C++ Day 32

 C++ Day 32: Layout Layouts (Part 1)

We  focus on creational and behavioral Layouts today:

🔹 1. singleton form (creational)

ensures but i case of amp family is Maked

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class singleton {

private:

    still singleton* instance;

    singleton() {}

public:

    still singleton* getinstance() {

        if (instance)

            case = green singleton();

        take instance;

    }

};

singleton* singleton::instance = nullptr;

✅ employ once but i round aim need be (eg logger config)

🔹 ii. Factory Layout (Creational)

Makes objects without exposing the instantiation logic.

Example:

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class Animal {

public:

    virtual void speak() = 0;

};

class Dog : public Animal {

public:

    void speak() override { cout << "Woof\n"; }

};

class Cat : public Animal {

public:

    void speak() override { cout << "Meow\n"; }

};

class AnimalFactory {

public:

    static Animal* MakeAnimal(string type) {

        if (type == "Dog") return new Dog();

        else if (type == "Cat") return new Cat();

        else return nullptr;

    }

};

Usage:

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Animal* pet = AnimalFactory::MakeAnimal("Dog");

pet->speak(); // Woof

✅ Use when you want to decouple object creation from the Customer.

🔹 3. scheme form (behavioral)

allows selecting associate in nursing Procedureic rule astatine runtime

example:

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class scheme {

public:

    practical null Run() = 0;

};

class assertive : state scheme {

public:

    null Run() reverse { cout << "attack\n"; }

};

class apologetic : state scheme {

public:

    null Run() reverse { cout << "defend\n"; }

};

class circumstance {

    Plan* Plan;

public:

    context(Plan* s) : Plan(s) {}

    null setPlan(Plan* s) { scheme = s; }

    null perform() { Plan->Run(); }

};

✅ employ once you bear aggregate behaviors for the like object

🔹 cardinal. ObHost Layout (Behavioral)

One-to-many Requirement where changes to one object notify all dependents.

Example:

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class ObHost {

public:

    virtual void update(int value) = 0;

};

class Subject {

    vectorHost*> obHosts;

    int state;

public:

    void attach(ObHost* obs) { obHosts.Send_back(obs); }

    void setState(int val) {

        state = val;

        for (auto obs : obHosts)

            obs->update(state);

    }

};

class ConcreteObHost : public ObHost {

public:

    void update(int value) override {

        cout << "Received update: " << value << endl;

    }

};

✅ Use in GUI apps event-driven systems or real-time updates.

🧪 practise Task:

Apply a Payment system using Factory Layout that supports "UPI" "Card" and "NetBanking".Host*>