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</o:shapelayout></xml><![endif]--></head><body lang=EN-NZ link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>The two are not comparable in function so cannot really be compared for efficiency:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='text-indent:36.0pt'><b><span style='font-family:"Courier New";color:#948A54'>if a is b then<o:p></o:p></span></b></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Will evaluate true if <b>a</b> is an instance of <b>b</b> or of any class derived from <b>b</b>.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='text-indent:36.0pt'><b><span style='font-family:"Courier New";color:#948A54'>if (abc.Classname = ‘TMyObject’) then<o:p></o:p></span></b></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Will evaluate true only if <b>abc</b> is an instance of <b>TMyObject</b> and only if the classname of <b>TMyObject</b> uses the exact capitalisation in the comparison string.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>So it depends what you are trying to do... if you need to test for an instance being of a specific class and only a specific class then the ClassName comparison is valid, but a more efficient and more type-safe alternative would be:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='text-indent:36.0pt'><b><span style='font-family:"Courier New";color:#948A54'>if (a.ClassType = TMyObject) then<o:p></o:p></span></b></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>But if you need to detect when <b>a</b> is of class <b>TMyObject</b> <i><u>or</u> some class that ultimately derives from</i> <b>TMyObject</b>, then an <b>is</b> or <b>InheritsFrom()</b> test is the <b>only</b> option.<o:p></o:p></span></p></div></body></html>