clang/test/CXX/expr/expr.prim/expr.prim.req/p3.cpp

   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'}}