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copied!<p><code>as</code> with an interface type uses an interface cast, which uses the GUID to find the interface. For a generic interface with a GUID, every instantiation gets the same GUID. If a single type implements multiple copies of the interface, then looking up by GUID will result in the first interface being returned.</p> <p>The program works as expected if you don't use an interface cast, and instead use an interface conversion like this:</p> <pre><code>procedure Test; var t : TTest<integer, string>; begin t := TTest<integer, string>.Create(39, 'Blah'); ShowMessage(ITest<string>(t).Val); ShowMessage(IntToStr(ITest<Integer>(t).Val)); end; </code></pre> <p>Originally, when generics were being implemented for Win32, GUIDs were not permitted on generic interfaces. However, dynamic querying for generic interfaces was desirable for generic container scenarios, and in general, as a mechanism for querying a service provider for type-specific services in the context of an algorithm (such as sorting or searching, which require things like comparers and equality tests). So a new plan was formed: have a GUID on the generic interface, but create a hash of the type arguments for generic instantiations and fold (e.g. xor) the hash into GUID to create a unique GUID for every distinct and incompatible instantiation. However, this was late in the day, and a good implementation was not possible within time constraints. But the requirement for dynamic querying remained, so the GUIDs stayed. That's why things are the way they are today.</p> <p>To solve your specific scenario, the best I can recommend is to use distinct descendants with explicit GUIDs; or use a different mechanism for querying for the interface.</p>

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