I got confused with the location where the ... should be put when using template parameter packs.
For example, in template parameter list, we should use typename ...Ts, while in a parameter list, it becomes Ts...ts.
When instantiate a template, it becomes tuple<Ts...> and most confused me is std::forward<Args>(args)..., the ... is out side the parentheses. Until then, I force myself to just remember this, until today I see this: sizeof...(Params), I think I must understand the regular pattern to avoid further confused.
So could anybody help how to treat the ... to fully understand the location where to put it?
It follows the thing being repeated. A name that follows is like multiple names.
In template<typename... Ts> we are declaring multiple typenames, e.g. template<typename Ts0, typename Ts1, typename Ts2>.
In void foo(Ts... ts), we are declaring multiple parameters, using the multiple types, e.g. void foo(Ts0 ts0, Ts1 ts1, Ts2 ts2)
In std::tuple<Ts...> we are using the multiple types to instantiate std::tuple, e.g. std::tuple<Ts0, Ts1, Ts2>
In std::forward<Args>(args)... we are using multiple expressions, e.g. std::forward<Args0>(args0), std::forward<Args1>(args1), std::forward<Args2>(args2)
sizeof... is a named operator, distinct from sizeof