std:: optional and std::expected

C++17 introduced std::optional, a template class that either has a value or has nothing. This is useful for situations where a function may or may not return a value. To better understand it, let’s go through the following example:

#include <cstdio>
#include <optional>
struct sensor {
    struct data {
        int x;
        int y;
    };
    static inline bool ret_val = true;
    static std::optional<data> get_data() {
        ret_val = !ret_val;
        if(ret_val) {
            return data{4, 5};
        }
        else {
            return std::nullopt;
        }
    }
};
int main()
{
    const auto get_data_from_main = [] () {
        auto result = sensor::get_data();
        if(result) {
            printf("x = %d, y = %d\r\n", (*result).x, (*result).y);
        }
        else {
            printf("No data!\r\n");
        }
    };
    get_data_from_main();
    get_data_from_main();
    return 0...