How to check if an arbitrary type is an iterator?

Question

This is an exact duplicate of this question, except that accepted answer is wrong, so I ask it again:

How do you correctly check to see if

Answer 1

How about something like this?

template
struct is_iterator
{
   static constexpr bool value = false;
};

template
struct is_iterator::value_type, void>::value>::type>
{
   static constexpr bool value = true;
};

example:

#include 
#include 
#include 

template
struct is_iterator
{
   static constexpr bool value = false;
};

template
struct is_iterator::value_type, void>::value>::type>
{
   static constexpr bool value = true;
};

int main()
{
   static_assert(!is_iterator::value, "ass");
   static_assert(is_iterator::value, "ass");
   static_assert(is_iterator::iterator>::value, "ass");
}

http://liveworkspace.org/code/7dcf96c97fd0b7a69f12658fc7b2693e