Not serialising to JSON/XML of key/value pairs if the value is at a default

[Bruno Nicoletti]

Is there a way to get cereal to elide key/value pairs from a JSON/XML stream if the value is at some default? This will save on size of the created archive which is useful if you have lots of values set to a default...

If not, I'd like to suggest an extension, so something like...

struct MyStruct {

public:

  int   i;

  float f;

  std::string s;

  template<class Archive>

  void serialize(Archive& ar)

  {

    ar(cereal::make_nvp_withdefault("i", i, 0));

    ar(cereal::make_nvp_withdefault("f", f, 1.0f));

    ar(cereal::make_nvp_withdefault("f", f, std::string()));

  }

};

So if we serialised a MyStruct where 'i' was still at the default of 0, the archivers would elide that key from the JSON and we would get....

{

  "MyStruct" : {

    "f" : 22.2,

    "s" : "bananas"

   }

}

When loading that archive it would see key was missing and then set the value to the specified default.

tx

b