it.

Then I might have a struct containing VecArray fields:

struct Data {
  VecArray<int, 10> int_vals_;
  VecArray<float, 20> float_vals_;
};
YLT_REFL(Data, int_vals_, float_vals_)

Then if I do this:

  Data data;
  data.int_vals_.push_back(1);
  data.int_vals_.push_back(2);
  data.int_vals_.push_back(3);
  data.float_vals_.push_back(4.56);
  std::string s;
  iguana::to_json(data, s);
  std::cout << s << std::endl;

then I would expect to see something like:

{
  "int_vals_" : [1, 2, 3],
  "float_vals_" : [4.56]
}

Specifically, the VecArray els_ and size_ field names don't appear in the output, and only VecArray::size() values are output.

Does that make sense? And if your example code shows me how to do this, apologies.

[matth1j]

After a bit more thinking, and looking at Iguana code... do I just need to implement is_sequence_container for VecArray (as well as override [], size() etc.)? I'll try to work out how to do that and give it a go.

[matth1j]

...I mean extend is_sequence_container (I'm having to work with an older version of Iguana eg. uses REFLECTION not YLT_REFL) - I thought is_sequence_container was STL but I can see it defined in traits.hpp.

[qicosmos]

You can extend to support your type like this:
https://github.com/qicosmos/iguana/blob/master/example/json_example.cpp#L141
https://github.com/qicosmos/iguana/blob/master/example/json_example.cpp#L118

you need to define your custom to_json/from_json function.

[qicosmos]

More simpler way, add YLT_REFL for template VecArray :

template<typename T, size_t N>
struct VecArray {
  std::array<T, N> els_;
  size_t size_ = 0;
  T& operator[](int index) { return els_[index]; }
  size_t size() const { return size_; }
  size_t capacity() const { return N; }
  void push_back(const T& el) { els_[size_++] = std::move(el); }
  YLT_REFL(VecArray, els_, size_);
};

struct Data {
  VecArray<int, 10> int_vals_;
  VecArray<float, 20> float_vals_;
};
YLT_REFL(Data, int_vals_, float_vals_);

int main() {
  Data data;
  data.int_vals_.push_back(1);
  data.int_vals_.push_back(2);
  data.int_vals_.push_back(3);
  data.float_vals_.push_back(4.56);
  std::string s;
  iguana::to_json(data, s);
  std::cout << s << std::endl;
}

output:

{"int_vals_":{"els_":[1,2,3,-858993460,-858993460,-858993460,-858993460,-858993460,-858993460,-858993460],"size_":3},"float_vals_":{"els_":[4.56E0,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8,-1.0737418E8],"size_":1}}