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89 lines
2.0 KiB
C++
89 lines
2.0 KiB
C++
/*
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* Copyright (c) 2022, Tim Schumacher <timschumi@gmx.de>
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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/NonnullOwnPtr.h>
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#include <AK/Variant.h>
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namespace AK {
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template<typename T>
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class MaybeOwned {
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AK_MAKE_NONCOPYABLE(MaybeOwned);
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public:
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template<DerivedFrom<T> U>
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MaybeOwned(NonnullOwnPtr<U> handle)
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: m_handle(static_cast<NonnullOwnPtr<T>&&>(move(handle)))
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{
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}
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// This is made `explicit` to not accidentally create a non-owning MaybeOwned,
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// which may not always be intended.
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explicit MaybeOwned(T& handle)
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: m_handle(&handle)
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{
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}
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MaybeOwned(MaybeOwned&&) = default;
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MaybeOwned& operator=(MaybeOwned&&) = default;
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template<DerivedFrom<T> U>
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MaybeOwned(MaybeOwned<U>&& other)
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: m_handle(downcast<U, T>(move(other.m_handle)))
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{
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}
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T* ptr()
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{
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if (m_handle.template has<T*>())
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return m_handle.template get<T*>();
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else
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return m_handle.template get<NonnullOwnPtr<T>>();
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}
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T const* ptr() const
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{
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if (m_handle.template has<T*>())
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return m_handle.template get<T*>();
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else
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return m_handle.template get<NonnullOwnPtr<T>>();
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}
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T* operator->() { return ptr(); }
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T const* operator->() const { return ptr(); }
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T& operator*() { return *ptr(); }
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T const& operator*() const { return *ptr(); }
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bool is_owned() const { return m_handle.template has<NonnullOwnPtr<T>>(); }
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private:
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template<typename F>
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friend class MaybeOwned;
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template<typename HT>
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using Handle = Variant<NonnullOwnPtr<HT>, HT*>;
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template<typename U, typename D>
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Handle<D> downcast(Handle<U>&& variant)
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{
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if (variant.template has<U*>())
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return variant.template get<U*>();
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else
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return static_cast<NonnullOwnPtr<T>&&>(move(variant.template get<NonnullOwnPtr<U>>()));
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}
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Handle<T> m_handle;
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};
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}
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#if USING_AK_GLOBALLY
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using AK::MaybeOwned;
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#endif
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