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/*
* Copyright (C) 2024 Samuel Weinig <sam@webkit.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <variant>
#include <wtf/StdLibExtras.h>
#include <wtf/VectorTraits.h>
namespace WTF {
// MARK: - Utility concepts/traits for std::variant.
template<typename> struct VariantAllAlternativesCanCopyWithMemcpyHelper;
template<typename... Ts> struct VariantAllAlternativesCanCopyWithMemcpyHelper<std::variant<Ts...>> : std::integral_constant<bool, all<VectorTraits<Ts>::canCopyWithMemcpy...>> { };
template<typename V> concept VariantAllAlternativesCanCopyWithMemcpy = VariantAllAlternativesCanCopyWithMemcpyHelper<V>::value;
template<typename> struct VariantAllAlternativesCanMoveWithMemcpyHelper;
template<typename... Ts> struct VariantAllAlternativesCanMoveWithMemcpyHelper<std::variant<Ts...>> : std::integral_constant<bool, all<VectorTraits<Ts>::canMoveWithMemcpy...>> { };
template<typename V> concept VariantAllAlternativesCanMoveWithMemcpy = VariantAllAlternativesCanMoveWithMemcpyHelper<V>::value;
// MARK: - Best match for std::variant construction.
// `VariantBestMatch` picks the type `T` from `Ts...` in `std::variant<Ts...>` that will be used when the
// `std::variant<Ts...>` is constructed from type `Arg`. Implementation based off of libc++.
struct VariantNoNarrowingCheck {
template<typename D, typename S> using apply = std::type_identity_t<D>;
};
struct VariantNarrowingCheck {
template<typename D> static auto test(D(&&)[1]) -> std::type_identity_t<D>;
template<typename D, typename S> using apply = decltype(test<D>({ std::declval<S>() }));
};
template<typename D, typename S> using VariantCheckForNarrowing = typename std::conditional_t<std::is_arithmetic_v<D>, VariantNarrowingCheck, VariantNoNarrowingCheck>::template apply<D, S>;
template<typename T, size_t I> struct VariantOverload {
template<typename U> auto operator()(T, U&&) const -> VariantCheckForNarrowing<T, U>;
};
template<typename... Bases> struct VariantAllOverloads : Bases... {
void operator()() const;
using Bases::operator()...;
};
template<typename Seq> struct VariantMakeOverloadsImpl;
template<size_t... I> struct VariantMakeOverloadsImpl<std::index_sequence<I...> > {
template<typename... Ts> using apply = VariantAllOverloads<VariantOverload<Ts, I>...>;
};
template<typename... Ts> using VariantMakeOverloads = typename VariantMakeOverloadsImpl<std::make_index_sequence<sizeof...(Ts)> >::template apply<Ts...>;
template<typename T, typename... Ts> using VariantBestMatchImpl = typename std::invoke_result_t<VariantMakeOverloads<Ts...>, T, T>;
template<typename V, typename Arg> struct VariantBestMatch;
template<typename Arg, typename... Ts> struct VariantBestMatch<std::variant<Ts...>, Arg> {
using type = VariantBestMatchImpl<Arg, Ts...>;
};
// MARK: - Type switching for std::variant
// Calls a zero argument functor with a template argument corresponding to the index's mapped type.
//
// e.g.
// using Variant = std::variant<int, float>;
//
// Variant foo = 5;
// typeForIndex<Variant>(
// foo.index(), /* index will be 0 for first parameter, <int> */
// []<typename T>() {
// if constexpr (std::is_same_v<T, int>) {
// print("we got an int"); <--- this will get called
// } else if constexpr (std::is_same_v<T, float>) {
// print("we got an float"); <--- this will NOT get called
// }
// }
// );
template<typename V, typename F> constexpr decltype(auto) typeForIndex(size_t index, NOESCAPE F&& f)
{
return visitAtIndex<0, std::variant_size_v<std::remove_cvref_t<V>>>(
index,
[&]<size_t I>() ALWAYS_INLINE_LAMBDA {
return f.template operator()<std::variant_alternative_t<I, std::remove_cvref_t<V>>>();
}
);
}
} // namespace WTF
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