How can I make this variadic template code shorter using features from C++14 and C++1z?

Question

This is a code snippet that I am going to use in order to check whether the variadic template types are unique:

template 
struct is_one_of         


        

Answer 1

I'm in line with Brian Rodriguez's and Piotr Scontnincki's answers, as far as it concerns the fold expressions part. Until folding expressions are in, you could shrink the existing code a little bit by getting rid of the incomplete primary templates as follows:

template 
struct is_one_of {
    static constexpr bool value = false;
};

template 
struct is_one_of {
    static constexpr bool value =
        std::is_same::value || is_one_of::value;
};

template 
struct is_unique {
    static constexpr bool value = true;
};

template 
struct is_unique {
    static constexpr bool value = is_unique::value && !is_one_of::value;
};