add variadic templates inheritance testcases

template/variadic_class_inheritance_example.cc

@@ -111,6 +111,77 @@ TEST(variadic_class_inheritance, example2) {
 
   oss << "1, 2, 3, 4, 5, 6, \n";
 
+#ifndef NDEBUG
+  debug_msg(oss, act_output);
+#endif
+
+  EXPECT_EQ(oss.str(), act_output);
+}
+
+namespace {
+
+template <typename... F> struct overload_set;
+
+template <typename F1> struct overload_set<F1> : public F1 {
+  overload_set(F1 &&f1) : F1(std::move(f1)) {}
+  overload_set(const F1 &f1) : F1(f1) {}
+  using F1::operator();
+};
+
+template <typename F1, typename... F>
+struct overload_set<F1, F...> : public F1, public overload_set<F...> {
+  overload_set(F1 &&f1, F &&...f) : F1(std::move(f1)), overload_set<F...>(std::forward<F>(f)...) {}
+  overload_set(const F1 &f1, F &&...f) : F1(f1), overload_set<F...>(std::forward<F>(f)...) {}
+
+  using F1::operator();
+  using overload_set<F...>::operator();
+};
+
+template <typename... F> auto overload(F &&...f) {
+  return overload_set<F...>(std::forward<F>(f)...);
+}
+
+// In C++17, we can do better, and it gives us a chance to demonstrate an alternative way of using
+// a parameter pack that does not need recursion.
+
+template <typename... F> struct overload_set_17 : public F... {
+  overload_set_17(F &&...f) : F(std::forward<F>(f))... {}
+
+  using F::operator()...; // C++17
+};
+
+// With deduction guide, there's no need to
+template <typename... F> auto overload_17(F &&...f) {
+  return overload_set<F...>(std::forward<F>(f)...);
+}
+
+// Deduction guide for this overload_set
+template <typename... F> overload_set_17(F &&...) -> overload_set_17<F...>;
+
+void example3() {
+  int i = 5;
+  double d = 7.3;
+
+  auto l = overload_set_17{[](int *i) { std::cout << "i = " << *i << std::endl; },
+                           [](double *d) { std::cout << "d = " << *d << std::endl; }};
+
+  l(&i);
+  l(&d);
+}
+
+} // namespace
+
+TEST(variadic_class_inheritance, example3) {
+  std::stringstream oss;
+  testing::internal::CaptureStdout();
+
+  example3();
+
+  oss << "i = 5\n"
+         "d = 7.3\n";
+
+  auto act_output = testing::internal::GetCapturedStdout();
+
 #ifndef NDEBUG
   debug_msg(oss, act_output);
 #endif