How to reverse the order of arguments of a variadic template function?

Question

I have a template function with varargs template arguments, like this

template
void ascendingPrint(         


        

Answer 1

Here is a recursive implementation of a specialized revert<>:

// forward decl
template
struct revert;

// recursion anchor
template<>
struct revert<>
{
    template
    static void apply(Un const&... un)
    {
        ascendingPrint(un...);
    }
};

// recursion
template
struct revert 
{
    template
    static void apply(T const& t, Tn const&... tn, Un const&... un)
    {
        // bubble 1st parameter backwards
        revert::apply(tn..., t, un...);
    }
};

// using recursive function
template
void descendingPrint(A const& a, An const&... an)
{
    revert::apply(an..., a);
}

It works with gcc-4.6/7/8 and clang and is probably standard compliant -- the only difficult part being the call of revert::apply(tn..., t, un...).

It has drawbacks though (as recursion often has), that it generates a lot of template-instantiations of the target function (code bloat) and does not use perfect forwarding, which may be an issue (but maybe could be improved to use it).