121 lines · cpp
1// RUN: %clang_cc1 -std=c++11 %s -fsyntax-only -fcxx-exceptions -verify2 3// expected-no-diagnostics4 5template<typename T> struct remove_reference { typedef T type; };6template<typename T> struct remove_reference<T&> { typedef T type; };7template<typename T> struct remove_reference<T&&> { typedef T type; };8 9template<typename T> constexpr T &&forward(typename remove_reference<T>::type &t) noexcept { return static_cast<T&&>(t); }10template<typename T> constexpr T &&forward(typename remove_reference<T>::type &&t) noexcept { return static_cast<T&&>(t); }11template<typename T> constexpr typename remove_reference<T>::type &&move(T &&t) noexcept { return static_cast<typename remove_reference<T>::type&&>(t); }12 13template<typename T> T declval() noexcept;14 15namespace detail {16 template<unsigned N> struct select {}; // : integral_constant<unsigned, N> {};17 template<typename T> struct type {};18 19 template<typename...T> union either_impl;20 21 template<> union either_impl<> {22 void get(...);23 void destroy(...) { throw "logic_error"; }24 };25 26 template<typename T, typename...Ts> union either_impl<T, Ts...> {27 private:28 T val;29 either_impl<Ts...> rest;30 typedef either_impl<Ts...> rest_t;31 32 public:33 constexpr either_impl(select<0>, T &&t) : val(move(t)) {}34 35 template<unsigned N, typename U>36 constexpr either_impl(select<N>, U &&u) : rest(select<N-1>(), move(u)) {}37 38 constexpr static unsigned index(type<T>) { return 0; }39 template<typename U>40 constexpr static unsigned index(type<U> t) {41 return decltype(rest)::index(t) + 1;42 }43 44 void destroy(unsigned elem) {45 if (elem)46 rest.destroy(elem - 1);47 else48 val.~T();49 }50 51 constexpr const T &get(select<0>) const { return val; }52 template<unsigned N> constexpr const decltype(static_cast<const rest_t&>(rest).get(select<N-1>{})) get(select<N>) const {53 return rest.get(select<N-1>{});54 }55 };56}57 58template<typename T>59struct a {60 T value;61 template<typename...U>62 constexpr a(U &&...u) : value{forward<U>(u)...} {}63};64template<typename T> using an = a<T>;65 66template<typename T, typename U> T throw_(const U &u) { throw u; }67 68template<typename...T>69class either {70 unsigned elem;71 detail::either_impl<T...> impl;72 typedef decltype(impl) impl_t;73 74public:75 template<typename U>76 constexpr either(a<U> &&t) :77 elem(impl_t::index(detail::type<U>())),78 impl(detail::select<impl_t::index(detail::type<U>())>(), move(t.value)) {}79 80 // Destruction disabled to allow use in a constant expression.81 // FIXME: declare a destructor iff any element has a nontrivial destructor82 //~either() { impl.destroy(elem); }83 84 constexpr unsigned index() const noexcept { return elem; }85 86 template<unsigned N> using const_get_result =87 decltype(static_cast<const impl_t&>(impl).get(detail::select<N>{}));88 89 template<unsigned N>90 constexpr const_get_result<N> get() const {91 // Can't just use throw here, since that makes the conditional a prvalue,92 // which means we return a reference to a temporary.93 return (elem != N ? throw_<const_get_result<N>>("bad_either_get")94 : impl.get(detail::select<N>{}));95 }96 97 template<typename U>98 constexpr const U &get() const {99 return get<impl_t::index(detail::type<U>())>();100 }101};102 103typedef either<int, char, double> icd;104constexpr icd icd1 = an<int>(4);105constexpr icd icd2 = a<char>('x');106constexpr icd icd3 = a<double>(6.5);107 108static_assert(icd1.get<int>() == 4, "");109static_assert(icd2.get<char>() == 'x', "");110static_assert(icd3.get<double>() == 6.5, "");111 112struct non_triv {113 constexpr non_triv() : n(5) {}114 int n;115};116constexpr either<const icd*, non_triv> icd4 = a<const icd*>(&icd2);117constexpr either<const icd*, non_triv> icd5 = a<non_triv>();118 119static_assert(icd4.get<const icd*>()->get<char>() == 'x', "");120static_assert(icd5.get<non_triv>().n == 5, "");121