How to check if a template parameter is an iterator type or not?

Question

template
struct is_iterator
{
    static const bool value = ??? // What to write ???
};

int main()
{
    assert(false == is_iterator::valu         


        

Answer 1

template
struct is_iterator
{   
    static T makeT();
    typedef void * twoptrs[2];  // sizeof(twoptrs) > sizeof(void *)
    static twoptrs & test(...); // Common case
    template static typename R::iterator_category * test(R); // Iterator
    template static void * test(R *); // Pointer

    static const bool value = sizeof(test(makeT())) == sizeof(void *); 
};