universal reference vs const reference priority?

Question

When I consider the two following overloads:

template  void f(const T&... x);
template  void f(const T& x);

Answer 1

There is not a universal priority between these two functions. They compete equally in the overload resolution algorithm. In general the so-called "universal reference" wins unless const T& is an exact match, and there the const T& wins.

struct A {};

int
main()
{
    f(std::declval());  // calls f(A&&), #1
    f(std::declval());  // calls f(const A&&), #1
    f(std::declval());  // calls f(A&), #1
    f(std::declval());  // calls f(A&&), #1
    f(std::declval());  // calls f(const A&&), #1
    f(std::declval());  // calls f(const A&), #2
}

Good advice is to never overload like this.