Reference types are always passed by reference so what’s the difference between passing a reference type by value or by ref keyword. Let’s try to understand by some code samples:

Let’s say we have a class MyClass defined below, Class in .Net is a reference type as you should know.

class Reftype
     {
      public int i;
     }

Let’s now consider below code where we are passing the class object normally i.e. by value as well by ref keyword:

public void RefTypePassNormal(Reftype refType)
 {
     refType.i =20;
 }
 public void RefTypePassByRef(ref Reftype refType)
 {
     refType.i =30;
 }

Here is the calling code

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Reftype refType = new Reftype();
     refType.i=10;
     
     RefTypePassNormal(refType);
     Console.WriteLine(refType.i);//Prints 20
     RefTypePassByRef(ref refType);
     Console.WriteLine(refType.i);//Prints 30

So as you can see right now no difference

Let’s Change the methods now as below to know the difference:

public void RefTypePassNormal(Reftype refType)
 {
     refType.i =20;
     refType =null;
 }
 public void RefTypePassByRef(ref Reftype refType)
 {
     refType.i =30;
     refType =null;
 }

Again let’s see the calling code

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Reftype refType = new Reftype();
     refType.i=10;
     
     RefTypePassNormal(refType);
     Console.WriteLine(refType.i);//This still Prints 20
     RefTypePassByRef(ref refType);
     Console.WriteLine(refType.i);//Null Reference Exception here