That static_assert will kick in only if the function is called:

#include <assert.h>
#include <cstdlib>

template <std::size_t Idx, typename T, std::size_t N>
constexpr T& get(T (&arr)[N]) noexcept {
    static_assert(Idx < N, "Index out of bounds");
    return arr[Idx];
}

int main(void) {
    constexpr int arr[99] = {1, 2, 3, 4};
    static_assert(get<2>(arr) == 3);

    typedef decltype(&get<99>(arr)) wtf;
    wtf p = &get<2>(arr); // works
}

C++20 requires variant is better.

DBJ

On Tue, 1 Mar 2022 at 17:39, Arthur O'Dwyer via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> On Tue, Mar 1, 2022 at 11:34 AM Barry Revzin <barry.revzin_at_[hidden]>
> wrote:
>
>> On Tue, Mar 1, 2022 at 9:59 AM Arthur O'Dwyer via Std-Proposals <
>> std-proposals_at_[hidden]> wrote:
>>
>>> On Tue, Mar 1, 2022 at 10:13 AM Nikolay Mihaylov via Std-Proposals <
>>> std-proposals_at_[hidden]> wrote:
>>>
>>>> Once again, why do we need the size?
>>>> Shall we check the size?
>>>> Via static_assert?
>>>> During runtime?
>>>>
>>>
>>> In the proposed std::get for C arrays, AIUI, the size would be part of
>>> the signature. It would look like this:
>>>
>>> template<size_t X, class T, size_t N> requires (X < N)
>>> constexpr T& get(T (&arr)[N]) noexcept {
>>> return arr[X];
>>> }
>>>
>>
>> No, it wouldn't. Paulo's email contained the correct implementation:
>>
>> template <std::size_t Idx, typename T, std::size_t N>
>> constexpr T& get(T (&arr)[N]) noexcept
>> {
>> static_assert(Idx < N, "Index out of bounds");
>> return arr[Idx];
>> }
>>
>> This would match what std::get does for std::array, std::pair, and
>> std::tuple.
>>
>
> Oh, gross. If it's not going to be SFINAE-friendly, then I don't
> particularly have an opinion what it does.
>
> –Arthur
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>