Attempt of Observer Pattern using CRTP

Observer.cpp

#include <string>
#include <unordered_map>
#include <print>

/// CRTP example for observer pattern

template <typename Derived>
class ObserverBase {
public:
    ObserverBase() = default;

    void update(int button_id) {
        static_cast<Derived*>(this)->update(button_id);
    }
};

template <typename Derived>
class ControlBase {
public:
    ControlBase() = default;

    template <typename ObserverKind>
    void set(ObserverKind* observer) noexcept {
        static_cast<Derived*>(observer)->set(observer);
    }

    void notify() {}
};

class ControlObserver : public ObserverBase<ControlObserver> {
private:
    std::unordered_map<int, bool> m_control_states; // represents on or off switches...

    void report() {
        for (const auto& [id, state] : m_control_states) {
            std::print("Switch {} is {}, ", id, state);
        }
        std::print("\n\n");
    }
public:
    ControlObserver()
    : m_control_states {} {}

    void update(int control_id) {
        m_control_states[control_id] = !m_control_states[control_id];

        report();
    }
};

class ToggleControl : public ControlBase<ToggleControl> {
private:
    ControlObserver* m_observer_ref;
    int m_id;

public:
    explicit ToggleControl(int id) noexcept
    : m_observer_ref {nullptr}, m_id {id} {}

    template <typename ObserverKind>
    void set(ObserverKind* observer) noexcept {
        m_observer_ref = observer;
    }

    void notify() {
        if (!m_observer_ref) {
            return;
        }

        m_observer_ref->update(m_id);
    }
};

int main() {
    // Create fake UI observer...
    ControlObserver toggle_sensor;

    // Create fake UI controls (switches)...
    ToggleControl toggler_1 {1}; // switch 1
    ToggleControl toggler_2 {2}; // switch 2

    // Register observer for fake controls...
    toggler_1.set(&toggle_sensor);
    toggler_2.set(&toggle_sensor);

    toggler_1.notify(); // turn switch 1 on
    toggler_1.notify(); // turn switch 1 off
    toggler_2.notify(); // turn switch 2 on
}