Difference between dynamic and System.Object

Question

What is the difference between a variable declared as dynamic and a variable declared as System.Object? Running the following function would seem to indicate that both variables get cast to the correct type dynamically:

void ObjectTest()
{
    System.Object MyTestVar = "test";
    dynamic MyTestVar2 = "Testing 123";

    Console.WriteLine("{0}", MyTestVar.GetType());
    Console.WriteLine("{0}", MyTestVar2.GetType());

    MyTestVar = 123;
    MyTestVar2 = 321;

    Console.WriteLine("{0}", MyTestVar.GetType());
    Console.WriteLine("{0}", MyTestVar2.GetType());
}

I wrote a post about this some time ago: blogs.msdn.com/b/csharpfaq/archive/2010/01/25/… — Alexandra Rusina
– Alexandra Rusina, Commented Aug 12, 2010 at 21:15

SLaks · Accepted Answer · 2010-08-12 01:32:43Z

11

The difference is that MyTestVar2.ToUpper() compiles and works, without any explicit casting.

object is a normal type.
dynamic is a basically a placeholder type that causes the compiler to emit dynamic late-bound calls.

GetType() is a normal function defined by the object class that operates on the instance that you call it on.
GetType() is completely unaffected by the declared type of a variable that refers to the object you call it on. (except for nullables)

edited Aug 12, 2010 at 1:32

answered Aug 12, 2010 at 1:25

SLaks

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1 Comment

SLaks Over a year ago

You can call any method on dynamic variables. The code dynamic x = 3; x.Explode(); will compile perfectly fine

Igor Zevaka · Accepted Answer · 2010-08-12 01:31:10Z

6

You should probably start with this excellent MSDN article. The differences can be summed up quite succinctly:

At compile time, an element that is typed as dynamic is assumed to support any operation.

System.Object only has a handful of operations that it supports - ToString(), Equals(), etc.

answered Aug 12, 2010 at 1:31

Igor Zevaka

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Dr. Mumtaz Ali Shah · Accepted Answer · 2010-10-05 00:31:25Z

The fundamental difference is compile-time(for object) vs runtime (for dynamic) resoulution of calls. Its also called early vs late binding. [ Note: add a reference to Microsoft.CSharp for the following code to compile.]

   object o = "Hello world";// fine because a derived type can be assigned to a base type
   dynamic d= "Hello world";// fine as well  

   Type otype=o.GetType();// compiles because it confirms that object has a GetType()
   Type dtype=d.GetType();// also compiles but for another reason (i.e.no binding yet)

   string upperd= d.ToUpper(); // compiles because no binding yet ( anything goes :)
   string uppero= o.ToUpper(); // Fails to compile. Object has no ToUpper() method

If you comment out the last call , the application should run fine because the CLR , when it reaches the second last call d.ToUpper() at runtime, it will look for a method ToUpper() in the string type and will find it there (because in the second statement d was assigned a string). The last call did not compile because ToUpper() was being searched in the System.Object type at the compile time which of course will not be there.

Sheriff · Accepted Answer · 2019-03-09 10:37:33Z

-2

The only difference in between object and dynamic.

In case of object you need to explicit type cast when you are going to retrieve value from object.

Kindly give a like if you find it suitable.

answered Mar 9, 2019 at 10:37

Sheriff

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