[fpc-devel] Newbie question: how does the compiler know the class type of an object ( the Is operator)

[Dennis Poon]

I am just curious, what is the instance size of an Tobject?

in many notifyevents, we would test whether an object is actually of a 
certain class by
if Sender is TComponent then
   ...
end;

How does the "is" operator work?  Is the memory space occupied by that 
object reference contain a pointer to a class table?
If that is true, the minimal instance size of an Tobject is 
sizeof(pointer)?

Sorry if my question is dumb.

Dennis
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