std::hash,std::hash,std::hash,(3)

NAME
std::hash,std::hash,std::hash, - std::hash,std::hash,std::hash,

Synopsis
   Defined in header <string_view>
   template<> struct hash<std::string_view>; (since C++17)
   template<> struct hash<std::wstring_view>; (since C++17)
   template<> struct hash<std::u8string_view>; (since C++20)
   template<> struct hash<std::u16string_view>; (since C++17)
   template<> struct hash<std::u32string_view>; (since C++17)
   Template specializations of std::hash for the various view classes for hashing
   views.
   These hashes equal the hashes of corresponding std::basic_string classes: If S is
   one of the standard basic_string types, SV is the corresponding string view type,
   and s is an object of type S, then std::hash<S>()(s) == std::hash<SV>()(SV(s)).

Example
// Run this code
 #include <iostream>
 #include <string_view>
 #include <unordered_set>
 using namespace std::literals;
 int main()
 {
     std::cout << "\"A\" #: " << std::hash<std::string_view>{}("A"sv) << '\n';
     std::cout << "L\"B\" #: " << std::hash<std::wstring_view>{}(L"B"sv) << '\n';
     std::cout << "u8\"C\" #: " << std::hash<std::u8string_view>{}(u8"C"sv) << '\n';
     std::cout << "u\"D\" #: " << std::hash<std::u16string_view>{}(u"D"sv) << '\n';
     std::cout << "U\"E\" #: " << std::hash<std::u32string_view>{}(U"E"sv) << '\n';
     // std::hash for string_view family makes it possible to keep these view-types
     // in unordered_* associative containers, such as unordered_set. But ensure
     // the lifespan of referenced strings is no less than lifespan of the container,
     // i.e. no dangling references occurred.
     std::unordered_set stars{"Rigel"sv, "Capella"sv, "Vega"sv, "Arcturus"sv};
     for (std::string_view const& s : stars)
         std::cout << s << ' ';
     std::cout << '\n';
 }

Possible output:
 "A" #: 6919333181322027406
 L"B" #: 11959850520494268278
 u8"C" #: 12432341034569643010
 u"D" #: 312659256970442235
 U"E" #: 18073225910249204957
 Arcturus Vega Capella Rigel

See also
   hash hash function object
   (C++11) (class template)
   std::hash<std::basic_string> hash support for strings
   (C++11) (class template specialization)