Richard Smith | ec92bc7 | 2012-03-03 23:51:05 +0000 | [diff] [blame] | 1 | // RUN: %clang_cc1 -std=c++11 %s -fsyntax-only -fcxx-exceptions |
| 2 | |
| 3 | template<typename T> struct remove_reference { typedef T type; }; |
| 4 | template<typename T> struct remove_reference<T&> { typedef T type; }; |
| 5 | template<typename T> struct remove_reference<T&&> { typedef T type; }; |
| 6 | |
| 7 | template<typename T> constexpr T &&forward(typename remove_reference<T>::type &t) noexcept { return static_cast<T&&>(t); } |
| 8 | template<typename T> constexpr T &&forward(typename remove_reference<T>::type &&t) noexcept { return static_cast<T&&>(t); } |
| 9 | template<typename T> constexpr typename remove_reference<T>::type &&move(T &&t) noexcept { return static_cast<typename remove_reference<T>::type&&>(t); } |
| 10 | |
| 11 | template<typename T> T declval() noexcept; |
| 12 | |
| 13 | namespace 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 | |
| 56 | template<typename T> |
| 57 | struct a { |
| 58 | T value; |
| 59 | template<typename...U> |
| 60 | constexpr a(U &&...u) : value{forward<U>(u)...} {} |
| 61 | }; |
| 62 | template<typename T> using an = a<T>; |
| 63 | |
| 64 | template<typename T, typename U> T throw_(const U &u) { throw u; } |
| 65 | |
| 66 | template<typename...T> |
| 67 | class either { |
| 68 | unsigned elem; |
| 69 | detail::either_impl<T...> impl; |
| 70 | typedef decltype(impl) impl_t; |
| 71 | |
| 72 | public: |
| 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. |
Sylvestre Ledru | f3477c1 | 2012-09-27 10:16:10 +0000 | [diff] [blame] | 79 | // FIXME: declare a destructor iff any element has a nontrivial destructor |
Richard Smith | ec92bc7 | 2012-03-03 23:51:05 +0000 | [diff] [blame] | 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 | |
| 101 | typedef either<int, char, double> icd; |
| 102 | constexpr icd icd1 = an<int>(4); |
| 103 | constexpr icd icd2 = a<char>('x'); |
| 104 | constexpr icd icd3 = a<double>(6.5); |
| 105 | |
| 106 | static_assert(icd1.get<int>() == 4, ""); |
| 107 | static_assert(icd2.get<char>() == 'x', ""); |
| 108 | static_assert(icd3.get<double>() == 6.5, ""); |
| 109 | |
| 110 | struct non_triv { |
| 111 | constexpr non_triv() : n(5) {} |
| 112 | int n; |
| 113 | }; |
| 114 | constexpr either<const icd*, non_triv> icd4 = a<const icd*>(&icd2); |
| 115 | constexpr either<const icd*, non_triv> icd5 = a<non_triv>(); |
| 116 | |
| 117 | static_assert(icd4.get<const icd*>()->get<char>() == 'x', ""); |
| 118 | static_assert(icd5.get<non_triv>().n == 5, ""); |