Implementation C++14 make_integer_sequence

Question

I tried to implement the C++14 alias template make_integer_sequence, which simplifies the creation of the class template integer_sequence.

templ         


        

Answer 1

Here is another slightly more general variation of Xeo's logarithmic answer which provides make_integer_sequence for arbitrary types. This is done by using std::integral_constant in order to avoid the dreaded "template argument involves template parameter" error.

template
struct integer_sequence
{
    using value_type = Int;
    static constexpr std::size_t size() noexcept
    {
        return sizeof...(Ints);
    }
};

template
using index_sequence = integer_sequence;

namespace
{
    // Merge two integer sequences, adding an offset to the right-hand side.
    template
    struct merge;

    template
    struct merge<
        std::integral_constant,
        integer_sequence,
        integer_sequence
    >
    {
        using type = integer_sequence;
    };

    template
    struct log_make_sequence
    {
        using L = std::integral_constant;
        using R = std::integral_constant;
        using type = typename merge<
            L,
            typename log_make_sequence::type,
            typename log_make_sequence::type
        >::type;
    };

    // An empty sequence.
    template
    struct log_make_sequence>
    {
        using type = integer_sequence;
    };

    // A single-element sequence.
    template
    struct log_make_sequence>
    {
        using type = integer_sequence;
    };
}

template
using make_integer_sequence =
    typename log_make_sequence<
        Int, std::integral_constant
    >::type;

template
using make_index_sequence = make_integer_sequence;

Demo: coliru