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AK: Avoid the use of typeinfo in Variant
typeid() and RTTI was a nice clutch to implement this, but let's move away from the horrible slowness and implement variants using type indices for faster variants.
This commit is contained in:
Ali Mohammad Pur
Linus Groh
parent
659c22e17e
commit
3038b6b7dc
Notes:
sideshowbarker
2024-07-18 18:20:35 +09:00
Author: https://github.com/alimpfard Commit: https://github.com/SerenityOS/serenity/commit/3038b6b7dca Pull-request: https://github.com/SerenityOS/serenity/pull/6978 Reviewed-by: https://github.com/Quaker762 ✅ Reviewed-by: https://github.com/sunverwerth ✅
1 changed files with 143 additions and 96 deletions
239
AK/Variant.h
239
AK/Variant.h
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@ -9,72 +9,102 @@
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#include <AK/Array.h>
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#include <AK/BitCast.h>
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#include <AK/StdLibExtras.h>
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#include <typeinfo>
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namespace AK::Detail {
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template<typename... Ts>
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struct Variant;
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template<typename T, typename IndexType, IndexType InitialIndex, typename... InTypes>
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struct VariantIndexOf {
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static_assert(DependentFalse<T, IndexType, InTypes...>, "Invalid VariantIndex instantiated");
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};
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template<typename F, typename... Ts>
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struct Variant<F, Ts...> {
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static void delete_(const std::type_info& id, void* data)
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template<typename T, typename IndexType, IndexType InitialIndex, typename InType, typename... RestOfInTypes>
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struct VariantIndexOf<T, IndexType, InitialIndex, InType, RestOfInTypes...> {
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consteval IndexType operator()()
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{
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if (id == typeid(F))
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bit_cast<F*>(data)->~F();
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if constexpr (IsSame<T, InType>)
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return InitialIndex;
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else
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Variant<Ts...>::delete_(id, data);
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}
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static void move_(const std::type_info& old_id, void* old_data, void* new_data)
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{
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if (old_id == typeid(F))
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new (new_data) F(move(*bit_cast<F*>(old_data)));
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else
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Variant<Ts...>::move_(old_id, old_data, new_data);
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}
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static void copy_(const std::type_info& old_id, const void* old_data, void* new_data)
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{
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if (old_id == typeid(F))
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new (new_data) F(*bit_cast<F*>(old_data));
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else
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Variant<Ts...>::copy_(old_id, old_data, new_data);
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}
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template<typename Visitor>
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static void visit_(const std::type_info& id, void* data, Visitor&& visitor)
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{
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if (id == typeid(F))
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visitor(*bit_cast<F*>(data));
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else
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Variant<Ts...>::visit_(id, data, forward<Visitor>(visitor));
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}
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template<typename Visitor>
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static void visit_(const std::type_info& id, const void* data, Visitor&& visitor)
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{
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if (id == typeid(F))
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visitor(*bit_cast<const F*>(data));
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else
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Variant<Ts...>::visit_(id, data, forward<Visitor>(visitor));
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return VariantIndexOf<T, IndexType, InitialIndex + 1, RestOfInTypes...> {}();
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}
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};
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template<>
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struct Variant<> {
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static void delete_(const std::type_info&, void*) { }
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static void move_(const std::type_info&, void*, void*) { }
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static void copy_(const std::type_info&, const void*, void*) { }
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template<typename T, typename IndexType, IndexType InitialIndex>
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struct VariantIndexOf<T, IndexType, InitialIndex> {
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consteval IndexType operator()() { return InitialIndex; }
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};
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template<typename T, typename IndexType, typename... Ts>
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consteval IndexType index_of()
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{
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return VariantIndexOf<T, IndexType, 0, Ts...> {}();
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}
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template<typename IndexType, IndexType InitialIndex, typename... Ts>
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struct Variant;
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template<typename IndexType, IndexType InitialIndex, typename F, typename... Ts>
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struct Variant<IndexType, InitialIndex, F, Ts...> {
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static constexpr auto current_index = VariantIndexOf<F, IndexType, InitialIndex, F, Ts...> {}();
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static void delete_(IndexType id, void* data)
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{
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if (id == current_index)
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bit_cast<F*>(data)->~F();
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else
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Variant<IndexType, InitialIndex + 1, Ts...>::delete_(id, data);
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}
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static void move_(IndexType old_id, void* old_data, void* new_data)
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{
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if (old_id == current_index)
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new (new_data) F(move(*bit_cast<F*>(old_data)));
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else
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Variant<IndexType, InitialIndex + 1, Ts...>::move_(old_id, old_data, new_data);
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}
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static void copy_(IndexType old_id, const void* old_data, void* new_data)
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{
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if (old_id == current_index)
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new (new_data) F(*bit_cast<F*>(old_data));
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else
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Variant<IndexType, InitialIndex + 1, Ts...>::copy_(old_id, old_data, new_data);
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}
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template<typename Visitor>
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static void visit_(const std::type_info&, void*, Visitor&&) { }
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static void visit_(IndexType id, void* data, Visitor&& visitor)
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{
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if (id == current_index)
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visitor(*bit_cast<F*>(data));
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else
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Variant<IndexType, InitialIndex + 1, Ts...>::visit_(id, data, forward<Visitor>(visitor));
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}
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template<typename Visitor>
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static void visit_(const std::type_info&, const void*, Visitor&&) { }
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static void visit_(IndexType id, const void* data, Visitor&& visitor)
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{
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if (id == current_index)
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visitor(*bit_cast<const F*>(data));
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else
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Variant<IndexType, InitialIndex + 1, Ts...>::visit_(id, data, forward<Visitor>(visitor));
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}
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};
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template<typename IndexType, IndexType InitialIndex>
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struct Variant<IndexType, InitialIndex> {
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static void delete_(IndexType, void*) { }
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static void move_(IndexType, void*, void*) { }
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static void copy_(IndexType, const void*, void*) { }
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template<typename Visitor>
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static void visit_(IndexType, void*, Visitor&&) { }
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template<typename Visitor>
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static void visit_(IndexType, const void*, Visitor&&) { }
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};
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struct VariantNoClearTag {
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explicit VariantNoClearTag() = default;
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};
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struct VariantConstructTag {
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explicit VariantConstructTag() = default;
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};
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template<typename T, typename Base>
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struct VariantConstructors {
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@ -118,15 +148,22 @@ struct Empty {
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template<typename... Ts>
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struct Variant
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: public Detail::VariantConstructors<Ts, Variant<Ts...>>... {
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private:
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using IndexType = Conditional<sizeof...(Ts) < 255, u8, size_t>; // Note: size+1 reserved for internal value checks
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static constexpr IndexType invalid_index = sizeof...(Ts);
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template<typename T>
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static constexpr IndexType index_of() { return Detail::index_of<T, IndexType, Ts...>(); }
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public:
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template<typename... NewTs>
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friend struct Variant;
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Variant(const Variant& old)
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: Detail::VariantConstructors<Ts, Variant<Ts...>>()...
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, m_type_info(old.m_type_info)
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, m_index(old.m_index)
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{
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Helper::copy_(*old.m_type_info, old.m_data, m_data);
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Helper::copy_(old.m_index, old.m_data, m_data);
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}
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// Note: A moved-from variant emulates the state of the object it contains
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@ -135,129 +172,139 @@ struct Variant
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// but it will still contain the "moved-from" state of the object it previously contained.
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Variant(Variant&& old)
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: Detail::VariantConstructors<Ts, Variant<Ts...>>()...
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, m_type_info(old.m_type_info)
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, m_index(old.m_index)
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{
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Helper::move_(*old.m_type_info, old.m_data, m_data);
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Helper::move_(old.m_index, old.m_data, m_data);
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}
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~Variant()
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{
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Helper::delete_(*m_type_info, m_data);
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Helper::delete_(m_index, m_data);
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}
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Variant& operator=(const Variant& other)
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{
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m_type_info = other.m_type_info;
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Helper::copy_(*other.m_type_info, other.m_data, m_data);
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m_index = other.m_index;
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Helper::copy_(other.m_index, other.m_data, m_data);
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return *this;
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}
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Variant& operator=(Variant&& other)
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{
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m_type_info = other.m_type_info;
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Helper::move_(*other.m_type_info, other.m_data, m_data);
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m_index = other.m_index;
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Helper::move_(other.m_index, other.m_data, m_data);
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return *this;
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}
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using Detail::VariantConstructors<Ts, Variant<Ts...>>::VariantConstructors...;
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template<typename T>
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void set(T&& t)
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void set(T&& t) requires(index_of<T>() != invalid_index)
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{
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Helper::delete_(*m_type_info, m_data);
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new (m_data) T(forward<T>(t));
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m_type_info = &typeid(T);
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using StrippedT = RemoveCV<RemoveReference<T>>;
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constexpr auto new_index = index_of<StrippedT>();
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Helper::delete_(m_index, m_data);
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new (m_data) StrippedT(forward<T>(t));
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m_index = new_index;
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}
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template<typename T>
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void set(T&& t, Detail::VariantNoClearTag)
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{
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new (m_data) T(forward<T>(t));
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m_type_info = &typeid(T);
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using StrippedT = RemoveCV<RemoveReference<T>>;
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constexpr auto new_index = index_of<StrippedT>();
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new (m_data) StrippedT(forward<T>(t));
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m_index = new_index;
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}
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template<typename T>
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T* get_pointer()
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{
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if (typeid(T) == *m_type_info)
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return reinterpret_cast<T*>(m_data);
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if (index_of<T>() == m_index)
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return bit_cast<T*>(&m_data);
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return nullptr;
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}
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template<typename T>
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T& get()
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[[gnu::noinline]] T& get()
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{
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VERIFY(typeid(T) == *m_type_info);
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return *reinterpret_cast<T*>(m_data);
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VERIFY(has<T>());
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return *bit_cast<T*>(&m_data);
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}
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template<typename T>
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const T* get_pointer() const
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[[gnu::noinline]] const T* get_pointer() const
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{
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if (typeid(T) == *m_type_info)
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return reinterpret_cast<const T*>(m_data);
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if (index_of<T>() == m_index)
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return bit_cast<const T*>(&m_data);
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return nullptr;
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}
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template<typename T>
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const T& get() const
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[[gnu::noinline]] const T& get() const
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{
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VERIFY(typeid(T) == *m_type_info);
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return *reinterpret_cast<const T*>(m_data);
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VERIFY(has<T>());
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return *bit_cast<const T*>(&m_data);
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}
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template<typename T>
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[[nodiscard]] bool has() const
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{
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return typeid(T) == *m_type_info;
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return index_of<T>() == m_index;
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}
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template<typename... Fs>
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void visit(Fs&&... functions)
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{
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Visitor<Fs...> visitor { forward<Fs>(functions)... };
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Helper::visit_(*m_type_info, m_data, visitor);
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Helper::visit_(m_index, m_data, visitor);
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}
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template<typename... Fs>
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void visit(Fs&&... functions) const
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{
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Visitor<Fs...> visitor { forward<Fs>(functions)... };
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Helper::visit_(*m_type_info, m_data, visitor);
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Helper::visit_(m_index, m_data, visitor);
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}
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template<typename... NewTs>
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Variant<NewTs...> downcast() &&
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{
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VERIFY(covers<NewTs...>());
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Variant<NewTs...> instance { m_type_info };
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Helper::move_(*m_type_info, m_data, instance.m_data);
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Variant<NewTs...> instance { Variant<NewTs...>::invalid_index, Detail::VariantConstructTag {} };
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visit([&](auto& value) {
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if constexpr (Variant<NewTs...>::template can_contain<RemoveCV<RemoveReference<decltype(value)>>>())
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instance.set(move(value), Detail::VariantNoClearTag {});
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});
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VERIFY(instance.m_index != instance.invalid_index);
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return instance;
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}
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template<typename... NewTs>
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Variant<NewTs...> downcast() &
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{
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VERIFY(covers<NewTs...>());
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Variant<NewTs...> instance { m_type_info };
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Helper::copy_(*m_type_info, m_data, instance.m_data);
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Variant<NewTs...> instance { Variant<NewTs...>::invalid_index, Detail::VariantConstructTag {} };
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visit([&](const auto& value) {
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if constexpr (Variant<NewTs...>::template can_contain<RemoveCV<RemoveReference<decltype(value)>>>())
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instance.set(value, Detail::VariantNoClearTag {});
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});
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VERIFY(instance.m_index != instance.invalid_index);
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return instance;
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}
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template<typename T>
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static constexpr bool can_contain()
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{
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return index_of<T>() != invalid_index;
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}
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private:
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static constexpr auto data_size = integer_sequence_generate_array<size_t>(0, IntegerSequence<size_t, sizeof(Ts)...>()).max();
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static constexpr auto data_alignment = integer_sequence_generate_array<size_t>(0, IntegerSequence<size_t, alignof(Ts)...>()).max();
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using Helper = Detail::Variant<Ts...>;
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using Helper = Detail::Variant<IndexType, 0, Ts...>;
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template<typename... NewTs>
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bool covers() const
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{
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return ((typeid(NewTs) == *m_type_info) || ...);
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}
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explicit Variant(const std::type_info* type_info)
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: Detail::VariantConstructors<Ts, Variant<Ts...>>()...
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, m_type_info(type_info)
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explicit Variant(IndexType index, Detail::VariantConstructTag)
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: Detail::MergeAndDeduplicatePacks<Detail::VariantConstructors<Ts, Variant<Ts...>>...>()
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, m_index(index)
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{
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}
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@ -275,7 +322,7 @@ private:
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// Note: Make sure not to default-initialize!
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// VariantConstructors::VariantConstructors(T) will set this to the correct value
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// So default-constructing to anything will leave the first initialization with that value instead of the correct one.
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const std::type_info* m_type_info;
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IndexType m_index;
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};
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}
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