Editing Flyweight pattern (section)

=== C++ ===
The C++ [[Standard Template Library]] provides several containers that allow unique objects to be mapped to a key. The use of containers helps further reduce memory usage by removing the need for temporary objects to be created.

<syntaxhighlight lang="c++">#include <iostream>
#include <map>
#include <string>

// Instances of Tenant will be the Flyweights
class Tenant {
public:
    Tenant(const std::string& name = "") : m_name(name) {}

    std::string name() const {
        return m_name;
    }
private:
    std::string m_name;
};

// Registry acts as a factory and cache for Tenant flyweight objects
class Registry {
public:
    Registry() : tenants() {}

    Tenant& findByName(const std::string& name) {
        if (!tenants.contains(name)) {
            tenants[name] = Tenant{name};
        }
        return tenants[name];
    }
private:
    std::map<std::string, Tenant> tenants;
};

// Apartment maps a unique tenant to their room number.
class Apartment {
public:
    Apartment() : m_occupants(), m_registry() {}

    void addOccupant(const std::string& name, int room) {
        m_occupants[room] = &m_registry.findByName(name);
    }

    void tenants() {
        for (const auto &i : m_occupants) {
            const int& room = i.first;
            const auto& tenant = i.second;
            std::cout << tenant->name() << " occupies room " << room << std::endl;
        }
    }
private:
    std::map<int, Tenant*> m_occupants;
    Registry m_registry;
};

int main() {
    Apartment apartment;
    apartment.addOccupant("David", 1);
    apartment.addOccupant("Sarah", 3);
    apartment.addOccupant("George", 2);
    apartment.addOccupant("Sarah", 12);
    apartment.addOccupant("Michael", 10);
    apartment.tenants();

    return 0;
}
</syntaxhighlight>