How to write a variadic template recursive function?

Question

I\'m trying to write a variadic template constexpr function which calculates sum of the template parameters given. Here\'s my code:

template<         


        

Answer 1

Your base case was wrong. You need a case for the empty list, but as the compiler suggests, your second try was not a valid template specialization. One way to define a valid instantiation for zero arguments is to create an overload that accepts an empty list

template
constexpr int f()
{
    return 0;
}
template
constexpr int f()
{
    return First + f();
}
int main()
{
    f<1, 2, 3>();
    return 0;
}

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EDIT: for completeness sake also my first answer, that @alexeykuzmin0 fixed by adding the conditional:

template
constexpr int f()
{
    return sizeof...(Rest)==0 ? First : First + f();
}