I’m using the type aliases for pointer and const pointer and I don’t understand why there is difference between returning a cost pointer and a const_pointer.

I assumed that const pointer, in this case, is equivalent to const int*, but I’m getting an invalid conversion compile error:
error: invalid conversion from 'const int*' to 'S::pointer {aka int*}

struct S
{
  using pointer = int*;
  using const_pointer = const int*;

  // const_pointer get() const { return &i; }    // OK
  const pointer get() const { return &i; } // ERROR

  int i = {};
};

int main()
{
  const S s;
  s.get();
}