mirror of
https://github.com/SerenityOS/serenity
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1a10e904b5
These recursive templates have a measurable impact on the compile speed of Variant-heavy code like LibWeb. Using these builtins leads to a 2.5% speedup for the measured compilation units.
83 lines
2.1 KiB
C++
83 lines
2.1 KiB
C++
/*
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* Copyright (c) 2020, the SerenityOS developers.
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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/StdLibExtras.h>
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namespace AK {
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template<typename... Types>
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struct TypeList;
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template<unsigned Index, typename List>
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struct TypeListElement;
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#if __has_builtin(__type_pack_element)
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template<unsigned Index, typename... Types>
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struct TypeListElement<Index, TypeList<Types...>> {
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using Type = __type_pack_element<Index, Types...>;
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};
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#else
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template<unsigned Index, typename Head, typename... Tail>
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struct TypeListElement<Index, TypeList<Head, Tail...>>
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: TypeListElement<Index - 1, TypeList<Tail...>> {
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};
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template<typename Head, typename... Tail>
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struct TypeListElement<0, TypeList<Head, Tail...>> {
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using Type = Head;
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};
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#endif
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template<typename... Types>
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struct TypeList {
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static constexpr unsigned size = sizeof...(Types);
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template<unsigned N>
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using Type = typename TypeListElement<N, TypeList<Types...>>::Type;
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};
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template<typename T>
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struct TypeWrapper {
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using Type = T;
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};
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template<typename List, typename F, unsigned... Indices>
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constexpr void for_each_type_impl(F&& f, IndexSequence<Indices...>)
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{
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(forward<F>(f)(TypeWrapper<typename List::template Type<Indices>> {}), ...);
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}
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template<typename List, typename F>
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constexpr void for_each_type(F&& f)
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{
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for_each_type_impl<List>(forward<F>(f), MakeIndexSequence<List::size> {});
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}
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template<typename ListA, typename ListB, typename F, unsigned... Indices>
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constexpr void for_each_type_zipped_impl(F&& f, IndexSequence<Indices...>)
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{
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(forward<F>(f)(TypeWrapper<typename ListA::template Type<Indices>> {}, TypeWrapper<typename ListB::template Type<Indices>> {}), ...);
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}
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template<typename ListA, typename ListB, typename F>
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constexpr void for_each_type_zipped(F&& f)
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{
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static_assert(ListA::size == ListB::size, "Can't zip TypeLists that aren't the same size!");
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for_each_type_zipped_impl<ListA, ListB>(forward<F>(f), MakeIndexSequence<ListA::size> {});
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}
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}
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#if USING_AK_GLOBALLY
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using AK::for_each_type;
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using AK::for_each_type_zipped;
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using AK::TypeList;
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using AK::TypeListElement;
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using AK::TypeWrapper;
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#endif
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