Hello folks! When downcasting object pointers, I often wish there was a way to check the cast before. Peter has already told, in one of the next alpha releases of GPC there will be a new downcast-operator named 'as' firing a runtime error in case of an invalid downcast; like this: ... tBar = object ( tFoo ) ...; ... foo: pFoo; ... with foo^ as tBar do (* if "foo^" isn't a tBar actually, the 'as' *) ... (* interrupts the program with a runtime error. *) Nevertheless I'd like to have a way to check the validity _before_ casting, thus preventing the runtime error in cases where I don't want the program to be interrupted. Currently, I'd suggest the following additional functions in GPC itself: Function getObjectType ( obj: object ): "type"; Function isOfObjectType ( obj: object; runtimeType: "type" ): boolean; Example: ... p: pObject; ... p:= new ( pBar, init ); ... getObjectType ( p^ ) ... (* returns "tBar" *) ... ... isOfObjectType ( p^, pFoo ) ... (* returns "true", since tBar *) (* is derived from tFoo. *) For downcasting, I'd only need the latter one, but the first function seems useful to me, too. Alternatively, I could need a mechanism to absorb the runtime error fired by "as" before it interrupts the program. Something like this: foo: pFoo; ... with foo^ as tBar do ...; catchRuntimeError ( @procedureToHandleRuntimeError, parameters ); Anyway, when implementing a catchRuntimeError mechanism in GPC, it would not seem reasonable to me to just do it for this special kind of runtime error; thus, here we'd need a general exception handling mechanism to catch and handle _any_ runtime error without interrupting the program. Hope this description of my ideas wasn't too confuse... Yours Markus -- http://www.gerwinski.de/~markus/