gcc/testsuite/g++.dg/template/sfinae5.C

   1 // DR 339
   2 //
   3 // Test of the use of member functions with SFINAE
   4 typedef char yes_type;
   5 struct no_type { char data[2]; };
   6
   7 template<typename T> T create_a();
   8
   9 template<bool, typename T = void> struct enable_if { typedef T type; };
  10 template<typename T> struct enable_if<false, T> { };
  11
  12 template<typename T>
  13   typename enable_if<(sizeof(create_a<T>().foo(), 1) > 0),
  14                      yes_type>::type
  15   check_has_member_foo(const volatile T&);
  16
  17 no_type check_has_member_foo(...);
  18
  19 template<typename T>
  20 struct has_foo
  21 {
  22   static const bool value =
  23     (sizeof(check_has_member_foo(create_a<T const&>())) == sizeof(yes_type));
  24 };
  25
  26 struct X { };
  27 struct Y {
  28   void foo();
  29 };
  30 struct Z {
  31   void foo(int);
  32 };
  33
  34 struct A {
  35   int foo;
  36 };
  37
  38 struct B {
  39   static int foo();
  40 };
  41
  42 int a1[has_foo<X>::value? -1 : 1];
  43 int a2[has_foo<Y>::value? 1 : -1];
  44 int a3[has_foo<Z>::value? -1 : 1];
  45 int a4[has_foo<int>::value? -1 : 1];
  46 int a5[has_foo<A>::value? -1 : 1];
  47 int a6[has_foo<B>::value? 1 : -1];