convert data_t members to a type-safe union with std::variant;

[kalwalt]

The variant class let define a variable with multiple types. May we use internally the data_t class?

[kalwalt]

For example you can do this:

#include<iostream>
#include<variant>
#include <string>
#include<vector>

using namespace std;

int main()
{
    std::variant<std::vector<int>, double, std::string> v;
    static_assert(std::variant_size_v<decltype(v)> == 3);
    std::vector<int> a(2,42);
    v = a;   // v contains int 42
    std::cout << "index = " << v.index() << '\n';
    v = 42.0; // v contains double 42.0
    std::cout << "index = " << v.index() << '\n';
    v = "42"; // v contains string "42"
    std::cout << "index = " << v.index() << '\n';
    
    return 0;
}

our data_t class members could became:

// actual implementation
Array<u_char> u8;
Array<int> i32;
Array<float> f32;
Array<double> f64;

// with std::variant we  can store the values in the same variable name:
std::variant<Array<u_char>, Array<int>, Array<float>, Array<double>> data;