std::hash(std::shared_ptr)
Since C++11
template<class T> struct hash<shared_ptr<T>>;
The template specialization of std::hash for std::shared_ptr<T> allows users to obtain hashes of objects of type std::shared_ptr<T>.
For a given std::shared_ptr<T> p, this specialization ensures that
std::hash<std::shared_ptr<T>>()(p) == std::hash<T*>()(p.get()) // Until C++17
std::hash<std::shared_ptr<T>>()(p) == std::hash<typename std::shared_ptr<T>::element_type*>()(p.get()) // Since C++17