c++ - boost::variant of const and non-const -

i want create template< typename f > using t = boost::variant< f, f const >; type store read-only , read-write accessible values same std::vector< t >. i've got following programming problem:

#include <iostream> #include <cstdlib>  #include <boost/variant.hpp>  int main() {     using f = double;     using cv = boost::variant< f const, f >;     f const c = 0.0;     cv c(c);     f v = 0.0;     cv v(v);     std::cout << c.which() << ' ' << v.which() << std::endl;      return exit_success; } 

output: 1 1. how can store const version of value of type f?

this not solution, usefull:

#include <iostream> #include <functional> #include <cstdlib>  #include <boost/variant.hpp>  int main() {     using f = double;     using cv = boost::variant< std::reference_wrapper< f const >, std::reference_wrapper< f > >;     f const c = 0.0;     cv c(std::ref(c));     f v = 0.0;     cv v(std::ref(v));     std::cout << c.which() << ' ' << v.which() << std::endl;      return exit_success; } 

this requires additional space store data if any. in cases, may more appropriate 1 in original formulation of question.