How do I serialize and deserialize std::mdspan (proposals) in C++?

In C++, serialization and deserialization of the `std::mdspan` (multi-dimensional span) can be achieved by converting the data it references into a format suitable for storage or transmission, such as JSON or binary. Below, we'll explore an example of how to serialize and deserialize a `std::mdspan` using a JSON-like approach.

// Example serialization and deserialization of std::mdspan

#include 
#include 
#include 
#include  // For JSON handling

using json = nlohmann::json;

// Utility function to serialize std::mdspan
template
json serialize_mdspan(std::mdspan> md)
{
    json j;

    // Create an array to hold the data
    for (std::size_t i = 0; i < md.extent(0); ++i)
    {
        std::vector row(md.extent(1));
        for (std::size_t j = 0; j < md.extent(1); ++j)
        {
            row[j] = md(i, j);
        }
        j.push_back(row);
    }
    return j;
}

// Utility function to deserialize std::mdspan
template
void deserialize_mdspan(json j, std::mdspan> md)
{
    for (std::size_t i = 0; i < md.extent(0); ++i)
    {
        for (std::size_t j = 0; j < md.extent(1); ++j)
        {
            md(i, j) = j[i]; // Modify with actual data mapping
        }
    }
}

int main()
{
    // Define a 2D array and wrap it into mdspan
    std::array<:array>, 2> data = { { {1, 2, 3}, {4, 5, 6} } };
    auto md = std::mdspan>(data.data(), 2, 3);

    // Serialize the mdspan
    json j = serialize_mdspan(md);
    std::cout << "Serialized mdspan: " << j.dump() << std::endl;

    // Deserialize the json back to mdspan (assuming proper index mapping)
    deserialize_mdspan(j, md);

    return 0;
}