#include <iostream>
#include <unordered_map>
#include <boost/utility/string_view.hpp>
#include <boost/functional/hash.hpp>

using namespace std;

// custom specialization of boost::hash
namespace boost
{
    template<>
    struct hash<boost::string_view>
    {
      std::size_t operator()(boost::string_view str) const
      {
        return boost::hash_range<const char*>(str.begin(), str.end());
      }
    };
}

namespace test
{
  class example
  {
   public:
    void check()
    {
      m["abc"] = 123;
      m["def"] = 456;
    }
    void print()
    {
      for (auto& elem : m)
      std::cout << elem.first << ":" << elem.second << std::endl;
    }
   private:
    std::unordered_map<boost::string_view, std::size_t, boost::hash<boost::string_view>> m;
  };
}

int main() {
  test::example p;
  p.check();
  p.print();
  return 0;
}