On Thu, Aug 17, 2023 at 12:41 PM Ville Voutilainen via Std-Proposals
<std-proposals_at_[hidden]> wrote:
>
> Well, yeah - the actual problem is that nothing prevents the
> implementation from putting a T[N+IMPL_DEFINED_CONSTANT] there.


I would feel safe using the following code on anything from an Arduino
microcontroller to an x86_64 Ubuntu PC. I don't anticipate a problem
with it, especially because of the two static_assert's. Do you think
it could possibly malfunction on even the strangest of platforms?

GodBolt: https://godbolt.org/z/c14YjqPvK

#include <cstddef> // size_t
#include <array> // array
#include <type_traits> // is_const, remove_const

template< typename T, std::size_t len > requires (!std::is_const_v<T>)
std::array<T,len> &pretend_is_std_array( T (&arg)[len] )
{
    static_assert( sizeof(std::array<T,len>) == sizeof(T[len]) );

    return *static_cast< std::array<T,len>* >(static_cast<void*>(&arg));
}

template< typename T, std::size_t len > requires std::is_const_v<T>
std::array< std::remove_const_t<T>, len > const &pretend_is_std_array(
T (&arg)[len] )
{
    static_assert( sizeof(std::array< std::remove_const_t<T>, len >)
== sizeof(T[len]) );

    return *static_cast< std::array< std::remove_const_t<T>, len >
const * >(static_cast<void const*>(&arg));
}

void SomeFunc ( std::array<int,16> & ) {}
void SomeFuncC( std::array<int,16> const & ) {}

int main(void)
{
    int monkey[16u] = {};
    int const donkey[16u] = {};

    SomeFunc ( pretend_is_std_array(monkey) );
    SomeFuncC( pretend_is_std_array(donkey) );
}