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PO"Method '%s' hides virtual method of base type '%s'". What's really being hidden?
 

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  1. PO"Method '%s' hides virtual method of base type '%s'". What's really being hidden?
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    <p>After having read <a href="https://stackoverflow.com/users/12597">Ian Boyd</a>'s constructor series questions (<a href="https://stackoverflow.com/questions/3874330/delphi-how-to-hide-ancestor-constructors">1</a>, <a href="https://stackoverflow.com/questions/3876040/delphi-understanding-constructors">2</a>, <a href="https://stackoverflow.com/questions/3876484/delphi-how-to-add-a-different-constructor-to-a-descendant">3</a>, <a href="https://stackoverflow.com/questions/3877063/delphi-when-does-reintroduce-hide-ancestors-and-when-does-it-show-them">4</a>), I realize I don't quite grasp the literal meaning on what's being hidden.</p> <p>I know (correct me if I'm wrong) <code>override</code>'s sole purpose is to be able to have polymorphic behavior, so that run-time can resolve a method depending on the actual type of an instance - as opposed to the declared type. Consider the following code:</p> <pre><code>type TBase = class procedure Proc1; virtual; procedure Proc2; virtual; end; TChild = class(TBase) procedure Proc1; override; procedure Proc2; // &lt;- [DCC Warning] end; procedure TBase.Proc1; begin Writeln('Base.Proc1'); end; procedure TBase.Proc2; begin Writeln('Base.Proc2'); end; procedure TChild.Proc1; begin inherited Proc1; Writeln('Child.Proc1'); end; procedure TChild.Proc2; begin inherited Proc2; Writeln('Child.Proc2'); end; var Base: TBase; begin Base := TChild.Create; Base.Proc1; Writeln; Base.Proc2; Base.Free; Readln; end. </code></pre> <p>Which outputs:</p> <blockquote> <p>Base.Proc1<br />Child.Proc1<br /><br />Base.Proc2</p> </blockquote> <p>The warning on <code>TChild.Proc2</code> <a href="http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate2/EN/html/devcommon/cm_hidden_virtual_xml.html" rel="nofollow noreferrer">states that</a> this method "<em>will hide access to the base's method of the same name</em>". What I see is, if I don't override <code>Proc2</code> I loose the ability of the method's resolving to its actual type, not of its base type. How's that hiding access to base's method?</p> <p>Further, down the documentation on the warning as a solution to the warning, it is stated that:</p> <blockquote> <p>First, you could specify override to make the derived class' procedure also virtual, and thus allowing inherited calls to still reference the original procedure.</p> </blockquote> <p>Now, if I create a 'TChild' instance from a 'TChild' (no polymorphism), the inherited call in the non-overridden method clearly refers to the original procedure. If I create the 'Child' instance from a 'TBase', the call does not even resolve to a 'TChild' method, how could I call 'Inherited' that would refer to anything at all?</p> <p>What am I misunderstanding? </p>
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