Which Code Runs Faster? The Answer May Surprise You....

I saw some code that piqued my interest a few days ago. Basically, this code compared object types instead of the name for the object type.  Being the developer that I am, it set me thinking about which way is faster. Here are a couple of routines that do the exact same thing. Which one do you think will run faster? This code is targeted for .NET 4 Client, but should also work in .NET 2 and later.

The StopWatch objects (oStopWatchA and oStopWatchB) are defined as Class level private System.Diagnostics.Stopwatch objects and initialized before the call to the Subs. The Object object (oObject) is defined as a Class level private System.Object object and initialized before the call to the Subs.  Each routine was run 1,000 times, swapping with each execution to eliminate external factors to the timing.

Private Sub CompareA()
  Dim iLoop As Integer

  oStopWatchA.Start()
  For iLoop = 1 To 1000000
    Select Case oObject.GetType().Name
      Case "Object"
      Case "Exception"
      Case Else
    End Select
  Next
  oStopWatchA.Stop()
End Sub

Private Sub CompareB()
  Dim iLoop As Integer

  oStopWatchB.Start()
  For iLoop = 1 To 1000000
    Select Case oObject.GetType()
      Case GetType(Object)
      Case GetType(Exception)
      Case Else
    End Select
  Next
  oStopWatchB.Stop()
End Sub

The elapsed time for each is listed below (lower numbers are better):

Were you surprised? I was!

Edit: The whole point of this tip is to not just do the same thing the same way you always have. Look at other methods to accomplish your goal. I was surprised by the speed difference of changing the comparison from a string to a type reference, mainly because I expected the compiler to be able to generate code that pulled the type's name once for the comparison. I was also expecting the GetType() calls to be executed on every comparison (each Case statement).