Create Extension Method.cs

Extension Method.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Xml.Linq;
+
+namespace ext
+{
+    public sealed class user 
+    {
+        public int id { get; set; }
+        public string name { get; set; }   
+        public void print()
+        {
+            Console.WriteLine($"{id} {name}");
+        }
+
+    }
+
+    //Extension class and its functions must be static.
+    //Extension class function cannot override the base class function,
+    //the extension function can be called in case the signature is different.
+    //With extension method we don't need to subclass the base class,
+    public static class AddFuncToUser
+    {
+        public static void print(this user u)
+        {
+            Console.WriteLine("Override");
+        }
+        public static string userData(this user u)
+        {
+            string user_rec = "";
+            user_rec += Convert.ToString(u.id);
+            return user_rec;
+        }
+        // Extension method cannot access the priavte/ protected fields.
+        // we cannot add property as a extension method.
+        // also cannot add a new variable/ field, but both can be done by inheritance.
+        //public string pro1
+        //{
+        //    property
+        //    get { return name; }
+        //    set { name = value; }
+        //}
+    }
+
+    public class main
+    {
+        public static void Main()
+        {
+            user u = new user();
+            u.name = "Bhaskar";
+            u.id = 1;
+            u.print();
+        }
+    }
+}