using System;
 
using System.Collections;
using System.Windows.Forms;
 
namespace PerformanceLibrary
{
   public sealed class SomeClass
   {
      private SomeClass() {}
 
      // This method violates the rule.
 
      public static void UnderPerforming(ArrayList list)
      {
         foreach(object obj in list) 
         {
            // The 'is' statement performs a cast operation.
            if(obj is Control) 
            {
               // The 'as' statement performs a duplicate cast operation.
 
               Control aControl = obj as Control;
               // Use aControl.
            }
 
         }
      }
 
      // This method satisfies the rule.
      public static void BetterPerforming(ArrayList list)
      {
         foreach(object obj in list) 
         {
            Control aControl = obj as Control;
            if(aControl != null) 
            {
               // Use aControl.
 
            }
         }
      }
   }
}
 

Imports System
Imports System.Drawing
Imports System.Windows.Forms
 
 
Namespace PerformanceLibrary
 
   Public Class SomeForm : Inherits Form
 
      Dim start, reset As Button
 
      Sub New()
 
         start = New Button()
         reset = New Button()
         AddHandler start.Click, AddressOf start_Click
         AddHandler reset.Click, AddressOf reset_Click
         Controls.Add(start)
         Controls.Add(reset)
 
      End Sub
 
      ' This method violates the rule.
      Private Sub start_Click(sender As Object, e As EventArgs)
 
         Dim controlSize As Size = DirectCast(sender, Control).Size
         Dim rightToLeftValue As RightToLeft = _ 
            DirectCast(sender, Control).RightToLeft
         Dim parent As Control = DirectCast(sender, Control)
 
      End Sub
 
      ' This method satisfies the rule.
      Private Sub reset_Click(sender As Object, e As EventArgs)
 
         Dim someControl As Control = DirectCast(sender, Control)
         Dim controlSize As Size = someControl.Size
         Dim rightToLeftValue As RightToLeft = someControl.RightToLeft
         Dim parent As Control = someControl
 
      End Sub
 
   End Class
 
End Namespace
 

using System;
 
using System.Drawing;
using System.Windows.Forms;
 
namespace PerformanceLibrary
{
   public class SomeForm : Form
   {
      Button start, reset;
 
      public SomeForm()
      {
         start = new Button();
         reset = new Button();
         start.Click += new EventHandler(start_Click);
         reset.Click += new EventHandler(reset_Click);
         Controls.Add(start);
         Controls.Add(reset);
      }
 
      // This method violates the rule.
 
      void start_Click(object sender, EventArgs e)
      {
         Size controlSize = ((Control)sender).Size;
         RightToLeft rightToLeftValue = ((Control)sender).RightToLeft;
         Control parent = (Control)sender;
      }
 
      // This method satisfies the rule.
      void reset_Click(object sender, EventArgs e)
      {
         Control someControl = (Control)sender;
         Size controlSize = someControl.Size;
         RightToLeft rightToLeftValue = someControl.RightToLeft;
         Control parent = someControl;
      }
   }
}