json_nullable types

nullable types are supported by using the json_nullable mapping type or appending the type name with _null to use the convenience wrapper. The requirement of the underlying type is that it will be default constructable for null values or support the Nullable Concept.

Take the following JSON

[
  {
    "member0": 5,
    "member1": "hello"
  },
  {
    "member1": "world",
    "member2": true
  }
]

The JSON document is an array of an object with two members, an optional int, a string, and an optional bool.

To see a working example using this code, refer to cookbook_optional_values1_test.cpp.

 {c++}
struct MyOptionalStuff1 {
  std::optional<int> member0;
  std::string member1;
  std::unique_ptr<bool> member2;
};
 
namespace daw::json {
  template<>
  struct json_data_contract<MyOptionalStuff1> {
    using type = json_member_list<
      json_number_null<"member0", std::optional<int>>, 
      json_string<"member1">,
      json_bool_null<
        "member2", 
        std::unique_ptr<bool>, 
        LiteralAsStringOpt::NoEscapedDblQuote, 
        UniquePtrConstructor<bool>
      >
    >;
 
    static inline auto to_json_data( MyOptionalStuff1 const &value ) {
      return std::forward_as_tuple( value.member0, value.member1, value.member2 );
    }
  };
}