1 // PR c++/71105 2 // { dg-do compile { target c++14 } } 3 4 template <typename T> T declval(); 5 template <typename, typename> struct is_same 6 { static constexpr bool value = false; }; 7 template <typename T> struct is_same<T, T> 8 { static constexpr bool value = true; }; 9 10 template <class F> 11 struct indirected : F { 12 indirected(F f) : F(f) {} 13 template <class I> 14 auto operator()(I i) -> decltype(declval<F&>()(*i)) { 15 return static_cast<F&>(*this)(*i); 16 } 17 }; 18 19 int main() { 20 auto f = [=](auto i) { return i + i; }; 21 auto i = indirected<decltype(f)>{f}; 22 static_assert(is_same<decltype(i(declval<int*>())), int>::value, ""); 23 } 24