std::hash(std::experimental::propagate_const)
From cppreference.com
                    
                                        
                    < cpp | experimental | propagate const
                    
                                                            
                    | Defined in header  <experimental/propagate_const> | ||
| template<class T> struct hash<std::experimental::propagate_const<T>>; | (library fundamentals TS v2) | |
The template specialization of std::hash for std::experimental::propagate_const<T> allows users to obtain hashes of objects of type std::experimental::propagate_const<T>.
For a given std::experimental::propagate_const<T> p, this specialization ensures that  std::hash<std::experimental::propagate_const<T>>()(p) == std::hash<T>()(p.t_), where p.t_ is the pointer-like object wrapped by p.
[edit] Example
| This section is incomplete Reason: no example | 
[edit] See also
| (C++11) | hash function object (class template) |