JSON

For JSON support, you must also include the header <rfl/json.hpp>.

Reading and writing

Suppose you have a struct like this:

struct Person {
    rfl::Rename<"firstName", std::string> first_name;
    rfl::Rename<"lastName", std::string> last_name;
    rfl::Timestamp<"%Y-%m-%d"> birthday;
    std::vector<Person> children;
};

You can parse JSON strings like this:

const rfl::Result<Person> result = rfl::json::read<Person>(json_string);

A Person struct can be serialized like this:

const auto person = Person{...};
const std::string json_string = rfl::json::write(person);

If you want a "pretty" JSON representation, you can do this:

const std::string json_string = rfl::json::write(person, rfl::json::pretty);

Loading and saving

You can also load and save to disc using a very similar syntax:

const rfl::Result<Person> result = rfl::json::load<Person>("/path/to/file.json");

const auto person = Person{...};
rfl::json::save("/path/to/file.json", person);

rfl::json::pretty will work here as well:

rfl::json::save("/path/to/file.json", person, rfl::json::pretty);

Reading from and writing into streams

You can also read from and write into any std::istream and std::ostream respectively.

const rfl::Result<Person> result = rfl::json::read<Person>(my_istream);

const auto person = Person{...};
rfl::json::write(person, my_ostream);

rfl::json::pretty will work here as well:

rfl::json::write(person, my_ostream, rfl::json::pretty);

Note that std::cout is also an ostream, so this works as well:

rfl::json::write(person, std::cout) << std::endl;

Custom constructors

One of the great things about C++ is that it gives you control over when and how you code is compiled.

For large and complex systems of structs, it is often a good idea to split up your code into smaller compilation units. You can do so using custom constructors.

For the JSON format, these must be a static function on your struct or class called from_json_obj that take a rfl::json::Reader::InputVarType as input and return the class or the class wrapped in rfl::Result.

In your header file you can write something like this:

struct Person {
    rfl::Rename<"firstName", std::string> first_name;
    rfl::Rename<"lastName", std::string> last_name;
    rfl::Timestamp<"%Y-%m-%d"> birthday;

    using JSONVar = typename rfl::json::Reader::InputVarType;
    static rfl::Result<Person> from_json_obj(const JSONVar& _obj);
};

And in your source file, you implement from_json_obj as follows:

rfl::Result<Person> Person::from_json_obj(const JSONVar& _obj) {
    const auto from_nt = [](auto&& _nt) {
        return rfl::from_named_tuple<Person>(std::move(_nt));
    };
    return rfl::json::read<rfl::named_tuple_t<Person>>(_obj)
        .transform(from_nt);
}

This will force the compiler to only compile the JSON parsing when the source file is compiled.