1 // DR 339 2 // 3 // Test of the use of the function call operator 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<typename T> struct type { }; 10 11 template<bool, typename T = void> struct enable_if { typedef T type; }; 12 template<typename T> struct enable_if<false, T> { }; 13 14 template<typename F, typename T1, typename T2> 15 typename enable_if<sizeof(create_a<F>()(create_a<T1>(), create_a<T2>()), 1), 16 yes_type>::type 17 check_is_callable2(type<F>, type<T1>, type<T2>); 18 19 no_type check_is_callable2(...); 20 21 template<typename F, typename T1, typename T2 = T1> 22 struct is_callable2 23 { 24 static const bool value = 25 (sizeof(check_is_callable2(type<F>(), type<T1>(), type<T2>())) 26 == sizeof(yes_type)); 27 }; 28 29 #define JOIN( X, Y ) DO_JOIN( X, Y ) 30 #define DO_JOIN( X, Y ) DO_JOIN2(X,Y) 31 #define DO_JOIN2( X, Y ) X##Y 32 33 #ifdef __GXX_EXPERIMENTAL_CXX0X__ 34 # define STATIC_ASSERT(Expr) static_assert(Expr, #Expr) 35 #else 36 # define STATIC_ASSERT(Expr) int JOIN(a,__LINE__)[Expr? 1 : -1] 37 #endif 38 39 40 struct A; 41 struct B; 42 43 struct A { 44 A(B); 45 }; 46 47 struct B { 48 B(A); 49 }; 50 51 struct F { 52 void operator()(A, A); 53 54 private: 55 void operator()(B, B); 56 }; 57 58 STATIC_ASSERT((!is_callable2<F, B, B>::value)); 59