C#

private void MyEventHandler(object sender, EventArgs e)
{
  ToolBarButton b = sender as Button;
  MenuItem mi = sender as MenuItem;
  
  if( b != null )
  {
    // User clicked the toolbar button
  }
  else if( mi != null )
  {
    // User clicked the menu item or 
    // used the shortcut keys
  }
}

Object o = new Something();
Something s = (Something)o;

Object o = new Object();
Something s = o as Something();
if(s != null)
{
   //... use s here.
}

void Function()
{
    try
    {
        IReferenceService refSvc = (IReferenceService) GetService(typeof(IReferenceService));
        // do something
    }
    catch (Exception exc)
    {
        throw new UsefulException(message, exc);
    }
}

void Function()
{
    IReferenceService refSvc = GetService(typeof(IReferenceService)) as IReferenceService;
    if (refSvc == null)
    {
        // alternatively, you could do it without refSvc
        throw new UsefulException(message);
    }
    // do something
}

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"When the only tool you have is a hammer, a sore thumb you will have."