Recursive variadic function template

Question

I want to write a class method that takes a template parameter pack, but zero arguments, and "iterate" over the types:

struct Bar {
    template <typename T, typename... Ts>
    void foo() {
        // something with T that involves Bar's members
        foo<Ts...>();
    }
};

What is the preferred way to implement this?

Answer 1

You may use the following:

struct Bar {
    template <typename... Ts>
    void foo() {
        int dummy[] = {0 /*Manage case where Ts is empty*/,
                       (bar<Ts>(), void() /* To avoid overload `operator,` */, 0)...};
        (void) dummy; // suppress warning for unused variable.
    }

    template <typename T>
    void bar()
    {
        // something with T that involves Bar's members
    }

};

In C++17, it can be simplified with Folding expression:

struct Bar {
    template <typename... Ts>
    void foo() {
        (static_cast<void>(bar<Ts>()), ...);
    }

    template <typename T>
    void bar()
    {
        // something with T that involves Bar's members
    }

};