c++templatesc++17function-templatesstdbind

How to generate a compile time initializer list of std::bind values?


I try to create an std::initializer_list of bind values, compile time using the following function.

However, I can't get it correctly.

template<class T, int N> auto b(T t) -> auto
{
    if constexpr (N == 0) {
        return std::initializer_list<????????>{ std::bind(t, 0) };
    }
    else {
        return std::initializer_list { b<decltype(t), N-1>(t), std::bind(t, 0) };
    }
}

All this is to avoid code like:


char F(int c) { return 42; /* do something with c or course */ }
// ....
auto fs = { std::bind(F, 0), 
    std::bind(F, 1), 
    std::bind(F, 2), 
    std::bind(F, 3),
    std::bind(F, 4), 
    std::bind(F, 5) /*, etc ...*/};

Is there anyone who can guide me towards a feasible solution?


Solution

  • I would recommend having a std::array of binded objects, instead of std::initializer_list of binded objects.

    Something along the lines

    namespace impli {
        template<typename T, std::size_t ...I>
        auto make_binded_funcs(T&& t, std::index_sequence<I...>)
        {
            return std::array{std::bind(t, I)...};
        }
    }
    
    template<std::size_t N, typename T> auto b(T&& t) 
    {
        return impli::make_binded_funcs(
                                std::forward<T>(t), std::make_index_sequence<N>{});
    }
    

    and you would call it like:

    auto fs{ b<5>(&F) };
    

    See a demo here


    In C++20, using template lambda this can be however in one function.

    template<std::size_t N, class T>
    auto b(T t)
    {
        return[t]<std::size_t ...I>(std::index_sequence<I...>) {
            return std::array{std::bind(t, I)...};
        }(std::make_index_sequence<N>{});
    }
    

    See a demo here