1 // RUN: %clang_cc1 -std=c++2a -verify %s
2 
3 namespace p3 {
4   void bar(...);
5   template <typename... Args> void foo(Args... args) {
6     (void)[... xs = args] {
7       bar(xs...);
8     };
9   }
10 
11   void use() {
12     foo();
13     foo(1);
14   }
15 }
16 
17 template<typename ...T> void f(T ...t) {
18   (void)[&...x = t] {
19     x; // expected-error {{unexpanded parameter pack 'x'}}
20   };
21 
22   // Not OK: can't expand 'x' outside its scope.
23   weird((void)[&...x = t] {
24     return &x; // expected-error {{unexpanded parameter pack 'x'}}
25   }...         // expected-error {{does not contain any unexpanded}}
26   );
27 
28   // OK, capture only one 'slice' of 'x'.
29   weird((void)[&x = t] {
30     return &x;
31   }...
32   );
33 
34   // 'x' is not expanded by the outer '...', but 'T' is.
35   weird((void)[&... x = t] {
36     return T() + &x; // expected-error {{unexpanded parameter pack 'x'}}
37   }...               // expected-error {{does not contain any unexpanded}}
38   );
39 }
40 
41 template<int ...a> constexpr auto x = [...z = a] (auto F) { return F(z...); };
42 static_assert(x<1,2,3>([](int a, int b, int c) { return 100 * a + 10 * b + c; }) == 123);
43 static_assert(x<1,2,3>([](int a, int b, int c) { return 100 * a + 10 * b + c; }) == 124); // expected-error {{failed}}
44 
45 template<int ...a> constexpr auto y = [z = a...] (auto F) { return F(z...); }; // expected-error {{must appear before the name of the capture}}
46 static_assert(y<1,2,3>([](int a, int b, int c) { return 100 * a + 10 * b + c; }) == 123);
47 static_assert(y<1,2,3>([](int a, int b, int c) { return 100 * a + 10 * b + c; }) == 124); // expected-error {{failed}}
48