mirror of
https://github.com/LadybirdBrowser/ladybird.git
synced 2024-09-30 00:31:14 +00:00
515e2d9734
This commit makes use of the conditionally trivial special member functions introduced in C++20. Basically, `Optional` and `Variant` inherits whether its wrapped type is trivially copy constructible, trivially copy assignable or trivially destructible. This lets the compiler optimize optimize a large number of their use cases. The constraints have been applied to `Optional`'s converting constructors too in order to make the API more explicit. This feature is not supported by Clang yet, so we use conditional compilation so that Lagom can be built on macOS. Once Clang has P0848R3 support, these can be removed.
431 lines
14 KiB
C++
431 lines
14 KiB
C++
/*
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* Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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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 <AK/TypeList.h>
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namespace AK::Detail {
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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 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 constexpr (IsSame<T, InType>)
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return InitialIndex;
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else
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return VariantIndexOf<T, IndexType, InitialIndex + 1, RestOfInTypes...> {}();
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}
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};
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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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ALWAYS_INLINE 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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ALWAYS_INLINE 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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ALWAYS_INLINE 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 const*>(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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};
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template<typename IndexType, IndexType InitialIndex>
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struct Variant<IndexType, InitialIndex> {
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ALWAYS_INLINE static void delete_(IndexType, void*) { }
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ALWAYS_INLINE static void move_(IndexType, void*, void*) { }
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ALWAYS_INLINE static void copy_(IndexType, const void*, void*) { }
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};
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template<typename IndexType, typename... Ts>
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struct VisitImpl {
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template<typename Visitor, IndexType CurrentIndex = 0>
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ALWAYS_INLINE static constexpr decltype(auto) visit(IndexType id, const void* data, Visitor&& visitor) requires(CurrentIndex < sizeof...(Ts))
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{
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using T = typename TypeList<Ts...>::template Type<CurrentIndex>;
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if (id == CurrentIndex)
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return visitor(*bit_cast<T*>(data));
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if constexpr ((CurrentIndex + 1) < sizeof...(Ts))
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return visit<Visitor, CurrentIndex + 1>(id, data, forward<Visitor>(visitor));
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else
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VERIFY_NOT_REACHED();
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}
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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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ALWAYS_INLINE VariantConstructors(T&& t)
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{
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internal_cast().clear_without_destruction();
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internal_cast().set(move(t), VariantNoClearTag {});
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}
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ALWAYS_INLINE VariantConstructors(const T& t)
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{
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internal_cast().clear_without_destruction();
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internal_cast().set(t, VariantNoClearTag {});
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}
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ALWAYS_INLINE VariantConstructors() { }
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private:
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[[nodiscard]] ALWAYS_INLINE Base& internal_cast()
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{
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// Warning: Internal type shenanigans - VariantsConstrutors<T, Base> <- Base
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// Not the other way around, so be _really_ careful not to cause issues.
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return *reinterpret_cast<Base*>(this);
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}
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};
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// Type list deduplication
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// Since this is a big template mess, each template is commented with how and why it works.
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struct ParameterPackTag {
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};
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// Pack<Ts...> is just a way to pass around the type parameter pack Ts
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template<typename... Ts>
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struct ParameterPack : ParameterPackTag {
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};
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// Blank<T> is a unique replacement for T, if T is a duplicate type.
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template<typename T>
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struct Blank {
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};
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template<typename A, typename P>
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inline constexpr bool IsTypeInPack = false;
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// IsTypeInPack<T, Pack<Ts...>> will just return whether 'T' exists in 'Ts'.
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template<typename T, typename... Ts>
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inline constexpr bool IsTypeInPack<T, ParameterPack<Ts...>> = (IsSame<T, Ts> || ...);
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// Replaces T with Blank<T> if it exists in Qs.
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template<typename T, typename... Qs>
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using BlankIfDuplicate = Conditional<(IsTypeInPack<T, Qs> || ...), Blank<T>, T>;
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template<unsigned I, typename...>
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struct InheritFromUniqueEntries;
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// InheritFromUniqueEntries will inherit from both Qs and Ts, but only scan entries going *forwards*
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// that is to say, if it's scanning from index I in Qs, it won't scan for duplicates for entries before I
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// as that has already been checked before.
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// This makes sure that the search is linear in time (like the 'merge' step of merge sort).
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template<unsigned I, typename... Ts, unsigned... Js, typename... Qs>
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struct InheritFromUniqueEntries<I, ParameterPack<Ts...>, IndexSequence<Js...>, Qs...>
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: public BlankIfDuplicate<Ts, Conditional<Js <= I, ParameterPack<>, Qs>...>... {
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using BlankIfDuplicate<Ts, Conditional<Js <= I, ParameterPack<>, Qs>...>::BlankIfDuplicate...;
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};
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template<typename...>
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struct InheritFromPacks;
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// InheritFromPacks will attempt to 'merge' the pack 'Ps' with *itself*, but skip the duplicate entries
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// (via InheritFromUniqueEntries).
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template<unsigned... Is, typename... Ps>
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struct InheritFromPacks<IndexSequence<Is...>, Ps...>
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: public InheritFromUniqueEntries<Is, Ps, IndexSequence<Is...>, Ps...>... {
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using InheritFromUniqueEntries<Is, Ps, IndexSequence<Is...>, Ps...>::InheritFromUniqueEntries...;
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};
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// Just a nice wrapper around InheritFromPacks, which will wrap any parameter packs in ParameterPack (unless it already is one).
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template<typename... Ps>
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using MergeAndDeduplicatePacks = InheritFromPacks<MakeIndexSequence<sizeof...(Ps)>, Conditional<IsBaseOf<ParameterPackTag, Ps>, Ps, ParameterPack<Ps>>...>;
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}
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namespace AK {
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struct Empty {
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};
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template<typename... Ts>
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struct Variant
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: public Detail::MergeAndDeduplicatePacks<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 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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template<typename... NewTs>
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friend struct Variant;
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#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
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Variant(const Variant&) requires(!(IsCopyConstructible<Ts> && ...)) = delete;
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Variant(const Variant&) = default;
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Variant(Variant&&) requires(!(IsMoveConstructible<Ts> && ...)) = delete;
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Variant(Variant&&) = default;
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~Variant() requires(!(IsDestructible<Ts> && ...)) = delete;
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~Variant() = default;
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Variant& operator=(const Variant&) requires(!(IsCopyConstructible<Ts> && ...) || !(IsDestructible<Ts> && ...)) = delete;
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Variant& operator=(const Variant&) = default;
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Variant& operator=(Variant&&) requires(!(IsMoveConstructible<Ts> && ...) || !(IsDestructible<Ts> && ...)) = delete;
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Variant& operator=(Variant&&) = default;
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#endif
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ALWAYS_INLINE Variant(const Variant& old)
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#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
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requires(!(IsTriviallyCopyConstructible<Ts> && ...))
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#endif
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: Detail::MergeAndDeduplicatePacks<Detail::VariantConstructors<Ts, Variant<Ts...>>...>()
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, m_data {}
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, m_index(old.m_index)
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{
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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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// so if a variant containing an int is moved from, it will still contain that int
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// and if a variant with a nontrivial move ctor is moved from, it may or may not be valid
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// but it will still contain the "moved-from" state of the object it previously contained.
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ALWAYS_INLINE Variant(Variant&& old)
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#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
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requires(!(IsTriviallyMoveConstructible<Ts> && ...))
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#endif
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: Detail::MergeAndDeduplicatePacks<Detail::VariantConstructors<Ts, Variant<Ts...>>...>()
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, m_data {}
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, m_index(old.m_index)
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{
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Helper::move_(old.m_index, old.m_data, m_data);
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}
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ALWAYS_INLINE ~Variant()
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#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
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requires(!(IsTriviallyDestructible<Ts> && ...))
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#endif
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{
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Helper::delete_(m_index, m_data);
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}
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ALWAYS_INLINE Variant& operator=(const Variant& other)
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#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
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requires(!(IsTriviallyCopyConstructible<Ts> && ...) || !(IsTriviallyDestructible<Ts> && ...))
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#endif
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{
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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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ALWAYS_INLINE Variant& operator=(Variant&& other)
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#ifdef AK_HAS_CONDITIONALLY_TRIVIAL
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requires(!(IsTriviallyMoveConstructible<Ts> && ...) || !(IsTriviallyDestructible<Ts> && ...))
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#endif
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{
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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::MergeAndDeduplicatePacks<Detail::VariantConstructors<Ts, Variant<Ts...>>...>::MergeAndDeduplicatePacks;
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template<typename T, typename StrippedT = RemoveCVReference<T>>
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void set(T&& t) requires(can_contain<StrippedT>())
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{
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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, typename StrippedT = RemoveCVReference<T>>
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void set(T&& t, Detail::VariantNoClearTag) requires(can_contain<StrippedT>())
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{
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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() requires(can_contain<T>())
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{
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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() requires(can_contain<T>())
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{
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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 requires(can_contain<T>())
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{
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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 requires(can_contain<T>())
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{
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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 requires(can_contain<T>())
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{
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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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ALWAYS_INLINE decltype(auto) visit(Fs&&... functions)
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{
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Visitor<Fs...> visitor { forward<Fs>(functions)... };
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return VisitHelper::visit(m_index, m_data, move(visitor));
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}
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template<typename... Fs>
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ALWAYS_INLINE decltype(auto) visit(Fs&&... functions) const
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{
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Visitor<Fs...> visitor { forward<Fs>(functions)... };
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return VisitHelper::visit(m_index, m_data, move(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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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<RemoveCVReference<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() const&
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{
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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<RemoveCVReference<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... NewTs>
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explicit operator Variant<NewTs...>() &&
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{
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return downcast<NewTs...>();
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}
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template<typename... NewTs>
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explicit operator Variant<NewTs...>() const&
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{
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return downcast<NewTs...>();
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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<IndexType, 0, Ts...>;
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using VisitHelper = Detail::VisitImpl<IndexType, Ts...>;
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template<typename T_, typename U_>
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friend struct Detail::VariantConstructors;
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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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ALWAYS_INLINE void clear_without_destruction()
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{
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__builtin_memset(m_data, 0, data_size);
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m_index = invalid_index;
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}
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template<typename... Fs>
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struct Visitor : Fs... {
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Visitor(Fs&&... args)
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: Fs(forward<Fs>(args))...
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{
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}
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using Fs::operator()...;
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};
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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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alignas(data_alignment) u8 m_data[data_size];
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IndexType m_index;
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};
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}
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using AK::Empty;
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using AK::Variant;
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