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303 lines
8.4 KiB
C++
303 lines
8.4 KiB
C++
// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
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#pragma once
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#include "Luau/Common.h"
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#ifndef LUAU_USE_STD_VARIANT
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#define LUAU_USE_STD_VARIANT 0
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#endif
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#if LUAU_USE_STD_VARIANT
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#include <variant>
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#else
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#include <new>
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#include <type_traits>
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#include <initializer_list>
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#include <stddef.h>
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#endif
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namespace Luau
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{
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#if LUAU_USE_STD_VARIANT
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template<typename... Ts>
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using Variant = std::variant<Ts...>;
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template<class Visitor, class Variant>
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auto visit(Visitor&& vis, Variant&& var)
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{
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// This change resolves the ABI issues with std::variant on libc++; std::visit normally throws bad_variant_access
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// but it requires an update to libc++.dylib which ships with macOS 10.14. To work around this, we assert on valueless
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// variants since we will never generate them and call into a libc++ function that doesn't throw.
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LUAU_ASSERT(!var.valueless_by_exception());
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#ifdef __APPLE__
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// See https://stackoverflow.com/a/53868971/503215
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return std::__variant_detail::__visitation::__variant::__visit_value(vis, var);
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#else
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return std::visit(vis, var);
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#endif
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}
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using std::get_if;
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#else
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template<typename... Ts>
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class Variant
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{
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static_assert(sizeof...(Ts) > 0, "variant must have at least 1 type (empty variants are ill-formed)");
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static_assert(std::disjunction_v<std::is_void<Ts>...> == false, "variant does not allow void as an alternative type");
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static_assert(std::disjunction_v<std::is_reference<Ts>...> == false, "variant does not allow references as an alternative type");
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static_assert(std::disjunction_v<std::is_array<Ts>...> == false, "variant does not allow arrays as an alternative type");
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private:
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template<typename T>
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static constexpr int getTypeId()
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{
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using TT = std::decay_t<T>;
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constexpr int N = sizeof...(Ts);
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constexpr bool is[N] = {std::is_same_v<TT, Ts>...};
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for (int i = 0; i < N; ++i)
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if (is[i])
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return i;
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return -1;
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}
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template<typename T, typename... Tail>
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struct First
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{
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using type = T;
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};
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public:
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using first_alternative = typename First<Ts...>::type;
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Variant()
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{
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static_assert(std::is_default_constructible_v<first_alternative>, "first alternative type must be default constructible");
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typeId = 0;
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new (&storage) first_alternative();
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}
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template<typename T>
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Variant(T&& value, std::enable_if_t<getTypeId<T>() >= 0>* = 0)
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{
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using TT = std::decay_t<T>;
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constexpr int tid = getTypeId<T>();
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typeId = tid;
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new (&storage) TT(value);
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}
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Variant(const Variant& other)
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{
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typeId = other.typeId;
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tableCopy[typeId](&storage, &other.storage);
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}
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Variant(Variant&& other)
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{
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typeId = other.typeId;
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tableMove[typeId](&storage, &other.storage);
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}
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~Variant()
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{
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tableDtor[typeId](&storage);
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}
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Variant& operator=(const Variant& other)
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{
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Variant copy(other);
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// static_cast<T&&> is equivalent to std::move() but faster in Debug
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return *this = static_cast<Variant&&>(copy);
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}
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Variant& operator=(Variant&& other)
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{
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if (this != &other)
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{
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tableDtor[typeId](&storage);
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typeId = other.typeId;
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tableMove[typeId](&storage, &other.storage); // nothrow
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}
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return *this;
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}
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template<typename T>
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const T* get_if() const
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{
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constexpr int tid = getTypeId<T>();
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static_assert(tid >= 0, "unsupported T");
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return tid == typeId ? reinterpret_cast<const T*>(&storage) : nullptr;
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}
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template<typename T>
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T* get_if()
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{
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constexpr int tid = getTypeId<T>();
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static_assert(tid >= 0, "unsupported T");
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return tid == typeId ? reinterpret_cast<T*>(&storage) : nullptr;
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}
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bool valueless_by_exception() const
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{
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return false;
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}
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int index() const
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{
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return typeId;
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}
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bool operator==(const Variant& other) const
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{
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static constexpr FnPred table[sizeof...(Ts)] = {&fnPredEq<Ts>...};
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return typeId == other.typeId && table[typeId](&storage, &other.storage);
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}
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bool operator!=(const Variant& other) const
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{
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return !(*this == other);
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}
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private:
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static constexpr size_t cmax(std::initializer_list<size_t> l)
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{
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size_t res = 0;
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for (size_t i : l)
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res = (res < i) ? i : res;
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return res;
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}
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static constexpr size_t storageSize = cmax({sizeof(Ts)...});
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static constexpr size_t storageAlign = cmax({alignof(Ts)...});
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using FnCopy = void (*)(void*, const void*);
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using FnMove = void (*)(void*, void*);
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using FnDtor = void (*)(void*);
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using FnPred = bool (*)(const void*, const void*);
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template<typename T>
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static void fnCopy(void* dst, const void* src)
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{
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new (dst) T(*static_cast<const T*>(src));
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}
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template<typename T>
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static void fnMove(void* dst, void* src)
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{
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// static_cast<T&&> is equivalent to std::move() but faster in Debug
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new (dst) T(static_cast<T&&>(*static_cast<T*>(src)));
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}
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template<typename T>
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static void fnDtor(void* dst)
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{
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static_cast<T*>(dst)->~T();
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}
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template<typename T>
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static bool fnPredEq(const void* lhs, const void* rhs)
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{
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return *static_cast<const T*>(lhs) == *static_cast<const T*>(rhs);
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}
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static constexpr FnCopy tableCopy[sizeof...(Ts)] = {&fnCopy<Ts>...};
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static constexpr FnMove tableMove[sizeof...(Ts)] = {&fnMove<Ts>...};
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static constexpr FnDtor tableDtor[sizeof...(Ts)] = {&fnDtor<Ts>...};
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int typeId;
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alignas(storageAlign) char storage[storageSize];
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template<class Visitor, typename... _Ts>
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friend auto visit(Visitor&& vis, const Variant<_Ts...>& var);
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template<class Visitor, typename... _Ts>
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friend auto visit(Visitor&& vis, Variant<_Ts...>& var);
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};
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template<typename T, typename... Ts>
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const T* get_if(const Variant<Ts...>* var)
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{
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return var ? var->template get_if<T>() : nullptr;
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}
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template<typename T, typename... Ts>
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T* get_if(Variant<Ts...>* var)
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{
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return var ? var->template get_if<T>() : nullptr;
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}
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template<typename Visitor, typename Result, typename T>
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static void fnVisitR(Visitor& vis, Result& dst, std::conditional_t<std::is_const_v<T>, const void, void>* src)
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{
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dst = vis(*static_cast<T*>(src));
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}
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template<typename Visitor, typename T>
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static void fnVisitV(Visitor& vis, std::conditional_t<std::is_const_v<T>, const void, void>* src)
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{
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vis(*static_cast<T*>(src));
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}
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template<class Visitor, typename... Ts>
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auto visit(Visitor&& vis, const Variant<Ts...>& var)
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{
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using Result = std::invoke_result_t<Visitor, typename Variant<Ts...>::first_alternative>;
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static_assert(std::conjunction_v<std::is_same<Result, std::invoke_result_t<Visitor, Ts>>...>,
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"visitor result type must be consistent between alternatives");
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if constexpr (std::is_same_v<Result, void>)
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{
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using FnVisitV = void (*)(Visitor&, const void*);
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static const FnVisitV tableVisit[sizeof...(Ts)] = {&fnVisitV<Visitor, const Ts>...};
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tableVisit[var.typeId](vis, &var.storage);
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}
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else
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{
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using FnVisitR = void (*)(Visitor&, Result&, const void*);
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static const FnVisitR tableVisit[sizeof...(Ts)] = {&fnVisitR<Visitor, Result, const Ts>...};
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Result res;
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tableVisit[var.typeId](vis, res, &var.storage);
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return res;
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}
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}
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template<class Visitor, typename... Ts>
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auto visit(Visitor&& vis, Variant<Ts...>& var)
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{
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using Result = std::invoke_result_t<Visitor, typename Variant<Ts...>::first_alternative&>;
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static_assert(std::conjunction_v<std::is_same<Result, std::invoke_result_t<Visitor, Ts&>>...>,
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"visitor result type must be consistent between alternatives");
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if constexpr (std::is_same_v<Result, void>)
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{
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using FnVisitV = void (*)(Visitor&, void*);
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static const FnVisitV tableVisit[sizeof...(Ts)] = {&fnVisitV<Visitor, Ts>...};
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tableVisit[var.typeId](vis, &var.storage);
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}
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else
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{
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using FnVisitR = void (*)(Visitor&, Result&, void*);
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static const FnVisitR tableVisit[sizeof...(Ts)] = {&fnVisitR<Visitor, Result, Ts>...};
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Result res;
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tableVisit[var.typeId](vis, res, &var.storage);
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return res;
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}
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}
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#endif
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template<class>
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inline constexpr bool always_false_v = false;
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} // namespace Luau
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