我试图理解从http://en.cppreference.com/w/cpp/utility/variant/visit获得的以下示例#include#include#include#include#include#includeusingvar_t=std::variant;templatestructoverloaded:Ts...{usingTs::operator()...;};//whatisthisdeclarationimply???templateoverloaded(Ts...)->overloaded;intmain(){std::vectorvec={10,15l