// Element access.
[[__nodiscard__]]
_GLIBCXX17_CONSTEXPR reference
operator[](size_type __n) noexcept
{
    __glibcxx_requires_subscript(__n);
    return _M_elems[__n];
}

_GLIBCXX17_CONSTEXPR reference
at(size_type __n)
{
    if (__n >= _Nm)
        std::__throw_out_of_range_fmt(__N("array::at: __n (which is %zu) "
                                          ">= _Nm (which is %zu)"),
                                      __n, _Nm);
    return _M_elems[__n];
}