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POUnused interface reference is not destroyed
 

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    <p>i had another bug in my app caused by careless usage of Delphi interfaces. When i pass an interface to a procedure which ignores that argument, the instance is never freed. See the following simple example:</p> <pre><code>ITest = interface procedure Test; end; Tester = class(TInterfacedObject, ITest) public procedure Test; end; Base = class public procedure UseTestOrNot(test : ITest); virtual; abstract; end; A = class(Base) public procedure UseTestOrNot(test : ITest); override; end; B = class(Base) public procedure UseTestOrNot(test : ITest); override; end; { A } procedure A.UseTestOrNot(test: ITest); begin test.Test(); end; { B } procedure B.UseTestOrNot(test: ITest); begin WriteLn('No test here'); end; // -------- Test --------------------------------------- var list : TObjectList&lt;Base&gt;; x : Base; t : ITest; begin ReportMemoryLeaksOnShutdown := true; list := TObjectList&lt;Base&gt;.Create; list.Add(A.Create); list.Add(B.Create); // 1 x Tester leak for each B in list: for x in list do x.UseTestOrNot(Tester.Create); // this is ok for x in list do begin t := Tester.Create; x.UseTestOrNot(t); end; list.Free; end. </code></pre> <p>Can you please explain what goes wrong with the reference counter? Can you give any best practice/ guideline (like "Never create an interfaced instance inside a function call [if you don't know what happens inside]).</p> <p>The best solution i can think of for this example is to write a template method in class Base that saves the passed test instance and calls an abstract <code>DoUseTestOrNot</code> method.</p> <p><strong>EDIT</strong> Delphi 2010</p>
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    1. USJeroen Wiert Pluimers
    1. UShansmaad
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      1. UShimself
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    1. COWhat version of Delphi is this?
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      1. USMason Wheeler
    2. COsorry, it's Delphi 2010
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      1. UShansmaad
    3. CODoes not matter, it is a bug regardless of version. wait until delphi ex 2? Cheers
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      1. USAPZ28
 

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