Call variadic function in C++ with array as arguments

Question

Suppose I have a simple variadic function like this:

template <typename... A>
void func(A... args)
{
    //Do stuff
}

And I need another function to call the arguments from an array, let's say:

int arg[3] = {1,2,3};

call the function

func(1,2,3);

Is it possible to do this without modifying the templated function?

Answer 1

You could write apply which takes a reference to an array and functor to call with the unpacked array (you might want to add perfect forwarding and such):

template <typename F, typename T, std::size_t N, std::size_t... Idx>
decltype(auto) apply_impl (F f, T (&t)[N], std::index_sequence<Idx...>) {
    return f(t[Idx]...);
}

template <typename F, typename T, std::size_t N>
decltype(auto) apply (F f, T (&t)[N]) {
    return apply_impl(f, t, std::make_index_sequence<N>{});   
}

Then call it like this, if foo is a functor class:

apply(foo{}, a);

If foo is just a normal template function like in your example, you could wrap it in a lambda:

apply([](auto...xs){foo(std::forward<decltype(xs)>(xs)...);}, a);

Live Demo