Extension Class and Method in C#

 In C#, extension methods allow you to "add" methods to existing types without modifying the original type or using inheritance. These methods are defined in a static class, and the method itself must also be static, with the first parameter preceded by the this keyword to indicate the type it's extending.

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🔹 Syntax of Extension Method

csharp

public static class ExtensionClass
{
    public static returnType MethodName(this TypeToExtend obj, other parameters)
    {
        // method body
    }
}

---

🔹 Example 1: Extension Method on string Type

csharp

// Extension class
public static class StringExtensions
{
    public static int WordCount(this string str)
    {
        if (string.IsNullOrWhiteSpace(str)) return 0;
        return str.Split(' ').Length;
    }
}

// Usage
class Program
{
    static void Main()
    {
        string msg = "Hello from TechForest Software";
        int count = msg.WordCount();  // Using extension method
        Console.WriteLine("Word Count: " + count);
    }
}

---

🔹 Example 2: Extension Method on Custom Class

csharp

public class Employee
{
    public string Name { get; set; }
    public double Salary { get; set; }
}

// Extension class
public static class EmployeeExtensions
{
    public static void DisplayInfo(this Employee emp)
    {
        Console.WriteLine($"Name: {emp.Name}, Salary: {emp.Salary}");
    }

    public static bool IsHighEarner(this Employee emp, double threshold)
    {
        return emp.Salary > threshold;
    }
}

// Usage
class Program
{
    static void Main()
    {
        Employee e = new Employee { Name = "Shiva", Salary = 85000 };
        e.DisplayInfo(); // Extension method
        bool isHigh = e.IsHighEarner(80000); 
        Console.WriteLine("Is High Earner: " + isHigh);
    }
}


🔍 Reflection in C# — Explained Simply
Reflection in C# is a powerful feature that allows you to inspect metadata about assemblies, types, and members (like properties, methods, fields) at runtime. It belongs to the System.Reflection namespace.

✅ Use Cases of Reflection


Get type information at runtime


Inspect methods, properties, and fields


Create instances of types dynamically


Invoke methods dynamically


Used in serialization, unit testing frameworks, dependency injection, etc.



📦 Required Namespace
csharp

using System;
using System.Reflection;


🔹 Simple Example: Inspecting a Class Using Reflection
csharp

using System;
using System.Reflection;

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }

    public void Display()
    {
        Console.WriteLine($"Id: {Id}, Name: {Name}");
    }
}

class Program
{
    static void Main()
    {
        // Get type info using typeof
        Type type = typeof(Student);

        Console.WriteLine("Class Name: " + type.Name);

        Console.WriteLine("\n--- Properties ---");
        foreach (PropertyInfo prop in type.GetProperties())
        {
            Console.WriteLine("Property: " + prop.Name);
        }

        Console.WriteLine("\n--- Methods ---");
        foreach (MethodInfo method in type.GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly))
        {
            Console.WriteLine("Method: " + method.Name);
        }
    }
}

🧩 Partial Class in C# – Simple Explanation with Example
A partial class in C# allows you to split the definition of a class into multiple files. When the application compiles, all the parts are combined into a single class.

✅ Why Use Partial Classes?


Helpful when working on large classes.


Supports code separation (e.g., designer code in one file, logic in another).


Allows multiple developers to work on the same class simultaneously.


Used heavily in WinForms, ASP.NET Web Forms, and Entity Framework.



🧪 Syntax
File 1: Student1.cs
csharp

public partial class Student
{
    public int Id { get; set; }
}

File 2: Student2.cs
csharp
public partial class Student
{
    public string Name { get; set; }

    public void Display()
    {
        Console.WriteLine($"ID: {Id}, Name: {Name}");
    }
}

File 3: Program.cs
csharp

using System;

class Program
{
    static void Main()
    {
        Student s = new Student();
        s.Id = 101;
        s.Name = "Shiva";
        s.Display();  // Output: ID: 101, Name: Shiva
    }
}


📘 Key Rules


All parts must use the partial keyword.


All parts must be in the same namespace and same assembly.


Access modifiers (like public) must be consistent.