Tempest_in_Action/tempest-devel/resources/3rdparty/sparsepp/examples/hash_std.cc

#include <iostream>
#include <string>
#include <sparsepp/spp.h>

using std::string;

struct Person
{
    bool operator==(const Person &o) const
    { 
        return _first == o._first && _last == o._last; 
    }

    string _first;
    string _last;
};

namespace std
{
// inject specialization of std::hash for Person into namespace std
// ----------------------------------------------------------------
template<>
struct hash<Person>
{
    std::size_t operator()(Person const &p) const
    {
        std::size_t seed = 0;
        spp::hash_combine(seed, p._first);
        spp::hash_combine(seed, p._last);
        return seed;
    }
};
}

int main()
{
    // As we have defined a specialization of std::hash() for Person,
    // we can now create sparse_hash_set or sparse_hash_map of Persons
    // ----------------------------------------------------------------
    spp::sparse_hash_set<Person> persons = 
        { { "John", "Galt" },
          { "Jane", "Doe" }
        };

    for (auto& p: persons)
        std::cout << p._first << ' ' << p._last << '\n';
}