<typeindex>
Include the standard header <typeindex> to define a class and function that support the indexing of objects of class type_info.
#include <typeindex>
Remarks
The hash Structure defines a hash function that's suitable for mapping values of type type_index to a distribution of index values.
The type_index class wraps a pointer to a type_info object to assist in indexing.
See Also
Reference
Thread Safety in the Standard C++ Library