C++でGoのようなJSONアクセスを可能にする

sample.cpp

#include <type_traits>
#include <iostream>
#include <string>
#include <boost/lexical_cast.hpp>
using boost::lexical_cast;
using namespace std;


struct key_value {
    std::string value;
public:
    char const* c_str() const { return value.c_str(); }
};

// T is default-constructible, copy assignable
template <typename T>
class val {
    key_value name_;
    T value_;

public:
    // init member name
    val(key_value name): name_{name} {}
    val(T const& value, key_value name): name_{name}, value_(value) {}
    val(T && value, key_value name): name_{name}, value_(std::move(value)) {}
    
    val& operator=(T const& src) {
        value_ = src;
        return *this;
    }
    val& operator=(T && src) {
        value_ = std::move(src);
        return *this;
    }

    // get variable name in JSON
    inline char const* name() const { return name_.c_str(); }
    
    // get raw-reference of value
    T&       value()       { return value_; }
    T const& value() const { return value_; }
    
    string to_s() const { return "\"" + name_ + "\":" + lexical_cast<string>(value_); }
};


struct Struct
{
    val<int>    foo{ 0,     key_value{"foo"} };    // 第1引数にメンバの初期値，
    val<string> bar{ "foo", key_value{"bar"} };    // 第2引数にJSONにおけるメンバ名を記載する
    val<float>  aaa{ key_value{"aaa"} };           // 初期値は省略可能

public:
    Struct() = default;
    
    Struct(int foo, string const& bar, float aaa)
    {
        this->foo = foo;
        this->bar = bar;
        this->aaa = aaa;
    }
    
    friend ostream& operator<<(ostream& os, Struct const& s) {
        return os << "{" << s.foo.to_s() << "," << s.bar.to_s() << "," << s.aaa.to_s() << "}";
    }
};

int main()
{
    cout << Struct{} << endl;

    Struct s1{ 1, "hoge", 0.01 };
    cout << s1 << endl;
    
    s1 = { 2, "fuga", 0.43 };
    cout << s1 << endl;
}

sample.go

import "encoding/json"

// Goだと構造体のメンバにこう書くことでJSONにおけるobjectとの相互変換が可能になる
type Member struct {
    FirstName string `json::"first_name"`
    LastName  string `json::"last_name"`
    Address   string `json::"address"`
}