Artur, if i use your solution like
printf("...", ForEach!(val => conv(val).c_str())(values).tuple);Than i would get a crash, because all the tuple elements would be char*'s, pointing to already freed memory, as std::string's destructor gets called each time right after alias function exits. Ths is what c++ unpacking operator for: i actually return a packed list of std::string's, apply .c_str() to each and than unpack the list to current context.
