🚀 go-pugleaf

In article <1993Jan8.181100.10727@ucc.su.OZ.AU>, maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) writes:
> In article <1993Jan8.150113.1643@lpi.liant.com> pkt@lpi.liant.com (Scott Turner) writes:
> >> maxtal>	Corollary: such objects have states not accessible via
> >> maxtal>	the contiguous storage allocated for them.
> >> maxtal>	(via virtual function calls)
> >> 
> >Since John MAX Skaller was drawing inferences from my belief that base
> >class subobjects are objects, I want to go on record.  I agree that
> >"abstract objects" can exist, but the corollary does not follow.  
> 
> 	Well, you can have a pointer to another object in an object,
> and access the other object via the pointer, right?
> 
> 	But this doesn't count :-) The pointer is part
> of the state of the object, and thus so is the object pointed
> to (and so on recursively)
> 
> 	In any case, I will fill in the hole:
> 
> 	class X {
> 	public:
> 		virtual int f()=0;
> 	};
> 
> 	class Y : public X {
> 		int i;
> 	public:
> 		int f() {return i;}
> 		void setint(int j) {i=j;}
> 	};
>  
> In this single example, the abstract subobject X in Y has
> public states  of measure 'int'. (There are 'int' values).
> Yet X has private storage of measure zero.
> 
> Where is the hole in this argument? Answer: X has a vtble
> pointer!  

Yes, that's close to the way I look at it.  X declares a virtual function f
with the consequence that any subobject of type X includes
some indication of how f has been overridden in constructing the enclosing
object.   f may refer to non-contiguous storage, but that's no more
problematic than if X had a pointer member which refers to non-contiguous
storage.
--
Prescott K. Turner, Jr.
Liant Software Corp. (developers of LPI languages)
959 Concord St., Framingham, MA 01701 USA    (508) 872-8700
UUCP: uunet!lpi!pkt                          Internet: pkt@lpi.liant.com