extension method

 What is an Extension Method in C#?

An extension method is a static method that allows you to "add" new methods to existing types (like string, int, custom classes, etc.) without modifying their source code or using inheritance.

 Key Points

Declared in a static class.

The first parameter uses the this keyword before the type you want to extend.

Can be called as if it were a regular method on the object.

 Example: Extension Method on string

1. Define Extension Method
public static class StringExtensions
{
    public static bool IsNumeric(this string input)
    {
        return int.TryParse(input, out _);
    }
}

 

2. Use it like a regular method:

string value = "12345";
bool result = value.IsNumeric();  // Output: true
 

Even though string has no IsNumeric() method, now you can call it as if it does!

 

Another Example: int Extension

 

public static class IntExtensions
{
    public static bool IsEven(this int number)
    {
        return number % 2 == 0;
    }
}

// Usage:
int num = 10;
bool isEven = num.IsEven(); // Output: true

 

 Why Use Extension Methods?

1. Add functionality to sealed types => e.g., string, int, DateTime, etc.
2. Keeps code cleaner =>Looks like native method calls
3. Promotes reusability => Share methods across projects easily
4. No need to modify existing class => Helpful when you can't access class source code