Mi json struct

Better way of serializing and deserializing nlohmann::json objects into and from structs. Though use boost::pfr, if you don't mind slower build times honestly

Motivational examples

No repetitions

// type_definition.hpp // type_definition.hpp
--------------------------------------------------------------------------------------------
| #include <mi_json_struct.hpp>
namespacens { |
structType | MI_STRUCT_WITH_FROM_AND_TO_JSON(
{ | ns, Type,
int a; | (int, a),
double b; | (double, b)
}; | )
} | |
ns::Type fronPath(constchar *path); | ns::Type fromPath(constchar *path);
|
---------------------------------------------------------------------------------------------
// type_definition.cpp | // type_definition.cpp
---------------------------------------------------------------------------------------------
#include<nlohmann/json.hpp> | #define MI_JSON_STRUCT_IMPL
#include<fstream> | #include <fstream>
#include"type_definition.hpp" | #include "type_definition.hpp"// Repetition, if the "Type" struct changes, | // this needs to be updated also |NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, a, b) | |
ns::Type fronPath(constchar *path) | ns::Type fromPath(constchar* path)
{ | {
std::ifstream file{path}; | std::ifstream file{path};
auto j = nlohmann::json::parse(file); | auto j = nlohmann::json::parse(file);
return j.get<Type>(); | return j.get<Type>();
} | }

The #include <mi_json_struct.hpp> is lightweight, as opposed to <nlohmann/json.hpp>
Therefore, usually it is beneficial, to only include the latter in a single source file with all the type definitions.

More granularity

Given this struct

#include<nlohmann/json.hpp>
#include<thread>structThreadsNumber
{
int value;
friendinlinevoidfrom_json(const nlohmann::json& j, ThreadsNumber& number)
{
int new_value = j.get<int>();
number.value = new_value > 0 ? new_value : std::thread::hardware_concurrency();
}
};

structType | MI_STRUCT_WITH_FROM_JSON(
{ | ns, Type,
ThreadsNubmer threads_number; | (ThreadsNumber, threads_number),
std::string other; | (std::string, other)
}; | )
| // ^// Will not work, `ThreadsNumber` | // Works perfectly fine, because we// needs `to_json` defined as well | // do not need `to_json`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE( | Type, threads_number, other) | 

Overview

Single header, no dependencies apart from nlohmann::json.
Defines three simple self-explanatory macros.

• MI_STRUCT_WITH_FROM_JSON
• MI_STRUCT_WITH_TO_JSON
• MI_STRUCT_WITH_FROM_AND_TO_JSON

The <nlohmann/json.hpp> header is only included if the directive:

#defineMI_JSON_STRUCT_IMPL

is defined.