1// RUN: %clang_cc1 -std=c++11 %s -fsyntax-only -fcxx-exceptions
2
3template<typename T> struct remove_reference { typedef T type; };
4template<typename T> struct remove_reference<T&> { typedef T type; };
5template<typename T> struct remove_reference<T&&> { typedef T type; };
6
7template<typename T> constexpr T &&forward(typename remove_reference<T>::type &t) noexcept { return static_cast<T&&>(t); }
8template<typename T> constexpr T &&forward(typename remove_reference<T>::type &&t) noexcept { return static_cast<T&&>(t); }
9template<typename T> constexpr typename remove_reference<T>::type &&move(T &&t) noexcept { return static_cast<typename remove_reference<T>::type&&>(t); }
10
11template<typename T> T declval() noexcept;
12
13namespace detail {
14  template<unsigned N> struct select {}; // : integral_constant<unsigned, N> {};
15  template<typename T> struct type {};
16
17  template<typename...T> union either_impl;
18
19  template<> union either_impl<> {
20    void get(...);
21    void destroy(...) { throw "logic_error"; }
22  };
23
24  template<typename T, typename...Ts> union either_impl<T, Ts...> {
25  private:
26    T val;
27    either_impl<Ts...> rest;
28    typedef either_impl<Ts...> rest_t;
29
30  public:
31    constexpr either_impl(select<0>, T &&t) : val(move(t)) {}
32
33    template<unsigned N, typename U>
34    constexpr either_impl(select<N>, U &&u) : rest(select<N-1>(), move(u)) {}
35
36    constexpr static unsigned index(type<T>) { return 0; }
37    template<typename U>
38    constexpr static unsigned index(type<U> t) {
39      return decltype(rest)::index(t) + 1;
40    }
41
42    void destroy(unsigned elem) {
43      if (elem)
44        rest.destroy(elem - 1);
45      else
46        val.~T();
47    }
48
49    constexpr const T &get(select<0>) { return val; }
50    template<unsigned N> constexpr const decltype(static_cast<const rest_t&>(rest).get(select<N-1>{})) get(select<N>) {
51      return rest.get(select<N-1>{});
52    }
53  };
54}
55
56template<typename T>
57struct a {
58  T value;
59  template<typename...U>
60  constexpr a(U &&...u) : value{forward<U>(u)...} {}
61};
62template<typename T> using an = a<T>;
63
64template<typename T, typename U> T throw_(const U &u) { throw u; }
65
66template<typename...T>
67class either {
68  unsigned elem;
69  detail::either_impl<T...> impl;
70  typedef decltype(impl) impl_t;
71
72public:
73  template<typename U>
74  constexpr either(a<U> &&t) :
75    elem(impl_t::index(detail::type<U>())),
76    impl(detail::select<impl_t::index(detail::type<U>())>(), move(t.value)) {}
77
78  // Destruction disabled to allow use in a constant expression.
79  // FIXME: declare a destructor iff any element has a nontrivial destructor
80  //~either() { impl.destroy(elem); }
81
82  constexpr unsigned index() noexcept { return elem; }
83
84  template<unsigned N> using const_get_result =
85    decltype(static_cast<const impl_t&>(impl).get(detail::select<N>{}));
86
87  template<unsigned N>
88  constexpr const_get_result<N> get() {
89    // Can't just use throw here, since that makes the conditional a prvalue,
90    // which means we return a reference to a temporary.
91    return (elem != N ? throw_<const_get_result<N>>("bad_either_get")
92                      : impl.get(detail::select<N>{}));
93  }
94
95  template<typename U>
96  constexpr const U &get() {
97    return get<impl_t::index(detail::type<U>())>();
98  }
99};
100
101typedef either<int, char, double> icd;
102constexpr icd icd1 = an<int>(4);
103constexpr icd icd2 = a<char>('x');
104constexpr icd icd3 = a<double>(6.5);
105
106static_assert(icd1.get<int>() == 4, "");
107static_assert(icd2.get<char>() == 'x', "");
108static_assert(icd3.get<double>() == 6.5, "");
109
110struct non_triv {
111  constexpr non_triv() : n(5) {}
112  int n;
113};
114constexpr either<const icd*, non_triv> icd4 = a<const icd*>(&icd2);
115constexpr either<const icd*, non_triv> icd5 = a<non_triv>();
116
117static_assert(icd4.get<const icd*>()->get<char>() == 'x', "");
118static_assert(icd5.get<non_triv>().n == 5, "");
119