[fpc-pascal] Find the nature of a pointer

[Marco van de Voort]

> I have a function that will receive a Handle. That handle could be a
> pointer to a structure, or a object. Is there any safe way to discover
> it's nature?

No you can't. 

> The following code will work when the Handle is an Object or nil, but
> will crash the application when the Handle is a structure:

It is not even 100% save for that, some systems use other values instead of
nil/0.