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std::hash(3) C++ Standard Libary std::hash(3) NAME std::hash - std::hash Synopsis Defined in header <variant> template <class... Types> (since C++17) struct hash<std::variant<Types...>>; The template specialization of std::hash for the std::variant tem- plate allows users to obtain hashes of variant objects. The specialization std::hash<std::variant<Types...>> is enabled (see std::hash) if every specialization in std::hash<std::remove_const_t<Types>>... is enabled, and is disabled otherwise. The member functions of this specialization are not guaranteed to be noexcept. Template parameters Types - the types of the alternatives supported by the variant ob- ject Notes Unlike std::hash<std::optional>, hash of a variant does not typi- cally equal the hash of the contained value; this makes it possible to distinguish std::variant<int, int> holding the same value as different alternatives. Example // Run this code #include <variant> #include <iostream> #include <string> using Var = std::variant<int, int, int, std::string>; template<unsigned I> void print(Var const& var) { std::cout << "get<" << var.index() << "> = " << std::get<I>(var) << "\t" "# = " << std::hash<Var>{}(var) << '\n'; } int main() { Var var; std::get<0>(var) = 2020; print<0>(var); var.emplace<1>(2023); print<1>(var); var.emplace<2>(2026); print<2>(var); var = "C++"; print<3>(var); } Possible output: get<0> = 2020 # = 2020 get<1> = 2023 # = 2024 get<2> = 2026 # = 2028 get<3> = C++ # = 15518724754199266859 See also hash hash function object (C++11) (class template) http://cppreference.com 2022.07.31 std::hash(3)
NAME | Synopsis | Template parameters | Notes | Example | Possible output: | See also
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