Implement std::hash<boost::intrusive_ptr<T>> for old Boost versions

Boost only implements it iself starting from version 1.74, but a specialization
of std::hash<> can be added trivially to allow the use of
std::unordered_set<boost::intrusive_ptr<T>> and
std::unordered_map<boost::intrusive_ptr<K>, V>.

Being unable to use such types already came up a few types in the past, often
resulting in the use of raw pointer instead which always involves an additional
"is this safe?"/"could the object go out of scope?" discussion. This commit
simply solves this for the future by simply allowing the use of intrusive_ptr
in unordered containers.
This commit is contained in:
Julian Brost 2025-03-10 11:56:23 +01:00
parent 4b18f62a11
commit 500ad70b8c
4 changed files with 25 additions and 0 deletions

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@ -38,6 +38,7 @@ set(base_SOURCES
filelogger.cpp filelogger.hpp filelogger-ti.hpp
function.cpp function.hpp function-ti.hpp function-script.cpp functionwrapper.hpp
initialize.cpp initialize.hpp
intrusive-ptr.hpp
io-engine.cpp io-engine.hpp
journaldlogger.cpp journaldlogger.hpp journaldlogger-ti.hpp
json.cpp json.hpp json-script.cpp

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@ -0,0 +1,22 @@
/* Icinga 2 | (c) 2025 Icinga GmbH | GPLv2+ */
#pragma once
#include "base/i2-base.hpp"
#include <memory>
#include <boost/smart_ptr/intrusive_ptr.hpp>
#include <boost/version.hpp>
// std::hash is only implemented starting from Boost 1.74. Implement it ourselves for older version to allow using
// boost::intrusive_ptr inside std::unordered_set<> or as the key of std::unordered_map<>.
// https://github.com/boostorg/smart_ptr/commit/5a18ffdc5609a0e64b63e47cb81c4f0847e0c087
#if BOOST_VERSION < 107400
template<class T>
struct std::hash<boost::intrusive_ptr<T>>
{
std::size_t operator()(const boost::intrusive_ptr<T>& ptr) const noexcept
{
return std::hash<T*>{}(ptr.get());
}
};
#endif /* BOOST_VERSION < 107400 */

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@ -5,6 +5,7 @@
#include "base/i2-base.hpp"
#include "base/debug.hpp"
#include "base/intrusive-ptr.hpp"
#include <boost/smart_ptr/intrusive_ptr.hpp>
#include <atomic>
#include <cstddef>

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@ -4,6 +4,7 @@
#define SHARED_H
#include "base/atomic.hpp"
#include "base/intrusive-ptr.hpp"
#include <boost/smart_ptr/intrusive_ptr.hpp>
#include <cstdint>
#include <utility>