🚀 go-pugleaf

In article <1993Jan20.173927.3061@vedge.com>, hendrik@vedge.com (Hendrik Boom) writes:
> In article <1993Jan11.190959.5305@lpi.liant.com>, pkt@lpi.liant.com (Scott Turner) writes:
> > If we have objects of a type which requires no state, e.g.
> >        struct B{} a, b;
> > then in order for them to have distinct identities an implementation
> > might allocate addresses that don't point to valid memory.  Again, no
> > storage is required.
> 
> But if nonempty class C inherits from B, you have trouble comparing
> pointers to B with pointers to C that have been converted to B,
> unless you are careful that addresses of B's are outside of usable
> memory.

The trouble is negligible almost all of the time.  For example,
	struct C : B { int i; };
an implementation could convert "pointer to C" to "pointer to B" using the
same representation for both values.  If some pointers to B are pointing to
invalid memory, the comparison will work out just right.

In unusual cases such as Johan Bengtsson's example, the compiler can "waste"
a byte for the base class.
--
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