clang/test/CXX/temp/temp.fct.spec/temp.deduct/p7.cpp

   1 // RUN: %clang_cc1 -std=c++11 -verify %s
   2 // RUN: %clang_cc1 -std=c++2a -verify %s
   3
   4 struct Q { typedef int type; };
   5
   6 // "The substitution occurs in all types and expressions that are used in [...]
   7 // template parameter declarations." In particular, we must substitute into the
   8 // type of a parameter pack that is not a pack expansion, even if we know the
   9 // corresponding argument pack is empty.
  10 template<typename T, typename T::type...> void a(T);
  11 int &a(...);
  12 int &a_disabled = a(0);
  13 int &a_enabled = a(Q()); // expected-error {{cannot bind to a temporary of type 'void'}}
  14
  15 template<typename T, template<typename T::type> class ...X> void b(T);
  16 int &b(...);
  17 int &b_disabled = b(0);
  18 int &b_enabled = b(Q()); // expected-error {{cannot bind to a temporary of type 'void'}}
  19
  20 template<typename T, template<typename T::type...> class ...X> void c(T);
  21 int &c(...);
  22 int &c_disabled = c(0);
  23 int &c_enabled = c(Q()); // expected-error {{cannot bind to a temporary of type 'void'}}
  24
  25 // The substitution proceeds in lexical order and stops when a condition that
  26 // causes deduction to fail is encountered.
  27 #if __cplusplus > 201702L
  28 namespace reversed_operator_substitution_order {
  29   struct X { X(int); };
  30   struct Y { Y(int); };
  31   struct Cat {};
  32   namespace no_adl {
  33     Cat operator<=>(Y, X);
  34     bool operator<(int, Cat);
  35
  36     template<typename T> struct indirect_sizeof {
  37       static_assert(sizeof(T) != 0);
  38       static const auto value = sizeof(T);
  39     };
  40
  41     // We should substitute into the construction of the X object before the
  42     // construction of the Y object, so this is a SFINAE case rather than a
  43     // hard error. This requires substitution to proceed in lexical order
  44     // despite the prior rewrite to
  45     //    0 < (Y(...) <=> X(...))
  46     template<typename T> float &f(
  47         decltype(
  48           X(sizeof(T)) < Y(indirect_sizeof<T>::value)
  49         )
  50     );
  51     template<typename T> int &f(...);
  52   }
  53   int &r = no_adl::f<void>(true);
  54   float &s = no_adl::f<int>(true);
  55 }
  56 #endif