How to properly use references with variadic templates

Question

I have something like the following code:

   template<typename T1, typename T2, typename T3, typename T4>
   void inc(T1& t1, T2& t2, T3& t3, T4& t4) { ++t1; ++t2; ++t3; ++t4; }

   template<typename T1, typename T2, typename T3>
   void inc(T1& t1, T2& t2, T3& t3) { ++t1; ++t2; ++t3; }

   template<typename T1, typename T2>
   void inc(T1& t1, T2& t2) { ++t1; ++t2; }

   template<typename T1>
   void inc(T1& t1) { ++t1; }

I'd like to reimplement it using the proposed variadic templates from the upcoming standard. However all the examples I've seen so far online seem to be printf like examples, the difference here seems to be the use of references. I've come up with the following:

inline void inc() { }

template<typename T>
inline void inc(T&& t) { ++t; }

template<typename T,typename ... Args>
inline void inc(T&& t, Args&& ... args) { ++t; inc(args...); }

What I'd like to know is:

• Should I be using r-values instead of references?

• Possible hints or clues as to how to accomplish what I want correctly.

• What guarantees does the new proposed standard provide in regard to the issue of the recursive function calls, is there some indication that the above variadic version will be as optimal as the original? (should I add inline or some-such?)

Answer 1

I would not use rvalue references here, because that will allow you to bind to rvalues which can allow such nonsensical code as:

inc(1);

So, I would stick with regular references:

template<typename T>
void inc(T& t) { ++t; }

template<typename T,typename ... Args>
void inc(T& t, Args& ... args) { ++t; inc(args...); }