1 // RUN: %clang_cc1 -std=c++2a -x c++ %s -verify
2 
3 // Examples from standard
4 
5 template<typename T, typename U>
6 concept convertible_to = requires(T t) { U(t); };
7 
8 template<typename T>
9 concept R = requires (T i) {
10   typename T::type;
11   {*i} -> convertible_to<const typename T::type&>;
12 };
13 
14 template<typename T> requires R<T> struct S {};
15 
16 struct T {
17   using type = int;
18   type i;
19   const type &operator*() { return i; }
20 };
21 
22 using si = S<T>;
23 
24 template<typename T>
25 requires requires (T x) { x + x; } // expected-note{{because 'x + x' would be invalid: invalid operands to binary expression ('T' and 'T')}}
26 T add(T a, T b) { return a + b; } // expected-note{{candidate template ignored: constraints not satisfied [with T = T]}}
27 
28 int x = add(1, 2);
29 int y = add(T{}, T{}); // expected-error{{no matching function for call to 'add'}}
30 
31 template<typename T>
32 concept C = requires (T x) { x + x; }; // expected-note{{because 'x + x' would be invalid: invalid operands to binary expression ('T' and 'T')}}
33 template<typename T> requires C<T> // expected-note{{because 'T' does not satisfy 'C'}}
34 T add2(T a, T b) { return a + b; } // expected-note{{candidate template ignored: constraints not satisfied [with T = T]}}
35 
36 int z = add2(1, 2);
37 int w = add2(T{}, T{}); // expected-error{{no matching function for call to 'add2'}}