119 lines
3.7 KiB
C++
119 lines
3.7 KiB
C++
// RUN: %clang_cc1 -std=c++11 %s -fsyntax-only -fcxx-exceptions
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template<typename T> struct remove_reference { typedef T type; };
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template<typename T> struct remove_reference<T&> { typedef T type; };
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template<typename T> struct remove_reference<T&&> { typedef T type; };
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template<typename T> constexpr T &&forward(typename remove_reference<T>::type &t) noexcept { return static_cast<T&&>(t); }
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template<typename T> constexpr T &&forward(typename remove_reference<T>::type &&t) noexcept { return static_cast<T&&>(t); }
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template<typename T> constexpr typename remove_reference<T>::type &&move(T &&t) noexcept { return static_cast<typename remove_reference<T>::type&&>(t); }
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template<typename T> T declval() noexcept;
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namespace detail {
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template<unsigned N> struct select {}; // : integral_constant<unsigned, N> {};
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template<typename T> struct type {};
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template<typename...T> union either_impl;
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template<> union either_impl<> {
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void get(...);
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void destroy(...) { throw "logic_error"; }
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};
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template<typename T, typename...Ts> union either_impl<T, Ts...> {
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private:
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T val;
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either_impl<Ts...> rest;
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typedef either_impl<Ts...> rest_t;
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public:
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constexpr either_impl(select<0>, T &&t) : val(move(t)) {}
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template<unsigned N, typename U>
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constexpr either_impl(select<N>, U &&u) : rest(select<N-1>(), move(u)) {}
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constexpr static unsigned index(type<T>) { return 0; }
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template<typename U>
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constexpr static unsigned index(type<U> t) {
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return decltype(rest)::index(t) + 1;
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}
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void destroy(unsigned elem) {
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if (elem)
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rest.destroy(elem - 1);
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else
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val.~T();
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}
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constexpr const T &get(select<0>) { return val; }
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template<unsigned N> constexpr const decltype(static_cast<const rest_t&>(rest).get(select<N-1>{})) get(select<N>) {
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return rest.get(select<N-1>{});
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}
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};
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}
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template<typename T>
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struct a {
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T value;
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template<typename...U>
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constexpr a(U &&...u) : value{forward<U>(u)...} {}
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};
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template<typename T> using an = a<T>;
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template<typename T, typename U> T throw_(const U &u) { throw u; }
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template<typename...T>
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class either {
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unsigned elem;
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detail::either_impl<T...> impl;
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typedef decltype(impl) impl_t;
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public:
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template<typename U>
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constexpr either(a<U> &&t) :
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elem(impl_t::index(detail::type<U>())),
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impl(detail::select<impl_t::index(detail::type<U>())>(), move(t.value)) {}
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// Destruction disabled to allow use in a constant expression.
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// FIXME: declare a destructor iff any element has a nontrivial destructor
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//~either() { impl.destroy(elem); }
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constexpr unsigned index() noexcept { return elem; }
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template<unsigned N> using const_get_result =
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decltype(static_cast<const impl_t&>(impl).get(detail::select<N>{}));
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template<unsigned N>
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constexpr const_get_result<N> get() {
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// Can't just use throw here, since that makes the conditional a prvalue,
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// which means we return a reference to a temporary.
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return (elem != N ? throw_<const_get_result<N>>("bad_either_get")
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: impl.get(detail::select<N>{}));
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}
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template<typename U>
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constexpr const U &get() {
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return get<impl_t::index(detail::type<U>())>();
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}
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};
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typedef either<int, char, double> icd;
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constexpr icd icd1 = an<int>(4);
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constexpr icd icd2 = a<char>('x');
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constexpr icd icd3 = a<double>(6.5);
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static_assert(icd1.get<int>() == 4, "");
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static_assert(icd2.get<char>() == 'x', "");
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static_assert(icd3.get<double>() == 6.5, "");
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struct non_triv {
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constexpr non_triv() : n(5) {}
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int n;
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};
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constexpr either<const icd*, non_triv> icd4 = a<const icd*>(&icd2);
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constexpr either<const icd*, non_triv> icd5 = a<non_triv>();
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static_assert(icd4.get<const icd*>()->get<char>() == 'x', "");
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static_assert(icd5.get<non_triv>().n == 5, "");
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