109 lines
4.4 KiB
C++
109 lines
4.4 KiB
C++
/*
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* Copyright (C) 2014 Apple Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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* THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <type_traits>
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namespace WTF {
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template <typename ExpectedType, typename ArgType, bool isBaseType = std::is_base_of_v<ExpectedType, ArgType>>
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struct TypeCastTraits {
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static bool isOfType(ArgType&)
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{
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// If you're hitting this assertion, it is likely because you used
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// is<>() or downcast<>() with a type that doesn't have the needed
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// TypeCastTraits specialization. Please use the following macro
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// to add that specialization:
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// SPECIALIZE_TYPE_TRAITS_BEGIN() / SPECIALIZE_TYPE_TRAITS_END()
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static_assert(std::is_void_v<ExpectedType>, "Missing TypeCastTraits specialization");
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return false;
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}
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};
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// Template specialization for the case where ExpectedType is a base of ArgType,
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// so we can return return true unconditionally.
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template <typename ExpectedType, typename ArgType>
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struct TypeCastTraits<ExpectedType, ArgType, true /* isBaseType */> {
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static bool isOfType(ArgType&) { return true; }
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};
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// Type checking function, to use before casting with downcast<>().
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template <typename ExpectedType, typename ArgType>
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inline bool is(ArgType& source)
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{
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static_assert(std::is_base_of_v<ArgType, ExpectedType>, "Unnecessary type check");
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return TypeCastTraits<const ExpectedType, const ArgType>::isOfType(source);
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}
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template <typename ExpectedType, typename ArgType>
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inline bool is(ArgType* source)
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{
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static_assert(std::is_base_of_v<ArgType, ExpectedType>, "Unnecessary type check");
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return source && TypeCastTraits<const ExpectedType, const ArgType>::isOfType(*source);
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}
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// Update T's constness to match Reference's.
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template <typename Reference, typename T>
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using match_constness_t =
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typename std::conditional_t<std::is_const_v<Reference>, typename std::add_const_t<T>, typename std::remove_const_t<T>>;
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// Safe downcasting functions.
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template<typename Target, typename Source>
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inline match_constness_t<Source, Target>& downcast(Source& source)
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{
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static_assert(!std::is_same_v<Source, Target>, "Unnecessary cast to same type");
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static_assert(std::is_base_of_v<Source, Target>, "Should be a downcast");
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ASSERT_WITH_SECURITY_IMPLICATION(is<Target>(source));
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return static_cast<match_constness_t<Source, Target>&>(source);
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}
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template<typename Target, typename Source>
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inline match_constness_t<Source, Target>* downcast(Source* source)
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{
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static_assert(!std::is_same_v<Source, Target>, "Unnecessary cast to same type");
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static_assert(std::is_base_of_v<Source, Target>, "Should be a downcast");
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ASSERT_WITH_SECURITY_IMPLICATION(!source || is<Target>(*source));
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return static_cast<match_constness_t<Source, Target>*>(source);
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}
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// Add support for type checking / casting using is<>() / downcast<>() helpers for a specific class.
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#define SPECIALIZE_TYPE_TRAITS_BEGIN(ClassName) \
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namespace WTF { \
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template <typename ArgType> \
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class TypeCastTraits<const ClassName, ArgType, false /* isBaseType */> { \
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public: \
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static bool isOfType(ArgType& source) { return isType(source); } \
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private:
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#define SPECIALIZE_TYPE_TRAITS_END() \
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}; \
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}
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} // namespace WTF
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using WTF::TypeCastTraits;
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using WTF::is;
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using WTF::downcast;
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