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      1 //===----------------------------------------------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is dual licensed under the MIT and the University of Illinois Open
      6 // Source Licenses. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 // <functional>
     11 
     12 // reference_wrapper
     13 
     14 // has weak result type
     15 
     16 #include <functional>
     17 #include <type_traits>
     18 
     19 class functor1
     20     : public std::unary_function<int, char>
     21 {
     22 };
     23 
     24 class functor2
     25     : public std::binary_function<char, int, double>
     26 {
     27 };
     28 
     29 class functor3
     30     : public std::unary_function<char, int>,
     31       public std::binary_function<char, int, double>
     32 {
     33 public:
     34     typedef float result_type;
     35 };
     36 
     37 class functor4
     38     : public std::unary_function<char, int>,
     39       public std::binary_function<char, int, double>
     40 {
     41 public:
     42 };
     43 
     44 class C {};
     45 
     46 template <class T>
     47 struct has_result_type
     48 {
     49 private:
     50     struct two {char _; char __;};
     51     template <class U> static two test(...);
     52     template <class U> static char test(typename U::result_type* = 0);
     53 public:
     54     static const bool value = sizeof(test<T>(0)) == 1;
     55 };
     56 
     57 int main()
     58 {
     59     static_assert((std::is_same<std::reference_wrapper<functor1>::result_type,
     60                                 char>::value), "");
     61     static_assert((std::is_same<std::reference_wrapper<functor2>::result_type,
     62                                 double>::value), "");
     63     static_assert((std::is_same<std::reference_wrapper<functor3>::result_type,
     64                                 float>::value), "");
     65     static_assert((std::is_same<std::reference_wrapper<void()>::result_type,
     66                                 void>::value), "");
     67     static_assert((std::is_same<std::reference_wrapper<int*(double*)>::result_type,
     68                                 int*>::value), "");
     69     static_assert((std::is_same<std::reference_wrapper<void(*)()>::result_type,
     70                                 void>::value), "");
     71     static_assert((std::is_same<std::reference_wrapper<int*(*)(double*)>::result_type,
     72                                 int*>::value), "");
     73     static_assert((std::is_same<std::reference_wrapper<int*(C::*)(double*)>::result_type,
     74                                 int*>::value), "");
     75     static_assert((std::is_same<std::reference_wrapper<int (C::*)(double*) const volatile>::result_type,
     76                                 int>::value), "");
     77     static_assert((std::is_same<std::reference_wrapper<C()>::result_type,
     78                                 C>::value), "");
     79     static_assert(has_result_type<std::reference_wrapper<functor3> >::value, "");
     80     static_assert(!has_result_type<std::reference_wrapper<functor4> >::value, "");
     81     static_assert(!has_result_type<std::reference_wrapper<C> >::value, "");
     82 }
     83