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Showing posts from November, 2008

Casting Restrictions ???

We all know that the runtime can detect the actual type of a System.Object instance. The primitive data types provided by the runtime are compatible with one another for casting (assuming that we do not truncate the values). So if I have an int, it can be cast to long or ulong. All that is fine. Watch this:-
interface IAppDataTypeBase { // Other methods GetValue(); } Since IAppDataTypeBase represents the mother of all types of data in my application, I have made GetValue to return the value as object (I could have used generics, that is for another day!).
IAppDataTypeBase longType = GetLongInstanceFromSomeWhere(); int i = (int)longType.GetValue();So are we discussing any problems here? Yes, we are. The problem is that the value returned by GetValue - System.Object - despite being inherently long cannot be cast to an int. It would result in an 'Specified cast is invalid' exception. If an object is one of the primitive types, it can only be cast to its actual type. In the ab…