📅Week-8 (Day-1) - How to Implement Prototype Design Pattern: A Guide with UML and Code

NOTE: - I started my 8-week system design journey with Coder Army. I will be journaling every day, recording what I learn, reflecting on it, and sharing it with my network to help newcomers to system design.

Namaste developers! 👋
Welcome to another power-packed day of the #8WeeksLLDChallenge — and today, we’re diving into something that every large system needs but is often overlooked — the Mediator Design Pattern!

Aaj ka challenge: Chat Room System — but with a twist!
Instead of users communicating with each other directly (which creates chaos in large systems), we’ll use a Mediator to handle message passing — creating a cleaner, more scalable architecture.

💠 What is the Prototype Design Pattern?

The Prototype Pattern allows you to create new objects by cloning existing ones, instead of building them from scratch every time.

(Hindi: Prototype Pattern aapko naye object banane ke liye existing object ka clone banane ki suvidha deta hai. Agar ek baar object bana liya hai, toh baar-baar naye create karne ki zarurat nahi — usi ka duplicate use karke kaam ho jata hai.)

💠Why Use It?

Creating a complex object from scratch every time can be:

• ❌ Time-consuming

• ❌ Expensive (resource-heavy calculations, DB calls, setup)

• ❌ Error-prone (repeat same values again & again)

Instead, just clone an existing template object and tweak it!

💠Real-Life Analogy

NPC Cloning in Games!

Imagine you're building a game like PUBG or Free Fire 🎮, and you need to create 100 aliens (Non-Player Characters).

• Without prototype: har alien ke liye manually stats bharne padenge

• With prototype: ek baar ek alien banao, baaki sab copy-paste (clone)!

(Hindi: Ek hi base alien se 100 copy banao — time bacha, kaam asaan hua )

💠UML Diagram

💠Code

📍without Prototype Pattern

#include <iostream>
#include <string>
#include <vector>
using namespace std;

// Simple NPC class — no Prototype
class NPC {
public:
    string name;
    int health;
    int attack;
    int defense;

    // “Heavy” constructor: every field must be provided
    NPC(const string& name, int health, int attack, int defense) {

        // call database
        // complex calc
        this->name = name;
        this->health = health;
        this->attack = attack;
        this->defense = defense;

        cout << "Creating NPC '" << name << "' [HP:" << health << ", ATK:" 
             << attack << ", DEF:" << defense << "]\n";
    }

    void describe() {
        cout << "  NPC: " << name << " | HP=" << health << " ATK=" << attack
             << " DEF=" << defense << "\n";
    }
};

int main() {
    // Base Alien
    NPC* alien = new NPC("Alien", 30, 5, 2);
    alien->describe();

    // Powerful Alien — must re-pass all stats, easy to make mistakes
    NPC* alien2 = new NPC("Powerful Alien", 30, 5, 5);
    alien2->describe();

    // If you want 100 aliens, you'd repeat this 100 times…

    // cleanup
    delete alien;
    delete alien2;
    return 0;
}

Benefits:

Every time you want a new NPC, you have to:

• Call constructor

• Refill all values again

• Risk mistakes and redundancy

📍with Prototype Pattern

#include <iostream>
#include <string>
#include <vector>
using namespace std;

// Cloneable (aka Prototype) interface
class Cloneable {
public:
    virtual Cloneable* clone() const = 0;
    virtual ~Cloneable() {}
};

class NPC : public Cloneable {
public:
    string name;
    int health;
    int attack;
    int defense;

    NPC(const string& name, int health, int attack, int defense) {
        // call database
        // complex calc
        this->name = name; 
        this->health = health; 
        this->attack = attack; 
        this->defense = defense;
        cout << "Setting up template NPC '" << name << "'\n";
    }

    // copy‐ctor used by clone()
    NPC(const NPC& other) {
        name = other.name;
        health = other.health;
        attack = other.attack;
        defense = other.defense;
        cout << "Cloning NPC '" << name << "'\n";
    }

    // the clone method required by Prototype
    Cloneable* clone() const override {
        return new NPC(*this);
    }

    void describe() {
        cout << "NPC " << name  << " [HP=" << health  << " ATK=" << attack 
             << " DEF=" << defense << "]\n";
    }

    // setters to tweak the clone…
    void setName(const string& n) { 
        name = n;
    }
    void setHealth(int h) { 
        health = h;
    }
    void setAttack(int a) {
         attack = a; 
    }
    void setDefense(int d){ 
        defense = d;
    }
};

int main() {
    // 1) build one “heavy” template
    NPC* alien = new NPC("Alien", 30, 5, 2);

    // 2) quickly clone + tweak as many variants as you like:
    NPC* alienCopied1 = dynamic_cast<NPC*>(alien->clone());
    alienCopied1->describe();

    NPC* alienCopied2 = dynamic_cast<NPC*>(alien->clone());
    alienCopied2->setName("Powerful Alien");
    alienCopied2->setHealth(50);
    alienCopied2->describe();

    // cleanup
    delete alien;
    delete alienCopied1;
    delete alienCopied2;
}

Benefits:

• Only one object is setup-heavy

• Rest are just copied (cloned)

• Easy to customize each new object

• Super efficient for games, simulations, testing, prototyping

💠Advantages of Prototype Pattern

✅ Performance boost (no re-computation)
✅ Reduced memory/resource consumption
✅ Makes code DRY (Don’t Repeat Yourself)
✅ Super useful in games, simulations, design tools, IDEs

💠When to Use

Use Prototype Pattern when:

• Object creation is expensive or slow

• You need many similar instances with small changes

• You're building test data, simulations, or design templates

💠 Summary

💠Final Thoughts

Prototype Pattern isn’t just a design pattern — it’s a developer’s shortcut when you need speed, scale, and simplicity

(Hindi: Prototype pattern aapki development ko fast aur efficient banata hai — kam coding, zyada cloning)

Week - 8 (Day-1) Completed ✅ System Design

NOTE : - A big thanks to my mentors Rohit Negi Sir and Aditya Sir for launching this amazing 8-week course absolutely free on YouTube via CoderArmy9 :- youtube.com/@CoderArmy9 . 🙌

👉 Share this blog with your connections! Let’s keep learning, growing, and supporting one another on this journey. 🚀

✍️ Payal Kumari 👩‍💻

Jai Hind 🇮🇳 | #CoderArmy #LearningInPublic #SystemDesign #TechForAll #MentorshipMatters #8weeksLLdChallenge #LowLevelDesign #LLD 👩‍💻