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/*
* Copyright (C) 2025 Apple Inc. All rights reserved.
*
* 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. AND ITS CONTRIBUTORS ``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 ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 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 <wtf/StdLibExtras.h>
namespace WTF {
// OptionalOrReference<T> is just like const T&, except that it can also optionally hold T.
//
// When T has an efficient default constructor, use ValueOrReference<T>; otherwise use OptionalOrReference<T>.
//
// OptionalOrReference<T> is an optimization when you need to return a value that is
// usually an existing reference, but sometimes a temporary, e.g.:
//
// OptionalOrReference<CSSParserContext> context()
// {
// if (canUseCachedContext()) [[likely]]
// return cachedContext(); // existing reference -- OptionalOrReference<T> avoids a copy
// return makeContext(); // temporary -- OptionalOrReference<T> holds T
// }
template<typename T> class OptionalOrReference {
public:
OptionalOrReference(OptionalOrReference&& other)
: m_value(WTFMove(other.m_value))
, m_reference(m_value.has_value() ? m_value.value() : other.m_reference)
{
}
OptionalOrReference(const T& reference LIFETIME_BOUND)
: m_reference(reference)
{
}
OptionalOrReference(T&& temporary)
: m_value(WTFMove(temporary))
, m_reference(m_value.value())
{
}
operator const T&() const LIFETIME_BOUND { return m_reference; }
const T& get() const LIFETIME_BOUND { return m_reference; }
const T* operator->() const LIFETIME_BOUND { return &m_reference; }
private:
std::optional<T> m_value;
const T& m_reference;
};
} // namespace WTF
using WTF::OptionalOrReference;
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