gistfile1.cpp

// functional:
return boost::join(map(_name.id_expression_value, [](auto && elem) { return elem.string; }), ".");

// C++:
std::vector<std::string> tmp;
tmp.reserve(_name.id_expression_value.size());
std::transform(_name.id_expression_value.begin(), _name.id_expression_value.end(), std::back_inserter(tmp), [](auto && elem) { return elem.string; });
return boost::join(tmp, ".");