Prototype Pattern in C# – Real-Time Example (Cloning Invoice Template)

What is Prototype Pattern?

The Prototype Pattern is a creational design pattern that creates new objects by cloning an existing object instead of creating from scratch.

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Why Use Prototype Pattern?

• Avoid expensive object creation
• Quickly duplicate existing objects
• Preserve object state (template-based creation)
• Improve performance

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Real-Time Scenario

In an Invoice System:

• You have a predefined invoice template
• You want to create multiple similar invoices

👉 Instead of building from scratch, you clone it

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Implementation

Step 1: Prototype Interface (Optional)

public interface IPrototype<T>
{
    T Clone();
}

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Step 2: Concrete Class

public class Invoice : IPrototype<Invoice>
{
    public string Customer { get; set; }
    public decimal Amount { get; set; }

    public Invoice Clone()
    {
        return (Invoice)this.MemberwiseClone(); // shallow copy
    }
}

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Usage Example

// Original template
var template = new Invoice
{
    Customer = "Template Customer",
    Amount = 1000
};

// Clone it
var invoice1 = template.Clone();
invoice1.Customer = "Sai";

var invoice2 = template.Clone();
invoice2.Customer = "Kumar";

Console.WriteLine(invoice1.Customer); // Sai
Console.WriteLine(invoice2.Customer); // Kumar

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Key Concept

Instead of:

var invoice = new Invoice();
// set all fields again ❌

We do:

var invoice = template.Clone();

👉 Faster and cleaner

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Shallow vs Deep Copy

Shallow Copy

• Copies reference (default MemberwiseClone)
• Faster but shared references

Deep Copy

public Invoice Clone()
{
    return new Invoice
    {
        Customer = this.Customer,
        Amount = this.Amount
    };
}

👉 Creates completely independent object

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Advantages

• Fast object creation
• Reduces repetitive initialization
• Improves performance
• Useful for template-based systems

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Disadvantages

• Deep copy can be complex
• Hidden bugs with shallow copy
• Requires careful implementation

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When to Use

• When object creation is costly
• When many similar objects are needed
• When cloning is easier than building
• When working with templates

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Real Project Mapping (.NET + Angular)

Feature	Usage
Invoice templates	Prototype
Copy existing records	Prototype
UI form duplication	Prototype
Configuration cloning	Prototype

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Pro Tip (Advanced .NET Usage)

• Use AutoMapper or serialization for deep copy
• Combine with Builder Pattern for flexible cloning + modification
• Useful in test data generation

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Summary

Prototype Pattern helps you:

• Clone existing objects efficiently
• Reduce object creation cost
• Work with templates easily

👉 Perfect for invoice templates, cloning data, reusable objects