1 // { dg-do compile { target c++20 } } 2 3 // ill-formed, no diagnostic required: the two expressions are 4 // functionally equivalent but not equivalent 5 template <int N> void foo(const char (&s)[([]{}, N)]); 6 template <int N> void foo(const char (&s)[([]{}, N)]); 7 8 // two different declarations because the non-dependent portions are not 9 // considered equivalent 10 template <class T> void spam(decltype([]{}) (*s)[sizeof(T)]); 11 template <class T> void spam(decltype([]{}) (*s)[sizeof(T)]); 12 13 template <class T> 14 using A = decltype([] { }); 15 // A<int> and A<char> refer to different closure types 16 17 template <class T> 18 auto f(T) -> decltype([]() { T::invalid; } ()); // { dg-error "invalid" } 19 void f(...); 20 21 template <class T, unsigned = sizeof([]() { T::invalid; })> // { dg-error "invalid" } 22 void g(T); 23 void g(...); 24 25 template <class T> 26 auto h(T) -> decltype([x = T::invalid]() { }); 27 void h(...); 28 29 template <class T> 30 auto i(T) -> decltype([]() -> typename T::invalid { }); 31 void i(...); 32 33 template <class T> 34 auto j(T t) -> decltype([](auto x) -> decltype(x.invalid) { } (t)); 35 void j(...); 36 37 template <class,class> struct different {}; 38 template <class T> struct different<T,T> { typename T::invalid t; }; 39 40 template <class,class> struct same; 41 template <class T> struct same<T,T> {}; 42 43 int main() 44 { 45 foo<1>(""); // { dg-error "ambiguous" } 46 spam<char>(nullptr); // { dg-error "ambiguous" } 47 different<A<int>,A<char>>(); 48 same<A<int>,A<int>>(); 49 f(0); // error: invalid expression not part of the immediate context 50 g(0); // error: invalid expression not part of the immediate context 51 h(0); // error: invalid expression not part of the immediate context 52 i(0); // error: invalid expression not part of the immediate context 53 j(0); // deduction fails on #1, calls #2 54 } 55