#include <cstdint>
#include <functional>
#include <iostream>
#include <string>
 
struct Employee
{
    std::string name;
    std::uint64_t ID;
};
 
namespace std {
template <>
class hash<Employee>
{
public:
    std::uint64_t operator()(const Employee& employee) const
    {
        // computes the hash of an employee using a variant
        // of the Fowler-Noll-Vo hash function
        constexpr std::uint64_t prime { 0x100000001B3 };
        std::uint64_t result { 0xcbf29ce484222325 };
 
        for (std::uint64_t i{}, ie = employee.name.size(); i != ie; ++i)
            result = (result * prime) ^ employee.name[i];
 
        return result ^ (employee.ID << 1);
    }
};
}
 
int main()
{
    Employee employee;
    employee.name = "Zaphod Beeblebrox";
    employee.ID = 42;
 
    std::hash<Employee> hash_fn;
    std::cout << hash_fn(employee) << '\n';
}