clang/test/CXX/temp/temp.constr/temp.constr.constr/function-templates.cpp

   1 // RUN: %clang_cc1 -std=c++2a -x c++ -verify %s
   2
   3 template<typename T>
   4 constexpr bool is_ptr_v = false;
   5
   6 template<typename T>
   7 constexpr bool is_ptr_v<T*> = true;
   8
   9 template<typename T, typename U>
  10 constexpr bool is_same_v = false;
  11
  12 template<typename T>
  13 constexpr bool is_same_v<T, T> = true;
  14
  15 template<typename T> requires is_ptr_v<T> // expected-note   {{because 'is_ptr_v<int>' evaluated to false}}
  16                          // expected-note@-1{{because 'is_ptr_v<char>' evaluated to false}}
  17 auto dereference(T t) { // expected-note   {{candidate template ignored: constraints not satisfied [with T = int]}}
  18                         // expected-note@-1{{candidate template ignored: constraints not satisfied [with T = char]}}
  19   return *t;
  20 }
  21
  22 static_assert(is_same_v<decltype(dereference<int*>(nullptr)), int>);
  23 static_assert(is_same_v<decltype(dereference(2)), int>); // expected-error {{no matching function for call to 'dereference'}}
  24 static_assert(is_same_v<decltype(dereference<char>('a')), char>); // expected-error {{no matching function for call to 'dereference'}}
  25
  26 template<typename T> requires (T{} + T{}) // expected-note {{because substituted constraint expression is ill-formed: invalid operands to binary expression ('A' and 'A')}}
  27 auto foo(T t) { // expected-note {{candidate template ignored: constraints not satisfied [with T = A]}}
  28   return t + t;
  29 }
  30
  31
  32 template<typename T> requires (!((T{} - T{}) && (T{} + T{})) || false)
  33 // expected-note@-1{{because substituted constraint expression is ill-formed: invalid operands to binary expression ('A' and 'A')}}
  34 // expected-note@-2{{and 'false' evaluated to false}}
  35 auto bar(T t) { // expected-note {{candidate template ignored: constraints not satisfied [with T = A]}}
  36   return t + t;
  37 }
  38
  39 struct A { };
  40
  41 static_assert(foo(A{})); // expected-error {{no matching function for call to 'foo'}}
  42 static_assert(bar(A{})); // expected-error {{no matching function for call to 'bar'}}