template <typename T>
struct is_op_ptr {
 private:
   template <class AT>
   static constexpr std::false_type is_it_a_ptr(...); // note the false_type return
   template <class AT>
   static constexpr typename ::std::enable_if<
      ::std::is_same<
         AT,
         typename operation<typename AT::element_type::result_type>::ptr_t>::value,
      std::true_type>::type  // note the true_type return
   is_it_a_ptr(int); // no definition needed
 
 public:
   // do everything unevaluated
   static constexpr bool value = decltype(is_it_a_ptr<T> /* you can just pass T explicitly */ (0))::value;
};
 

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