From cppreference.com
structowner_equal;(since C++26)This function object provides owner-based (as opposed to value-based) mixed-type equal comparison of both
and
. The comparison is such that two smart pointers compare equivalent only if they are both empty or if they share ownership, even if the values of the raw pointers obtained by get() are different (e.g. because they point at different subobjects within the same object).
It is the preferred comparison predicate when building unordered associative containers with
and
as keys together with std::owner_hash, that is, std::unordered_map<std::shared_ptr<T>,U,std::owner_hash,std::owner_equal> or std::unordered_map<std::weak_ptr<T>,U,std::owner_hash,std::owner_equal>.
Nested types
Member functions
compares its arguments using owner-based semantics
(function)std::owner_equal::operator()
template<classT,classU>constexprbooloperator()(conststd::shared_ptr<T>&lhs,conststd::shared_ptr<U>&rhs)constnoexcept; (1) (since C++26)template<classT,classU>constexprbooloperator()(conststd::shared_ptr<T>&lhs,conststd::weak_ptr<U>&rhs)constnoexcept; (2) (since C++26)template<classT,classU>constexprbooloperator()(conststd::weak_ptr<T>&lhs,conststd::shared_ptr<U>&rhs)constnoexcept; (3) (since C++26)template<classT,classU>constexprbooloperator()(conststd::weak_ptr<T>&lhs,conststd::weak_ptr<U>&rhs)constnoexcept; (4) (since C++26)Compares lhs and rhs using owner-based semantics. Effectively calls lhs.owner_equal(rhs).
The equal comparison is an equivalence relation.
lhs and rhs are equivalent only if they are both empty or share ownership.
Parameters
lhs, rhs - shared-ownership pointers to compare Return value
true if lhs and rhs are both empty or share ownership as determined by the owner-based equal comparison, false otherwise.
Notes
macro ValueStdFeature
__cpp_lib_smart_ptr_owner_equality
(C++26)Enabling the use of std::shared_ptr and std::weak_ptr as keys in
unordered associative containers
(C++26)Constexpr std::owner_equalSee also
(C++26)
provides owner-based equal comparison of shared pointers
(public member function of std::shared_ptr<T>)
(C++26)
provides owner-based equal comparison of weak pointers
(public member function of std::weak_ptr<T>)