boost_parameter_optional.cpp

#include <iostream>
#include <string>

#include <boost/parameter.hpp>

BOOST_PARAMETER_NAME(firstName)
BOOST_PARAMETER_NAME(lastName)
BOOST_PARAMETER_NAME(age)
BOOST_PARAMETER_NAME(email)

BOOST_PARAMETER_FUNCTION(
    (void),
displayPerson,
    tag,
    (optional
        (email, (std::string), "No email provided")
    )
    (deduced
        (required
            (firstName, (std::string))
            (lastName, (std::string))
            (age, (int))
        )
    )
)
{
  std::cout << "First name: "<< firstName << '\n';
  std::cout << "Last name: "<< lastName << '\n';
  std::cout << "Age: "<< age << '\n';
  std::cout << "Email: "<< email << '\n';
}

int main()
{
    displayPerson(_age = 42, _lastName = "Doe", _firstName = "John");
}