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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
// SPDX-FileCopyrightText: 2024 - 2025 Kohei Yoshida
//
// SPDX-License-Identifier: MIT
#pragma once
#include <functional>
#include <type_traits>
namespace mdds { namespace detail {
/**
* Custom const reference wrapper with an equality operator and a hash
* adaptor.
*/
template<typename T>
class cref_wrapper
{
std::reference_wrapper<std::add_const_t<T>> m_value;
public:
cref_wrapper(const T& v) noexcept : m_value(std::cref(v))
{}
const T& get() const noexcept
{
return m_value;
}
bool operator==(const cref_wrapper& r) const
{
return get() == r.get();
}
bool operator!=(const cref_wrapper& r) const
{
return !operator==(r);
}
struct hash
{
std::size_t operator()(const cref_wrapper& v) const noexcept(noexcept(std::hash<T>{}(v.get())))
{
// NB: hash value must be based on the wrapped value, else two
// identical values located in different memory locations may end up
// in different buckets, and the lookup may fail.
return std::hash<T>{}(v.get());
}
};
};
}} // namespace mdds::detail
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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