fig15_20 compile error

[fancyerii]

the following codes can't compile:

   const std::array ints1{1, 2, 3, 4, 5}; // has random-access iterators

   auto result1{customDistance(ints1.begin(), ints1.end())};

template <std::input_iterator Iterator>
auto customDistance(Iterator begin, Iterator end) {
   // for random-access iterators subtract the iterators
   if constexpr (std::is_base_of_v<std::random_access_iterator_tag,
      typename Iterator::iterator_category>) {
      std::cout << "customDistance with random-access iterators\n";
      return end - begin; // O(1) operation for random-access iterators
   }

I am using g++-13 and the error messages are:

$ g++-13 -std=c++20 fig15_20.cpp -o fig15_20
fig15_20.cpp: In instantiation of ‘auto customDistance(Iterator, Iterator) [with Iterator = const int*]’:
fig15_20.cpp:40:31:   required from here
fig15_20.cpp:16:23: error: ‘const int*’ is not a class, struct, or union type
   16 |    if constexpr (std::is_base_of_v<std::random_access_iterator_tag,
      |                  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   17 |       typename Iterator::iterator_category>) {
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It seems the Iterator of std::array is a raw int *. std::is_base_of_v need a class/struct/union type.

If I changed std::array to std::vector, it works.

And I searched C++20 std::random_access_iterator is a better way:

   if constexpr (std::random_access_iterator<Iterator>) {
      std::cout << "customDistance with random-access iterators\n";
      return end - begin; // O(1) operation for random-access iterators
   }

It work well with both std::array and std::vector.