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What kind of requirement can go for multiple instance creation?

What kind of requirement can go for multiple instance creation?

    ✅ Requirements That Call for Multiple Instances

    1. Modeling Real-World Entities
      Each entity should have its own set of data, hence its own instance.

    Example:

    class Customer
    {
    public string Name { get; set; }
    public int Age { get; set; }
    }

    ✅ Use case: A shopping app where each Customer represents a different user.

    1. Stateless Service Calls or Independent Processing
      When each instance needs to perform a different task independently.

    Example:

    class ReportGenerator
    {
    public string GenerateReport(string data) => $”Report for {data}”;
    }

    ✅ Use case: Generating multiple reports at the same time with different data.

    1. Thread Safety
      When you need isolated instances per thread to avoid conflicts or shared state.

    Example:

    class Logger
    {
    public void Log(string message) => Console.WriteLine(message);
    }

    ✅ Use case: A separate logger per thread for better log management and no race conditions.

    1. Temporary or Session-Based Data
      For objects that are valid only for a short duration or specific session.

    Example:

    class ShoppingCart
    {
    public List Items = new List();
    }

    ✅ Use case: One shopping cart per user session in an e-commerce app.

    1. Different Configurations or Behaviors
      Each instance behaves differently based on how it was initialized.

    Example:

    class Printer
    {
    public string PrinterName { get; }
    public Printer(string name) => PrinterName = name;
    }

    ✅ Use case: Managing multiple printers with different names or settings.

    1. Unit Testing / Isolation
      When testing classes, you create separate instances to ensure isolation and no state carry-over.

    ✅ Use case: In xUnit, each test creates its own object instance to test independently.

    1. Factory Pattern or Dependency Injection
      You might need new instances per request or scope.

    Example:

    services.AddTransient(); // Creates new instance every time

    ✅ Use case: ASP.NET Core DI where services have different lifetimes.

    ❗When NOT to go for multiple instances?
    When the class holds global/shared state (e.g., ConfigurationManager, Logger).

    If the object is expensive to create and can be reused safely (use singleton).

    When only one instance should exist logically (like a DatabaseConnectionManager).

    TL;DR – You Need Multiple Instances When:
    Each object represents a unique item or person

    Each instance holds different data/state

    You need thread isolation or short-lived usage

    Independent behavior/config is required