🚀 go-pugleaf

David Gudeman writes:

   In article  <3656@lanl.gov> jlg@lanl.gov (Jim Giles) writes:

   ]Of course, pointers and one dimensional arrays - in spite of their
   ]similarity - are indeed different.  For one thing: arrays are bounded.

   You know, Jim, it doesn't help your argument any when you keep
   bringing up the same points long after they have been discredited.
   Pointers are bounded just like array indexes.  Yes, most
   implementations of C don't check the bounds, but that is because in
   the definition of the C language, run-time errors are generally
   [rest omitted]

That's not what Jim means by "bounded" (if I understand him correctly) - his
point is that given two *arrays* A, B then it is *known* that A and B have no
locations (ie, updatable bits of store) in common, so assignments within A 
cannot affect the values accessible from B.

This is in contrast to two pointers P, Q (of the same type); an assignment
through P (*P = 42, or P[42] = MAX_INT) might well change values accessible
through Q.

Jim wants ALIAS declarations for the cases where variables can overlap.
Presumably in the case of a procedure with a header something like

    void example( T A[Bound], T B{Bound] ) ...

where A and B are not to be aliased (so the comoiler can do its wizzy 
optimisations), all calls have a proof obligation to show that the actual 
arguments are *in fact* not aliased.

Is that right, Jim? [I'm not sure I agree with Jim. But I'd rather disagree
about the same thing that about two different ones, which is what I think David
is in danger of doing.]

--

Regards, Kers.      | "You're better off  not dreaming of  the things to come;
Caravan:            | Dreams  are always ending  far too soon."