Ufuk SURMEN Ufuk SURMEN - 12 days ago 7
C# Question

Is object a reference type or value type?

I have still doubts about

object
. It is the primary base class of anything, any class. But is it reference type or value type. Or like which of these acts it? I need to get this clarified. I have difficulty understanding that.

object obj1 = "OldString";
object obj2 = obj1;
obj1 = "NewString";
MessageBox.Show(obj1 + " " + obj2);
//Output is "NewString OldString"


In this case it acts like a value type. If object was reference type then why obj2 value is still "OldString"

class SampleClass
{
public string Text { get; set; }
}

SampleClass Sample1 = new SampleClass();
Sample1.Text="OldText";

object refer1 = Sample1;
object refer2 = refer1;

Sample1.Text = "NewText";

MessageBox.Show((refer1 as SampleClass).Text + (refer2 as SampleClass).Text);
//OutPut is "NewText NewText"


In this case it acts like reference type

We can deduce that
object
's type is what you box inside it. It can be both a reference type and value type. It is about what you box inside. Am I right?

Answer

It is a reference type

Doing an example with string isn't very illuminating, because string is also a reference type (as is SampleClass, obviously); your example contains zero "boxing".

if object is reference type then why obj2 value is still "OldString"

Why wouldn't it be? When you create a new string, that doesn't change old references to point at the new string. Consider:

 object obj1 = "OldString";
 // create a new string; assign obj1 the reference to that new string "OldString"

object obj2 = obj1;
 // copy the reference from obj1 and assign into obj2; obj2 now refers to
 // the same string instance

 obj1 = "NewString";
 // create a new string and assign that new reference to obj1; note we haven't
 // changed obj2 - that still points to the original string, "OldString"