🚀 go-pugleaf

In <comp.std.c++> maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) writes:
>>>
>>>In fact, p==q iff objects equal is unimplementable on some machines.
>>>That is, even the existing ARM requirement is unworkable.
>
>Perhaps we can conceive two types of pointers, type 1 
>provides no comparisons at all, type 2 allows equality test.

I think we're sliding away from the original discussion.

The goal was to write data structures that use the ordering of
pointers to improve search time.  What I need is mechanism that
compares the pointers -- what they actually point to is not relevant.

Let me try to put it differently: the element type is "pointer to X",
not "X" itself.

C and C++ has some notion of equality between pointers.  You can
clobber the semantics of this equality with memory mapping and what
not, but that is in my view an issue beyond the language.

I would finally like to return to a claim I made earlier, but nobody
has commented on (as far as I know).  I belive that even if you
imposed a total ordering on pointers in a segmented architecture
(e.g., Inte 8086 family), compilers would be able to handle the
follwing common case efficiently:

	void zap(int* a, unsigned n)
	{
		for (int* p = a; p < a+n; p++)
			*p = 0;
	}

and produce the same code as today (without the total ordering).
After all, the assignment "p = a" says that "p" must point to the same
segment as "a".  Any comments?

		-- Dag