program_options optional option of type optional<string>

[BernardIE5317]

Greetings Kind Regards i am new to boost and am attempting to learn boost::program_options . so far so good until i add an option of type std::optional<string> unless the line adding this type is commented out the code will not compile . does boost::program_options not support options of type std::optional<string> Thank You Kindly</string>

#include <iostream>
#include <optional>
using namespace std;
#include <boost\program_options.hpp>
using namespace boost;

int main(int argc, const char* argv[])
{
     cout << "Hello World\n" << boolalpha;

     program_options::options_description options_description("options");
     options_description.add_options()
          ("help", "please help me get this code to compile w/o error . the line below needs to be commented out for a clean compile . does boost not permit an options optional<> type ? Thank You Kindly")
          ("optional string", program_options::value<std::optional<string>>, "this option is optional")
          ;
}