+
+template<typename T>
+struct Number
+{
+ explicit
+ Number(T t = 0) : i(t)
+ { }
+
+ template<typename U, bool B = std::is_convertible<U, T>::value,
+ typename = typename std::enable_if<B>::type>
+ explicit
+ Number(Number<U> n) : i(n.i)
+ { }
+
+ T i = 0;
+
+ Number& operator+=(Number n) { i += n.i; return *this; }
+ Number& operator-=(Number n) { i -= n.i; return *this; }
+ Number& operator*=(Number n) { i *= n.i; return *this; }
+ Number& operator/=(Number n) { i /= n.i; return *this; }
+ Number& operator%=(Number n) { i %= n.i; return *this; }
+
+ Number operator+(Number n) { return Number{ i + n.i }; }
+ Number operator-(Number n) { return Number{ i - n.i }; }
+ Number operator*(Number n) { return Number{ i * n.i }; }
+ Number operator/(Number n) { return Number{ i / n.i }; }
+ Number operator%(Number n) { return Number{ i % n.i }; }
+};
+
+namespace std
+{
+ // Specialise common_type to give a different type
+ template<>
+ struct common_type<Number<int>, Number<int>>
+ { using type = Number<long>; };
+}
+
+void
+test03()
+{
+
+ using D4 = duration<Number<int>, ratio<49, 21>>;
+ static_assert( is_same<common_type<D4>::type,
+ duration<Number<long>, ratio<7, 3>>>::value,
+ "common_type_t<duration<R,P>> uses common_type_t<R>" );
+
+ D4 d4;
+ static_assert( is_same<decltype(+d4), common_type<D4>::type>::value,
+ "unary + returns type with common_type_t<D4::rep> as rep" );
+ static_assert( is_same<decltype(-d4), common_type<D4>::type>::value,
+ "unary - returns type with common_type_t<D4::rep> as rep" );
+}