20 Memory management library [mem]

20.3 Smart pointers [smartptr]

20.3.2 Shared-ownership pointers [util.sharedptr]

20.3.2.5 Struct owner_hash [util.smartptr.owner.hash]

The class owner_hash provides ownership-based hashing.
namespace std { struct owner_hash { template<class T> size_t operator()(const shared_ptr<T>&) const noexcept; template<class T> size_t operator()(const weak_ptr<T>&) const noexcept; using is_transparent = unspecified; }; }
template<class T> size_t operator()(const shared_ptr<T>& x) const noexcept; template<class T> size_t operator()(const weak_ptr<T>& x) const noexcept;
Returns: x.owner_hash().
[Note 1: 
For any object y where x.owner_equal(y) is true, x.owner_hash() == y.owner_hash() is true.
— end note]