How can I make a C typename nest itself and "infinitely" recurse?-CodePudding

Im trying to turn this piece of JSON into a C type using a neat little JSON parsing library I have created.

[
 "a",
   [
      "b",
      [
         "c",
         [  
            "d", 
            ["... so on so forth"] 
         ]
      ]
   ]
]

Currently, this is technically what the type would look like in C , however this is obviously invalid as the typename cannot reference itself:

typename std::variant<std::string, std::vector<requirements_type>> requirements_type;

Is there any way to make an infinitely recurring typename that can handle this sort of structure?

CodePudding user response：

As mentioned in comments, you cannot have an infinetely nested type like your requirements_type. The size of objects of a type is finite. Also in practice your JSON will not be infintely nested. You need to stop the nesting somewhere.

A type alias cannot refer to itself, but you can refer to the class while declaring its members:

struct requirements_type {
    std::variant< std::string, std::vector< requirements_type > > data;
};

CodePudding user response：

As mentioned in 463035818_is_not_a_number's answer

Instead of using a typename I can use a class that references itself:

struct RequirementArray {
    std::variant<std::string, std::vector<RequirementArray>> self;
};

I can recurse through this by using this simple method:

void recurseAndOutput(RequirementArray array, int i) {
  try {
    std::vector<RequirementArray> requirementArrays = std::get<std::vector<RequirementArray>>(array.self);
    for (RequirementArray requirementArray: requirementArrays) {
      recurseAndOutput(requirementArray, i   1);
    }
  } catch (std::bad_variant_access const & ignored) {
    std::string string = std::get<std::string>(array.self);
    printf("%s - %i", string.c_str(), i);
  }
}