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/*
* Copyright (C) 2018 Yusuke Suzuki <yusukesuzuki@slowstart.org>.
* Copyright (C) 2016-2017 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. ``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,
* 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.
*/
// The idea of Markable<T> is derived from markable<T> at
// https://github.com/akrzemi1/markable.
//
// Copyright (C) 2015-2018 Andrzej Krzemienski.
//
// Use, modification, and distribution is subject to the Boost Software
// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
#pragma once
#include <optional>
#include <type_traits>
#include <wtf/Hasher.h>
#include <wtf/StdLibExtras.h>
namespace WTF {
// Example:
// enum class Type { Value1, Value2, Value3 };
// Markable<Type, EnumMarkableTraits<Type, 42>> optional;
template<
typename EnumType,
typename std::underlying_type<EnumType>::type constant = std::numeric_limits<typename std::underlying_type<EnumType>::type>::max()>
struct EnumMarkableTraits {
static_assert(std::is_enum<EnumType>::value);
using UnderlyingType = typename std::underlying_type<EnumType>::type;
constexpr static bool isEmptyValue(EnumType value)
{
return static_cast<UnderlyingType>(value) == constant;
}
constexpr static EnumType emptyValue()
{
return static_cast<EnumType>(constant);
}
};
template<typename IntegralType, IntegralType constant = 0>
struct IntegralMarkableTraits {
static_assert(std::is_integral<IntegralType>::value);
constexpr static bool isEmptyValue(IntegralType value)
{
return value == constant;
}
constexpr static IntegralType emptyValue()
{
return constant;
}
};
struct FloatMarkableTraits {
constexpr static bool isEmptyValue(float value)
{
return value != value;
}
constexpr static float emptyValue()
{
return std::numeric_limits<float>::quiet_NaN();
}
};
// The goal of Markable is offering Optional without sacrificing storage efficiency.
// Markable takes Traits, which should have isEmptyValue and emptyValue functions. By using
// one value of T as an empty value, we can remove bool flag in Optional. This strategy is
// similar to WTF::HashTable, which uses two values of T as an empty value and a deleted value.
// This class is intended to be used as a member of a class to compact the size of the class.
// Otherwise, you should use Optional.
template<typename T, typename Traits>
class Markable {
WTF_MAKE_FAST_ALLOCATED;
public:
constexpr Markable()
: m_value(Traits::emptyValue())
{ }
constexpr Markable(std::nullopt_t)
: Markable()
{ }
constexpr Markable(T&& value)
: m_value(WTFMove(value))
{ }
constexpr Markable(const T& value)
: m_value(value)
{ }
template<typename... Args>
constexpr explicit Markable(std::in_place_t, Args&&... args)
: m_value(std::forward<Args>(args)...)
{ }
constexpr Markable(const std::optional<T>& value)
: m_value(bool(value) ? *value : Traits::emptyValue())
{ }
constexpr Markable(std::optional<T>&& value)
: m_value(bool(value) ? WTFMove(*value) : Traits::emptyValue())
{ }
constexpr explicit operator bool() const { return !Traits::isEmptyValue(m_value); }
void reset() { m_value = Traits::emptyValue(); }
constexpr const T& value() const& { RELEASE_ASSERT(bool(*this)); return m_value; }
constexpr T& value() & { RELEASE_ASSERT(bool(*this)); return m_value; }
constexpr T&& value() && { RELEASE_ASSERT(bool(*this)); return WTFMove(m_value); }
constexpr const T& unsafeValue() const& { return m_value; }
constexpr T& unsafeValue() & { return m_value; }
constexpr T&& unsafeValue() && { return WTFMove(m_value); }
constexpr const T* operator->() const { RELEASE_ASSERT(bool(*this)); return std::addressof(m_value); }
constexpr T* operator->() { RELEASE_ASSERT(bool(*this)); return std::addressof(m_value); }
constexpr const T& operator*() const& { RELEASE_ASSERT(bool(*this)); return m_value; }
constexpr T& operator*() & { RELEASE_ASSERT(bool(*this)); return m_value; }
template <class U> constexpr T value_or(U&& fallback) const
{
if (bool(*this))
return m_value;
return static_cast<T>(std::forward<U>(fallback));
}
operator std::optional<T>() &&
{
if (bool(*this))
return WTFMove(m_value);
return std::nullopt;
}
operator std::optional<T>() const&
{
if (bool(*this))
return m_value;
return std::nullopt;
}
std::optional<T> asOptional() const
{
return std::optional<T>(*this);
}
private:
T m_value;
};
template <typename T, typename Traits> inline void add(Hasher& hasher, const Markable<T, Traits>& value)
{
add(hasher, value.asOptional());
}
template <typename T, typename Traits> constexpr bool operator==(const Markable<T, Traits>& x, const Markable<T, Traits>& y)
{
if (bool(x) != bool(y))
return false;
if (!bool(x))
return true;
return x.value() == y.value();
}
template <typename T, typename Traits> constexpr bool operator==(const Markable<T, Traits>& x, const T& v) { return bool(x) && x.value() == v; }
template <typename T, typename Traits> constexpr bool operator==(const T& v, const Markable<T, Traits>& x) { return bool(x) && v == x.value(); }
} // namespace WTF
using WTF::Markable;
using WTF::IntegralMarkableTraits;
using WTF::EnumMarkableTraits;
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