🚀 go-pugleaf

In article <1992Oct28.184135.25475@ucc.su.OZ.AU> maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) writes:

|	I dont understand. For a start, there is NO requirement
|that I can see that < is a partial order. Have I missed something?

What you have missed is the implication of this statement.  *No requirement*
is equivalent to a *Permission* for compiler vendors and programmers to
write compilers and programs making use of that *Permission.*  Such compilers
and programs are perfectly legal and valid C and C++ compilers/programs.
They are *conforming* -- they're just not *strictly conforming* programs.

|	As I understand it the rules are:
|
|	1) pointers to the same object compare ==
|	2) within an array, < is a total order
|	3) In other cases < is implementation defined.

	4) Don't gratuitously change C++ from C so as to break existing
	legal C programs.

|Any program relying on some implementation defined order (3) cannot
|be portable. 

*It doesn't have to be portable to be legal!*  It is quite legitimate to
write legal programs that aren't portable -- in fact obviously 99.9% of
the interesting C/C++ programs *aren't* strictly portable!  "Portability"
then is the wrong measure when it comes to standards.  Instead, the issue
is legality.  You cannot gratuitously take a large class of programs and
make them all illegal.  Such destroys the compatibility that C++ is justly
famous for.

|If a total ordering was required, programs utilising
|this requirement would be portable. 

Nope.  They would only become portable if this was the last non-portability
in that program -- hardly likely.

On the converse side, tons of previously legal but not *strictly* portable 
programs would now become illegal.

Thus your trade-off would represent a major lose:  Lots of legal programs
become busted in exchange for making an unlikely few programs portable.

|Surely very few implementation
|defined orderings would not be total orders anyhow, so very few
|existing programs would be broken if the rules changed?

Segment hacks in programs for x86 systems are EXTREMELY common.  If 
you were to require a total ordering on pointers a HUGE amount of currently
conforming C/C++ programs would suddenly become illegal.  This is clearly
not acceptable, and not well thought out.  My off-the-top-of-my-head
estimate for the number of C++ programmers that would fall in this 
category would be several hundred thousand.  [Based on C++ compiler sales
numbers]  The number of C programmers affected would probably be even larger --
unless you expect C/C++ compilers to implement total ordering on C++ 
programs but partial orderings on C programs?  Wrong.

Besides, total ordering would require non-flat model programs to become
bigger and slower.  But you guys already know that.  Now how about cutting
out the game playing -- this issue has already been fought out in the
ANSI C committees.  Why reopen old ground?