On Sat, 30 Nov 2024 at 17:30, Jonathan Wakely <cxx_at_[hidden]> wrote:

>
>
> On Sat, 30 Nov 2024, 14:16 Desmond Gold via Std-Proposals, <
> std-proposals_at_[hidden]> wrote:
>
>>
>>
>> ---------- Forwarded message ---------
>> From: Desmond Gold <desmondbongcawel922_at_[hidden]>
>> Date: Sat, Nov 30, 2024 at 8:15 PM
>> Subject: destructurable std::integer_sequence
>> To: <std-proposals_at_[hidden]>
>>
>>
>> After P1061R10 <https://wg21.link/P1061R10> has been approved for
>> C++26, it's now time to let std::integer_sequence be a destructurable
>> type for improved usability while still remain its niche
>>
>> auto [...Is] = std::make_index_sequence<N>();
>>
>> This addition helps simplify metaprogramming implementations that rely on
>> std::integer_sequence. Most of these implementations declare another
>> helper function that takes std::integer_sequence that does the actual
>> work. But with this addition, you don't need to do that.
>>
>> // before:
>> template <typename Array, std::size_t... I>
>> constexpr auto array_to_tuple_impl(const Array& a,
>> std::index_sequence<I...>)
>> {
>> return std::make_tuple(a[I]...);
>> }
>>
>> template <typename T, std::size_t N, typename Indx =
>> std::make_index_sequence<N>>
>> constexpr auto array_to_tuple(const std::array<T, N>& a)
>> {
>> return details::array_to_tuple_impl(a, Indx{});
>> }
>>
>> // after:
>> template <typename T, std::size_t N>
>> constexpr auto array_to_tuple(const std::array<T, N>& a)
>> {
>> auto [...Is] = std::make_index_sequence<N>();
>> return std::make_tuple(a[Is]...);
>> }
>>
>
> Can't you just do:
>
> auto& [e...] = a;
> return std::tuple(e...);
>
> ?
>

Actually you don't even need that, because std::array is tuple-like so you
can just say std::tuple(a) and it works.

But let's say we have some structural type that isn't tuple-like, then you
can just unpack it into a pack, and then expand that. You don't need an
index_sequence.

auto [e...] = a; // unpack a into e...
return SomethingElse(e...);