--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp37.C	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,61 @@
+// { dg-do compile { target c++17 } }
+
+#include <memory>
+#include <tuple>
+#include <string>
+
+struct X : private std::shared_ptr<int>
+{
+  std::string fun_payload;
+};
+
+template<int N> std::string& get(X& x)
+{
+  if constexpr(N==0) return x.fun_payload;
+}
+
+namespace std {
+  template<> class tuple_size<X> : public std::integral_constant<int, 1> {};
+  template<> class tuple_element<0, X> {public: using type = std::string;};
+}
+
+struct X2 : private std::shared_ptr<int>
+{
+  int fun_payload;
+  template <class T> void get();
+};
+
+template<int N> int& get(X2& x)
+{
+  if constexpr(N==0) return x.fun_payload;
+}
+
+namespace std {
+  template<> class tuple_size<X2> : public std::integral_constant<int, 1> {};
+  template<> class tuple_element<0, X2> {public: using type = int;};
+}
+
+class X3
+{
+  double fun_payload;
+public:
+  template <int N> double& get()
+  {
+    if constexpr(N==0) return fun_payload;
+  }
+};
+
+namespace std {
+  template<> class tuple_size<X3> : public std::integral_constant<int, 1> {};
+  template<> class tuple_element<0, X3> {public: using type = double;};
+}
+
+int main()
+{
+  X x;
+  auto& [b1] = x;
+  X2 x2;
+  auto& [b2] = x2;
+  X3 x3;
+  auto& [b3] = x3;
+}