From 3226272a2d49bcbaec72ec735c22b4e0cc2a5c57 Mon Sep 17 00:00:00 2001
From: Jacob Palecki <JacobPalecki@gmail.com>
Date: Mon, 27 Jul 2020 19:31:09 -0700
Subject: skeleton

---
 common/external/tagged-union-single.h | 202 ++++++++++++++++++++++++++++++++++
 1 file changed, 202 insertions(+)
 create mode 100644 common/external/tagged-union-single.h

(limited to 'common/external')

diff --git a/common/external/tagged-union-single.h b/common/external/tagged-union-single.h
new file mode 100644
index 0000000..bcfc1cf
--- /dev/null
+++ b/common/external/tagged-union-single.h
@@ -0,0 +1,202 @@
+#pragma once
+
+using size_t = decltype(alignof(char));
+
+namespace type_traits {
+
+template< class T > struct remove_cv { typedef T type; };
+template< class T > struct remove_cv<const T> { typedef T type; };
+template< class T > struct remove_cv<volatile T> { typedef T type; };
+template< class T > struct remove_cv<const volatile T> { typedef T type; };
+template< class T > using remove_cv_t = typename remove_cv<T>::type;
+
+template< class T > struct remove_reference { typedef T type; };
+template< class T > struct remove_reference<T&> { typedef T type; };
+template< class T > struct remove_reference<T&&> { typedef T type; };
+template< class T > using remove_reference_t = typename remove_reference<T>::type;
+
+template< class T >
+struct remove_cvref {
+    using type = remove_cv_t<remove_reference_t<T>>;
+};
+template< class T > using remove_cvref_t = typename remove_cvref<T>::type;
+
+namespace detail {
+
+template <class T> struct type_identity { using type = T; };
+
+template <class T>
+auto try_add_lvalue_reference(int)->type_identity<T&>;
+template <class T>
+auto try_add_lvalue_reference(...)->type_identity<T>;
+
+template <class T>
+auto try_add_rvalue_reference(int)->type_identity<T&&>;
+template <class T>
+auto try_add_rvalue_reference(...)->type_identity<T>;
+
+} // type_traits::detail
+
+template <class T> struct add_lvalue_reference : decltype(detail::try_add_lvalue_reference<T>(0)) {};
+template< class T > using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;
+
+template <class T> struct add_rvalue_reference : decltype(detail::try_add_rvalue_reference<T>(0)) {};
+template< class T > using add_rvalue_reference_t = typename add_rvalue_reference<T>::type;
+
+template <typename T, typename U> inline constexpr bool is_same_v = false;
+template <typename T> inline constexpr bool is_same_v<T, T> = true;
+template <typename T> inline constexpr bool is_void_v = is_same_v<remove_cv_t<T>, void>;
+
+} // type_traits
+
+template<class T> type_traits::add_rvalue_reference_t<T> declval() noexcept;
+
+template <typename T>
+inline constexpr T maxv(const T& a, const T& b) {
+    return (b < a) ? a : b;
+}
+
+template <typename T>
+inline constexpr T minv(const T& a, const T& b) {
+    return (a < b) ? a : b;
+}
+
+template <typename T>
+inline constexpr T clampv(const T& v, const T& lo, const T& hi) {
+    return minv(maxv(v, lo), hi);
+}
+
+template <typename T>
+inline constexpr const T& select_ref(bool pred, const T& t, const T& f) {
+    return pred ? t : f;
+}
+
+template <typename First, typename... Rest>
+inline constexpr size_t max_size_of = maxv(sizeof(First), max_size_of<Rest...>);
+
+template <typename T>
+inline constexpr size_t max_size_of<T> = sizeof(T);
+
+template <typename First, typename... Rest>
+inline constexpr size_t max_align_of = maxv(alignof(First), max_align_of<Rest...>);
+
+template <typename T>
+inline constexpr size_t max_align_of<T> = alignof(T);
+
+namespace detail {
+
+template <typename... Ts>
+struct b1_index_of_impl {
+
+    template <typename...>
+    struct idx {
+        static constexpr size_t value = 0;
+    };
+
+    template <typename T, typename First, typename... Rest>
+    struct idx <T, First, Rest...> {
+        static constexpr size_t value = []() {
+            if constexpr (type_traits::is_same_v<T, First>) {
+                return sizeof...(Ts) - sizeof...(Rest);
+            }
+            return idx<T, Rest...>::value;
+        }();
+    };
+};
+
+} // detail
+
+template <typename T, typename First, typename... Rest>
+inline constexpr int base1_index_of =
+detail::b1_index_of_impl<First, Rest...>::template idx<T, First, Rest...>::value;
+
+/*
+Requirements: Every type is trivially-copyable and is not an array type
+
+Can be initialized to an empty state as if by using
+std::variant<std::monostate, First, Rest...>
+*/
+template <typename First, typename... Rest>
+struct tagged_union {
+
+    // Requirements: The return type of Visitor is default-constructible (or void)
+    // Returns a value-initialized object when in an empty or invalid state
+    template<typename Visitor>
+    inline constexpr auto visit(Visitor vis) {
+        return visit_impl<Visitor, First, Rest...>(vis);
+    }
+
+    template<typename Visitor>
+    inline constexpr auto visit(Visitor vis) const {
+        return visit_impl<Visitor, First, Rest...>(vis);
+    }
+
+    template<typename T>
+    static constexpr int id = base1_index_of<T, First, Rest...>;
+
+    int tag = 0;
+
+    struct storage_t {
+        alignas(max_align_of<First, Rest...>) char bytes[max_size_of<First, Rest...>];
+
+        template <typename T>
+        inline constexpr T& as() {
+            static_assert(id<T> != 0, "tagged_union can not hold T");
+            return reinterpret_cast<T&>(bytes);
+        }
+
+        template <typename T>
+        inline constexpr const T& as() const {
+            static_assert(id<T> != 0, "tagged_union can not hold T");
+            return reinterpret_cast<const T&>(bytes);
+        }
+
+    } storage;
+
+    constexpr tagged_union() noexcept = default;
+
+    template<typename T>
+    inline constexpr tagged_union(const T& val) noexcept {
+        tag = id<T>;
+        storage.template as<T>() = val;
+    }
+
+    template<typename T>
+    inline constexpr tagged_union& operator=(const T& val) noexcept {
+        tag = id<T>;
+        storage.template as<T>() = val;
+        return *this;
+    }
+
+private:
+    template<typename Visitor, typename T1, typename... TRest>
+    inline constexpr auto visit_impl(Visitor vis) const {
+        if (tag == id<T1>) {
+            return vis(storage.template as<T1>());
+        }
+        if constexpr (sizeof...(TRest) > 0) {
+            return visit_impl<Visitor, TRest...>(vis);
+        }
+        else {
+            using ReturnType = decltype(vis(declval<First&>()));
+            if constexpr (!type_traits::is_void_v<ReturnType>) return ReturnType{};
+        }
+    }
+
+    template<typename Visitor, typename T1, typename... TRest>
+    inline constexpr auto visit_impl(Visitor vis) {
+        if (tag == id<T1>) {
+            return vis(storage.template as<T1>());
+        }
+        if constexpr (sizeof...(TRest) > 0) {
+            return visit_impl<Visitor, TRest...>(vis);
+        }
+        else {
+            using ReturnType = decltype(vis(declval<First&>()));
+            if constexpr (!type_traits::is_void_v<ReturnType>) return ReturnType{};
+        }
+    }
+};
+
+template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
+template<class... Ts> overloaded(Ts...)->overloaded<Ts...>;
-- 
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