Use of Supports() function with generic interface type

Question

I just tried my first use of generics in Delphi 2009 and am perplexed on how to use a generic type as the input to the Supports function used to see if an object implements

Answer 1

There is no guarantee that T has a GUID associated with it, and there is no means in the language to write a constraint on the type parameter to make that guarantee.

The interface name is converted into a GUID by the compiler looking up the name in the symbol table, getting the compiler's data structure representing the interface, and checking the corresponding field for the GUID. But generics are not like C++ templates; they need to be compiled and type-checked and known to work for any valid type parameter, and that means constraining the type parameter in its declaration.

You can get the GUID using RTTI (first checking that T does indeed represent an interface) with something like GetTypeData(TypeInfo(T))^.Guid and pass the GUID to Supports that way.