Cherno Map Unordered

#include <map>
#include <unordered_map>
#include <iostream>

struct CityRecord
{
    std::string Name;
    uint64_t Population;
    double Latitude, Longitude;
};

namespace std
{
    template<>
    struct hash<CityRecord>
    {
        size_t operator()(const CityRecord& key)
        {
            // Have to construct and then call it, syntax is weird
            // Cherno doesn't remember it, just ends up copy/pasting it from somewhere else
            return hash<std::string>()(key.Name);
        }
    };
}

int main()
{
    //std::unordered_map<CityRecord, uint32_t> foundedMap;

    //foundedMap[CityRecord{ "Melbourne", 5000000, 2.4, 9.4 }] = 1850;

    // Index operator [ will always insert things in, no const version of this operator
    // If thing being inserted doesn't exist, it creates it and inserts it into unordered map and gives ref to new CityRecord
    //uint32_t melBourneFounded = foundedMap[CityRecord{ "Melbourne", 3487382, 2.4, 9.4 }];

    std::unordered_map<std::string, CityRecord> cityMap;
    cityMap["Melbourne"] = CityRecord{ "Melbourne", 5000000, 2.4, 9.4 };
    cityMap["Lol-town"] = CityRecord{ "Lol-town", 5000000, 2.4, 9.4 };
    cityMap["Paris"] = CityRecord{ "Paris", 5000000, 2.4, 9.4 };
    //cityMap["Berlin"] = CityRecord{ "Berlin", 5000000, 2.4, 9.4 };
    cityMap["London"] = CityRecord{ "London", 5000000, 2.4, 9.4 };

    // If you want to retrieve data without inserting it, use .at()
    const auto& cities = cityMap;
    //const CityRecord& berlinData = cities.at("Berlin");

    // How to check if data at .at is there
    if (cities.find("Berlin") != cities.end())
    {
        const CityRecord& berlinData4 = cities.at("Berlin");
    }

    // Below example but in C++14 AKA Stone Age
    //for (auto& kv : cityMap)
    //{
    //  const std::string& name = kv.first;
    //  CityRecord& city = kv.second;
    //}

    // Iterate through entire data structure
    // [ ] is structured bindings from C++17
    for (auto& [name, city] : cityMap)
    {
        std::cout << name << "\n Population: " << city.Population << std::endl;
    }

    std::cin.get();

    // More efficient vs one below, doesn't copy as it creates it in place and references the memory
    //CityRecord& berlinData2 = cityMap["Berlin"];
    //berlinData2.Name = "Berlin";
    //berlinData2.Population = 5;

    // Ends up copying from last line, not preferred to one above
    //CityRecord berlinData3;
    //berlinData3.Name = "Berlin";
    //berlinData3.Population = 5;
    //cityMap["Berlin"] = berlinData3;
}