1 files changed, 118 insertions, 0 deletions
diff --git a/clang/test/SemaCXX/discrim-union.cpp b/clang/test/SemaCXX/discrim-union.cpp
new file mode 100644
index 0000000..15c9a22
--- /dev/null
+++ b/clang/test/SemaCXX/discrim-union.cpp
@@ -0,0 +1,118 @@
+// RUN: %clang_cc1 -std=c++11 %s -fsyntax-only -fcxx-exceptions
+
+template<typename T> struct remove_reference { typedef T type; };
+template<typename T> struct remove_reference<T&> { typedef T type; };
+template<typename T> struct remove_reference<T&&> { typedef T type; };
+
+template<typename T> constexpr T &&forward(typename remove_reference<T>::type &t) noexcept { return static_cast<T&&>(t); }
+template<typename T> constexpr T &&forward(typename remove_reference<T>::type &&t) noexcept { return static_cast<T&&>(t); }
+template<typename T> constexpr typename remove_reference<T>::type &&move(T &&t) noexcept { return static_cast<typename remove_reference<T>::type&&>(t); }
+
+template<typename T> T declval() noexcept;
+
+namespace detail {
+  template<unsigned N> struct select {}; // : integral_constant<unsigned, N> {};
+  template<typename T> struct type {};
+
+  template<typename...T> union either_impl;
+
+  template<> union either_impl<> {
+    void get(...);
+    void destroy(...) { throw "logic_error"; }
+  };
+
+  template<typename T, typename...Ts> union either_impl<T, Ts...> {
+  private:
+    T val;
+    either_impl<Ts...> rest;
+    typedef either_impl<Ts...> rest_t;
+
+  public:
+    constexpr either_impl(select<0>, T &&t) : val(move(t)) {}
+
+    template<unsigned N, typename U>
+    constexpr either_impl(select<N>, U &&u) : rest(select<N-1>(), move(u)) {}
+
+    constexpr static unsigned index(type<T>) { return 0; }
+    template<typename U>
+    constexpr static unsigned index(type<U> t) {
+      return decltype(rest)::index(t) + 1;
+    }
+
+    void destroy(unsigned elem) {
+      if (elem)
+        rest.destroy(elem - 1);
+      else
+        val.~T();
+    }
+
+    constexpr const T &get(select<0>) { return val; }
+    template<unsigned N> constexpr const decltype(static_cast<const rest_t&>(rest).get(select<N-1>{})) get(select<N>) {
+      return rest.get(select<N-1>{});
+    }
+  };
+}
+
+template<typename T>
+struct a {
+  T value;
+  template<typename...U>
+  constexpr a(U &&...u) : value{forward<U>(u)...} {}
+};
+template<typename T> using an = a<T>;
+
+template<typename T, typename U> T throw_(const U &u) { throw u; }
+
+template<typename...T>
+class either {
+  unsigned elem;
+  detail::either_impl<T...> impl;
+  typedef decltype(impl) impl_t;
+
+public:
+  template<typename U>
+  constexpr either(a<U> &&t) :
+    elem(impl_t::index(detail::type<U>())),
+    impl(detail::select<impl_t::index(detail::type<U>())>(), move(t.value)) {}
+
+  // Destruction disabled to allow use in a constant expression.
+  // FIXME: declare a destructor iff any element has a nontrivial destructor
+  //~either() { impl.destroy(elem); }
+
+  constexpr unsigned index() noexcept { return elem; }
+
+  template<unsigned N> using const_get_result =
+    decltype(static_cast<const impl_t&>(impl).get(detail::select<N>{}));
+
+  template<unsigned N>
+  constexpr const_get_result<N> get() {
+    // Can't just use throw here, since that makes the conditional a prvalue,
+    // which means we return a reference to a temporary.
+    return (elem != N ? throw_<const_get_result<N>>("bad_either_get")
+                      : impl.get(detail::select<N>{}));
+  }
+
+  template<typename U>
+  constexpr const U &get() {
+    return get<impl_t::index(detail::type<U>())>();
+  }
+};
+
+typedef either<int, char, double> icd;
+constexpr icd icd1 = an<int>(4);
+constexpr icd icd2 = a<char>('x');
+constexpr icd icd3 = a<double>(6.5);
+
+static_assert(icd1.get<int>() == 4, "");
+static_assert(icd2.get<char>() == 'x', "");
+static_assert(icd3.get<double>() == 6.5, "");
+
+struct non_triv {
+  constexpr non_triv() : n(5) {}
+  int n;
+};
+constexpr either<const icd*, non_triv> icd4 = a<const icd*>(&icd2);
+constexpr either<const icd*, non_triv> icd5 = a<non_triv>();
+
+static_assert(icd4.get<const icd*>()->get<char>() == 'x', "");
+static_assert(icd5.get<non_triv>().n == 5, "");